Zimmerman
This originated as a 1930 selection made by the late Dr. G. A. Zimmerman, Linglestown, Penna. Very few sound nuts of Zimmerman have ever been produced, for soon after the first crop the identity of the tree became lost and eventually it was destroyed together with others in an overgrown nursery row where it stood. In one known case where there are grafted trees of bearing age, the nuts are regularly destroyed by weevils. Such nuts as have been seen by the writer have been of a dull brown color and have had surface down only about the apex.
The Zimmerman was first catalogued in 1938-39 by Dr. Smith. It is probable that as many trees of this variety have been sold and planted as of any one variety but performance records are difficult to obtain.
Potential Varieties
Other varietal selection are being made, mainly by the Bureau of Plant Industry, Soils, and Agricultural Engineering from trees at its various field stations. Some of these are already under test as grafted stock in various parts of the country. The most promising will be released to commercial nurserymen as soon as their superiority over existing varieties is established.
Pollination
There is much evidence that chestnut pollen is largely carried by insects although this has not been fully established. The Chinese chestnut is largely, although apparently not wholly, self sterile; more than a single seedling or grafted variety should be included in any planting. Several seedlings or several varieties would be better. In seedling plantings, all trees that produce inferior nuts should be removed in order to avoid danger of undesirable pollen influence, either on nut characters, or on the genetic makeup of the embryos if the nuts are to be used as seed.
Harvesting and Curing
Chestnuts should be harvested daily as soon as some begin to ripen and drop to the ground. They should be placed at once on shelves or in curing containers with wooden or metal bottoms through which the larvae of any weevils with which the nuts may be infested cannot penetrate and reach the ground. In areas of infestation, these grubs soon begin to bore their way out of the nuts and leave conspicuous holes in the shells. All infested nuts should be promptly burned.
In order to cure chestnuts to best advantage, they should be spread thinly on floors, or on shelves, or in shallow containers as just described, and held in a well-ventilated room. They should be stirred frequently and held for from 5 to 10 days depending both upon the condition of the nuts and the atmospheric conditions at the time of harvest: During the period of curing, the nuts will shrink rapidly in weight and the color will change materially. Both luster and brightness will largely disappear and, although still attractive, the nuts will quickly become dull brown. Three weeks is about as long as Chinese chestnuts usually remain edible without special treatment.