Citrullus lanatus
Watermelons are the most ambitious crop a UK gardener can attempt — requiring sustained high temperatures, a long season, and considerable attention. But the reward of a home-grown watermelon split open still warm from the vine in August is genuinely extraordinary. Small icebox varieties are significantly more achievable than full-sized types and are the recommended starting point for UK growers.
The number of varieties shown for each crop is based on UK consumption data (2025/26) — the more popular the crop, the more variety choices we include.
The most widely grown and most reliable watermelon for UK conditions. Small, round, dark-green-skinned fruits with deep red flesh and high sugar content. Compact plant. Shorter growing season than full-sized varieties. The standard starting point for UK watermelon growing.
The earliest-ripening watermelon variety — skin turns from green to golden when ripe, providing an unmistakeable ripeness indicator. Very small but reliably sweet pink flesh. The best choice for northern UK gardens and short-season situations. Easy to judge ripeness.
A compact, early, seedless watermelon with very sweet, crisp red flesh. F1 hybrid giving reliable performance. One of the most recommended varieties for UK polytunnel growing. The seedless quality is a significant practical advantage.
The classic striped American watermelon. Good flavour with high sugar content. Needs a longer warm growing season than icebox types — best in the south or in a heated greenhouse. A satisfying achievement when it ripens fully, producing a recognisable full-sized watermelon.
An unusual heirloom watermelon with bright orange flesh — visually striking and quite different in flavour from red-fleshed types, with a honey-melon character. Needs a full warm season. Grown as much for its novelty and striking appearance as for culinary use.
Bred in the mountains of Idaho for short growing seasons and cooler temperatures — one of the most cold-tolerant standard watermelons available. Deep green-black skin, red flesh, good flavour. The best choice for attempting a full-sized watermelon in UK conditions.
A yellow-fleshed watermelon with pale ivory-yellow flesh and very sweet, mild, honey-like flavour quite different from red varieties. Early ripening. Birds and insects are sometimes confused by the yellow flesh and leave it longer. A striking novelty with genuine flavour quality.
A heritage variety from Saskatchewan, Canada — bred for short northern growing seasons. Cream to pale pink flesh with very sweet, delicate flavour. Early ripening. Of historical interest as well as practical value for UK growers wanting a heritage variety with cold tolerance.
The famous Japanese premium watermelon — black-skinned, unusually crisp texture, and exceptionally sweet flavour. A specialist choice for the most ambitious UK growers with a heated greenhouse. Difficult to ripen in UK conditions but remarkable when achieved.
Watermelon seed is available from most major UK seed suppliers, though the choice for icebox varieties suited to UK conditions (Sugar Baby, Golden Midget, Mini Love F1) is best from specialist greenhouse-crop or heirloom seed companies. Full-sized varieties like Crimson Sweet or the novelty Densuke are more often found through specialist online suppliers than general garden centres.
Watermelons need higher germination temperatures than ordinary melons. A thermostatically controlled propagator at 25–30°C is strongly recommended. Sow one seed per 9cm pot on its side. Germination 5–8 days. Grow on at minimum 20°C.
Black polythene mulch over the greenhouse bed absorbs heat and raises soil temperature significantly — this is particularly important for watermelons which need soil temperatures of 20°C+ throughout. Warm soil speeds ripening and prevents root stress.
Plant 1–1.5m apart into fertile, well-drained beds enriched with compost. Choose the sunniest corner of the greenhouse — even within a single structure, positions vary in temperature.
Tie the main stem vertically. Pinch out when 5 leaves form to encourage laterals. Female flowers (tiny striped embryo behind the petals) appear on the laterals. Hand pollinate daily at midday — transfer pollen from male to female with a soft brush.
A UK-grown watermelon plant can ripen 1–2 fruits in a good summer. Remove all other developing fruits decisively. Attempting more means none ripen. One perfectly ripened home-grown watermelon is the goal.
Watermelons reach 2–6kg. Every developing fruit must be supported in a strong string hammock or netting bag from when it reaches the size of a tennis ball. Without support, the stem breaks under the weight.
Thought to repel aphids and whitefly, and improve the flavour of neighbouring plants.
Marigolds are thought to deter nematodes and attract pollinators and predatory insects.
Higher temperatures than standard melons. A heated propagator with a thermostat is important. One seed per 9cm pot on its side. Do not water excessively — keep compost moist but not wet.
After germination, maintain 20°C minimum. Lower temperatures cause stunted growth that the plant never fully recovers from. A consistently warm environment is more important than high peak temperatures.
| Region | Sow / plant | Harvest | Notes |
|---|---|---|---|
| Scotland & Far North | Apr–May | Aug–Sep | |
| Northern England | Apr–May | Aug–Sep | |
| Midlands & Wales | Apr–May | Aug–Sep | |
| Ireland & Isle of Man | Apr–May | Aug–Sep | |
| South & SE England | Apr–May | Aug–Sep | |
| South Coast & SW | Apr–May | Aug–Sep |
Watermelons are always grown from seed annually. A heated propagator at 25–30°C is necessary for reliable germination. They cannot be propagated vegetatively.
Heated Propagator Essential — Sow at 25–30°C in a thermostatically controlled propagator. Without reliable heat at this level, germination is erratic and slow. Grow on at minimum 20°C after germination.
Not Reliable — Watermelon germination at temperatures below 20°C is unreliable. A heated propagator is strongly recommended. A very warm windowsill above a radiator may achieve adequate temperatures but cannot be relied upon.
Place the flat seed horizontally in a 9cm pot of moist compost. One seed per pot. Set propagator to 25–30°C. Germination in 5–8 days.
Watermelon roots are sensitive to disturbance. Handle root balls very carefully when potting on. Never allow serious pot-binding.
Watermelons need sustained temperatures of 25–30°C during the day and minimum 20°C at night to develop and ripen successfully. A UK summer that stays consistently below 20°C — common in poor years and in the north — will not produce ripe watermelons regardless of any other management. In such conditions, even the most cold-tolerant varieties (Sugar Baby, Golden Midget) will fail to ripen. A heated greenhouse maintains these temperatures regardless of outdoor conditions; an unheated polytunnel depends entirely on the summer being warm. This temperature dependency is what makes watermelons the most challenging fruit in this guide.
Judging watermelon ripeness is the defining challenge of growing them — the fruit gives very few external clues. Use all of these indicators together: the tendril nearest the fruit dries out and turns brown (the most reliable single indicator); the ground spot (where the fruit rests) changes from pale white to creamy yellow; tapping the fruit produces a dull thud rather than a hollow ring when unripe; the skin loses some of its shine and becomes slightly dull. Do not cut too early — an underripe watermelon is white-fleshed, unsweet, and deeply disappointing. Patience for an extra week is almost always rewarded.
Watermelons in UK greenhouse conditions must be hand-pollinated. Identify male flowers (slender stalk, no embryo fruit) and female flowers (visible striped embryo watermelon behind the petals). At midday, collect pollen from a fully open male flower using a soft brush and transfer to the stigma of the female flower. In a good summer with bees occasionally entering the greenhouse, natural pollination may occur, but hand pollination every day during the flowering period ensures maximum fruit set. A single successful pollination per flower is sufficient.
This is the most important management decision: allow only 1–2 fruits per plant to develop. Remove all other developing fruits as they form — this requires decisive action, as every small embryo watermelon looks promising. A UK-grown watermelon plant trying to ripen 4 or 5 fruits will fail to ripen any of them fully. A plant allowed to concentrate on a single fruit consistently produces a ripe, sweet result. This restriction is even more critical for watermelons than for ordinary melons because watermelon fruits require a longer ripening period.
Powdery mildew attacks foliage in warm, dry conditions — ensure ventilation and water at the base. Aphids and red spider mite in hot greenhouse conditions — inspect weekly and treat with soap spray or predatory insects. Root rot from overwatering is rapidly fatal. Failure to ripen before autumn is the most common outcome in cool UK summers — accept this and grow smaller, earlier varieties next time.
Full identification and treatment advice is in the Pests and Diseases sections.
A ripe home-grown watermelon should be eaten as soon as possible after cutting — ideally shared immediately with family. Refrigerate cut watermelon for up to 3 days. Serve at room temperature rather than cold for maximum flavour. The experience of splitting a fully ripe home-grown watermelon — the crack of the rind, the fragrance, the deep red flesh — is one of the most satisfying moments in kitchen garden growing.
Surplus watermelon blends into an outstanding granita — purée the flesh, add a little lime juice and icing sugar, freeze in a shallow tray and fork through regularly as it freezes to create ice crystals. Watermelon and mint granita is one of the finest summer desserts. Also excellent: watermelon, feta, and mint salad — the classic Turkish combination.
Watermelon rind pickle is a traditional American preserve — the white rind beneath the green skin becomes a sweet-sour condiment. An excellent way to use the entire fruit with minimal waste. Follow a tested recipe.
Both are icebox-type watermelons with small to medium fruit that require a shorter growing season than full-sized varieties. Sugar Baby is the most widely grown and reliable UK watermelon. Golden Midget is the earliest of all and the most achievable in northern gardens. Start with these before attempting larger varieties.
Laying black polythene over the greenhouse or polytunnel bed significantly raises soil temperature — sometimes by 5°C or more compared to bare soil. This simple step is particularly important for watermelons and genuinely improves fruit development and ripening. Combine with drip irrigation under the polythene for consistent watering without losing the heat benefit.
Growing a ripe watermelon in the UK is a genuine achievement. Some summers simply do not provide adequate heat regardless of everything the grower does. Accept this as part of the challenge, choose the most cold-tolerant early variety, maintain the heating, wait patiently for ripeness, and when it works — it is deeply satisfying.