The peanut, or Arachis hypogaea, is a warm-weather annual crop belonging to the legume family. Successful growth depends entirely on sustained heat. Unlike many garden vegetables, the peanut requires a long, hot growing season to develop its fruit underground. The timing of planting is not flexible, and rushing the process often results in poor germination and a reduced harvest.
Soil Temperature Requirements
The single most important factor determining the best time to plant peanuts is the temperature of the soil, not the air. Peanuts are extremely sensitive to cold soil, which can cause the seed to rot before it sprouts. The minimum acceptable temperature for germination is \(65^{\circ}\text{F}\) (\(18^{\circ}\text{C}\)), but this only results in about 70% success.
For the best stand establishment and a high germination rate, the soil temperature at a 4-inch depth should consistently reach \(68^{\circ}\text{F}\) to \(70^{\circ}\text{F}\) (\(20^{\circ}\text{C}\) to \(21^{\circ}\text{C}\)) for at least three consecutive days. Planting in this ideal range can increase the germination rate to 90% or higher, ensuring a strong, uniform crop. Planting below this threshold significantly increases the risk of seedling diseases caused by soilborne fungi. These fungi thrive in cool, moist environments and can wipe out an entire planting.
Geographic Timing and Last Frost
Translating the temperature requirement into a calendar date provides a practical rule of thumb for gardeners and farmers. Planting should generally occur two to four weeks after the average last spring frost date for your specific region. This buffer period allows the soil to absorb enough warmth to maintain the necessary temperature at the seeding depth.
The window for planting peanuts is typically late April through May in the traditional peanut-growing belt of the southern United States. Regions with shorter summers must choose early-maturing varieties and strictly monitor local conditions. A long season of 120 to 150 frost-free days is required for the underground pods to mature fully. Growers should use a soil thermometer to verify the temperature at the 4-inch depth, as relying solely on air temperature or a calendar date can lead to premature planting.
Preparing the Ground for Success
Peanuts are unique because the fertilized flower, called a “peg,” must push down and penetrate the soil to form the pod. This requires specialized soil conditions. The ideal medium is a loose, well-draining, sandy loam that offers minimal resistance to this downward growth. Heavy clay or compacted soils will impede the peg’s entry, resulting in low yields or misshapen pods.
Before planting, the soil should be tilled to a depth of at least 8 to 12 inches to ensure a deep, loose seedbed. Peanuts thrive in a slightly acidic environment, with an optimal soil pH range between 5.9 and 6.5. A soil test is advisable to confirm the pH and nutrient levels, as proper preparation is foundational to a successful crop.
A calcium source is important for peanut development because the pods absorb calcium directly from the surrounding soil. Calcium is required for proper kernel development and pod fill, and a deficiency can lead to “pops,” or empty pods. This nutrient is often applied as gypsum, a calcium sulfate compound, which should be incorporated into the top layer of soil before the seeds are planted. Initial weed control is also necessary, as young peanut plants are slow to establish and cannot compete with aggressive weeds.
Planting Methods and Techniques
Once the soil is warm and prepared, the physical act of planting must be precise to ensure a good start. Only shelled, raw, untreated peanut kernels should be used for planting, as roasted or boiled peanuts will not germinate. The seed should be placed at a depth of 1 to 2 inches, with a slightly deeper placement often recommended in sandy soils to maintain moisture.
The seed spacing within the row should be approximately 6 to 8 inches apart, allowing each plant enough room to develop its underground pods. Rows should be spaced 2 to 3 feet apart to facilitate light penetration and air circulation. If peanuts have never been grown in the location before, the seed should be treated with a peanut-specific commercial inoculant to ensure the presence of nitrogen-fixing bacteria. After planting, the ground should be gently watered, maintaining consistent moisture until the seedlings emerge, which typically takes 5 to 10 days in warm soil.