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Feature Article of the Month

Introduction by Jerry Henkin, NNGA Librarian

Dr. David Griffith, the author of "Breeding Better Walnuts for the Southeast," was a dentist and a horticultural hobbyist from Alabama who often gave presentations at NNGA meetings on a variety of topics based on his meticulous observations of nut trees over a long period of time. David Griffith passed away in 2009. We are publishing his article to recognize his inspiration and passion for nut growing. He was a creative thinker with a vision.

This article suggests a long-term project for obtaining superior black walnut trees for timber in the southeastern United States. The progeny test and the grafting protocol that Dr. Griffith proposes, along with site selection guidelines and care of the seedlings, will hopefully yield superior black walnut trees for timber in the South. His advice might also be applicable to chestnut and other kinds of nut trees.

Breeding Better Walnuts for the Southeast
by David N. Griffith

Much of the history of timber and timberland management in America has been a disgrace. Most of the pioneers considered trees to have only a negative value, that is, trees were something that had to be disposed of before one could plow the ground. Since the initial clearing, much of what has been considered timberland has been clear-cut or high graded, harvesting the best and leaving the rejects for survival and reseeding. After a few rounds of that, there is often little left but cull stuff, and with it, the lowering of the average level of genetic excellence.

Since walnut is commonly considered quite valuable, it has been under extra pressure. Since it is very site demanding and reseeds poorly, there are now very few marketable trees in much of its natural range, especially in the Lower South. Most of the trees we see have short crooked boles, have been struck by lightning, bent or broken over, full of nails or wire, or have too many large knots. However, I have found several trees that appear to have the genes for growing quality timber.

In the spring of 1985, I made my first planting of walnuts, starting as a progeny test of several local trees that I thought had the right genes. They may have been shabby specimens, but some of them already had several seedlings about them exhibiting good timber form. The progeny test consists of planting a row of seeds or seedlings from a particular tree, and beside it, those from another tree, and so on. As these seedlings grow, one can compare the performance of the progeny of one tree with that of others on such issues as growth-rate, straightness of trunk, duration of apical dominance, resistance to disease and pests, etc. I have been generally pleased with the results of this progeny test. Only a couple of rows are considered undesirable. The laws of heredity apply to walnut trees just as they do to other plants and animals, and the inheritability

For the second phase of this project, I have found over twenty-five trees in the South that appear to have the right genes which I have started top working (grafting) onto trees in the progeny-test area to form a seed orchard. With these grafts and the best of the progeny-test planting pollinating among themselves and making seed, there is becoming a seed source of southern origin, which can be planted with greater confidence in the South.

Among seedlings from this orchard, some will be notably better than others, and I want you to select the very best five percent to graft and make a second generation seed orchard which could make this present seed orchard obsolete in thirty to fifty years. Seedlings from this second orchard would be better and more consistent than any available now.

There is an unending argument over the relative importance of genetics and environment. My stand is simple. Either one without the other is meaningless. Also, if either is very bad, the results will be poor regardless of how good the other may be. On the other hand, good genes in a good environment can be very rewarding. This is to say that excellent walnut trees, on an excellent site, with appropriate care can produce more value per acre per year than any other timber tree I know!

To grow good walnut trees, three things are needed:

1. First and foremost is a good growing site. Deep, well drained fertile soil, full sun, and a pH of 6 to 7 seems to be preferred. One should avoid heavy clays that drain poorly, droughty soils that drain too rapidly, and soils with hardpans or other barriers closer than 3 to 4 feet (90 to 120 centimeters) from the surface. Bottom land that slope to the north or east seem to be preferred.

2. A source of seed or seedlings selected for timber-type growth in your geographic area. At the present time, I think that mine is the only southern seed orchard planned and executed as described above. I just regret that heavy production of seed from most of these grafts is still a few years off. However, the small quantity being produced now should be very good.

3. Reasonable care for the first few years. This consists mostly of controlling weed competition which may be done mechanically or with herbicide. There are some glowing reports from the use of plastic tree shelters of various brands. Corrective pruning and training is usually not necessary until the trunk is two to three inches in diameter.

In removing lower limbs to produce a clear bole, a couple rules of thumb should be observed. First, do not remove more than one-third of the leaf area during any one year, and second, do not prune up more than half its height.

There is a growing belief that the best walnut timber is grown in a mixed stand, that is, in a more forest-like community of trees. This concept is being implemented in several of our forestry programs where successful growth of walnut seems probable within an assortment of other trees.

There are several good articles in Walnut Council literature on walnut culture, which I would encourage you to read. I would also encourage you to use the services of a soil scientist and an open-minded forester.

It is commonly stated that southern-grown walnut timber is never very good. That is in part based on the observations of our timber being mostly what remains after repeated top-cropping, and I can't deny that observation. They also say that even if we produce straight logs of good size, that the rich deep color for which walnut is famous is lacking and that the wood grain itself is less than excellent. My response is that with all the steaming, staining, and finishing techniques that are available, this really isn't much of an issue.

There are already some good walnut breeding programs under way in the upper Midwest, and I commend them for it. In the Deep South, I am trying to pursue a similar course, but with much less resources and fewer trees to select from, but if I don't do it, who will? If not now, when? And if not this way, how?

The South may never catch up with the upper Midwest in quality or quantity of walnut timber or nuts, but we can do a lot better than we have.

One of our popular jokes is that in order to get a reasonable price for our walnut logs they should be hauled to market in Tennessee on a truck bearing a Kentucky tag!

But we can do better than that, so let's do it.

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Updated: February 7, 2017