Flat stems of feathery, blue-green foliage and ornamental combine to make Leyland cypress an appealing choice for medium to large landscapes. Leyland cypress trees grow 3 feet (1 m.) or more per year, making it an excellent choice for a quick specimen, lawn tree, or a privacy hedge. Information about Leyland cypress will help with growing healthy trees.
I. Appearance and CharacteristicsÂ
The Leyland cypress, Cupressus × leylandii, × Cuprocyparis leylandii or × Cupressocyparis leylandii, often referred to simply as leylandii, is a fast-growing coniferous evergreen tree much used in horticulture, primarily for hedges and screens. The tree is a hybrid of Monterey cypress (Cupressus macrocarpa) and Nootka cypress (Cupressus nootkatensis).
A large, evergreen tree, Cupressus × leylandii reaches a size between 20 and 25 m high, with its leaves giving it a compact, thick and regular habit. It grows very fast with yearly increases of 1 m. The leaves, about 1 mm long and close to the twig, are presented in flaky, slightly aromatic branches. They are dark green, somewhat paler on the underside, but can have different colors, depending on the cultivar. The crown of many forms is broadly columnar with slightly overhanging branch tips. The branches are slightly flattened and densely populated with scaly needles. The tree bark is dark red or brown and has deep grooves.
The seeds are found in cones about 2 cm in length, with eight scales and five seeds with tiny resinous vesicles. With the tree being a hybrid, its seeds are sterile. Over time, the cones shrink dry and turn gray or chocolate brown and then have a diameter of 1 cm.
Leyland cypress is light-demanding, but is tolerant of high levels of pollution and salt spray. A hardy, fast-growing natural hybrid, it thrives on a variety of soils, and sites are commonly planted in gardens to provide a quick boundary or shelter hedge, because of their rapid growth. Although widely used for screening, it has not been planted much for forestry purposes. In both forms of the hybrid, Leyland cypress combines the hardiness of the Nootka or Alaska cypress with the fast growth of the Monterey cypress.
The tallest Leyland cypress documented is about 40 m (130 ft) tall and still growing. However, because their roots are relatively shallow, a large leylandii tends to topple over. The shallow root structure also means that it is poorly adapted to areas with hot summers, such as the southern half of the United States. In these areas, it is prone to develop cypress canker disease, which is caused by the fungus Seiridium cardinale. Canker causes extensive dieback and ultimately kills the tree. In California’s Central Valley, they rarely live more than 10 years before succumbing, and not much longer in southern states like Alabama. In these areas, the canker-resistant Arizona cypress is much more successful. In northern areas where heavy snows occur, this plant is also susceptible to broken branches and uprooting in wet, heavy snow. The tree has also been introduced in Kenya on parts of Mount Kenya.
The sap can cause skin irritation in susceptible individuals.
II. How to Grow and Care
Sunlight
While Leyland cypress is forgiving of most light conditions, it does not tolerate dense shade. It grows best in open, sunny conditions or partially shaded areas.
Temperature and Humidity
Leyland cypress trees are best grown in USDA hardiness zones 6 to 10, with temperatures no lower than minus 8 degrees Fahrenheit. However, zone 5 gardeners have been successfully growing them by providing mulch and an A-frame shelter in the winter months to protect them from snow and ice damage. Such sheltering is feasible only while the plants are young—unless you keep them short by pruning. Luckily, once the plants have matured, sheltering becomes unnecessary, as they are often sufficiently cold-hardy in zone 5.
Watering
To help its roots get established after spring or summer planting, water your Leyland cypress regularly. A Leyland cypress will take a few months to get established and needs frequent deep watering during this time, but after that, a good rule of thumb is to give the tree about 1 gallon of water per week for each foot of height—a 10 feet tree will need roughly 10 gallons of water weekly. This can be divided into two equal waterings each week during the active growing season. In winter, reduce watering to just once or twice a month. Use soaker hoses, not sprinklers that will wet the foliage.
The tree tolerates occasional drought or brief waterlogging, but take care not to allow it to soak in wet soil for long periods, as this can encourage root rot.
Soil
Although it prefers moist, fertile, well-drained soil, this tree tolerates a wide range of soil types—clay, loam, sand, acidic, or alkaline. However, dense, wet soils are a prescription for root rot, which is usually fatal.
Fertilizing
Fertilize Leyland cypress in early spring, before new growth begins. Spread a general-purpose, 10-10-10 fertilizer around the tree’s drip line, according to product label instructions.
Pruning
This tree tends to grow best with a central trunk, so it’s wise to trim away competing leaders immediately after planting it. (Leyland cypress can, however, be grown as a multi-stemmed shrub, a favored method if using them in a hedge.)
The height of a Leyland cypress can be controlled but only through persistent pruning that starts when the plants are young. Trim the sides of Leyland cypress trees every year in July. After the leader has reached the height you want the tree to retain, make a pruning cut a few inches below that (which will leave room for the vertical growth of minor branches) to preclude any further significant upward growth, as you would do when pollarding a tree.
When individual branches turn brown and die back, they should be pruned out immediately, as this can be a sign of canker disease beginning. If caught early enough, you can sometimes save the tree from immediately perishing by pruning away affected limbs before the fungus spreads throughout the tree. But this usually just slows the progression of the disease rather than stopping it.
If growing these plants as hedge shrubs, they will bear pruning as much as three times during each growing season.
Propagation
Since the tree is a hybrid, the seeds produced by Leyland cypress are often sterile, and if they are fertile, planting them usually results in a tree that looks quite different than the parent plant. Thus, this tree is best propagated from cuttings. Take these steps:
In February or March, use sterilized pruners to take 6- to 8-inch semi-softwood cuttings (brown wood at the bottom, fresh green growth at the top), from a tree that is less than 10 years old.
Dip the end of the stem in rooting hormone, then plant in a small pot filled with a porous growing medium, such as three parts perlite blended with one part peat moss.
Maintain the cutting in a warm, humid environment. Cover with shade cloth to diffuse direct sunlight. Keep moist (water the roots twice a day). Rooting generally occurs within six to 10 weeks.
Once the plant develops roots, it can be transplanted into a gallon-sized container.
After six to nine months, it will be ready to plant outside in the spring.
Potting and RepottingÂ
Leyland cypress is such a fast-growing tree that container culture is not very common, though it is sometimes used as a living Christmas tree. If you decide to try growing it in a pot, use a large, wide, container with good drainage holes (heavy-duty plastic is a good choice), and fill it with a standard well-draining potting mix. It will likely need repotting every year as the roots fill the pot, but rather than potting up to larger containers, it’s best to trim back the roots, then replant in the same container with fresh soil around the reduced root ball. Handled this way, you may be able to slow the otherwise rapid growth rate of this plant.
Once it is 5 to 7 feet tall, the tree is ideal as a living Christmas tree, but when it grows larger than this, it is best to either discard it or attempt to transplant it into the landscape. Most gardeners grow weary of root-pruning this sizable tree every year to keep it small enough for a container.
Overwintering
These trees can be prone to branch damage in regions with heavy snowfall, so vigorous pruning up through midsummer may prevent this from occurring.
In colder regions, shielding the shrub with a burlap tent or wrap can protect it from winter burn, especially while the tree is young. An evergreen covered with burlap does not make for a very attractive winter specimen, however, so gardeners in zones 5 and 6 may want to grow a different species.
Watering should be reduced to once a month in winter, as these trees are especially prone to root rot in cold, wet soil.
Pests and Diseases
Common Pests & Plant Diseases
The frequency with which Leyland cypress succumbs to insect damage and disease is one reason why some landscape experts now shy away from recommending this plant.
A very serious insect problem for Leyland cypress is bagworms, which can strip a tree of foliage within a few weeks unless you diligently pick off the silky nest bags as soon as they appear. You may also experience infestations of spider mites on this tree. A good solution for this problem is to spray with neem oil.8
Leyland cypress is susceptible to root rot caused by Amillaria and Phytophthora fungi, and cankers caused by Seiridium and Botryosphaeria fungi. Cankers are most likely to occur during periods of extended drought. Both root rot and canker disease are incurable, and they are prevalent enough to make planting this tree a questionable choice, especially in areas where the diseases are commonly seen.8
Common ProblemsÂ
Aside from common problems with canker fungus and bagworms, there are a couple of other common complaints with this tree.
Aggressive Growth and Shallow Roots
The most common complaint with Leyland cypress is that it grows faster than expected—and to a size that can overwhelm landscapes. And this fast growth, combined with a shallow root system, means that this tree can topple over easily in strong wind, especially when soil becomes saturated. This is a tree that requires vigorous pruning yearly if you want to keep it at a manageable size.
Branch Dieback
It is normal for Leyland cypress to experience some dieback of individual limbs as it grows large. These can simply be pruned off. This is a very dense tree, and the center portions can die back due to lack of sunlight, so selectively pruning out limbs to open up the center to light and air is a good practice. However, there are other dieback issues to watch for.
- Winter scald: If browning is found on one side of the tree, you are likely witnessing winter scald—caused by a combination of cold temperatures and harsh winds. This is most common with younger trees, and it can be prevented by using burlap to wrap or tent the plant for the winter.
- Canker: Dieback on the inside or outside of the tree can be a sign that a serious canker disease is beginning. Affected limbs should be pruned back to well below whatever canker or oozing wounds you find. If cankers continue to form (likely) the tree will need to be removed.
- Root rot: Similarly, root rot can cause this kind of dieback, especially in wet conditions or if the tree is planted in wet soil where it doesn’t get enough sun. Withhold all watering during wet weather, and if the tree’s branches continue to die back, the tree will need to be removed.
III. Uses and BenefitsÂ
They continue to be popular for cultivation in parks and gardens. Leyland cypress trees are commonly planted to quickly form fence or protection hedges. However, their rapid growth (up to 1 m per year), their thick shade and their large potential size (often more than 20 m high in garden conditions, and they can reach at least 35 m) make them problematic.
