Chapter 95 Gingko biloba

95.1 Gingko; maidenhair tree

A clump-style gingko. Gingkos rarely form multi-trunk trees, making this an exceptional artistic effort. Link to original image

95.2 Soil: Rich Mix

Ratio: 4 parts bark, 1 part coir, 1 part grit

Add-ins: dolomitic limestone (~5 lbs/yd), Tree-Tone (15 lbs/yd)

pH: ~6.5 (slightly below neutral)

Moisture: moisture retaining

Coconut coir increases water holding capacity without the soil staying too wet. Gingkos like even moisture during the growing season.

95.3 Cultivation Notes

95.3.1 Potting and Root Pruning

Repot in early spring. Young trees may need annual repotting, older trees every two years, and mature trees every three years.

95.3.1.0.1 Top & Branch Pruning:

Heavy pruning: Cut branches in fall after leaves drop. Cuts will not scar over so choose where to cut carefully. Do NOT try to cut flush or make a concave cut. Gingkos are prone to dying back when branches are cut, often months later. Leave a short stub when pruning, then return and re-prune in about a month after the cut stub has dried out.

Fine pruning: Trim new growth to shape them in spring and autumn. Cut to a leaf facing the desired direction for the new shoot. Gingkos will not form fine ramification, so do not need to be pruned as frequently as maples or elms.

Leaf pruning: Not recommended. Leaves do not reduce very much compared to other species.

Avoid wiring branches as the bark is thin and scars easily. Use guy wiring and string ties instead.

This gingko has a strong trunk and nebari, but still needs further development of the foliage to create a more dramatic silhouette. Link to original image.

95.3.2 Feeding

Feed on a routine schedule with dilute 3:1:2 ratio fertilizer.

95.3.3 Pests & Problems

Gingkos are mostly pest-free.

95.3.4 Winter Storage

Keep on the dry side and well insulated in winter. Roots are fleshy so do not tolerate frost well.

95.4 Propagation Notes

Gingkos are easy to grow from seed if you can find a female tree (most ornamental trees are males.) Look for the round fruits, about the size of a seedless grape. The fruits are very smelly when fresh; old, partly decomposed fruits lying under the tree will smell less strongly. Soak partly defleshed seeds in water overnight to soften the remaining fruit, then rub on paper towels to strip the seeds clean. Let them dry out for 2-3 days, then store in a ziplock bag in the refrigerator.

To start the seed, soak them overnight in warm water, then plant about 1/2 inch deep in a deep pan with 4-6 inches of loose soil. Put the pan outdoors all winter to stratify. Locate the pan in a place protected from squirrels and mice. The seeds will germinate in spring. Typically I get about 50% germination of seed collected in fall and stratified the same winter. Viability of stored seeds drops rapidly; after 1-2 years they usually fail.

95.5 Artistic & Styling Notes

Gingkos often are spindly or gangly when young. They need several years of growth in open ground or a large deep pot in order to develop much trunk caliper. Do not try to develop taper by a clip and grow strategy; let the trunk get to full size, then cut back once to the desired height.

95.6 Additional Information

95.6.1 Natural History

Gingkos are “living fossils” in they have changed very little over millions of years. Two hundred million years ago, gingkos and their kin were the dominant trees of the Northern Hemisphere. Fossilized leaf imprints from 50 million years ago are almost identical to leaves of today. They dwindled out as modern flowering trees displaced them, and by about 5 million years ago their range had been reduced to a small area in central China. All trees currently planted worldwide today come from these small founder populations.

Their growth habits suggest this species is adapted to streamside areas that are prone to flooding. After seeds germinate the main sprout often bolts several feet high before producing side branches, similar to other flood-adapted species.

95.6.2 In Cultivation

Ginkgos have been grown in China for at least 2000 years. Some trees associated with Buddhist and Confucian temples are thought to be 1,500 years old. Ithas escaped cultivation and become naturalized widely in Korea and Japan.

The first record of Europeans encountering gingkos is in 1690 in Japanese temple gardens by the German botanist Engelbert Kaempfer. The famous French botanist and gardener, André Michaux, introduced gingkos to the U.S. sometime between 1785 and 1791

Properly situated, gingkos are very tough trees. They tolerate air pollution, root crowding, and low fertility soil. Six gingkos are among the handful of trees that survived within the 1.5 mile blast radius of the atomic bombing of Hiroshima. These trees are still alive today and are tourist attractions.