UT Gardens November 2014 Plant of The Month: Ginkgo tree

By James Newburn, assistant director, UT Gardens, Knoxville

As fall foliage puts on one final show of brilliance in November, one of the most outstanding trees is the Ginkgo or Maidenhair tree (Ginkgo biloba). Many may recognize this plant from street plantings in cities and towns and be familiar with its vivid gold autumn foliage. The color always reminds me of the yellow-gold of aspen trees in the Rocky Mountains.

Ginkgo is a truly unique tree. It is a broad-leaf gymnosperm, a literally naked-seed plant, similar to conifers and cycads. In terms of evolution it is a very old tree that dates from 100-plus million years ago. Often referred to as a “living fossil,” Ginkgo biloba is the only living member of the Ginkgo family – the others having gone extinct.

Found rarely in the wild in China, ginkgo is now widely cultivated, available and valued around the world. It is extremely tough and resistant to pollution toxicity, making it an ideal choice in urban settings. It has interesting, fan-shaped leaves, with parallel leaf veins, which, as mentioned, turn bright yellow in fall. The nut of the fruit, which must be properly prepared, is also enjoyed in the Far East as a delicacy.  Finally, it has been valued for centuries in China and now in the West for medicinal purposes.

The ginkgo tree is either male or female. The male is desired because the female develops a strawberry- sized fruit that is foul smelling when it ripens and drops. It can take years for a tree to produce fruit, so it is not a good idea to plant a seedling tree since there is no way of determining whether it is male or female until it is reproductively mature. To avoid female selections, be sure to purchase a male-grafted cultivar. Purchasing plants from reputable nurseries can insure that you get the type you want.

Ginkgo trees are typically pyramidal in shape when young and can appear somewhat gangly as juveniles. As they mature they fill out and become a bit more wide spreading. They are long lived, and most cultivated varieties can reach 60 to 80 feet in height. These trees need full sun and moderately moist soil, but once they are established can survive heat, drought and environmental stresses relatively well as is evidenced by the species’ durability.

Several cultivars are available that have desirable characteristics. ‘Autumn Gold’ is said to exhibit the most striking fall color, but ‘Presidential Gold™’ and ‘Golden Globe’ are also favorites. ‘Chase Manhattan’ is a dwarf, small-leafed cultivar that can reach 6 x 6 feet in 10 years. The UT Gardens, Knoxville, has a dwarf, high-graft, multi-branched cultivar named ‘Merikan’ that is about 6-feet tall and looks like a golden lollipop in fall. Both of these cultivars are ideal for the smaller landscape.

Ginkgo leaves are relatively late in turning in the fall, but nothing beats their bright color against a deep blue sky, sometimes up until mid November. A unique characteristic is that they often drop their leaves overnight. This sometimes happens after a hard freeze while the leaves are still green, but more typically occurs after the leaves have changed color. So don’t be surprised if you enjoy your beautiful bright golden ginkgo one day and your equally beautifully carpeted lawn the next.

James Newburn is the assistant director of the UT Gardens in Knoxville. The gardens includes plant collections located in Knoxville, Jackson and Crossville. Designated as the official botanical garden for the State of Tennessee, the collections are part of the UT Institute of Agriculture. The gardens’ mission is to foster appreciation, education and stewardship of plants through garden displays, educational programs and research trials. The gardens are open during all seasons and free to the public.

Source:tennessee.edu