Peanuts are an easy-to-grow crop, as long as you can provide the right growing conditions and climate. A warm-weather plant, peanuts require a long, hot growing season, loose sandy soil to develop in and careful adherence to watering requirements. Northern gardeners often have a difficult time cultivating peanut crops because the growing season is too short and does not stay hot enough. Very dry climates can work, provided adequate moisture can be supplied.
Peanuts require a soil temperature of 65 degrees F for germination. Several days after germination, peanut plants emerge from the ground. At that point, the warmer the temperature, the better. Peanuts grow best when the temperatures are at least 86 F. While some production can still be had at lower temperatures, the low end of the temperature spectrum is 56 degrees for peanut production. Little to no production can be achieved at this or lower temperatures.
Not only do peanut prefer temperatures of 86 degrees, they need a sustained 120 frost-free days to grow, a relatively long growing season. The more of those growing days that remain near the ideal temperature of 86 degrees, the better the crop you can expect -- assuming all other conditions are within optimal growing parameters. This greatly limits the areas capable of growing successful peanut crops.
Rainfall is critical to a peanut crop, particularly during the flowering period. Flowers emerge six to eight weeks after the plant breaks ground. Once the flower is fertilized, it drops off and the remaining stem curves downward and penetrates the soil. This process takes about 10 days. During this period, the peanut plants should receive a good soaking, to a depth of of 6 to 8 inches each week. If rainfall is not adequate, water must continue to be supplied after flowering. If the peanut plants are allowed to dry out after flowering, the crop will be reduced, perhaps substantially.
While it is important that the plants receive adequate rainfall or irrigation, too much watering can be harmful. Over-watering can cause the nuts to sprout in the ground. A weekly watering of 4 to 6 inches should be adequate for most home gardens. As harvest time draws near, pay attention to weather forecasts. Sudden and heavy rains just before harvest can also cause the nearly mature nuts to begin sprouting.