Written by thetreecenters • February 14 Cypress Trees – The Complete Guide
Introduction
Gardeners today have access to a wide variety of evergreen trees, both those with broad leaves and those with needle leaves. These are used in a variety of ways in the garden and landscape, as specimens, hedges and privacy screens, depending on the needs of the location. Their main virtue is their persistence throughout all the seasons in a green, leafy state, so that they give a sense of permanence and structure to the garden, a background to the comings and goings of more seasonal plants. During the vibrant, colorful seasons they fade into the background and in winter they become more prominent, standing out against the wintery sky and snow.
An important group of these evergreen trees is the Cypress trees. This is a small group of conifers found in North America, southern Europe and across the Himalaya ranges into China and Vietnam. At various times botanists have made it larger or smaller, but today it contains about 18 different trees, of which about seven are grown to any extent in gardens and parks. However it also contains a hybrid tree – the product of gardening – which has a unique and special place in garden life for its vigorous and rapid growth and great value as a screening plant. This tree, the Leyland Cypress, would alone be enough to make Cypress trees one of the most important groups of evergreen trees grown in gardens.
The Features of Cypress Trees
Cypress trees are part of that group of plants known as conifers. These trees are more ancient that flowering plants and produce cones, not flowers, to reproduce. Almost all of them are evergreen but should not be confused with other flowering trees that also do not lose their leaves in winter. Those trees should more accurately be called broad-leaf evergreens, to distinguish them from their needle-leaves relatives, the conifers.
Unlike many conifers the needles of ‘adult’ cypress do not grow out from the branches like a pine tree, but are flat and grip the branches as minute scales, running in four rows along the smaller branches and eventually dropping and leaving brown bark on the stems and trunk of the tree. When young, many cypress trees show ‘juvenile’ foliage. The leaves of juvenile foliage are broader and pointed, resembling junipers, with a spiny tip. They grow outwards from the stem, making the plant more bristly and protecting it from being eaten when young. This is only seen in seed-grown plants and is replaced by the ‘adult’ foliage as the plant matures. In some species this can take 5-10 years, so that young plants look very different from adults and have sometimes been mistakenly seen as separate species.
Cypress trees produce small cones, both male and female on the same tree. The tiny male cones release their pollen in the wind and then die. Pollinated female cones develop into seed cones that are rounded and covered in mushroom-shaped scales with a pronounced central bump in each scale. The cones take two years to mature and release many seeds when they ripen and the scales separate. There are differences in size and form between one species of cypress and another, and these differences are important for identification, since in many trees the foliage is quite similar.
Although superficially similar, cypress trees can be distinguished from the related Thuja or Arborvitae Trees because the young branches areusually irregular in form, not neatly arranged in sprays as they are in Thuja and as they also are in the other related group, False cypress (Chamaecyparis), which includes such trees as the Hinoki Cypress tree.
Unfortunately the names ‘Cypress’ and ‘False Cypress’ are given to a range of evergreen conifers, showing that common names are not a good guide to relationships between these trees and gardeners should make an effort to use botanical names instead to avoid confusion.
Cypress trees vary in size, from shrubby plants less than 10 feet tall to giants of 150 feet. Their final size is greatly affected by soil conditions and climate, so that the same plant in one area may be a large shrub and in other areas a towering forest tree.
Cypress In The Garden and Landscape
Cypress trees can be the backbone of any garden, providing screens and hedges in any part of the country, depending on which type is chosen. The hybrid cypress called Leyland Cypress, is always the first choice for large screens and hedges in all but the coldest and hottest regions, but other types are very useful too, for variety or when the conditions are suitable.
As Screens:
Cypress trees make great screening plants. They are naturally dense, upright and lush green all-year-round. If you have sufficient space they can be left to grow naturally without clipping and will still be upright and dense. Even in narrow spaces plants such as the Italian Cypress will become tall but remain very narrow, ideal for narrow spaces where screening is needed. Cypress trees will soon reach 20 feet in height and grow even taller if needed, creating a solid barrier that filters wind, noise and pollution as well as giving complete privacy to your property.
As a screening plant, nothing beats the Leyland Cypress, which has a remarkable growth-rate between three and five feet a year. With perfect healthy foliage all year round it will always make an impressive statement. It quickly fills in, becoming dense and also increases in height so rapidly that it makes an excellent screen more quickly than almost any other evergreen. It can grow unclipped up to 60 feet, so it makes the perfect tall screen too, although with clipping it can be kept at any height.
In drier regions the Arizona Cypress makes a great screening plant and is amazingly drought-resistant. So is the Italian Cypress, which naturally stays just a few feet wide, making it the ideal choice for a restricted area where height is important but there is not much width available.
As Hedges:
Cypress trees also make great hedges because they take well to clipping and shearing, so they can be turned into formal hedges easily. They quickly fill-in and become solid and dense, making the perfect backdrop to all kinds of garden designs and styles. If clipped from an early stage they can be as short as four feet, or as tall as 30 feet or even more. By choosing the right variety, a perfect hedge for any climate can be easily grown to almost any size and form. For larger hedges Leyland Cypress is the first and best choice.
As Accent Specimens:
Cypress trees have more to offer than just hedges and screens. They make excellent specimen plants too, framing doorways, filling corners around the home, or planted on either side of a driveway entrance. They make terrific evergreen accent plants anywhere in the garden. The Italian Cypress is a perfect needle-point exclamation mark in the garden, catching the eye and conjuring up images of Tuscany and Provence, where it is grown widely on almost every property.
In beds cypress trees blend well with flowering shrubs and other evergreens, giving permanence and structure all year and bringing rich green color to contrast with the brightness of your flowering shrubs and trees.
Hybrid Cypress
When different but related trees grow in different parts of the world, of course there is no chance of them ‘meeting up’ and producing seeds. However when we cultivate together trees that are brought from different continents, breeding together is something that can and does happen, either naturally or with the help of plant breeders.
One of the significant consequences of the meeting of two species is that when they cross together the strengths of one masks the weaknesses of the other, producing trees that are stronger, hardier, faster-growing and more vigorous than either of the parent trees. Plant breeders call this ‘hybrid vigor’ and it is an important and valuable consequence of plant breeding. The ability to hybridize is also a good indication of close relationships between plants, since trees that are only distantly related rarely if ever produce hybrid seed capable of germinating or growing.
Leyland Cypress
This remarkable hybrid tree was first found over 100 years ago. It has become the main and most important cypress tree grown in horticulture, being remarkable for its rapid, vigorous growth, adaptability to a wide range of soils and growing conditions and its ability to always remain healthy and attractive in all seasons. All these characteristics are a result of the hybrid vigor of this tree.
In 1888 a certain Mr. John Naylor, who lived in Leighton Hall, Wales, a few miles from the border with England, decided to sow the seeds he had taken from a cone of a Nootka cypress tree growing in his garden. When the seedlings grew he noticed that six of them seemed different from the rest, so he put them aside. John Naylor was the nephew of Christopher Leyland, a banker, who had purchased Leighton Hall in 1845 and later given it to his nephew as a wedding present. The grounds had been landscaped by one of the leading landscape architects of the time, Edward Kemp. He had planted the grounds with a wide variety of newly introduced trees from around the world, including a variety of different conifers[11]. It was from one of these trees that Naylor took that cone.
John Naylor had a son, Christopher John, who in 1892 inherited the estate of the original Christopher Leyland, Haggerston Hall, in the county of Northumberland. Christopher took the name Leyland when he took over Haggerston Castle and when he moved, along no doubt with many other belongings he took those six special seedlings his father had grown and planted them on his property,. Five of those trees can still be seen growing at Haggerston Hall, the sixth having been blown down in a freak storm in 1953.
In 1911 Mr Leyland’s nephew, Captain J M Naylor, picked a cone from a Monterey cypress growing 150 feet from the Nootka cypress which had yielded the first cone. He raised some seedlings and two which were different were planted on a hill behind Leighton Hall. So this was a reverse hybrid, with the pollen passing in the opposite direction.
Almost all of the current millions of plants of Leyland Cypress around the world were definitely grown from the original batch of six seedlings, chiefly from the most vigorous tree, named ‘Haggeston Grey’ by Mr Leyland. A second was named ‘Green Spire’. The other trees were not as vigorous and do not seem to have been propagated and distributed. One of the reverse hybrids found in 1911 was named ‘Leighton Green’ and the other ‘Naylor’s Blue’.
These activities have to be seen in the context of the times, when gardening was a pursuit suitable for wealthy gentlemen, who these men were – among the wealthiest in Britain. The collecting of new imported plants and the growing of novelties and unusual forms was a genteel competitive sport among such people, who vied with each other to grow and show their latest and rarest acquisitions. Conifers were a particular passion of that time although the exact nature of these unusual plants was not clear to them.
In 1925 a Professor William Dawson, of Cambridge University, was staying at Haggeston Castle. He took with him some pieces of these mystery trees and showed them to the conifer expert of the time, William Dallimore, who worked at the Royal Botanic Gardens, Kew, just outside London. He had recently published his Handbook of Coniferae and Ginkgoaceae, a definitive work on conifers, along with Albert Bruce Jackson, a botanist who also worked at Kew Gardens. These two studied the material given to them and concluded that the mystery trees were hybrids, with the Nootka cypress that had yielded the cone being the female parent and the male being the nearby Monterey cypress. In March, 1926, under the heading ‘A New Hybrid Conifer’, Dalimore and Jackson published their finding in the Kew Bulletin of March, 1926 and named the tree Cupressus x leylandii, in honor of Christopher Leyland.
By this time at least one of the original trees was 35 feet tall and the potential of this rapidly growing, dense and healthy tree was beginning to be realized. Cuttings were taken by Kew Gardens, Edinburgh Botanic Gardens and Bedgebury Pinetum in Kent and by 1930 the famous nursery Hilliers was listing this plant in their extensive catalogue.
Around 1870, the same cross had occurred in a garden in Rostrevor, County Down, Ireland. There are few records of this plant. Apparently cuttings were taken and the plant was named ‘Rostrevor’, but it is not clear what contribution they made to the current stock of Leyland Cypress.
In the 1930s this chance hybridization occurred again in a garden in Ferndown, Dorset. It was discovered in 1940, named ‘Stapehill’, after the nursery which took the plant and propagated it, but it fell out of commercial production in the 1970s when it proved not to be drought-resistant.
Leyland himself had recognized the potential of this ‘super-tree’, noticing its rapid growth and resistance to the salt-laden winds blowing across his property from the seas off Cornwall. This spurred nurseries to offer the tree as a specimen and hedging plant, although in the limited space of most English gardens it proved too large unless regularly trimmed.
Although all attempts to artificially produce this cross again failed, it did occur naturally on a number of other occasions, the most interesting occurring in 1962, at the Castlewellan Forest Park in County Down, Ireland where a tree was raised from the golden form of Monterey Cypress growing near the golden form of the Nootka cypress. This tree was compact with golden foliage and was named ‘Castlewellan’. There are other golden forms of the Leyland Cypress listed from time to time, which differ little if at all from the original ‘Castlewellan’.
There have also been some introductions in more recent times, most notably from the Van den Dool Nurseries, Waddinxveen, The Netherlands. These are ‘Leylandii 2001’, which is a more compact form especially suitable for specimens; ‘Blue Jeans’®; and ‘Relax’®, but all these forms are not widely available.
Although the trees survived, Haggerston Castle did not. In 1926 Mr. Leyland died and the estate was sold off and the castle was demolished. Leighton Hall did better, and although the house is unoccupied, the farm and grounds are a horse stud farm today.
Although originally kept separate, most of the varieties have now become mixed in commercial growing and are no longer sold by specific names. This is of minor importance to ordinary buyers, since the differences between these various forms are slight and do not affect the usefulness of this plant. Most plants are derived from ‘Haggerston Gray’, which despite its name is green in color. It is also the easiest to propagate. ‘Leighton Green’ is a little more dense and compact, and produced a large number of sterile cones, meaning they normally do not produce seed that will germinate.
Once the virtues of this tree became apparent it was widely produced and sold for hedging. In 1941, the first plants appeared in the United States when rooted cuttings were sent to the Institute of Forest Genetics at Placerville, California. About 1950, the tree was introduced at the Strybing Arboretum in San Francisco and to the University of Washington Arboretum in Seattle at about the same time. It was officially introduced in the east at the U. S. National Arboretum in 1953. From these original introductions it was distributed in the south by 1965, through Clemson University in South Carolina, and soon became as popular as it was in Europe.
Description
The Leyland Cypress is a large, upright tree that can grow to 50 feet in just 15 years, growing from 2 to 4 feet a year. If well-watered and fertilizer it can even grow 5 feet in a single year when young. It makes a dense, upright evergreen tree with rich-green foliage throughout the year. It can be grown as a specimen tree, as a windbreak or screen, or clipped into a hedge of almost any size and proportion.
The Leyland Cypress is hardy from zones 5 to 9 doing especially well in zones 6 to 8, where it tolerates and even thrives in the heat and humidity of the South, unlike either of its parents. Only south of South Carolina may problems develop from high summer heat and humidity.
It will grow in almost all kinds of soil, from sand to clay and tolerate both damp conditions and periods of drought. It also tolerates urban air-pollution, traffic fumes and salt-spray, meaning it can be grown along highways and the seashore. It is also hardly ever affected by pests and diseases, its only enemy being deer, who will graze on the foliage in winter if they can. However with such rapid growth it will usually recover from moderate deer-damage very quickly.
As a hedging plant it can be clipped at almost any time of year and maintained as a short narrow hedge or allowed to grow larger. Because of the rapid growth regular clipping is necessary even with mature hedges. In some areas, such as the South, Leyland Cypress is grown as a Christmas tree plant.
One mistake sometimes made by gardeners is to underestimate the future size of the Leyland Cypress. In ten years unclipped trees can be 30 feet tall and mature trees can be 20 feet wide. In 20 years trees will be 50 feet tall. So they are most suitable for tall screens on larger property and less suitable for smaller screens and hedges that do not need regular clipping. Consider the various types of Thuja, or Arborvitae trees for smaller screens and hedges.
Cypress Trees Around The World
The most ancient kind of cypress is the Italian cypress. It is referred to in Greek and Roman writing and has been planted and cultivated for millennia. Since it lives for centuries, ancient specimens can be seen all across the southern parts of Europe and around the Mediterranean, as well as younger but still beautiful trees in California and other warmer states.
The Italian Cypress is related to several other cypress trees that are found from North Africa to China. These are together called the Old Word Cypress. Most of these trees are adapted to drier conditions, with some, such as the Sahara Cypress, living in very arid areas, while others are found at high altitudes in mountainous regions, for example the Tibetan Cypress. They are often valued by local people and planted around temples and sacred places. This has been an important way they have been protected from de-forestation and over-grazing – so much so that in many cases they are rare in the wild but widely planted by humans. This makes it difficult to know where exactly some trees were originally wild, which in turn makes it difficult for botanists to study their relationships.
When the first settlers reached the west of America, they found many cypress trees growing from Arizona to Alaska. These vary from towering forest trees to shrubby plants that are part of the chaparral in many dry areas. These New World Cypress vary enormously. Some, like the Arizona Cypress and its relatives are suitable for very hot, dry locations and in that resemble many of the Old World Cypress. Others, such as the Monterey Cypress and the Nootka Cypress prefer cooler conditions, with the Nootka Cypress in particular growing in very cold areas and needing damp soil. The Monterey Cypress is a symbol of the rugged California coast-line and visits to the oldest and most famous trees are part of the tourist itinerary of every visitor.
When these New World Cypress were first discovered, they were taken back to Europe and grown as novelties in the gardens of the rich and famous. It was the bringing together of trees that naturally grew in different places that led to the creation of the hybrid Leyland Cypress, by far the most important of all the cypress trees in gardens.
So whatever type of cypress tree you choose for your garden, you are growing history and a lesson in geography as well. These trees may sometimes be taken for granted as garden work-horses, serving important purposes but in the end being seen as a green background. However they are as interesting and have as rich a history as the most exotic garden plant and deserve to be appreciated for their diversity and interest. They include some of the rarest trees on the planet, standing on the brink of extinction, as well as some of the most widely grown, thriving around the globe in the most unexpected places.
The Species and Variety of Cypress
There are around 18 different species of Cupressus known, but only about eight are grown to any extent in gardens. In fact the most widely-grown Cypress is not a wild species at all but the remarkable hybrid Leyland Cypress.
Cypress are distributed over a large part of the globe and they show groupings based largely on where they naturally grow. They can be divided into three groups, the Old World Cypress, the New World Cypress (Hesperocyparis) and a third group with just two members, technically called Callitropsis or Xanthocyparis.
| Major Groups Of Cypress Trees | ||
|---|---|---|
| Old World Cypress | New World Cypress | Xanthocyparis |
| Bhutan Cypress Cupressus cashmeriana |
Arizona Cypress Cupressus arizonica |
Nootka Cypress Cupressus nootkatensis |
| THE MAJOR GROUPS OF CYPRESS TREES | ||
| Old World Cypress | New World Cypress | Xanthocyparis |
| Bhutan Cypress Cupressus cashmeriana |
Arizona Cypress Cupressus arizonica |
Nootka Cypress Cupressus nootkatensis |
| Cheng Cypress Cupressus chengiana |
Baker Cypress Cupressus bakeri |
Vietnam Cypress Cupressus vietnamiensis |
| Yunnan Cypress Cupressus duclouxiana |
Gowen Cypress Cupressus goveniana |
|
| Sahara Cypress Cupressus dupreziana |
Guadalupe Cypress Cupressus guadalupensis |
|
| Chinese Weeping Cypress Cupressus funebris |
Mexican White Cedar Cupressus lusitanica |
|
| Tibetan Cypress Cupressus gigantea |
MacNab Cypress Cupressus macnabiana |
|
| Italian Cypress Cupressus sempervirens |
Monterey Cypress Cupressus macrocarpa |
|
| Himalayan Cypress Cupressus torulosa |
Sargent Cypress Cupressus sargentii |
|
Old World Species of Cypress
Sahara Cypress, Cupressus dupreziana
This critically endangered species is certainly the rarest of all the cypress trees. It grows in the Sahara desert, hundreds of miles from any other trees, in the Tassili n’Ajjer mountains of southern Algeria. There are only 233 trees left of this species, which seems unable to reproduce itself in the wild because of the dry conditions resulting from desertification of the region. Most of the trees are between 1,000 and 2,000 years old, meaning they were around when North Africa was a major source of grain for the Roman Empire. To preserve this plant, about 1,000 have been raised from seed and successfully planted at the National Arboretum in Canberra, Australia, as part of their 100 Forests, 100 Gardens project.
The closely related Moroccan Cypress (Cupressus dupreziana var. atlantica) is found only in the valley of the Oued n’Fiss river in the High Atlas Mountains of Morocco. It is sometimes treated as a separate species (Cupressus atlantica) and suffers from the same problems as the Sahara Cypress, with overgrazing by goats severely limited the potential for regeneration, leaving a small population of old trees.
Tibetan Cypress, Cupressus gigantea
This remarkable cypress grows to a great size and is found in the south-east of Tibet and neighboring parts of China. A tree estimated to be over 2,500 years old is 160 feet tall and almost 19 feet in diameter. This tree is revered by Tibetan Buddhists, who call it the ‘God of Tree’. It is also called ‘King Cypress’ and stands in a grove of other very tall and old trees in the village of Bajie in south-eastern Tibet.
Bhutan, or Weeping Cypress, Cupressus cashmeriana
This attractive and ornamental tree is cultivated for the beauty of its pendulous branches. Overall the tree has an upright, conical to columnar habit, with upward-growing main branches. However the smaller side-branches fall vertically, with flattened branchlets, giving a weeping habit. Trees grow between 60 and 150 feet in height. The foliage is blue-green in color, on thin, flattened shoots.
The Bhutan Cypress is native to that small country, where it is the official national tree and it is often planted around monasteries. It is also found growing naturally in Arunachal Pradesh, India and it is cultivated in China and Nepal. Wild populations are only found in a very limited area and are considered threatened.
This tree is hardy only in zone 9 and also needs hot summers to thrive. Trees planted in milder places with damp summers, such as the British Isles, as usually short-lived. Although there are no specifically named cultivars it seems likely that planted trees have been selected for their pendulous habit, since many wild trees don’t show this features in a pronounced way.
Cheng Cypress, Cupressus chengiana
This is a rare cypress tree growing in a few locations in Northern China. It is sometimes listed as Cupressus jiangeensis.
Yunnan Cypress, Cupressus duclouxiana
The threatened species grows in isolated parts of Western China.
Chinese Weeping Cypress, Cupressus funebris
Although widely cultivated across China and in many other countries as well, true wild populations of this tree are only known from a few locations in western China, in Guizhou, Hunan and Sichuan provinces[1]. Because of its attractive form, this tree is also grown in California and other warmer locations and even as a houseplant in cooler areas. It is hardy in zone 9.
The Chinese Weeping Cypress forms an attractive tree from 60 to 100 feet in height, although cultivated trees are normally much smaller, with dense, bright green foliage in pendulous clusters. Young trees may show mostly juvenile (spiny) foliage for up to ten years before developing the characteristic scale-like Cypress foliage.
This tree is considered by some botanists to be very close to and possible just a variant form of the Himalayan Cypress, Cupressus torulosa.
Italian Cypress, Cupressus sempervirens
This is a widely grown Cypress and it is characteristic of the landscape in many parts of the Mediterranean, in California and in other warmer areas. It is a tree growing 80-150 feet tall but just a few feet wide and with a trunk up to 3 feet in diameter. It is found in two distinct forms, the most common and most attractive being a narrow, upright or ‘fastigiate’ form found in Italy and France. The other form has horizontal branches and occurs mostly in Greece and the eastern Mediterranean. The foliage is scale-like and a very dark green color, making trees very prominent in the landscape. The round to oblong cones are ¾ to 1¼ inches long.
This is the cypress seen in paintings and photographs of Tuscany and Provence, often clustered on hillsides or planted along roads or as avenues leading to the entrances of large homes. It is also widely used as a hedging plant, clipping into a dense screen of a rich deep green color and the perfect background for a formal garden. It is likely that the ‘wild’ tree is the form found in Greece, Turkey, Lebanon and Israel, while the narrow form, often variously called var. sempervirens, var. stricta, or Cupressus pyramidalis has probably been cultivated for millennia and is found growing in wild situations throughout the Mediterranean region.
Italian cypress is a long-lived tree, thriving for centuries. Visitors to Florence who go to the famous Boboli Gardens can see an avenue of cypress over 300 years old, still healthy and robust. A famous tree once grew in northern Italy on the road to the Simplon Pass into Switzerland. This tree was reputed to have been planted before the birth of Christ and was so famous that Napoleon re-routed his army to avoid damaging it. The tree was blown down during a storm in 1944[2]. There are trees in Iran reputed to be 4,000 years old.
Besides its striking beauty, the Italian cypress is also useful. Indeed, when God commanded Noah to build the Ark, he told him to, “Make thee an ark of gopher wood”[3], which is taken by many to mean cypress. The wood is very durable, pleasant smelling and repels clothes moths. It has been used for centuries to build chests for storing clothes and linens, in the same manner as cedar chests. The Holy Door of St. Peter’s cathedral in Rome was made from cypress2 and was still sound after 1,100 years when it was replaced with a bronze door in 1949[4].
Italian Cypress is hardy to zone 7 and prefers areas with hot, drier summers, so it is best grown in areas that do not have a lot of summer rain. Once established, trees are very drought resistant. It will grow in all kinds of soil, from sand to clay, making this a very versatile tree that can be grown in all the warmer parts of the world. Growth in young trees is rapid, up to 3 feet in a year, so a mature form and good height are quickly achieved. Growth slows as trees mature.
New World Species of Cypress
Arizona cypress, Cupressus arizonica
This cypress is found growing naturally at higher altitudes in mountain regions of Arizona, into adjacent parts of New Mexico and Texas, as well as in Mexico. It forms a tree that is typically about 40 feet tall, but it can sometimes reach 90 feet. It is conical or rounded in shape with shedding bark that is dark brown when freshly exposed. The foliage resembles the adult form of Junipers and is pale bluish-green in color, with a slight silvery sheen.
The Arizona Cypress is adapted to hot, dry conditions and is grown as an ornamental tree is climates of that kind around the world. It is hardy to zone 7 and is often used as a windbreak in dry states, where its drought-tolerance makes it a good low-maintenance tree.
There are some selected forms of the Arizona Cypress available:
- ‘Compacta’: a lower growing form with a neat, conical shape
- ‘Gareei’: a form with more silver-blue foliage
- ‘Glauca’: notable for its silvery-grey foliage color
- ‘Greenwood’: a medium-sized form with silver, grey-green foliage
- ‘Oblonga’: a spreading form with horizontal branches and grey-green foliage
- ‘Verhalenii’: a graceful and more colorful form with bright silver-blue blue foliage of a softer texture
- ‘Watersii’: a compact form making a narrow pyramid
Botanists recognize several varieties of the Arizona Cypress, which are sometimes listed as separate species:
- Cupressus arizonica var. arizonica
- Cupressus arizonica var. glabra
- Cupressus arizonica var. montana
- Cupressus arizonica var. nevadensis
- Cupressus arizonica var. stephensonii
Baker cypress, Cupressus bakeri
This rare tree, which can reach 75 feet in height, is native to the mountains of northern California.
Gowen cypress, Cupressus goveniana
This endangered species is another of the Californian cypress trees.
Guadalupe cypress, Cupressus guadalupensis
(Probably identical to C. forbesii)
The endangered cypress is only found growing on Guadalupe Island, off Baja California, [not the Caribbean island of Guadeloupe].
MacNab cypress, Cupressus macnabiana
This tree can be large or shrubby, depending on growing conditions. It is wide-spread in Northern California as an important part of the chaparral[5].
Mexican white cedar, Cupressus lusitanica
This cypress tree is native to central America, occurring naturally in Belize, Guatemala, Honduras, El Salvador and Mexico, usually in mountains between 4,000 and 10,000 feet up, often on rocky slopes and cliffs either in pure stands or mixed with other forest trees. It grows into a large tree 75-100 feet tall, pyramidal in shape. Some very old trees in the wild are almost 200 feet tall. Mature trees often develop pendulous branches. The foliage is blue-green and the bark reddish-brown.
The name lusitanica means ‘from Portugal’, because this tree was first described in 1768 from specimens growing at the monastery of Buçaco near Coimbra in Portugal. The botanist Miller who described it thought it may have come from the Portugese colony of Goa and it is still sometimes called Cedar-of-Goa. However it has been shown that these trees were in fact planted in 1634 from seeds brought back from Mexico2
This tree is widely planted in Mexico as an ornamental, as well as being harvested from wild and planted trees for lumber. It has been planted for timber all around the world, including New Zealand, South Africa, Argentina, Bolivia and Colombia. It is grown ornamentally in the UK and in the southern US, especially in Texas. It is especially useful as a wind-break and screen because it has a dense branching habit from an early age. The Mexican White Cedar is hardy to zone 9. It thrives in warm, sunny climates with limited rainfall.
Monterey cypress, Cupressus macrocarpa
The Monterey Cypress is widely cultivated, but in its native area, which is central California, it is only found in two forests, now protected areas. These are the Point Lobos State Reserve and the Del Monte Forest. These parks are very small, just a mile or two long along the cliffs, and going inland just one or two hundred yards. Montery Cypress is considered a vulnerable species in its natural habitat. With such small areas remaining, the risk of destruction by fire is of concern to conservationists. However genetically there is no risk of extinction, since planted and naturalized trees are widespread around the globe.
In its natural habitat winters are mild but summers are moist and cool, with almost constant sea mists. Outside its protected areas the tree is widely grown both in other parts of California and also around the world, from Europe to Australia and New Zealand. It thrives in all areas with a similar climate of cooler, damp summers, but when grown in areas with hot summers it is susceptible to a disease – cypress canker (Seiridium cardinale, a fungus) – which usually quickly kills trees planted in unsuitable locations. On the other hand, it has found the climate in New Zealand so suitable that it has become naturalized and is found growing wild throughout the islands.
Although there are trees in California reputed to be 2,000 years old, studies have so far only found a tree that was 284 years old in the 1920’s[6]. The main feature seen on the famous trees along the coast of California is their windswept habit, with a few horizontal branches and a very picturesque outline. When grown under garden conditions the tree has a pyramidal habit, only becoming flat-topped when mature. At that stage the trees resemble the famous Cedar of Lebanon, a source of confusion, although these two trees are not in any way closely related. Cultivated trees in favorable climates reach 60 to 90 feet in height.
Mature trees show the typical flattened leaf scales pressed against the stem, but young trees have the pronounced juvenile foliage seen in other cypress, with sharp, pointed leaves sticking out from the stems. Trees in hedges that are regularly clipped will continue to produce new shoots of this juvenile form2, making identification difficult.
The Monterey Cypress is hardy between zones 7 and 9 and tolerates a wide range of soils from sand to clay and from slightly alkaline to acidic. It does not tolerate wet soil. It is also very tolerant of wind and also of salt, making it ideal for planting in coastal areas.
A variety of special forms of this tree have been selected, including:
forma fastigiata the branches of this common form, regularly seen in batches of seedlings, are erect-growing, giving a tree a columnar appearance. This division into plants with an upright form and plants with a spreading form is also seen in the Italian Cypress (C. sempervirens)
‘Lutea’; Donard Gold’; ‘Goldcrest’; and ‘Golden Pillar’ are all forms with young shoots and leaves of a beautiful yellow color. ‘Brunniana Aurea’ and ‘Gold Rocket’ combine gold foliage with a columnar form. As it typical with golden forms of most conifers, the gold color develops best on trees grown in full sun.
‘Aurea Saligna’ is a columnar tree with cascading, thread-like side branches with golden foliage
‘Greenstead Magnificent’ is a dwarf form with blue-green foliage
‘Pygmaea’ is a very dwarf and dense form.
Sargent cypress, Cupressus sargentii
This is another California species that can grow to 50 feet in height.
Himalayan cypress, Cupressus torulosa
(Probably identical to C. tonkinensis)
This large tree, growing to almost 50 feet tall, is found in the western Himalaya. It may also grow in western China and Vietnam, but it is probably not in fact truly wild there.
Xanthocyparis Cypresses
Nootka cypress, Cupressus nootkatensis
(Also known as Callitropsis nootkatensis or Xanthocyparis nootkatensis)
The Nootka cypress, also called Sitka cypress, Alaskan cedar, yellow cypress or yellow-cedar, is a tree that is widespread across a large part of the Pacific Coast Region of north-west North America, from Prince William Sound in Alaska, through British Columbia in Canada, Washington State and through Oregon into the Siskyou Mountains in northern California. Because of its wide distribution it is not considered under any threat, although its distribution is being affected by climate change[7].
This tree grows up to 130 feet tall in the wild, where it is usually found in damp soil at high altitudes close to the tree line. The trunk can be six feet in diameter near the base. It has slightly pendulous branches with the foliage in flattened sprays, rather than in the irregular form typical of most other cypress[8]. The cones are similar to those of the Mexican cypress, which can also show flattened sprays of foliage. The leaves have a strong, slightly unpleasant smell when crushed, which distinguishes the tree from the Port Orford cedar, or Lawson cypress, Chamaecyparis lawsoniana, which it otherwise closely resembles.
The characteristic pendulous branches allow this tree to shed snow readily, avoiding breakage and making it possible for the tree to thrive in areas that often receive 30 feet in snow during a winter[9]. Trees live to a great age, over 1,000 years, with stumps over 1,800 years old having been found in logged areas. There is a standing tree that is almost 200 feet tall at Kelsey Bay on Vancouver Island in British Columbia.
In gardens Nootka cypress grows to around 35 feet, with a spread of perhaps 20 feet. It normally retains a single central trunk for its whole life. This tree grows best in moist soils and more humid areas, but it is hardy to minus 40 degrees Fahrenheit (zone 4). This tree is always attractive and healthy, with no serious pests or diseases when grown in a suitable area.
There are a small number of cultivated varieties including:
- ‘Compacta’ A dwarf form of dense habit.
- ‘Lutea’ Young shoots yellow, finally green. Sometimes wrongly referred to as ‘Aurea’.
- ‘Pendula’ A striking variety with an upright trunk, the primary branches horizontal and the branchlets hanging from the lower side of the branches in a completely vertical line. This selection is an extreme form of the natural pendulous habit of this tree.
Vietnam cypress, Cupressus vietnamensis
(Also known as Xanthocyparis vietnamensis)
This is a rare, newly discovered species from Vietnam, found only in 1997. It is found in just 5 or 6 small locations in mountains at high altitude, mostly in the Bat Dai Son Mountains and some other nearby areas. It is a small tree to around 40 feet and is unique for showing juvenile, adult and intermediate foliage forms on mature trees. There are estimated to be a little more than 500 individual trees in existence. It is considered an endangered species[10] and has been protected from logging by the government of Vietnam.
It was the discovery of this tree that led to the re-organization of the different cypress species and the realization of the close relationship between this tree and the Nootka Cypress, despite being separated by the enormous Pacific Ocean.
The Names of Cypress Trees
Anyone beginning to read about the different species of cypress trees will quickly become confused. They will notice that these plants appear under a variety of different names, depending on which book or source is looked at, and also when the material was originally published. For anyone with some experience in reading about plants, using the names given them by botanists, this is not a unique experience.
Like many other plants, cypress trees have been re-named frequently by botanists[12] as more were discovered and more research carried out. In particular, in this century the use of DNA analysis has revealed relationships that were not recognized before.
When first named, the only cypress tree of importance was the Italian cypress, Cupressus sempervirens, and this tree was known in Persian, Greek and Roman times. The Greeks called the tree ‘kyparissos’. It was always associated with funerals and death and is still seen today growing in cemeteries. For all that time it has kept the Latin name Cupressus, which was ‘officially’ given to it in 1753 by the famous botanist Linnaeus. A variety of other trees, some not even conifers, are commonly called ‘Cypress’, which can and does cause confusion among gardeners.
As other cypress trees were discovered, at first they were simply added to the original group, but following the discovery and study of the North American cypress trees, new names and new divisions began to develop. For example, if you look in some sources you will find the Chinese Weeping Cypress (C.funebris) and the Nootka Cypress (C. nootkatensis) listed as Chamaecyparis – a related genus of conifers. The reverse of this also occurs, where the Lawson Cypress (Chamaecyparis lawsoniana) is sometimes listed among the true Cypress.
For a long time it has been clear to botanists that the ‘Old World Cypress’, which include the Italian Cypress and the Chinese species, are different from the ‘New World Cypress’, made up of the Arizona Cypress and other American species. In addition it was thought that Chamaecyparis was close to or part of the cypresses.
The development of DNA analysis in recent decades has revolutionized the naming of plants in a remarkable way that has however also caused a lot of confusion for gardeners. DNA analysis is used to measure the ‘closeness’ of different species of plants to each other and generate maps showing this.
Among the many plants being studied and re-organized, conifers have had a lot of attention and for cypress, the discovery at the end of the last century of a new species of cypress, the Vietnam Cypress, caused large changes. Much of this work has been done by Aljos Farjon[13], one of the world’s premier conifer taxonomist and we can summarize the current situation as follows:
- Cypress trees are related to Junipers, their closest relatives.
- Chamaecyparis is less closely related and is not in fact a part of the cypress group.
- The Old World Cypresses and New World Cypresses are distinct as groups and should probably be separated. The name Hesperocyparis is becoming widely accepted for the New Word cypresses and will probably become the normal name in time.
- The Vietnam Cypress and the Nootka Cypress are closely related to each other and less closely related to the other cypress. They are probably also sufficiently separate from each other to be called Xanthocyparis vietnamensis and Callitropsis nootkatensis, but this is still being studied and disputed among the experts. If it is decided to put them together in the same group, that group will be called Xanthocyparis[14].
Many gardeners become upset when the names of familiar plants are changed, especially at this time with the very large changes that are occurring from DNA analysis. However it should be remembered that the plants themselves remain the same and that the only thing changing is our understanding of how they are related to each other. ‘A rose by any other name’, as the saying goes.
Diagram showing the relationships, based on DNA analysis, between the different cypress trees and the junipers.[15]
CHOOSING THE RIGHT CYPRESS
Hardiness Zone
Because of their natural distribution over large parts of the world, different Cypress grow in many different climates, so no matter where you live, there is a suitable type for your climate and growing conditions. Depending on your growing zone, different cypress trees will do best, so choose from this table the best type for your area.
| USDA Hardiness Zone | Some Suitable Cypress | ||||
| Arizona Cypress | Monterey Cypress | Leyland Cypress | Italian Cypress | Nootka Cypress | |
| Zone 4 | X | ||||
| Zone 5 | X | X | |||
| Zone 6 | X | X | |||
| Zone 7 | X | X | X | X | X |
| Zone 8 | X | X | X | X | X |
| Zone 9 | X | X | X | X | |
| Zone 10 | X | X | |||
Rainfall and Drought-resistance
The idea cypress trees for drier areas with periods of drought are the Italian Cypress and the Arizona Cypress. Both have excellent drought tolerance and thrive in hot conditions.
For mild areas with cool summers and good rainfall, such as east and west coasts, the Monterey Cypress grows well, while in cooler areas with good rainfall the Nootka Cypress will thrive.
For almost all but the hottest and coldest regions the Leyland Cypress is the first and premier choice for all purposes.
Light and Shade
Cypress trees, like most evergreens, grow best in full sun. This is especially true of the drought tolerant species like the Arizona Cypress and the Italian Cypress. Leyland Cypress also likes full sun, at least on one side of a hedge or screen. Those that thrive in damper areas, like Nootka Cypress, will grow well in partial shade, especially when young and they will usually grow up into the sun over time.
Soil Types
Cypress trees generally do well in most types of soil. The New Word Cypress, including the Arizona Cypress, do well on alkaline soils but will grow well in any well-drained soil. Monterey Cypress is known for its tolerance of rocky, poor soil and exposed situations. Nootka Cypress does best in richer soils, with organic material and a good supply of water. Leyland Cypress is remarkable for its tolerance of a wide range of soils, from acid to alkali and from sand to clay, although it does best in soils that are not constantly wet.
Planting Cypress Trees
Spacing
When planting your Cypress in rows or groups it is important to space them correctly. If they are too close they will not develop well, but if they are too far apart they may take years to meet, or even always stay slightly separated. The ideal spacing will allow the plants to grow, yet mean that in a few years they will form a single mass of plants.
For a screen, there are two methods of spacing and planting used:
- Single row: this is the most obvious method and for a shorter hedge plants should be placed 3 to 6 feet apart, depending on their final size and your needs. If your screen or hedge is against a building, plant 6 feet from the wall, to protect the foundations. If you are planting against a fence, plant 3 feet from the fence so that the lower part of the plants remains bushy and the hedge remains on your side of the property line. Use the wider spacing given here for vigorous plants like Leyland Cypress, and the smaller spacing for others types.
- For a shorter hedge, less than 8 feet tall, plant 3 feet apart.
- For a larger hedge or screen, plant 4 to 6 feet apart.
- Double row: This method will give a quicker screen and use slightly fewer plants for the density of screen created. Make a double row, allowing 3-4 feet between the rows. Space the plants 6 to10 feet. Stagger the plants so each one is in the space of the other row. This method will give a good dense screen in a short time.
To calculate how many plants you need for a screen, first measure the distance. Then decide on the spacing. Divide the distance by the spacing and round-up to the next number if the answer is a fraction. For a double row multiply this number by 2. Remember that the first plant will be placed half the spacing distance from the end of the row, and the last plant will be placed in the same way. Place these plants first and then balance out the remaining plants in-between at even distances.
Remember that whatever spacing you use it is important to keep everything at the same distance and place the trees very evenly spaced. Use a measuring tape to get everything laid-out before planting. The extra work will be worth it when you see the perfect screen you have created.
If you want your screen to have foliage right to the ground it is important to start trimming early in the life of your screen. Although Cypress are better than many other plants at retaining their foliage closer to the ground, if you let the plants grow untrimmed until they are the height you want they will be thin lower down and may not give you the screening you are trying to develop. Some cypress trees, like the Monterey Cypress, are known for developing a tall trunk with a few spreading branches, so they are not suitable for screens or hedges.
For a Specimen take the width given for your tree, add it to the final widths of the nearest other trees or shrubs and divide by two. Plant the trees at that distance apart. That way your garden will not become overgrown and crowded, forcing you to constantly prune and clip your plants.
Planting in groups is a great way to work with Cypress trees when used as specimens. Always plant your shrubs using odd numbers, 3, 5, 7, 9, 11, etc. This will give your planting a more natural look. Look at the width you particular tree will reach and space your plants at about 75% of that. In a few years they will have grown together into an attractive group.
Planting
It is worth taking a little effort to give your Cypress trees a good start in life. Once the planting positions have been decided, dig over the area, going down to the full depth of a spade and turning the soil over while removing weeds and their roots. Don’t worry about taking out stones unless they are bigger than your clenched fist. Add some organic material to the soil to encourage root development. This could be garden compost, well-rotted manure or rotted leaves. If you don’t have these materials, then some peat-moss can be used instead and that is readily available everywhere. Mix a big bucket of this organic material into the soil of the planting area of each tree.
When planting hedges it is often easier to dig a trench along the line, rather than individual holes. This makes it easier to space the plants correctly and adjust them to get a perfectly even and straight row.
The night before planting, give the potted trees a heavy watering. Dig a hole two or three times the width of the pot, but only to the same depth as the pot. Once you have dug your hole, add soil if necessary and press with your foot in the bottom of the hole to make sure the soil is firm underneath the plant. Cypress should be planted at the same depth in the ground as they were in the pot – do not bury the lower foliage, or leave part of the root-ball exposed above ground.
Place the plant in the hole and put back about three-quarters of the soil. Using the feet, firm the soil down around the roots, so that there are no air-pockets in the soil and so that the tree is held firmly and can’t shift around. Fill the hole to the top with water and wait for it all to drain away. When all the water has gone, replace the rest of the soil and make everything level and neat. No more water needs to be added, unless the surrounding soil is very dry. Mulch the roots with a thick layer of organic mulch. This should be 2-3 inches thick and completely cover the root zone and a little further out. Keep the mulch off the foliage and trunk of the tree. The mulch will reduce weeds, conserve water and keep the soil cooler during the hottest weather.
You do not need to use a stake on your tree, in fact that is a bad idea, rather like giving a child a walking stick – your plant will be stronger and tougher without being held up artificially.
During the first growing season water your plants deeply at least once a week, and twice a week during hot, dry weather. Leaving a hose running slowly near the base of the plant is better than spraying water onto the soil – you disturb the soil less and the water will have a chance to penetrate deeply around the roots. For hedges and screens installing a trickle hose along the base of the hedge makes watering much easier. This can be left in place as the hedge grows so that it can be used during dry spells in future years.
Caring For Cypress Trees
One of the great things about most of the Cypress trees is that they don’t need much care. Leyland Cypress in particular is one of the most low-maintenance plants available. However a little seasonal care will give the best possible results and make sure that your trees grow vigorously, always look lush and green and remain healthy.
Fertilizer
Each spring add a layer of mulch over the roots of your plant. This should be 3 inches deep and should extend out beyond the line of the foliage, but not touch the trunk of your tree. Use something organic like garden compost or rotted leaves rather than bark or stones, which will not add any nutrients to the soil. Old mulch from previous years can be removed if it is woody and hard, but otherwise it can just be covered with the new mulch.
When your plants are young, some fertilizer is helpful to encourage them to grow vigorously and become well-established. Use a fertilizer designed for evergreen trees. This will give a good supply of the nitrogen these trees need to keep them healthy and deep green.
When they are young a liquid fertilizer is best, but for mature plants a granular fertilizer is more suitable and it should be applied in spring. This should be sprinkled over the root zone and can be place over mulch too. Evergreen fertilizer has a lot of nitrogen in it, so look for something with a high first number, like 20-10-10. A light sprinkle of fertilizer over the whole root-zone is all that is needed and you should avoid heavy fertilizing. This zone extends about two feet further out from the plant than the spread of the foliage. Keep fertilizer away from the trunk. If you want to grow your Cypress trees organically, products like soya-bean meal, cotton-seed meal or alfalfa pellets are suitable, although usually rich mulch will be all that is needed.
Trimming and Shearing Cypress Trees
All the different kinds of Cypress can be grown without any clipping and they will become attractive plants and make dense screens. A little clipping in late summer of young plants will help to make them denser later in life.
However if you want to trim your screen or hedge regularly, for appearance or to keep it smaller, then this should begin during the first year. Do not wait until the trees reach the desired height and then start clipping. Worse, do not wait until they become too large and then try to cut them back hard. Cypress trees will not re-sprout from bare branches, so they cannot be lopped and trimmed as many deciduous trees can be. When clipping or trimming, it is essential to always leave some foliage in the clipped area, as bare branches will never sprout new leaves.
Begin clipping lightly as soon as the plants are established. Always trim so that the upper part is a little narrower than at ground level. In other words, the sides should slope inwards slightly. This only need be by a few degrees, but if there is no inward slope the lower branches will become thin over time and then become bare and may eventually die. Because the upper growth will always be more vigorous, this means trimming more from the upper part of the plants than the lower part. Many new gardeners make the mistake of taking the same amount off all over the plant, resulting in hedges that bulge out towards the top, causing the lower parts to thin and die over time..
The best times for trimming Cypress hedges and screens are in late spring, early summer and early to mid-fall. Avoid trimming during hot and dry weather, as the foliage could burn, especially if the soil is dry. In mild areas hedges can also be trimmed in winter.
Use gas or electric hedge shears, or hand clippers, for your hedge. Do not use coarse cutting machinery like chain saws (yes, some people do!). Cut branches so they grow horizontally and do not try to ‘tuck in’ shoots, or leave long shoots growing upwards on the outside, or your hedge will fall apart easily, especially under snow.
Pests and Diseases[16]
Cypress trees are tough, hardy trees that do not have serious problems, but there are a few things to watch for. All Cypress can be eaten by deer. If low-maintenance is your goal, The Leyland Cypress is especially pest and disease resistant, making it the ideal choice for almost any area. Generally disease and pest problems are greatest when plants are grown outside their ‘comfort zone’ for humidity, cold and moisture, so select the best tree for your area and most problems will not be seen.
Potential Insect Pests
Spider Mites: these minute relatives of spiders are sometimes found, especially in hot, dry conditions. They are too small to be seen easily, but cause a yellowing or ‘bronzing’ of the foliage. Sometimes fine webbing can also be seen, indicating a heavy infestation. Spraying the plants regularly with water during dry weather usually prevents them from becoming a problem, or insecticidal soap will normally kill them.
Shoot blight: this fungus is only seen on weak plants, causing the stems to brown and die. Plants that are well-watered and fertilized will normally not suffer from this problem.
Cypress bark beetle: this tiny beetle burrows beneath the bark, causing twigs and branches to die. It is usually only seen on weak and dry trees, so keep trees well-watered and fertilized to prevent this pest.
Scale Insects: these insects live under a hard shell and look like bumps on the bark or leaves. Small amounts are not a problem and larger infestations can be treated with systemic insecticides.
Bagworms: these insects, which eat the leaves, make bags of web and twigs, which hang from the branches like Christmas decorations. Large quantities can cause significant leaf-loss. The organic sprays Spinosad and BT give good control if applied in May.
| Pests of Cypress Trees | ||
| Symptoms | Cause | Treatment |
| Yellow and bronze foliage | Spider mites | Water jet or insecticidal soap |
| Brown bumps on stems and leaves | Scale Insects | Systemic insecticide if severe |
| Small bags of web and twigs hanging on branches | Bagworms | Spinosad or BT sprays |
Potential Diseases
Dieback (Botryosphaeria and Seiridium): These fungal diseases causes dark, oval or elongated dry dead areas on stems, often with a raised border, with healthy living tissue around them, although the surrounding bark may be darker brown to purplish. These may occur mostly on stems, branches and in the fork between branches. A single canker will not grow and does not form a significant threat, but if multiple cankers form around a branch, water flow may be reduced, causing upper foliage to dry. Often a lot of resin may flow from cracks around the dead area, but this may also have other causes. If the fungus gets into the main trunk, it can kill the entire tree. Severe drought and winter freezes make it more likely that trees will become infected. Avoiding drought-stress will usually prevent the development of this die-back.
Phytophthora Root Rot: This soil disease is usually only seen in young trees planted in wet clay soils. If planting in these areas improve the drainage by adding plenty of coarse organic material to the soil. Infected trees show yellowing and dropping of the foliage and may eventually die.
[1] Cupressus funebris, IUCN Red List of Threatened Species. http://www.iucnredlist.org/details/42218/0
[2] Trees and Shrubs Hardy in the British Isles, Bean, W.J. (1914-1975) on-line edition
[3] Genesis 6:14
[4] The Rite of the Holy Door, The Vatican, http://www.vatican.va/news_services/liturgy/documents/ns_lit_doc_14121999_porta-santa_en.html
[5] Chaparral is a type of low-growing tree and shrub vegetation characteristic of warm, dry areas. It is often subject to fire, which is an important factor in controlling the amount of growth and mix of species.
[6] The Trees of California 2nd ed., W. L. Jepson, 1923, p. 75-79.
[7] Xanthocyparis nootkatensis, ICUN Red List of Endangered Species: http://www.iucnredlist.org/details/44029/0
[8] This feature led to the Nootka cypress being placed in the genus Chamaecyparis from 1842 until quite recently.
[9] Cupressus nootkatensis, Gymnosperm Data Base. http://www.conifers.org/cu/Cupressus_nootkatensis.php
[10] Xanthocyparis vietnamensis, Thomas, P. 2013. The IUCN Red List of Threatened Species 2013: http://dx.doi.org/10.2305/IUCN.UK.2013-1.RLTS.T44028A2991576.en .
[11] Those original trees now make up the core of a grade 1 listed arboretum managed today by the Royal Forestry Society. They include some coastal redwood trees over 120 feet tall, among the tallest in Europe.
[12] Manual of Cultivated Conifers, Krüssman, G., Timber Press 1972/1985 translation (by Epp, M.E.)
[13] A Monograph Of Cupressaceae And Sciadopitys, Farjon, Aljos. RBG Kew, 2005
[14] Personal communication, Robert Adams, Baylor University, Texas.
[15] A molecular re-examination of phylogenetic relationships among Juniperus, Cupressus, and the Hesperocyparis-Callitropsis-Xanthocyparis clades of Cupressaceae, Randall G. Terry, R.G., Adams, R.P. Phytologia (Jan 2, 2015) 97(1), pp.67-75
[16] Clemson Cooperative Extension: http://www.clemson.edu/extension/hgic/pests/plant_pests/trees/hgic2004.html
