Arachis hypogaea aka Peanut

Arachis hypogaea, the peanut, belongs to the pea family. Growers raise it as an annual for its edible seeds. It comes from South America, though sources differ on origin. Kew places its crop origin in Bolivia; NC State names central Brazil. No truly wild populations are known, according to Useful Tropical Plants. Farmers now grow peanuts across much of the world.

Garden plants reach about 0.75–1.6 feet [0.23–0.5 metres] tall and wide. Useful Tropical Plants reports stems reaching 2.3 feet [0.7 metres]. Plants may stand upright or spread along the ground. Green stems start smooth and round near the base. Older stems become more angular and grow hairs. Each green leaf has four oval leaflets with smooth edges. A clear midrib runs through each leaflet.

Small yellow flowers have orange lines and a pea-flower shape. They grow near the plant’s base from July to September. Flowers can pollinate themselves, then form a stalk called a peg. The peg pushes the ovary into the soil. There, it grows into a brown pod holding the seeds. This makes the peanut a legume, not a true nut. Pods take about 120–150 days from sowing to ripen. Plants keep making new pods, so their ages differ at harvest.

Peanuts need full sun and a long, warm growing season. They grow best in fertile, light soil with good drainage. Sandy loam suits them, though they can tolerate heavier soils. Keep the soil moist without letting water collect around roots. The plant cannot survive frost; RHS rates it H2. Sources list USDA zones 2–11 for growing it as an annual. Most UK gardens lack enough summer warmth for good crops outdoors. RHS recommends growing it under glass in light compost. Seeds provide new plants, and plants need no pruning.

Peanuts suit food beds, pots, and greenhouse growing. Root nodules house bacteria that fix nitrogen, helping enrich soil. People eat the seeds raw, roasted, or cooked. They also make peanut butter, oil, and flour from them. Young leaves and shoot tips may serve as cooked greens. Hulls and other plant parts supply feed, fuel, and industrial materials. Birds and small mammals also use peanuts as food.

Garden sources report few serious pest problems, but diseases can occur. These include leaf spots, stem rot, black rot, and wilt. The plant can also release substances that slow nearby plants’ growth. Mould can taint damaged seeds during growth or storage. Some moulds make aflatoxins, which can cause cancer. Peanut proteins can trigger severe allergies through eating or other exposure. RHS also flags seeds as harmful to people and pets.