Peanuts are generally grown in southern climes. Most are produced in China, India, Nigeria, and the southern United States—all of which fall squarely in climates in or similar to USDA hardiness zones 8-11. That is to say, their summers are long enough to permit the up to 150 days necessary for the plants to reach maturity.
But with some planning, successful peanut growing can spread as far north as zone 6 for home growers who want to grow snack peanuts, peanut butter and, of course, bragging rights.
If you live in one of those more northern areas, direct sowing isn’t possible, and you’ll have to either buy starter plants or start seeds rather early indoors—or in a greenhouse if you happen to have one—then transplant them outdoors two to three weeks after danger of frost has passed.
Knowing that date, research your first fall frost date and see if there are enough days between them to allow the variety of peanut you’ve selected to mature. For example, Valencia takes 90-110 days; Spanish, 90-120; Virginia and runner types, 130-150. If not, figure out how many additional days they’ll need to form indoors, then plant the seeds that many days ahead—it won’t be any less than 14 additional days. Don’t subtract more days than needed, or this will cause the seedlings to be leggy and stressed.
I recommend purchasing seeds from a specialty garden center or a seed catalog. Yes, you can crack open raw, unsalted in-the-shell peanuts from the grocery store and plant those — and if you do, take care not to remove the red seed coat — but you will have no way of knowing what variety you are planting or how long they’ve been sitting in their shells and under what conditions.
In zones 8-11, directly in the outdoors plant seeds in complete sun in a slope facing toward the south between the middle of April and the middle of June. Loosen soil to a depth of 12 inches; then sow in rows 20 inches apart 10 inches apart, 2-inch deep. Keep the soil moist till they sprout, then provide 1 to 1½ inches of water per week, including rainfall.
In zones 6 and 7, indoors start seeds about an inch deep in separate biodegradable pots, and put them under grow lights or by a sunniest window. Water once a week; then move the whole pot outdoors two to three weeks after the soil temperature warms to at least 60 degrees and the danger of frost has passed. If using starter plants, set it out at the same time.
Start, when plants are a foot tall, trucking hills of soil up around bases of plants, and mulch with 2 inches of straw or dried grass clippings. This promotes “pegging,” or the formation of seeds underground. Those seeds are, of course peanuts, so they have to be dug up harvest.
Because peanuts aren’t technically nuts, but more of a relative to beans and peas as legumes, they fix nitrogen from the atmosphere into the soil, so don’t fertilize plants with nitrogen.
Notice yellow, self-pollinating flowers should appear in about 40 days. When the petals drop you’ll know peanut formation, or pegging has begun below ground.
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This coloring may vary according to your variety and growing conditions, but in most growing methods, it is four to five months from seed sowing that the leaves turn yellow.
Dig up plants — roots and all — shake off extra soil, and let sit in a sunny location with good air circulation for two to three days until the remaining foliage is dry. Remove peanut pods from the roots, then roast, or store unshelled peanuts in airtight containers. They will keep for about one year.