key growing information

How to Grow Watermelon From Seed

How to grow watermelons: soil, watering before ripening, plastic mulch and row covers, starting transplants, direct sowing, seeding rates, seedless types, pests, sudden wilt, ripeness signs and storage.

By Hensley’s Seed Co. September 3, 2026

Watermelons - Key Growing Information

Three watermelon varieties, selected for adaptability, early maturity, flavor, and yield.

SCIENTIFIC NAME:

Citrullus lanatus var. lanatus

CULTURE:

Watermelons do best in light, well-drained soil with a southern exposure and a pH of about 6.0–7.0. Keep soil evenly moist early on and while fruit is setting, then hold off watering in the final week before ripening, since too much water can make fruit bland. Because watermelons need steady warmth, plastic mulch and row covers bring earlier harvests and higher yields, especially in northern areas. Take the covers off once female flowers appear, with a tiny fruit at the base of the blossom.

DAYS TO MATURITY:

Counted from transplanting; add about 10 days for direct sowing.

TRANSPLANTING:

Start seed indoors in 50-cell plug trays or 2–3" peat pots in late April, or one month before planting out and no earlier. Plant 2 seeds per cell or pot, ½–1" deep, and keep them at 80–90°F (27–32°C) until they sprout. Handle seedlings gently and never let the mix dry out. Grow them on at 75°F (24°C), then harden off for a week by cutting back on water and warmth. Once the weather is warm, settled and frost-free, plant 2–3' apart in rows 6–8' apart; or thin each pot or cell to one plant with scissors and set them 18" apart. Even hardened seedlings are tender, so avoid disturbing the roots and water well after planting.

DIRECT SEEDING:

Sow outdoors 1–2 weeks after the last frost, once the soil is warmer than 70°F (21°C): ½–1" deep, 3 seeds every 18–36", thinned to one plant per spot.

AVG. DIRECT SEEDING RATE:

At 3 seeds every 18" in 6' rows: about 340' per oz., 500' per 1,000 seeds, 3 oz. per 1,000', or 1⅓ lb. per acre.

TRIPLOID/SEEDLESS VARIETIES ONLY:

Seedless types need good conditions to germinate well, so start them indoors. They also need a pollenizer, an ordinary seeded watermelon, planted nearby to set fruit. The fruit is nearly seedless, though a few seeds may form if plants are stressed.

INSECT PESTS:

Guard against cucumber beetles with floating row covers put on at transplanting, or use insecticides such as pyrethrin or azadirachtin.

DISEASE:

Pick varieties with resistance to the diseases common where you live. Sudden wilt, a combination of disease and cold stress that hits in late summer when plants carry a heavy load of ripening fruit, can collapse vines almost overnight; good fertility and steady watering help prevent it.

RIPENESS:

Three signs of ripeness: 1) the tendril closest to where the fruit stem joins the vine turns brown and dies; 2) the spot where the melon sits on the ground turns from greenish white to a richer yellow, orange or cream; 3) a flick of the finger gives a dull, hollow sound, while unripe melons ring higher and sharper.

STORAGE:

Keeps 2–3 weeks at 45–50°F (7–10°C) and 85–95% relative humidity.

TRANSPLANTS:

About 550 transplants per oz. on average.

SEEDS/LB. (AVG.):

9,700.

PACKET:

See each variety.