Japanese winterberry bonsai

Placement

Japanese winterberry is grown outdoors all year. It needs plenty of sun to flower and then set fruit: give it a spot with several hours of direct sun each day, because a tree kept in too much shade flowers and fruits far less. On the hottest summer days, however, protect it from intense heat and scorching sun, for example with light afternoon shade.

Male and female. The species is dioecious: only female trees bear berries, and only if a male tree blooms at the same time. Keep the two trees very close together, especially in spring, so they share the same conditions and bloom together. The tiny pale pink flowers are easy to miss; the red fruit that follows can last until the next spring.

Birds. They love these berries and eat them as soon as they start to redden. To enjoy the fruit on bare branches in fall and winter, protect the tree with netting or a cage of some kind.

Winter. The tree tolerates frost, but its roots are exposed in a bonsai pot. Protect the root ball once temperatures drop below 23 °F: set the pot on the ground out of the wind, or bury it. Where nights often fall below 14 °F, a cold frame or unheated greenhouse becomes useful. Don’t put it away too early: a temperate tree needs cold to go dormant. In spring, protect young shoots from late frosts.

Pests. In spring, aphids sometimes attack young shoots; a suitable insecticide controls them easily. Start at half strength if you can. Other hollies sometimes get scale insects, which are worth watching for too.

Soil mix

A blend of akadama and pumice with a little humus works well. For a deciduous tree, a common ratio is half akadama, a quarter pumice and a quarter lava rock. Like other deciduous hollies, the tree prefers a neutral to acidic reaction, so avoid alkaline components. Akadama starts to break down after about two years, which matches the repotting rhythm. If you can’t water often, add more akadama; in a very wet climate, add more lava rock.

Watering

Never let the mix dry out completely. Water thoroughly as soon as the surface starts to dry: push a finger about 0 in deep to check, rather than following a schedule. Pour until water runs out of the drainage holes. Rainwater is ideal, but tap water is fine too.

Needs peak in spring and summer, when the tree is growing and heat quickly dries out a small pot; they drop clearly in winter, when the tree is leafless and the mix dries slowly. During winter dormancy, water only when the mix dries.

Fertilizer: from early spring to mid-fall, apply a balanced liquid fertilizer every week, or use a solid organic fertilizer. A fertilizer slightly higher in phosphorus can encourage flowering. Do not feed during dormancy, and never overdo the dose.

Pruning

Maintenance pruning: let each new shoot develop four leaves, then cut it back to keep only two. This is done throughout the growing season and gradually builds dense ramification.

No full defoliation: unlike some other deciduous trees, never remove all the foliage. The tree needs its leaves to produce the energy its fruit requires.

Structural pruning: best done in early spring or, in some cases, late fall. A healthy tree copes with losing a third of its foliage, but don’t combine heavy structural pruning and repotting in the same year.

Styles and sizes: the species suits all forms and sizes. It is especially popular at shohin size, though larger trees exist too. In Japan, some museum specimens are over a century old: one, estimated at about 160 years and 2 ft tall, has an imposing trunk that has naturally engulfed a stone.

Propagation: from seed or cuttings. Sow seeds outdoors in fall; germination can take two to three years. Take semi-ripe cuttings in late summer or early fall.

Wiring

The ideal period runs from fall to spring, while the tree is leafless. On a leafy twig, the leaves come off at the lightest touch while you apply the wire. As with other deciduous trees, choose aluminum wire about one third as thick as the branch, wound at roughly 45°.

Branches thicken around the wire within one to four months: check them often and remove the wire as soon as it starts to mark the bark, cutting it at every turn rather than unwinding it. Don’t wire a weak or freshly repotted tree.

Repotting

Repot every two years in spring, as the buds begin to swell, pruning the roots; never in summer or in the depths of winter. Don’t remove more than about 30% of the roots at once. An older tree can wait three to five years between repottings. Reuse the akadama and pumice mix described above.