Monday, July 13, 2009

Cotoneaster - A Bright Little Ground Cover Shrub

Cotoneaster is a genus of small shrubs comprised of 300 species, the majority being somewhere in between low-growing and erect bushes. A few are small trees that grow up to 45’ tall, like C. frigidus, but most are prostrate shrubs or tall ground covers that are used as borders, low barriers, foundations, non-traditional ground covers or features, even bonsai. Any species provides beautiful color and charm in your garden.

Pronounced "Co-TOE-nee-aster," the name translates as "quince-like " from the Greek "Kotoneon" (quince) and the Latin "ad istar" (similarity). Both quince and Cotoneaster belong to the Rosaceae family. Native to Asia, the plant naturalized in the U.S. in Zones 4-9. Some varieties can be evergreen, semi-evergreen or deciduous depending on the climate. All varieties are loved for their mounding growth habit, bright flowers and showy berries. Although they don’t look much like the plant for which they’re named, cotoneasters are popular because, unlike their relatives, Pyracanthas, they have no thorns.

Cotoneaster grows slowly and matures between 18" and 36" tall. It sprawls, but it can also climb if it has a supportive structure. If planted in a raised bed, its branches cascade down gracefully. It prefers full sun to partial shade and moist, well-drained soil. However, it is proven to thrive in urban areas with stress from poor soils, various soil pH and condition, pruning mistakes and winter road salt.

The cultivar you buy in a container will have a distinct main stem and branches, but as the branches spread they often root with soil contact. Older stems are brown and new ones that branch off the sides are reddish. Foliage is ovoid, alternate, 0.5" long, and glossy dark green with a pointed tip. In the fall the leaves may turn shades of green, yellow, orange or burgundy. In addition to the colors provided by the leaves, flowers bud in April and bloom in white or pink in May and June. The clusters are beautiful but don’t dominate the plant. The real show begins in August with glossy red berries. The contrast with the dark green leaves demands your attention. These quarter-inch berries, inedible for humans, can last into November if they aren’t eaten sooner by birds.

Cotoneaster may be planted any time you have shovel handy, but if planted in summer you must take care to provide adequate irrigation until the plant is established. If grown in containers or planters, mature plants should be repotted yearly using fast-draining soil. Don’t be timid here - you can remove a third of the roots and it will be fine. It may seem like a waste to throw those roots away, but Cotoneaster resists being bare-rooted. Immediately after planting and fertilizing lay down mulch to prevent weeds from invading up through the arched branches. Irrigate frequently to keep the soil moist.

Because Cotoneaster naturally arches and spreads, you may have to prune it depending on why you bought it and where you planted it. If you want a spreading Cotoneaster, it will sucker naturally and there is no need remove new shoots that will root on the soil. But if you want a plant with a single trunk, new shoots must be removed every few weeks to promote trunk growth. If grown near a wall, Cotoneaster will try to climb, so you may have to prune back. On the other hand, Cotoneaster espaliered against a wall or trellis and trained in elegant forms. If it gets too big, Cotoneaster may be pruned after the berries have dropped.

This popular plant is unfortunately not without unpopular pests, but deer aren’t among them. Cotoneaster be bothered by aphids, scale, spider mites, webworm, leaf blight, crown-gall and bacterial fireblight. These are primarily cosmetic problems and are easy to recognize and remedy.

Aphids are yellowish/pink/green 0.125" long plant lice. They are found on nearly all varieties of plants, vegetables, field crops, and fruit trees. Control and prevention are important for new plants, where sap removal by aphids prohibits development. Early detection is key. A fungus called sooty mold grows on aphid waste that accumulates on leaves, turning them black. The appearance of it on plants may be the first time that an aphid infestation is noticed. To prevent sooty mold, you must control the insects so look for them on the affected plants, but also plants in close proximity. Aphids can be controlled chemically, but this also tends to kill other good bugs in the area. Try spot treatment first.

Scale is an insect infestation that is best treated with systemic pesticides. It’s easy to spot because the plant will look like it’s covered in powder. This powder is actually hundreds of tiny white structures that house juice sucking bugs. Scale can be a serious problem if found in a mass planting because it spreads quickly to other plants. If you don’t see the problem for several months and you notice it when the plant looks like it’s covered in powder and also gray mildew, it’s too late and you’ll have to dig up and throw away all the infected plants.

Spider mite and webworm can cause moderate to severe cosmetic leaf damage. Spider mites cause dappled yellow to brown color on otherwise green leaves, while webworm cosmetic leaf damage is often severe, with a webbed matrix covering the brown and dead leaves on entire stems. Foliage is subject to mite and/or webworm damage because of drought stress. Spider mites require pesticides that are specifically developed for spider mite control (miticides or acaricides). Because most miticides do not affect eggs, a repeat application at an approximately 10- to 14-day interval is usually needed for control.

Leaf blight is first recognized when the leaves turn yellow, but don’t fall off. Soon lesions will appear on the leaves and rapidly engulf surrounding plant tissue. If leaf blight is confirmed on your plant it can be treated chemically with a product from your garden center or a specific remedy can be recommended by your agricultural extension agent.

Crown-gall describes large lesions on the plant at the soil line where the main roots join the stem but sometimes are higher up. Crown gall is best controlled by removing the plant and treating the soil with a suitable fumigant. Chemical treatments are also available.

Bacterial fireblight affects young stems of plants in the Rosaceae family, which includes apples, pears, Cotoneaster. Fireblight is triggered by warm, wet weather during bloom time. The ends of twigs and branches become brown or black and may curl over into a shepherd's crook shape. Dead leaves may remain attached to the tree. Pruning diseased branches early and frequently is the surest way to prevent fireblight from spreading, but remember to disinfect pruning tools frequently. Chemical treatments are also available.

Just let me say that if all these diseases were frequent and hard to solve, Cotoneaster would not be sought out by so many from novice gardeners to enthusiasts. I’ve had Cotoneaster in pots and around the yard for years and they attracted aphids once. This beautiful woody ground cover isn’t going to be perpetually infested with something.

There are hundreds of species out there and I prefer the shorter ones because they’re easier for me to maintain. Here are four of my favorites:

  • C. adpressus "Tom Thumb": Also known as "Little Gem", this evergreen rarely blooms or produces berries. I like it because it is an attractive and unique dwarf specimen with dark green miniature, ruffled leaves. A very slow grower that gets only 24" wide and 12" high, it grows best in full sun in Zones 4-9. Prefers moist, well-drained soil.
  • C. dammeri 'Coral Beauty': Growing best in Zones 4-8, this variety is easy to grow and drought tolerant. It gets 30" tall and has bright pink flowers. Plant them 18" apart.
  • C. dammeri 'Lowfast': A very hardy variety that grows from Zone 4-10, it prefers full sun to get the best evergreen foliage color. It grows 18" tall, produces solitary and profuse white flowers and abundant red fruit. It is low and fast spreading.
  • C. salicifolius 'Scarlet Leader': A taller shrub that gets up to 36" tall. Does best in Zones 6-9 and has pleasant red/purple foliage in the fall after its white flowers and red berries have dropped. It has very strong disease and insect resistance.
Think how beautiful your yard would be with a wavy, arching evergreen shrub covered in bright flower and red berries. Think of other plants you know that thrive despite enduring all kinds of abuse and yet look great year round. What else could do that and be used as a dramatic feature, tall ground cover, border or foundation?

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