Pecan Seed GerminationLetís plant a pecan from seed. Natureís way is simple, native pecan seeds fall to the ground, overwinter in litter, squirrels bury them or floods cover them with soil and they germinate in the spring. One million acres in Texas have been planted by this method, but no one is depending on the system for growing nursery trees. When we want to grow nursery trees, the system can go in as many directions as there are nurseries. Their secrets are not for me to explore, so I will present some of the basic concepts here.
By Dr. George Ray McEachern
Professor and Extension Horticulturist
Texas A&M University, College Station, Texas
J. W. Worthington in the Texas Pecan Handbook discusses pecan seed germination, and I will summarize. The seeds are taken from dry storage, placed in moist soil, absorb water through the shell for about 2 weeks, enzymes stimulate growth, the kernels swell, the shell splits, the young root emerges and grows l/2 inch per day, extending a foot or more into the soil before the shoot emerges through 2 or 3 inches of soil. Germination is staggered for each individual seedling and 4 to 8 weeks is required for all seed to come up.
Dry Storage is required for the nuts as soon as they are harvested. Kernel percent moisture needs to be reduced from 20 at harvest to 6, 5, or 4 before going into storage. The drying needs to be as fast as possible without using heat.
Stratification is the period of time from drying to planting. For pecans they can be stratified with moist chilling or dry chilling. The ideal temperature is 45 degrees F and in a polyethylene bag to allow oxygen and carbon dioxide movement through the bag, but no loss of moisture. Some stratify pecan seeds in poly bags with both pecans and a very slightly moist packing medium such as sand, peat moss, or vermiculite. Some stratify as nuts only with no medium. The temperature should never go below 35 degrees F because freezing will kill the embryo. Stratification should be from as soon as the nuts are dry until they are presoaked for planting in late February. Most people are now using dry stratification.
Pre Soaking is used to stimulate germination. The nuts are placed in a mesh bag, submerged in a water bath, and soaked in running water for one to four days. Barrels, irrigation canals, or rivers have been used, just so that the water is not standing still. Top quality seed will swell and split in only one day. These seed should be checked at least twice daily, handled carefully and planted immediately without allowing them to dry.
Seed Bed should be ready so that the swollen nuts can be planted immediately.
Variety Seedstock for pecan rootstock is discussed by L.J. Grauke in the Texas Pecan Handbook and is summarized but not limited to the following: Giles in north, Riverside in west and central, Apache in the southwest, and Elliott in east and southeast Texas. Outstanding native trees in the area can also be used for seedstock. High quality kernels which are well filled should be used.
Sprouting on the Tree or premature germination while the nuts are on the tree has been a major problem in the year 2000. Why does this occur? The pecan, like all deciduous trees, has a rest period which controls seed germination and spring bud break. Surprisingly, the two systems are very similar. In general, the seed goes through three stages of rest: pre rest, mid rest, and post rest. The rest is controlled in part by an inhibitor hormone called Abscisic Acid (ABA). This hormone is produced in healthy leaves from bud break to leaf fall. In late August and September if a heavy loaded pecan tree is stressed, its leaves will stop producing ABA and consequently the mature seed in the shucks on the tree have no inhibitor, thus sprouting can occur when rain and warm weather occur together. Once pecans are harvested and dried they are in mid rest and will not germinate. Once stratified for 30 to 90 days, the seeds enter post rest and will germinate when soaked or planted.
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