Pecan Carya illinoinensis (Wangenh.) K.Koch Juglandaceae

Species description Pecan trees are tall, deciduous, long-lived perennial trees. The canopies are erect and oval to round. Leaves are alternate and pinnately compound, and the light grey bark is moderately furrowed. Pecan trees are slow to begin fruiting, with juvenile period lasting ten years in natural conditions. Trees undergo "masting," a periodic, regional, synchronous fruit production. Pecans are a riverine species with a long taproot, and in natural conditions grow along floodplains and stream benches. The trees have a wide range of cold hardiness, depending on the cultivar. Pecan trees are monoecious with male and female flowers are borne on the same tree. Wind-pollinated flowers appear in spring. The fruit is an oblong drupe-like nut with a pointed tip. The outer, leathery husk splits away at maturity, usually from September through December. Inside the shell, nut kernels are two-lobed and separated inside by internal septum.

Natural and cultural history Pecans are native to the midwestern and southern U.S. through northeastern Mexico, with small populations occurring farther south in Mexico. Indigenous peoples utilized and traded the nuts, possibly enhancing native populations and dispersing the species outside of its natural range. The first cultivated groves of pecan trees were established in the U.S. in 1775.

Planting considerations and propagation techniques Pecans are immense trees, especially by Arizona standards; they grow to 60 to 120 feet tall, with a canopy that measures 35-75 feet in diameter. They should be planted 40 to 60 feet apart to allow room for the trees to mature. They can be used as an over-story tree if spaced widely enough so that sunlight can reach the understory plants. Pecan trees live for 200+ yrs. They grow best in the sandy, well-drained, alluvial soils of river drainages. The trees require 400-500 chill hours, and do not produce well in the low desert areas. Cold hardy varieties available in Arizona can survive freezing temperatures to 0ºF when mature, however, most grow best with warmer winter lows. Pecan trees are wind pollinated monoecious trees. They should be propagated by grafting known varieties onto seedling rootstock.

Water needs Pecan trees are high water-users; the amount a tree withdraws may vary from a gallon or less for a young tree to as much as 150-250 gallons per day for a mature tree, from April to October.

Care Pecan trees are often trained to a single trunk with a modified central leader to enable mechanical shaking during harvest. The trees grow tall, making traditional pruning methods difficult for the backyard grower. Commercial growers do mechanical hedging or thinning of branches yearly to improve light penetration into the canopy. The most common disease to affect pecan trees is “pecan scab,” caused by Fusicladium effusum. The disease may be controlled by preventative methods such as disease-resistance cultivars and orchard spacing, or directly using insecticides.

Harvesting and processing In commercial groves, trees are harvested using mechanical shakers to agitate the trunk. In backyard orchards, trees may be shaken manually, or nuts picked from the branches, or collected from the ground. Pecans are ready to harvest when the nuts can be shaken easily from their outer husks. Nuts can be stored in their shell at room temperature for a season, but they will last much longer, either in or out of their shell in cold storage (refrigeration or freezing). Pecan nuts have a rich flavor and can be eaten fresh or used in baked goods, cheeses, confections, breakfast cereals, toppings, and snack mixes.

References and resources Grauke, L.J. and T.E. Thompson. 2008. Carya illinoinensis, pecan, pp. 421-425. Eds. Janick, J. and R.E. Paull. The Encyclopedia of Fruit and Nuts. CABI Publishing, Cambridge, MA. Ladybird Johnson Wildflower Center. Native Plant Database (NPIN). 2015. Carya illinoinensis. http://www.wildflower.org/plants/result.php?id_plant=CAIL2 Plants for a Future (PFAF). n.d. Carya illinoinensis - (Wangenh.)K.Koch. http://www.pfaf.org/user/Plant.aspx?LatinName=Carya+illinoinensis Rieger, M. n.d. Pecan – Carya Illinoensis. http://www.fruit-crops.com/pecan-carya-illinoensis/ University of Georgia Cooperative Extension. 2012. Pecans. http://extension.uga.edu/agriculture/ag-fruits- vegetables/pecans/

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