Rock Cotoneaster Bonsai Care Guide
A native of China and the Himalayas, Rock Cotoneaster is a low-growing shrub that grows to just one to three feet high, depending upon cultivar. It can, however spread out to as wide as seven feet. This plant is often mispronounced as "cotton Easter"; the actual pronunciation is "ka-tone-e-aster". Cotoneaster horizontalis is a deciduous plant that is favored for bonsai because of its long-lasting color show and tolerance for beginner error.
This plant boasts dense foliage made up of small leaves that grow in an attractive, organized herringbone pattern and change in color from light to dark green as the seasons progress. The grayish trunk is sometimes narrow but may have appealing curvature and visually interesting color patterning. Depending upon the variety, the Cotoneaster will produce white, pink, or red blossoms which appear early in the season. Later in the year these beautiful blooms give way to bright red berries, continuing the color show late into the fall. In temperate climates the leaves will then fall from the plant.
This is a hardy bonsai plant that thrives on a cooler period of dormancy, and will lose its foliage in temperate zones. Some cultivars do well in hot climates as well. Cotoneaster may be brought indoors during extreme freezing weather conditions. It prefers full sun to partial shade. Offer protection in strong freezing winds.
Rock Cotoneaster bonsai do not like wet feet. The soil should not be allowed to completely dry out, and when the plant does need water it should done thoroughly. This species can benefit from the use of a humidity tray, particularly if kept indoors..
Cotoneaster horizontalis should be fed every two weeks beginning in the spring, after the flowering phase. An all-purpose plant food may be used, diluted to half-strength. Switch to a nitrogen-free formula throughout late summer and autumn. No fertilization is necessary in winter.
Common Styles – cascade, semi-cascade, clump, root-over-rock, slanting, exposed root, multi-trunk.
Rock Cotoneaster bonsai are notorious for suckering. In order to encourage trunk growth suckers must consistently be removed, especially at the base of the tree. These bonsai are enthusiastic growers and controlling the canopy density requires vigilance to clipping shoots. This bonsai can tolerate heavy pruning, and old wood will bud back. Clip new shoots back to one or two leaves in late spring, working just above a node.
Because of the fishbone growing pattern of the leaves, shaping and rebuilding is predictable. In order to guide branches in the desired direction, cut back to a leaf that is facing the direction you want the branch to grow. Cotoneaster can be wired; if desired, this should be carried out in spring prior to blossoming.
This bonsai may be propagated by seeds, cutting, or layering, although growing from seed typically results in inferior plants. If growing from seed you should cold treat them and sow them in early spring. To grow from cuttings, take softwood in early summer – these will take roughly six weeks to set root. Air-layering should be done in the spring when buds are swelling.
Rock Cotoneaster bonsai should be repotted every year or two in the spring. They can tolerate up to about a third of their root system being removed. Never allow this plant to be bare-root. Transplant into a well-drained soil mixture – half grit, half organic material is a good choice.
Insects/Pests & Diseases:
Cotoneaster horizontalis may be affected by mites, aphids, and scale. Scale should be removed by hand or with a sharp knife edge; alternatively you can apply rubbing alcohol to the outer shell to kill the adult. Keep in mind that the eggs are harbored underneath this protective coating and so further treatment will probably be necessary.
Mites and aphids can usually be washed off in a jet stream of water, or with a gentle solution of a teaspoon of liquid dish detergent in warm water. Rinse with plain water after spraying with the soapy mixture.
One of the biggest threats specific to Cotoneaster as well as other pome-related plants like apple, pear, and pomegranate is fire blight. This destructive disease is caused by the bacterium Erwinia amylovora and can be deadly to bonsai. The condition can be passed from plant to plant by rain or by infected tools. Signs include shoots and leaves appearing burned or rusty, and a tell-tale "shepherd's crook" curvature at the tips of affected foliage.
The problem with fire blight is that it's very hard to cure in bonsai because oftentimes large areas of the plant must be pruned out in order to eradicate the disease. It can quickly consume a plant as small as a Rock Cotoneaster bonsai. The best cure is prevention. Always clean and disinfect tools between working on trees. Avoid nitrogen-heavy fertilizer, particularly in summer when new growth is vulnerable to infection. Some experts recommend the use of preventative antibiotic sprays, but each owner should research and decide for their self.