Ginkgo bonsai

Placement

Ginkgo biloba is a deciduous tree from China, the only living member of a lineage that appeared some 270 million years ago. It naturally grows very narrow and upright, with a columnar outline when young that broadens with age. It is an outdoor bonsai year-round: it needs the rhythm of the seasons and a true winter rest.

Give it full sun. Young trees, however, do better in partial shade, especially on the hottest days. The tree is tough, adapts to a wide range of situations and tolerates air pollution, which is why it is so often planted along busy streets. It is also one of the species recommended for starting a collection.

In the ground, ginkgo handles frost very well, but in a pot its roots remain vulnerable. They hold a lot of water and can burst when temperatures fall below 23 °F: below that threshold, shelter the root ball from frost. In spring the leaves come out late, usually after the last frosts. If a night frost is still forecast once the young leaves have emerged, bring the tree in for the night to avoid serious damage.

Soil mix

Ginkgo is not fussy about soil type: it tolerates a wide pH range, from acidic to distinctly alkaline. A standard bonsai mix therefore works, as long as it drains well. A common base combines akadama, pumice and lava rock in equal parts. Add more akadama if you cannot water often, and more lava rock in a humid climate. What matters is that water never stands in the pot.

Watering

From spring to fall, water generously until water runs from the drainage holes, then wait until the surface of the soil starts to dry before watering again. Watch the color of the soil and lift the pot: a light pot needs water. Ginkgo likes water, but it must not sit in soggy soil. Hard water does not bother it. In summer, a bonsai in full sun can need watering once or twice a day.

In winter, keep the root ball barely moist, on the dry side: waterlogged roots cope far less well with frost. Still, keep an eye on the pot during dry spells, since a week without rain is enough to dry out a small volume of soil.

Fertilizer: start as soon as the buds open. In spring, a high-nitrogen fertilizer matters: it pushes the tree to produce long shoots. Without it, an older tree forms only short shoots and ramification stops improving. Then apply a liquid fertilizer every week, or every two weeks at a reduced rate, until the leaves turn yellow in fall. A solid organic fertilizer also works; combining the two gives a developing tree more vigor. Avoid overfeeding, which produces soft growth that is more prone to pests.

Pruning

During the growing season, let new long shoots form five or six leaves, then cut them back to one or two leaves. Repeating this pruning builds a denser branch structure. Branches are shortened in fall, after leaf drop, when the structure is easy to read.

Ginkgo’s great weakness as a bonsai is its wounds. The tree does not form a callus around a cut and heals very slowly: avoid large cuts wherever possible, especially on the front of the tree, and seal with cut paste any you cannot avoid. Plan the structure before letting a branch thicken.

Given its narrow, upright habit, ginkgo is usually styled as a formal or informal upright, with upswept branches, and mostly in medium to large sizes. With age, its bark turns from light gray to dark gray and becomes furrowed. Some old trees develop hanging growths called “chichi,” which look like stalactites.

Wiring

Ginkgo can be wired at any time of year, and its branches are fairly flexible. For a deciduous tree, though, late winter remains the most comfortable time: the tree is bare and every branch is easy to see. Choose aluminum wire about one-third the thickness of the branch and coil it at roughly 45° from the base toward the tip.

The bark of branches and twigs is soft: protect it, and check the wire regularly during the growing season, since a branch can grow around wire within one to four months. To remove wire, cut it at each turn rather than unwinding it. Branches that are too thick are better positioned with guy wires, padding the bark where they attach.

Repotting

Repot in early spring, as the buds begin to extend. Repot a young tree every year until it is about ten years old; repot an older tree every two to five years, once roots circle the root ball. Avoid heavy root pruning: gently remove the old soil, trim only overlong roots and never remove more than about a third of the root mass. After repotting, keep the tree in a sheltered spot, with no fertilizer or major pruning until new growth gets going.

Ginkgo is propagated from seed, cuttings and air layers. The seeds have a hard shell: sow them outdoors as soon as they are ripe, or stratify or scarify them before sowing, and allow up to two years for germination. Semi-ripe cuttings are taken in summer, and air layering is done in spring, once the first flush of shoots has hardened.

The species is dioecious, with separate male and female trees. The ripe fruit of female trees smells very unpleasant, but a bonsai rarely sets fruit. Finally, ginkgo is very resistant: insects and fungal diseases rarely attack it.