General Cotoneaster information: Pronounced "Cot-o-ne-as-ter," the name is taken from the Greek "Kotoneon" (quince) and the Latin "ad istar" (similarity). Although it really doesn't seem similar to quince, this plant is a popular shrub as well as a bonsai favorite. Some varieties of Cotoneaster are evergreen, some deciduous, and some, like the rockspray, will either retain their leaves or lose them depending on the climate.
Most Cotoneasters are prostrate shrubs which will also climb over rocks and walls, but a few - the most notable being C. frigidus - will grow into trees. All varieties are well-loved for their showy berries, and many Cotoneasters have attractive pink or white flowers as well. Coates points out that Cotoneasters have an advantage over most Pyracanthas - no thorns!
Lighting: Varies according to variety, although most Cotoneasters prefer full sun.
Temperature: Some varieties are occasionally used for indoor bonsai, but most sucessfully grown outdoors. Generally hardy to zones 6 or 7, but frost protection is advised. Most Cotoneasters do well in hot climates.
Watering: The Samsons claim that Cotoneaster likes a dry soil - allow it to dry out a bit between waterings, then water it well. Tomlinson takes the opposite view - that the Cotoneaster should be kept moist at all times! Although Cotoneaster likes good drainage, it dislikes a dry atmosphere, and can benefit from regular misting.
Feeding: Every two weeks until flowering, then monthly during growth. Use liquid bonsai fertilizer or half-strength plant food.
Pruning and wiring: Cotoneaster likes to sucker, so if it is not being grown as a clump, suckers must be vigilantly removed to promote trunk growth. New shoots should be shortened to one or two leaves throughout the growing season. The Cotoneaster takes
well to wiring, which can be performed just before bud break in spring. Protect the bark when wiring. Cotoneasters lend themselves to mame and shohin, but are harder to grow as large bonsai.
Propagation: Cuttings may be taken in June-July, and should take about six weeks to root. Air-layering may be used as well; the most optimal time is during bud-swelling in the spring. Cotoneaster may be grown from seed collected from the berries in fall, but the Samsons claim that seed grown plants are inferior to other methods. The seeds must be cold treated and sown in early spring.
Repotting: Annually in spring, using fast-draining soil, we recommend Hollow Creek Farms Professional Main Soil. . Up to a third of the roots may be removed. Cotoneaster does not like to be bare-rooted.
Pests and diseases: Aphids, wooly aphids, scale, leaf blight, crown-gall and bacterial fireblight. A showy display of beries can be decimated by a hungry blackbird. C. horizontalis is particularly attractive to bees and wasps - which doesn't bother the plant, but may be a risk to unsuspecting bonsaists!