Scientific Name: Ginkgo biloba
Common Names: ginkgo, ginkgo biloba, fossil tree, maidenhair tree, Japanese silver apricot, baiguo, bai guo ye, yin gou, kew tree, yinhsing (yin-hsing), ichou, ginnan
Cultivars: ‘Aurea’ Yellow leaves in summer.
‘Autumn Gold’ Male cultivar with a broad, symetrical growth and intense autumn colour.
‘Chichi Icho’ desirable cultivar, has smaller leaves and a textured trunk.
‘Fastigiata’ narrow, pyramid habit.
‘Laciniata’ deeply divided leaves.
‘Pendula’ a cultivar with nodding branches.
‘Princeton Sentry’ Male cultivar with an upright tapered form.
‘Variegata’ Variegated cultivar with strong white-yellow stripes on the leaves.
History: Ginkgo biloba is a living fossil, dating back over 250 million years, the last surviving member of its family. For that matter, the last surviving member of its division. The ginkgo is classified in its own division, the Ginkgophyta, comprising the single class Ginkgoopsida, order Ginkgoales, family Ginkgoaceae.They flourished across the Northern Hemisphere, from the Mediterranean to the Arctic Circle, from North America to China. There were once many species in the genus, but around the Pliocene era, Ginkgo fossils disappeared from the fossil record around the world, and it was thought that this family of plants had gone extinct, out competed by their conifer cousins and the more newly evolved angiosperms (flowering plants, with seeds that are protected by an ovary wall).
The West “rediscovered” the tree in China, Korea and Japan (much to their general amusement… after all, they hadn’t “lost” the tree to begin with!), though it was first encountered in Japan by the German botanist Engelbert Kaempfer in Temple gardens in 1690. The trees in Korea and Japan had been brought there from China, naming practices of the species seeming to point to the Kamakura period of Japan or earlier. The genetic uniformity suggests that even these still growing, naturalized in China were planted and preserved over 1000 years ago, rather than naturally occuring populations. Though the Ginkgo has been spread through cultivation all over the world, there is little case, and no findings, for naturally occuring populations that have survived.
Anatomy: Ginkgo are classified as gymnosperms, plants that created seeds that are not protected by an ovary wall. Most gymnosperms are conifers, though the classification also includes Cycads, and several other related plants. Though Ginkgo are often called deciduous conifers, it is a misnomer, as they are not conifers at all, merely related.
Very large trees, Ginkgo can be over 100 feet tall in the landscape, and are extremely long lived. The oldest reported is over 3000 years old, in the Shandong province of China. It naturally grows with an angular crown, young trees being tall and slender, the crown filling in with age.
Foliage: Light to medium green, fan-shaped leaves, borne both on new shoots(alternate and spaced out), and on shorter growth spurs (where they will be clustered at the tips) They resemble the Maidenhair fern, Adiantum, hence one of the common names. They have characteristic parallel veins that radiate out from the leaf blade- two veins enter the leaf blade at the base and fork repeatedly in two (known as dichotomous venation). The leaves are usually 5-10 cm (2-4 inches), but sometimes up to 15 cm (6 inches) long. Leaves of longer shoots will often be lobed, while the leaves occuring on shorter, stubbier growth will be smoother and more rounded.
Leaves change to golden in autumn, but individual trees can be very independent in their turning habits. A single ginkgo forest can include completely golden trees, completely green trees, and mottled specimens showing both colours and others completely bare. Autumn colour is short lived however, as once individual trees start to drop their leaves, all will have fallen in the span of a few days.
Stems and Trunk: Bark is pale grey, often appearing slightly reflective in larger, landscape trees. It is very easily bruised and damaged. From leaf axils, growth spurs (also known as short shoots, and spur shoots) will develop on second year growth. These spurs have shorter internodes and slower growth, and the leaves that occur on them will often be unlobed. They are short and knobby, arranged regularly on branches of two years and older. Because of such short internodes, the leaves appear clustered at the tips of the spurs. Flowers and catkins will only occur at the tips of these spurs, not on new growth. Due to the nature of the short shoots and long shoots changing, seemingly at random over any number of years, to the other, Ginkgo seem to have an erratic growth habit, with only a few centimeters of growth occurring over several years and then suddenly growing very swiftly, or vice versa.
Flowers: Ginkgo are dioecious (separate male and female trees), producing male pollen cones(penulous, short catkins) and female “flowers” (actually two ovules the form at the end of the stalk, Ginkgos do not produce true flowers) on separate trees. Occasionally one can find female trees with male branches grafted on for pollination purposes, but this will not occur in the wild. Unlike other higher trees, pollination is achieved by motile spores, which is normal to ferns, cycads, moss and algae. Fertilization of the seeds generally occurs right before, or just after, the seeds fall in autumn. Gingko trees can take up to 20 years to begin producing cones and flowers.
Fruits: “Fruit” (the sarcotesta) occurs on the female trees, singly or in pairs, and is yellow green to orange brown when ripe, containing a single seed each. The fleshy growth is not a true fruit, rather a simple protective covering. The fruit-like outer covering gives of an unpleasant, downright nasty scent, due to butanoic acid (the chemical that gives rancid butter its unpleasant smell). Bonsai ginkgo rarely fruit, though if this is a concern, seek out male plants, as that will avoid the problem.
Other Features: Very old ginkgo can begin to put off aerial roots that form on the underside of branches and grow downwards, called chichi (meaning nipple or breast)in Japanese, zhong-ru (meaning stalactite)in Chinese. Usually a tree will not begin to produce these growths until they are over a hundred years old, and it can take hundreds of more years before they reach the ground. For some reason, female trees that have produced larger aerial roots frequently stop producing seeds. These rarely occur on bonsai growth from seed or grafted. The most reliable way to have this effect is to do an air-layer on one of the roots already growing. An airlayer directly from one of those roots is more likely to continue to make the aerial roots, as opposed to waiting hundreds of years for them, as gingko rarely grow chichi in bonsai cultivation. Good luck, however, finding one of these trees outside of China or Japan, and getting permission, as many of the most ancient are protected by law.
Hardiness: Zone 3 in the landscape. Zones 5-8 with winter protection in bonsai cultivation. Take careful notice of roots, and keep them from freezing for prolonged periods. Keep in an insulated garage or shed for the winter, or a cold frame that stays above freezing.
Light: Full sun to partial shade. Maximum light for mature trees will help ensure the best autumn colouring, while younger trees will benefit from some protection in the hottest part of the summer during the middle of the day.
Soil: Will grow in almost any soil in nature. Use a standard bonsai mix suited to your area.
Watering: Water well in growing season. Lessen in winter, keeping roots barely moist, just enough to keep it from drying out completely.
Fertilizer: Balanced feed through the growing season, twice a month. No special needs.
Pests and Diseases: Largely pest free. Tolerate pollution well, and are often used in city landscaping for that tolerance.
Repotting: One to five years, depending on the age and growth rate of the tree. Repot in spring, before new growth begins, and be sure to give extra protection from late frosts. Root prune lightly, as they have a lower tolerance for serious root reduction.
Pruning and Styling: It is best to style Gingko based on their natural inclinations toward a column, or flame shaped tree. Ginkgo can resent pruning, and as a result, many ginkgo bonsai have a similar look, due to the nature of how they show their dislike. Pruned branches are prone to dieback even further either shortly after being pruned or the following winter. This can result in a heavy trunk with relatively few, slightly upward facing branches. Twigs will grow in clusters from the branches. As the growth and replacement of branches is repeated over the years, in can result in interesting, gnarled areas on the trunk. Fortunately, not *all* shoots will dieback, but predicting which ones will and which ones won’t is nearly impossible.
Pruning wounds do not heal over with ginkgo as they do with most other species. Do not make concave cuts, or even cut flush to the trunk. Instead leave short stubs of old branches, and remove them gently a year or so later as they dry out.
Prune back to two or three leaves from new growth, which will leave a little extra leeway for dieback. New branches will grow in the direction of the last leaf on the branch, so keep that in mind when pruning, typically leaving the last leaf pointing out. Remove branches that died over the winter in early spring, as swelling buds will inform you of what has made it through the winter.
Wiring: Avoid wiring unless strictly necessary, as the bark is very easily damaged, and will not heal well. Wrap branches in raffia if wiring is required and check the tree regularly to keep the wire from biting in.
Leaf Reduction: Ginkgo leaves do not reduce well, so by necessity, bonsai are usually medium sized and larger. Good light and controlled watering combined with being confined to a pot will reduce them slightly, but not significantly. There have been mixed reports on utilizing defoliation techniques.
Special: Girdling the trunk of a Ginkgo seedling with wire or bark ringing might be able to stimulate the forming of a chichi-like (aerial root) structure above the girdle.
Cuttings: This is the best way to ensure the sex of the tree. Soft, or semi-ripe cuttings, about 15 cm long in spring to mid summer. Hardwood cuttings can also be taken from current years growth in winter.
Grafting: Often used by nurseries to ensure gender, by grafting male branches onto rootstock. Also used to graft male branches to female trees to increase fertilization. Vegetative propagated Ginkgos seldom have a dominant central leader, as a lateral branch (rooted or grafted) will continue growing in the direction it had when still attached on the parent trunk. Nurseries stimulate the production of vertical shoots by cutting back the trees once growing vigorously.
Seeds: No way to control gender. Harvest seeds in autumn, after ‘fruits’ have dropped from the trees (wear gloves, as the butanoic acid can give some people a rash). Remove pulpy outer layer by putting the fruits in warm water, crushing the coat and removing the seeds by hand (still wearing your gloves, right?), then rinse the seeds a few times in clean water. Floating seeds will not germinate, so discard them. The seeds should be very clean, with no trace of the fruit, or you’ll end up with a very stinky storage area. Scarification can help increase germination. Seeds can also be dipped in a bleach mixture (1 part bleach to 9 parts water) for about ten minutes to kill fungus, and then rinsed thoroughly again. Dry gently with a paper towel, then keep them in a mixture of moist (but not soaking) sphagnum moss and sand or perlite in a cool place that will remain above freezing (refrigerator works well) for two months. Germination is between 30-60 days, and seeds will occasionally germinate during stratification, especially if scarred, so time accordingly so germination will coincide with your spring. Stratification is not necessary, but will improve germination. Plant in a mixture of sand and peat and keep at room temperature for 2-3 weeks. To sow outdoors, sow in fall if you have a cold frame that will not go below freezing. Or sow in spring, after threat of frost.
Airlayering: In spring.
Styles and Forms: Broom, formal and informal upright, clump, forest.
Other Information and Trivia:
-The tenacity and survival abilities of Ginkgos are illustrated no where as clearly as in Hiroshima, Japan. Four ginkgo trees were growing less than two kilometers from the atomic bomb explosion, and were some of the few living things in the area to survive the blast. Though charred and damaged at the time, they survived and continued their ponderous growth. The trees are still alive.
-Gingko seeds (‘nuts’) are edible, once the fruit-like outer covering has been removed, and are frequently roasted and eaten. An extract of the leaves is also used to improve memory and circulation in herbal medicines.
-The name, Ginkgo, is actually a mistake. The Japanese characters for the tree, normally pronounced ginnan could also be mistakenly pronounced ginkyo. When Kaempfer first encountered the tree, he wrote down the incorrect version, and his ‘y’ was eventually mistaken for a ‘g’. As it was published in his Amoenitates Exoticae in 1712, the misspelling stuck.
Reference.com on The Gingko http://www.reference.com/search?q=Ginkgo%20biloba%20
Bonsai Survival Manual Colin Lewis, 1996
Trees and Shrubs Ernie Wasson, Tony Rodd, 2004
Trees of the World Tony Russel, Catherine Cutler, Martin Walters, 2006
The Gingko Pages, by Cor Kwant – http://www.xs4all.nl/~kwanten/index.htm
NCCAM Ginkgo Entry – http://nccam.nih.gov/health/ginkgo/
Wikipedia, Ginkgo – http://en.wikipedia.org/wiki/Ginkgo