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Growing watermelons

Citrullus lanatus. A sprawling summer vine grown for its big, juicy fruit, sown where it grows or raised in small pots. It wants sun, a long hot season, plenty of room and steady water, its fruit ripens only on the vine, and frost kills it. These steps work anywhere: they go by soil and weather, not by month.

How a watermelon grows

1. 
   SowA few seeds in a low moundUp in 1–2 weeks
2. 
   ThinKeep the strongest twoAbout 2 weeks
3. 
   Vines runKeep the weeds down4–6 weeks
4. 
   FlowerMale flowers open firstAbout 6–8 weeks
5. 
   PollinateFemales have a tiny melon behindA week or two later
6. 
   SwellStraw goes down; fruit grows fast1–3 weeks after flowering
7. 
   RipenOn a board; water less5–6 weeks after flowering
8. 
   PickTendril dry, underside creamyFrom about 10–14 weeks

Times run from sowing in the bed and vary with the variety and the weather: small kinds are quickest, big ones take the longest. Seedlings raised in pots go out at 3–4 weeks old.

Growing it, step by step

1. Is it right for you?

   • Watermelons need a long, hot, frost-free season: about three months for most kinds, with days around 21–29°C (70–85°F).
   • Frost kills them. In cool summers they grow slowly, and the fruit comes small and less sweet. Where summers are short, small kinds grown in a greenhouse or polytunnel give the best chance.
   • They take room: the vines sprawl well beyond their spacing. Small kinds can be trained up a strong frame, with each fruit held in a sling so its weight doesn't snap the stem.

2. When to plant

   Sow where they are to grow once the soil is at least 20°C (68°F) and the last frost has passed: seed rots in cold soil. For an earlier start, sow in small pots indoors three to four weeks before you plan to plant out, kept warm at 21°C (70°F) or more, and plant out once the soil in the bed has reached 20°C (68°F) and the last frost has passed.

   Short, cool summers: start seeds in pots indoors, choose small, quick kinds, and grow them in a greenhouse or polytunnel, or outside over black plastic and under fleece. Mild climates: sow in late spring, once the soil is warm, for fruit in late summer. Hot or subtropical places: sow in spring as soon as the soil is warm. Shade the fruit lightly from the fiercest sun. Tropics: the cooler, drier months, on mounds or raised beds so the roots drain.

3. Prepare the bed

   • A warm, sunny spot, sheltered from strong wind. A few weeks before sowing, dig plenty of compost or well-rotted manure into each planting spot.
   • Light, free-draining soil suits them best. On heavy clay, build low mounds of soil and compost and sow or plant into them.
   • In cool places, lay black plastic over the bed a week or two before planting to warm the soil, and cut holes to plant through.
   • Slightly acid to neutral soil suits them, pH 6.0–7.0. See soil pH.
   • Avoid beds that grew melons, cucumbers, zucchini or pumpkins in the last two to three years. They share the same pests and diseases.

4. Sow and plant

   • Sow three or four seeds 2–3 cm (about 1 in) deep in each spot where plants are to grow.
   • Or sow two seeds 2 cm (¾ in) deep in a small pot, about 7.5 cm (3 in) across, keep it warm, and keep the stronger seedling. Sow seedless kinds one to a pot.
   • A week or so before planting out, harden seedlings off: put them outside by day and bring them in at night. Plant them at 3–4 weeks old, at the same depth as in the pot, without disturbing the roots. Bigger seedlings move badly.
   • Space plants 90 cm (3 ft) apart, in rows 1.8 m (6 ft) apart. Big kinds sprawl further: give them more room if you have it.

5. Get it started

   • Water well after sowing, then keep the soil just moist until the seedlings are up. Seed rots in cold, wet soil.
   • Water seedlings you plant out every day for the first week, until they settle.
   • About two weeks after sowing, keep the strongest two seedlings in each spot and snip the others off at soil level.
   • Protect young plants from slugs and snails, and cover them with fleece on cold nights. Take covers off once the flowers open, so bees can reach them.

6. Keep it growing

   • Water: a deep soak at the base about twice a week, more in hot, dry weather, best in the morning. Most roots are in the top 30 cm (1 ft), so water deeply rather than often, and water the soil, not the leaves. Keep it steady while the fruit sets and grows: dry spells then soakings cause blossom end rot. Once the fruit is full-sized and ripening, ease off to about once a week, for sweeter melons.
   • Weed and mulch: hoe weeds out shallowly while the vines are young. Once fruit has set and the soil is warm, spread straw about 5 cm (2 in) deep to hold moisture and keep the fruit clean. Keep it off the stem.
   • Feed: good soil needs little or nothing. On poor soil, or if growth is slow, give two high-potash liquid feeds two weeks apart once the fruit has set, and none once it is ripening. Too much nitrogen grows vine instead of fruit.
   • Fruit set: the first flowers are mostly male and fall off, which is normal. Female flowers have a tiny melon behind them, and each needs many bee visits. If those baby fruits shrivel or grow lopsided (poor fruit set), hand-pollinate in the morning: pull the petals off a male flower and dab its pollen into an open female flower. Seedless kinds set fruit only with an ordinary seeded kind growing within about 3 m (10 ft).
   • Vines: no pruning needed. Guide the runners where you want them to go.
   • Lift the fruit: once the fruits are a good size, slip straw or a board under each one so the underside doesn't rot on damp soil. On a frame, hold each fruit in a sling tied to the frame.

7. Watch for problems

   The common ones, with a Garden help page each where there is one:

   Powdery mildewDowny mildewAnthracnoseGummy stem blightFusarium wiltMosaic virusBlossom end rotPoor fruit setAphidsCucumber beetlesSpider mitesSquash bugsSlugs and snailsRoot-knot nematodes

8. Harvest

   • Leave them on the vine until fully ripe: a watermelon gets no sweeter once it is picked. Most are ready about five to six weeks after flowering.
   • Look for three signs together: the curly tendril nearest the fruit has turned brown and dry, the patch underneath where it lay has turned from white or pale green to creamy yellow, and the skin has gone from shiny to dull.
   • Tapping helps less than people think. A ripe one sounds dull and hollow, but trust the other signs first.
   • Cut the stalk with secateurs or a sharp knife rather than pulling, and pick them all before the first frost.

9. After harvest

   • Whole melons keep two to three weeks somewhere cool, around 10–15°C (50–60°F), or about a week at room temperature. Once cut, wrap them, keep them in the fridge and eat within two or three days.
   • Pull the vines out once you've picked the last melons. Bin plants with mosaic virus rather than composting them.
   • Next in that bed: a cool-season crop such as peas, broad beans, garlic or leafy greens. Keep melons, cucumbers, zucchini and pumpkins out for two to three years.

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Sources

• Iowa State University Extension: Growing watermelon in the home garden
• Clemson Cooperative Extension: Watermelon
• University of Illinois Extension: Watermelon
• University of Georgia Extension: Home garden watermelon
• Gardening Australia: Mini melons

Facts checked Friday 23 October 2026. General guidance only: local advice comes first.