Pecan

Sowing: Pecan trees can be direct-sown or transplanted as bare-root stock, though seedlings do not come true to type, so orchard trees are grown on seedling rootstocks. Bare-root trees are best planted in winter, from November through February, and because the tree develops a long taproot it can be difficult to transplant successfully.

Siting: Pecan needs long, hot summers and full sun to fruit well, and takes five to ten years after planting before it begins to bear. Trees eventually reach 70 to 100 feet tall with a spread of 40 to 75 feet, so spacing is generous - traditional orchards hold about 50 trees per acre - and two different varieties should be planted near one another because pecan is wind-pollinated and its male and female flowers on the same tree mature at different times, with the tree also prone to alternate bearing heavily one year and lightly the next.

Soil and water: The tree does best in deep, moist, well-drained soil with a pH between 6 and 7, though it also tolerates heavier clay, and a full-sized tree needs around 40 inches of water a year. Nitrogen and zinc are the nutrients most often required annually, while phosphorus and potassium are rarely needed.

Pruning: Pecan requires only minimal pruning to produce nuts, though young trees are trained to a central leader with six to ten widely angled, spiraled side branches so the heavy nut crop is well supported, and orchard trees are kept smaller through pruning to ease harvest and optimize light.

Aphids: The yellow pecan aphid and black margined aphid are common pests, piercing leaf veins to draw off water and photosynthates, which can distort and stunt the growth of shoots and roots.

Disease and disorders: Pecan can be susceptible to Verticillium wilt and to sudden summer limb drop, a branch failure occurring mid-limb on large horizontal branches during hot, windless summer days; preventive thinning of major limbs by a professional can reduce this risk. Squirrels have also been known to strip bark from trees severely enough to damage them, and nuts left lying on the ground attract insects, mold, and birds.

Harvest: Most varieties need at least 180 days to mature, ripening from late August through November; nuts are ready once the green hulls begin to split and the shells inside turn brown. Growers knock nuts down with a pole hook or, commercially, a hydraulic trunk shaker, then remove the hulls promptly, since hulls that resist separating signal the nuts are not yet mature. Hulled nuts are washed and spread in a shaded, well-ventilated spot to dry for several days with daily stirring, protected from birds, and are considered cured once a cracked kernel breaks cleanly rather than bending; a mature tree can yield 40 to 50 pounds of nuts a year.

Storage: In the shell, pecans keep for several months to a year in a cool, dry, ventilated place, or for up to two years if frozen at 0°F. Shelled kernels keep for three to six months refrigerated and for a year or more in the freezer, with pecan pieces having a shorter shelf life than halves in proportion to their exposed surface area.

Culinary: The pecan's seed is eaten as a snack and used in recipes such as praline candy and pecan pie.

Ornamental: Its size and broad, filtered-shade canopy also suit the tree to large landscapes, parks, and city parkways as a shade tree.

Other: The wood is used for flooring, cabinets, and furniture.

Pecan is native to the south-central United States and to northeastern and central Mexico, centered on the Mississippi River region. A fossil pecan recovered from Mississippi River floodplain sediments near Muscatine, Iowa, has been dated to roughly 7,280 years before present, showing the tree was already near its present-day northern limit in the early Holocene. Its abundance at Early Archaic archaeological sites, coinciding with peaks in Carya pollen in the upper Mississippi Valley, suggests humans may have helped disperse pecan northward long before it entered orchard cultivation.