Kousa dogwood bonsai

Placement

Cornus kousa is a small deciduous tree from China, Korea and Japan. As a bonsai it lives outdoors year-round, in full sun or partial shade, in a spot with good air circulation. Light directly drives flowering: with too much shade, bracts become scarce. During the hottest weeks of summer, give it light shade at midday and in the early afternoon.

In the ground the species is very hardy and survives winters down to -4–5 °F. In a pot its roots are far more exposed: a kousa dogwood bonsai is hardy to about 14 °F. Below that, shelter the pot in a cold frame or unheated greenhouse, wrap it in insulation, or bury it in the garden up to the roots, out of the wind.

This dogwood’s appeal lies in its four seasons. In late spring, about a month after native flowering dogwood, tiny greenish flowers in heads barely 0 in across are framed by four white bracts 1–2 in long that act as petals. Some cultivars have bracts in other colors. Next come fleshy red fruits that resemble a strawberry and ripen from late summer to early fall; they are edible. In fall, the oval, wavy-edged leaves turn reddish purple to scarlet for three to five weeks. Finally, on older trunks, the bark exfoliates in tan and brown patches.

Soil mix

Kousa roots are shallow and cannot stand waterlogging, so the mix must drain freely while holding a little moisture. A common deciduous mix is half akadama, one quarter pumice and one quarter lava rock; sift the akadama to remove dust. Aim for a neutral to slightly acidic pH: in the garden, the species prefers acidic soil. In a rainy climate, add more lava rock; if you cannot check on watering often, add more akadama.

Watering

Water thoroughly as soon as the surface of the mix dries, until water runs from the drainage holes. Kousa handles dry spells better than native flowering dogwood, but in a pot you should avoid both long droughts and constant wetness. Water needs rise sharply in summer, in sun and full leaf; in winter, the leafless tree uses little, so water less but never let the root ball dry out.

During the growing season, apply a solid organic fertilizer monthly or a liquid fertilizer weekly. If the leaves turn pale, add an iron-rich fertilizer. Stop feeding at the end of the season, during dormancy.

Pruning

Let new shoots extend to four or five leaf pairs, then cut them back to one or two pairs. Repeated trimming builds denser ramification. Heavier branches are pruned after flowering, as is the shaping of new shoots: cutting earlier would remove that year’s bracts.

If you are not interested in fruit, remove spent flowers to save the tree’s energy; if you want fruit, leave them and keep pruning to what is necessary. Cut with clean, sharp tools and keep an eye on wounds: deadwood, which looks natural on a conifer, suits a deciduous tree poorly and tends to rot.

Wiring

Carefully wire young branches and shoots in fall or winter, when the tree is bare and its whole structure is visible. For a deciduous tree, aluminum wire works well. Choose wire about one third the thickness of the branch, apply it at 45°, anchoring it with at least one turn around the trunk or a neighboring branch, then bend gradually. Watch the wire as soon as growth resumes: the shoot thickens and the wire can scar the bark for good within one to four months. Remove it by cutting at every turn rather than unwinding it. Stiff older branches are better lowered with guy wires. Do not wire a freshly repotted or weakened tree.

Repotting

Repot in early spring, as the leaf buds begin to extend: every two to three years for a young tree, less often for an old, large specimen. Normal root pruning is well tolerated; do not remove more than about one third of the root mass. This dogwood’s shallow roots make transplanting tricky, so handle the root ball gently. After repotting, protect the tree from wind, scorching sun and frost, and wait for new growth before feeding.

Informal styles, upright or slanting, with one or several trunks, suit it well, mostly in medium to large sizes. It is propagated from seed, sown outdoors in fall or stratified and sown in spring, from softwood or semi-hardwood cuttings in summer, and by layering. Watch for aphids, vine weevils, caterpillars and scale. It is fairly resistant to anthracnose, though not immune, but can suffer from gray mold, powdery mildew, leaf spot and crown canker; good air circulation limits these diseases. Its garden care is covered in the kousa dogwood plant profile.