How to grow watermelon: a commercial guide

Seeded, seedless and mini types

Seeded versus seedless

Watermelons are seeded (diploid) or seedless (triploid). Seedless plants make non-viable pollen, so a seeded variety or a non-edible pollenizer must be planted nearby for the fruit to set. Order pollenizer seed with the seedless seed.¹

Flesh and rind

Standard types have striped rinds on dark or light green, but some, such as Sweet Gem, have a plain dark green rind. Red flesh is most familiar; yellow, orange and white flesh types exist.¹

Match the type to the buyer

Fruit size and shape differ by variety and region, so check seed-company information and the Midwest Vegetable Trial Report before choosing.¹

Transplant into warm soil on plastic mulch

Date and temperature

Plant after the danger of frost is past. Air temperatures below 10°C (50°F) cause chilling injury, and direct-seeded crops need soil above 16°C (60°F); Penn State waits until soil 7.5 cm (3 inches) deep reaches 16°C (60°F) before transplanting seedless types.^1,2

Transplants and mulch

Transplants are often used, grown in the greenhouse for about 4 weeks (Penn State: 18–24 days at 24–32°C (75–90°F) container soil). Plastic mulch is recommended for all transplanted watermelons.^1,2

Population

The Midwest guide gives rows 1.8–3.7 m (6–12 ft) apart and plants 0.9–1.8 m (3–6 ft) apart. Penn State lists 6,920–10,870 plants per ha (2,800–4,400 plants per acre) in single rows 1.5–2.4 m (5–8 ft) apart with 61–91 cm (24–36 inches) between plants. The two differ, so use the recommendation for your region and fruit size.^1,2

Plan pollination for seedless types

Pollenizer pattern

Use one pollenizer plant for every two to four seedless plants in the row, or one row of seeded watermelons for every two to four rows of seedless. Penn State describes every third and outside row as the seeded variety (2:1), or every third or fourth plant in the row (2–3:1).^1,2

Bees

Penn State recommends about 2.5 hives per hectare (one per acre) for maximum fruit production. Protect bees: apply contact insecticides in the evening when flowers are closed.^2,1

Feed and water

Soil pH

Maintain pH 6.0–6.8 (6.3–6.8 for melons). Below 5.5 can cause manganese toxicity, and melons are particularly sensitive to low pH.¹

Nutrient uptake

Melon, watermelon, pumpkin and squash crops accumulate roughly 165–180 kg/ha (145–160 lb/acre) N, 34–50 kg/ha (30–45 lb/acre) P2O5 and 180–200 kg K2O/ha (160–180 lb K2O per acre) in vines and fruit. Adjust N for soil organic matter and credits; set P and K by soil test.¹

Programmes

On plastic with drip, apply 34–39 kg/ha (30–35 lb/acre) N before planting and fertigate 0.6–2.2 kg N/ha (0.5–2 lb N per acre) per day. On plastic without irrigation, up to 110 kg/ha (100 lb/acre) N preplant and 34–50 kg/ha (30–45 lb/acre) sidedressed later. Penn State: 40-50-50 banded at planting and 30-50-50 injected, no more than 5.6–7.8 kg/ha (5–7 lb/acre) N per application.^1,2

Water

Watermelons are deep-rooted, so rainfall is often adequate and irrigation may not pay on heavier soils. Moisture matters most early for vigorous growth and during blossoming and fruit development.¹

Scout cucumber beetles and drainage

Cucumber beetle thresholds

From seedling to the 4-leaf stage treat at 1 beetle per plant; from 4-leaf to harvest treat at 5 per plant. Weekly scouting is enough. Contact insecticides go on in the evening when bees are not foraging.¹

Phytophthora

Phytophthora blight follows heavy rain and poor drainage, starting in low spots. Avoid fields with a history of it, disinfest hands after touching an infected fruit and keep harvested fruit dry.¹

Harvest and store

Maturity is hard to judge

The Midwest guide calls picking at the right stage critical and difficult. Use several signs together: the ground spot changing from white to yellow, browning of the tendrils nearest the fruit, and a dull or hollow sound when thumped.^1,2

Cut, do not pull

Cut fruit from the plant, leaving 2.5–5 cm (1–2 inches) of stem, to avoid vine damage and stem-end rot.¹

Cooling and storage

Penn State recommends cooling to 7–10°C (45–50°F) to remove field heat. Fruit keeps 21–28 days at 8–13°C (47–55°F) and 85–90% humidity.²

Yield and economics

US watermelon production in 2025 was 1.76 million t (38.7 million cwt) from 40,000 ha harvested (98,900 acres; 102,900 acres or about 41,600 ha planted), worth $741 million. That is about 43.8 t/ha (391 cwt per acre) as a national average, all for the fresh market.

What drives margin

Seedless seed, transplants, plastic and drip are large per-hectare costs, and price is set by fruit size and market timing. Put your own numbers into the crop ROI estimator before choosing acreage.³

Frequently asked questions

When do you plant watermelon?

After the danger of frost, once soil 7.5 cm (3 inches) deep is above 16°C (60°F) and nights stay above 10°C (50°F). Transplants are usually grown about 4 weeks first.

How far apart do you plant watermelons?

The Midwest guide gives rows 1.8–3.7 m (6–12 feet) apart with plants 0.9–1.8 m (3–6 feet) apart, one plant per hill. Penn State uses 6,920–10,870 plants per ha (2,800–4,400 plants per acre) in rows 1.5–2.4 m (5–8 feet) apart.

How long does watermelon take to grow?

About 68–92 days from transplanting depending on variety, per Penn State.

How do you know when a watermelon is ripe?

The ground spot turns from white to yellow, the tendril nearest the fruit browns and dries, and the fruit sounds dull or hollow when thumped.

Do seedless watermelons need a pollenizer?

Yes. Plant one pollenizer for every two to four seedless plants, or one seeded row for every two to four seedless rows, and use about 2.5 bee hives per hectare (one per acre).

How long does watermelon keep?

About 21–28 days at 8–13°C (47–55°F) and 85–90% humidity after cooling to 7–10°C (45–50°F).