How to Grow Watermelon: Planting, Spacing, Care & Harvest
Quick answer
Transplant or direct sow about 2 weeks after last frost (UNH). Start indoors about 3–4 weeks before set-out — planner last frost −2 to −1 (UNH; UMD says 3 weeks before transplanting). Space about 3–4 ft in the row × 6–7 ft between rows, or hills 6–8 ft apart (UMD). Fruit does not ripen off the vine; look for a yellowish ground spot (UMD).
Watermelon at a glance
Weeks relative to last frost (LF). Colored weeks show when our ZIP planner schedules each step.
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Planting dates for your ZIP: the ZIP planting planner counts each window from your local frost dates.
Organic pests and diseases: see also organic pest control. Use any product as the label directs.
Planting timing
UNH melon timing: seed to transplant 3–4 weeks; set out 2 weeks after last frost. (UNH when to plant) UMD melons: “Direct sow … when all danger of frost is past and the soil is warm. For earlier fruit, start seeds indoors 3 weeks prior to transplanting.” Days 80–100 from transplanting. (UMD melons) Planner: Transplant or direct sow last frost +2; Start indoors last frost −2 to −1 (UNH 3–4 weeks before set-out at +2; UMD’s “3 weeks prior to transplanting” alone lands near −1).
Depth and spacing
UMD watermelon: about 3–4 ft in the row × 6–7 ft between rows; or 2–3 plants in hills 6–8 ft apart. Black plastic mulch can improve yield and earliness (UMD).
Sun, soil and water
Full sun, well-drained, warm soil (UMD). Medium fertility — prefer compost and a soil test; excess nitrogen side-dress may lower yield and quality (UMD), so we do not print synthetic rates here. Bee pollination is required; avoid insecticides during bloom (UMD).
Care
Train vines in 1–2 directions to save space (UMD). Seedless types need a diploid pollenizer nearby (UMD).
Harvest
Watermelon does not ripen off the vine. UMD: look for a yellowish ground spot where the fruit rests on the soil. About 80–100 days from transplanting (UMD); other planning tables list about 85 days — check your seed packet.
Pests and diseases
UMD lists cucumber beetles, squash vine borer; bacterial wilt; downy and powdery mildew. Cultural: row cover until bloom (remove for bees); sanitation. For cucumber beetles see UMN cucumber beetles; powdery mildew cultural notes on UMD powdery mildew on vegetables. Prefer cultural controls first; use any product as the label directs.
Related: ZIP planner · organic pest control · all grow guides · cantaloupe
Frequently asked questions
When do I plant watermelon?
Transplant or direct sow about 2 weeks after last frost (UNH). Start indoors about 3–4 weeks before set-out.
How much space does watermelon need?
About 3–4 × 6–7 ft in rows, or hills 6–8 ft apart (UMD).
How do I know a watermelon is ripe?
It does not ripen off the vine. Look for a yellowish ground spot (UMD).
More grow guides: All grow guides
Sources
- UNH Extension: When to Plant Your Vegetable Garden
- University of Maryland Extension: UMD melons; UMD powdery mildew on vegetables
- University of Minnesota Extension: UMN cucumber beetles