The basic technique for bench grafting nut trees has been described by Leslie Wilmoth in the 64th and 68th Annual Report of NNGA. He describes using bench grafting for propagation of black and Persian walnuts. I first observed and learned his technique in 1980, and at that time we also applied the technique to Carya species. From our observations we soon realized that it is actually easier to bench graft pecan and hickory than walnut. With healthy rootstock and scions collected from vigorously growing trees, we usually are able to achieve a better than ninety percent take on the grafts we make. Such a high rate of success in bench grafting Carya outweighs the main disadvantage of the technique, namely, the fact that the rootstock must be dug up before grafting. A main advantage of bench grafting is that it eliminates failure due to rootstock bleeding that is characteristic of young nut trees.
Pecan seedlings serve as the rootstock for all pecan, hican and shagbark and shellbark hickory cultivars. Seedling pecans grown from the Major variety are well suited as a hardy rootstock, and have withstood temperatures of at least -26 degrees R, and windchill of between -40 and -50 degrees F with no observable damage. These trees are dug with a backhoe when they are the appropriate diameter of _ to 1 inch diameter at ground level. The rootstock trees are dug 2 to 4 weeks before the last spring frost, although I have dug and used trees that were already budding out in May, with no ill effect. Freshly dug trees are trimmed back to about 6 inches above the root crown, and the roots are washed and cut to a length of 18 to 24 inches. The seedling trees are stored in a pile of aged sawdust until they are grafted. They are never allowed to dry out.
Scionwood is collected in late winter and early spring, and stored, without adding wet paper, etc., in a plastic bag in a refrigerator. The best scions appear to be cut from 2 and 3 year old wood, which is contrary to what many have said in regard to using only 1 year old wood for scions. One year wood can be used if it is from vigorous growth of relatively large diameter (approaching _ inch). As a tree grows, an annual ring scar containing many dormant buds forms at the shoot terminals at the end of each growing season. These rings are evident when a branch several years old is examined. There are also many dormant buds present at the base of twigs that branch from the main shoot. If scions are cut so as to contain an annual ring scar, or half inch of a small branch, buds will almost always initiate growth from these areas. Consequently, scions from wood 4 to 8 years old can successfully be grafted on to sturdy 3 to 5 year old rootstock.
Grafting begins at about the time of the last spring frost. I use the whip-and-tongue method and a rubber budding band to hold the scion in place. Scions of _ inch and larger are also nailed with two small wire nails. Newly grafted trees are placed in containers filled with hardwood sawdust. The condition of the sawdust is critical to success. It should be at least 6 months old and low in moisture content. I like to collect the sawdust in January or February. The containers, which are old deep freezers, stock watering tanks, or boxes lined with plastic, can be filled at this time, and damp sawdust can be occasionally turned, and gradually dried out. When squeezed, sawdust at the correct moisture level should not dampen the hand.
Proper temperature is also critical for success. The room containing the sawdust bins is heated to about 80 degrees F, usually 4 or 5 days before the grafting begins, in order that the sawdust will be thoroughly heated when the newly grafted trees are placed in the containers. The trees are usually placed at about a 45 degree angle and covered completely with sawdust. The top of the scion is covered by 1 inch of sawdust. The grafted trees are placed side by side, usually about 1 inch apart. Thus, an average freezer, for example, may contain 200 to 300 trees. The temperature is maintained at about 80 degrees F for the entire callousing period of 9 to 14 days. White callous first appears at the graft union at about 6 to 7 days, and all the trees are removed from the tank as the first few buds begin to emerge from the sawdust.
I like to time my grafting so that I will be setting the trees outside after all danger of frost is past. Roots must be protected from drying out during the transfer and planting period. Rootstock usually begins to sprout while in the callousing tanks, and all such sprouts should be removed, and the rubber bands cut when the trees are set out. Adequate moisture should be provided to the trees while they become established. Finally, one-year old grafts should be protected from winter freeze damage. This is most easily accomplished by mulching with straw and sawdust, or mounding up soil, at least several inches above the graft union.
As might be expected, grafts on larger rootstock tend to grow more than those on smaller rootstock. They also can withstand more adverse conditions than the small grafts. Typically, pecans and hicans initiate a second round of growth the first year, and some trees grow 18 inches or more. On the other hand, hickory grafts are not likely to initiate a second growth period, and thus are more susceptible to heat stress and insect predation. They are therefore likely to require extra attention.
* John O. Brittain can be reached at Nolin River Nut Tree Nursery, 797 Port Wooden Road, Upton, KY 42784
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