Flowering

Pecans, hickories, walnuts, filberts, and chestnuts have both male and female parts on the same shoot, but in separate flowers. In pistachio the male and female flowers are borne on separate trees. Flowers of these species are not showy and are largely wind-pollinated, except for chestnut which is both wind- and insect-pollinated.

Walnuts and hickories, including pecans, shed pollen about a month after the buds break in spring, while filberts flower during the winter or early spring before vegetative growth begins. Chestnuts, by contrast, flower later, about two months after shoot growth begins in spring.

Many pecan, walnut, filbert, and chestnut varieties or seedlings are unfruitful unless they receive pollen from another tree of the same species. Failure of self-pollination may be due to a difference in time of pollen shedding and female receptivity on the same tree, or a pollen incompatibility. To ensure cross pollination, two or more varieties need to be present in a planting.

Almond related to peach, plum, and other stone fruits and macadamia have colorful flowers and are pollinated by honey bees, which are usually prevalent in residential areas. Macadamia is self-fertile. Almond flowers are self-incompatible, so two or more compatible varieties must be selected for a planting to insure pollination.

Numerous superior pecan trees have been selected from native groves. Recently, outstanding varieties have been developed from the breeding program sponsored by the U. S. Department of Agriculture at Brownwood, Tex.

Newer selections of Persian walnut, like pecan, are considerably improved over older varieties. Many of the new Persian walnut varieties bear on lateral branches or spur shoots and are capable of producing more nuts. They have also been selected for hot or for cool climates. Characteristics of several of the older and newer varieties grown on the West Coast are given in the second table.

Many varieties of Carpathian walnut are adapted to the Midwest and East. These include Colby, Hansen, Lake and Metcalfe. Unfortunately, such selections are not readily available from nurseries.

The most widely planted almond variety is Nonpareil. Mission, Ne Plus Ultra, and Peerless are often used to pollinate it. However, the newer varieties Davey, Karpareil, Merced, and Thompson are also good pollinators for Nonpareil, and produce better quality kernels.

Barcelona is relatively resistant to most insects and diseases but the nuts are poorly filled. Several new hybrids yield more kernel per nut but produce smaller crops. In Washington, Noosack is commonly grown with Alpha and DeChilly as pollinators. Royal is adapted to colder areas along with Gem or Hall's Giant.

Availability of varieties of walnuts, butternuts, heartnuts, chestnut, filberts for the East, and shellbark and shagbark hickories is like that for Carpathian walnuts. Outstanding trees selected for vigor, production, nut size, and good cracking have been named and propagated, largely by amateur nut growers, but few nurseries list them.

Location, Spacing

Pecans and the large walnut trees should be spaced at least 40 to 50 feet from building, trees, and other obstacles if they are to remain a long time. Trees on poor soils with inadequate water will reach only half to three-quarters the size of those growing under good conditions. In areas of late spring frosts, plant on the north side of buildings to delay bud break in spring. Or plant on the upper portion of slopes to avoid frost pockets.

Smaller filbert and almond trees may be spaced about 25 feet apart. Almond is drought-hardy and tolerates poor soil, but it must not be exposed to late spring frosts. Filberts have shallow roots and can be grown on relatively shallow soils.

Chinese chestnut trees grow to about 40 feet and should be planted about 40 feet apart. They prefer an acid soil, pH 5.5, in contrast to the various walnuts which generally perform better on less acid soil, pH 6.5.

All nut trees should be planted when dormant after leaf fall and before leafing-out in spring. If the roots of a dug tree are allowed to dry, the tree will probably die. Buy young trees from reputable nurseries.

A narrow, deep hole is required to accommodate the pecan's tap root; roots of other nut trees spread out more as a rule. The hole should be large enough so tree roots are not twisted and folded back.

Once in the hole with soil filled back in, the tree should be gently lifted a little so the roots point down. Final depth of the tree in the soil should be the same as in its former location, and can be determined by the different bark color at the old soil line. Apply water to settle soil around the roots and prevent the tree from drying out.

For the first year after planting, the goal is to keep the trees alive. Ample soil moisture is the most critical factor. An inch of water per week by rain or irrigation is adequate. Excessive daily watering may waterlog the soil and kill a tree as readily as lack of water.

Maintenance of an area around the tree base free of weeds and sod will maximize tree growth. A mulch or herbicides will assist in controlling weeds and conserving moisture.

Pruning can begin the winter after the first summer of growth. Large trees like pecan and Persian walnut should be trained to a modified central leader (main trunk) rather than an open vase. A tree of this type has 5 or 6 main branches radiating from the trunk, beginning at a height of 5 feet to prevent limbs sagging to the ground. The central leader system gives greater strength and results in less limb breakage. After the first 5 years, when the tree is shaped, little pruning need be done except to thin crowded or dead branches.

As trees mature, prune out crowded branches. But don't cut back the terminal portion of pecan twigs, because these bear the fruit. The terminals can be pruned back on most walnuts because they bear on lateral twigs. If the variety does not fruit well on lateral branches, cut the main branches about a quarter of the way back.

On older pecan and walnut trees where seasonal growth is only a few inches, many small cuts may be necessary to thin fruiting wood and open up crowded areas of the tree. This type of pruning will stimulate new growth and rejuvenate the fruiting wood.

Filberts commonly form suckers at the base and grow in bush form. In the Northwest, suckers are removed to maintain single-stemmed trees. In the East, filberts grow best as multi-stemmed shrubs, but thin suckers constantly to maintain tree vigor.