Forest Chestnuts

The American chestnut (Castanea dentata) was one of the largest growing forest trees in eastern North America. It was important for timber as well as nuts for human use as well as wildlife. A deadly fungus disease, introduced from the Orient effectively wiped out this chestnut in the first half of the 20th century.

Efforts are currently being made at Meadowview in Virginia by the American Chestnut Foundation to "bring the American chestnut back" as a forest tree again through a back cross technique using a highly fungus resistant Chinese chestnut as a source of resistance genes. After the first cross with an American chestnut is made, the progeny are screened to recover the trees that have the resistance genes. These trees are then back crossed to another American chestnut and the offspring are screened again. This process is repeated several times to "wash out" most of the Chinese chestnut genes, leaving a nearly pure American chestnut with the fungus resistance genes in place. When two of these trees with the resistance genes are subsequently crossed with each other, 100% of the offspring will inherit the resistance genes and the trees can be reintroduced to the forests. The Chinese chestnut cannot be used as a reforestation tree simply because it does not reach the height of the American native and would never be able to dominate the forest. It is hoped that this backcross tree will have the height requirement necessary. This long term project is past the half way point, with a few years to go in its program.

A second effort to bring back the American chestnut at Syracuse University in NY involves a genetic engineering technique. Pure American chestnut trees are grown in tissue culture and "hit" with a packet of genes that will provide a very high level of fungal resistance to the trees. This project has broken new ground in a number of research areas. Success is expected in a few years.

Orchard Chestnuts

Chestnuts maturing and dropping

Chinese (C. mollissima), Japanese (C. crenata) and the less resistant European chestnut (C. sativa) trees have since been introduced into Canada and the United States to take the place of the orchard type American chestnut trees. They were only partially successful as they often lacked the hardiness of the American cousin. As time went by, and hybrids were developed with American and European trees, good orchard trees were developed with a fairly high degree
of resistance to the blight fungus. These complex hybrids are the trees that are currently being used by growers in Ontario.

Jack Gellatly of West Bank, BC developed a number of largely Chinese chestnut selections. These were introduced to Ontario. One cultivar, Layeroka, stood out as an outstanding breeder tree. Layeroka has been superceded by a number of selections from its offspring as well as others. Many orchards have been planted using these seedlings and grafted trees.

Commercial orchards of grafted trees are suited to the mild areas of zone 6 and 7 (close to Lakes Erie and Ontario) in Southwestern Ontario and the Niagara Peninsula. They are best grown on well drained sandy and light clay loams with a pH of 5 to 6. Generally, the peach soils are well suited to commercial chestnut orcharding. Irrigation is important in August and September to help in the sizing and filling of the nuts.

The Four Most Desirable Chestnut Characteristics

1. Nut Size Large size nuts (diameter greater than 1.1 inches) are sold for a premium. Seedling trees or cultivars that regularly produces 80% or more large size nuts is the most desirable for the fresh market trade.
2. Production Trees must produce annual crops of nuts with reasonable cropping from year to year. A tree that produces too many nuts that can't size up to premium size is no better than a tree that bears light crops alternate years.
3. Ripening Time Chestnuts that ripen early (mid September to early October) are more desirable. They reach the market first, ahead of the imports and command the premium price. They also avoid the chance of injury from early fall freezes that could destroy the crop.
4. Blight Resistance Though Chinese and Japanese chestnuts are our most blight resistant orchard trees, they often lack nut size, vigor, form and hardiness. The hybrids overcome these undesirable characteristics, but may lose some of the blight resistance. Under these circumstances, the blight may be managed by mudpacking, pruning and using hypovirulent blight strains.

Chestnut Cultivars.
There are too many selections to mention. A few are included here.

Grimo 112X - This is a seedling selection of unknown origin (possibly a Layeroka seedling). The tree is vigorous and productive. The nuts are sweet, large and early to mid season ripening. It is moderately resistant to chestnut blight. It is a good pollinator.

Grimo 114W - This is a hand cross of Layeroka x Douglass Manchurian. The Manchurian is a pure Chinese chestnut that has never blighted. 114W has been very resistant to blight too, but has the vigor and upright form needed in a good orchard selection. The nuts are large with some variability in size, sweet and attractive. It is pollen sterile and so can't be used without another pollen source.

Grimo 142Q - This is a selected seedling of Layeroka. It is very early ripening, starting to drop nuts about mid September. It is a consistent cropper of large, sweet very attractive nuts. The tree is vigorous and hardy, but moderately susceptible to blight. It has sterile pollen.

Chestnut trees are self infertile. That means that they must have another chestnut tree nearby with viable pollen to produce nuts. For commercial plantings a planting plan like the one shown on the following page will help growers to establish trees with permanent pollinators in place. If all seedlings are used then a careful distribution of varieties is not necessary. It is advisable to consider field drainage tiles between the rows and irrigation for prolonged dry spells of 6 weeks or more during the growing season.

Click here to view the Chestnut planting plan