How Peanuts Grow: Flower, Peg, Pod Underground

Peanuts do not grow on trees. A peanut plant is a low legume whose yellow flowers form above ground, then send a stem called a peg down into the soil, where the pod grows and ripens. UF/IFAS Gardening Solutions calls this habit geocarpy: the plant flowers aboveground, but the fruit forms and matures underground. The whole cycle takes about 120 to 150 days from planting (NC State’s Plant Toolbox). For the growing method, start with our peanut growing guide.

Do peanuts grow on trees?

No, and the confusion is understandable, because walnuts, almonds and pecans do. A peanut is not a tree nut. UF/IFAS says the nuts are legume pods like peas and beans, but unlike other legumes they mature underground. The plant itself is small: NC State’s Plant Toolbox lists a height of 9 in. to 1.5 ft (23–46 cm) and a width of the same, and says it grows as an erect or runner form. Its species name, hypogaea, means “under the earth”.

The peanut life cycle, stage by stage

Step 1: The flower

NC State’s Plant Toolbox says the flowers are orange-veined, yellow and self-pollinating, produced near the base of the plant about 40 days after planting, and that in North Carolina they typically bloom from July to September. The flowers pollinate themselves, so the plant does not depend on a second plant for pollen.

Step 2: The peg

Here the peanut becomes strange. UF/IFAS Gardening Solutions says that once the flowers begin to fade, a self-pollinated peanut ovary forms, commonly called a peg. This peg grows downward and enters the soil, and only underground do the peanuts begin to form. NC State’s Plant Toolbox says the flower stems, once the flowers are fertilized, begin to grow into the soil where the irregularly ovoid seed pod develops.

Water matters most now. Clemson says water is the most common limiting factor in peanut production, and that it is most critical from 60 to 110 days after planting, as the pegs enter the soil and the pod begins to develop. Clemson also says to avoid wetting the leaves when watering.

Step 3: The pod

Underground, the pod fills. NC State says the peg and developing pod absorb calcium directly from the soil, so calcium must be readily available in the pegging zone, and that when soils have high temperatures, pegs cannot survive. Rapid canopy closure results in cooler soil temperatures in the pegging zone. So a canopy that closes quickly helps the pegs.

Why all the pods mature together

UF/IFAS Gardening Solutions says the plants continue to grow and flower while pods form, but your peanuts should all be ready to harvest at about the same time. The first pegs that form mature more slowly than those that form later.

Peanut or groundnut?

NC State’s Plant Toolbox lists many common names for the same plant, among them groundnut, goober, monkey nut and earthnut, all of which describe the same underground habit.

What this means for growing peanuts

• Plant when the soil is warm. Peanuts are not frost-hardy and suit areas with long warm summers (NC State Toolbox).
• Water well in the pegging window, 60–110 days after planting (Clemson).
• Keep calcium available and soil cool. Pegs need calcium and cannot survive high soil temperatures (NC State).
• Check the pods before digging. Dig when most pods are filled with the kernel but not dark inside the hull (Clemson). Our peanut harvesting guide explains the test.

Where this sits in the garden

Sweet potatoes also produce underground, but by a different mechanism: they grow from slips. See the sweet potato guide to compare. If you are growing in a pot, check peanuts in containers.