Ginkgo

Identification and origin

Ginkgo biloba belongs to the Ginkgoaceae, the ginkgo family. It is often called a “living fossil”: ginkgo has existed, seemingly unchanged, for hundreds of millions of years. In the wild it is native to southeastern China; it has been introduced elsewhere in China, in Japan and in Korea.

It is a very long-lived deciduous tree, pyramidal or conical when young, becoming more irregular and spreading with age. It commonly reaches 49–78.5 ft tall. Growth is slow, especially in the first years after planting.

Its fan-shaped leaves, often notched in the middle into two lobes, hence the epithet biloba, are 2–3 in long and up to 5 in wide. Their veins fork repeatedly. They grow in clusters of three to five on short spur shoots, or singly on long shoots. Bright green in summer, they turn a brilliant golden yellow in fall, then drop quickly, carpeting the ground in gold. The gray-brown bark develops ridges and furrows with age.

Ginkgo is a gymnosperm, like the conifers: it produces neither flowers nor true fruit. Male and female organs are borne on separate trees. Male trees carry small pollen cones; female trees carry ovules at the end of a stalk, which develop into fleshy, yellow-orange seeds 1–2 in long whose pulp smells very unpleasant when ripe. They drop in fall and make a mess on the ground.

There are many male, seedless cultivars: ‘Autumn Gold’, conical with fine fall color; ‘Princeton Sentry’ and ‘Fastigiata’, narrow and upright; ‘Sky Tower’, compact and columnar; ‘Jade Butterfly’, a dwarf with densely clustered leaves; and ‘Mariken’, a dwarf that barely exceeds 3–4 ft. Its sculptural form also makes it a popular bonsai subject.

Light

Ginkgo grows best in full sun, with at least six hours of direct sun a day. It tolerates light partial shade, but a sunny spot encourages steady growth and intense fall color. Any aspect suits it, and it copes with windy sites.

Watering

Once established, ginkgo is very drought tolerant. In its first years, however, it settles in slowly and grows faster with an adequate water supply: water deeply when the soil is dry several inches down, then let it drain and dry somewhat before watering again.

Do not overwater: constantly soggy soil harms it, even though it tolerates occasional wet spells. Keep turf well away from the trunk while the tree is establishing.

Potting mix

Ginkgo is not fussy about soil. It grows in clay, loam, sandy or chalky soils, acid to alkaline, even compacted ones, as long as they drain well. Just avoid poorly drained sites where water stands. A moderate feeding in spring can speed up the growth of a young tree.

It tolerates urban pollution, road salt and moderate salt spray, which makes it an excellent street tree.

Temperature

Ginkgo is very cold-hardy: it is grown in USDA zones 3a to 9b and withstands severe cold. It also tolerates heat, although the hottest, driest summers of warm regions do not suit it well.

Repotting

Ginkgo transplants easily. Plant it in a wide hole at the same depth as in its container, then water thoroughly. Choose a grafted tree of a male cultivar: there is no way to tell the sex of a young seedling, and a female tree can take twenty years or more to produce its first seeds.

Give it the room it needs: female trees spread wider than males. In a small yard, choose a narrow or dwarf form.

Pruning

Ginkgo needs very little pruning. On a young tree, early structural pruning helps keep a single central leader; a large branch sometimes grows so strongly that it seems to form a second tree on the trunk. Prune preferably in spring, and afterwards limit yourself to dead wood and badly placed branches. The wood is strong and resists storm damage well.

Propagation

Cultivars are propagated by grafting, the method that guarantees a male tree. Semi-hardwood cuttings can also be rooted.

Growing from seed is easy, but you will not know the sex of the tree until it first bears seed. Collect seeds in fall under a female tree, wearing gloves, and remove all of the irritating pulp before sowing.

Common problems

• Strong smell and messy ground in fall: seeds from a female tree. The only lasting solution is to plant a male cultivar.
• Very slow growth after planting: normal for a few years; adequate water and a little fertilizer help.
• Skin irritation: contact with the seed pulp.
• Lopsided shape: an overly vigorous scaffold branch, corrected by structural pruning.
• Decline: rarely, honey fungus. Otherwise ginkgo is practically free of serious pests and diseases and resists verticillium wilt.
• Short-lived fall color: the leaves drop quickly; this is a trait of the species.

The same symptom can have several causes: consider the soil, watering and age of the tree before drawing conclusions.

Toxicity

Only the seeds are a concern. Their pulp contains alkyl phenols and ginkgolic acid: its juice irritates the skin on contact, and eating it irritates the lips, mouth and throat and causes stomach pain, nausea and diarrhea. Toxicity to people is low and becomes serious only if large quantities are eaten; in fact the kernel, freed of its pulp, washed and then boiled or roasted, is eaten. The seeds are also toxic to pets. Wear gloves to pick them up and, if any are swallowed, contact a doctor, a veterinarian or a poison control center.