When to sow melons

Melons come from warm regions and need more heat than any other common garden crop. In the UK and in Germany, Austria and Switzerland, sow them indoors from mid-April to mid-May. Earlier sowings only make sense if you have a heated greenhouse to plant them into.

The young plants are ready to go out after about four to five weeks, when they have three or four true leaves. Into an unheated greenhouse, polytunnel or cold frame that is usually late May or June; outdoors, wait until early June at the earliest. What matters is the night temperature: it should no longer drop below about 54–59°F.

Outdoors, melons only ripen reliably in warm areas, such as wine-growing regions, and in the sunniest, most sheltered spot you have. Everywhere else a greenhouse or polytunnel is the safer bet.

Sow two seeds per small pot of about 3 in, 0.4–0.6 in deep, and keep them at 68–77°F. Below 64°F they barely germinate; at 77°F seedlings appear in about a week, at 68°F it takes nearer two. Keep the stronger seedling and snip off the other. Like all cucurbits, melons resent root disturbance, so don't prick them out.

Harden off plants for the outdoors for a week or so. Plant into rich soil with plenty of compost, and water around the plant rather than onto the stem.

Give each plant 18 in if you train it up a trellis or strings, and about 35 in if it trails across the ground. A 120 × 80 cm raised bed takes two trailing plants, or three trained up a trellis along the long side. In containers, use pots at least 16 in wide and deep.

Melons fruit on side shoots, so a little training pays off, especially under glass. A common method: pinch out the growing tip once the plant has five leaves, keep the four strongest side shoots, and stop each fruiting shoot two or three leaves beyond a young fruit. Aim for about four fruits per plant; more means smaller, less sweet melons.

Each plant carries separate male and female flowers. Female flowers have a tiny swelling, the future fruit, behind the petals. Outdoors, bees and bumblebees do the work. In a greenhouse, open the doors on warm days and help out by hand: pick a male flower, remove its petals and dab the pollen onto the centre of the female flowers.

Keep the soil evenly moist but never waterlogged, and water the soil rather than the leaves. From early summer give a general organic feed every 10 to 14 days, switching to a high-potassium feed once the fruits are the size of a walnut. Stop feeding when the fruits start to ripen. Rest heavy fruits on a board or support them in a net if the plant climbs.

Greenhouse melons ripen from late July into early autumn; outdoor melons towards late summer. Fruits are usually ready about five weeks after pollination.

Use your nose first: a ripe melon smells sweet and unmistakably of melon. Other signs are fine cracks where the stalk joins the fruit, a rind that turns from green towards yellow or cream, and a base that gives slightly under your thumb. Cantaloupe and netted types come away from the stalk with a gentle push when fully ripe; this is called slipping. Some honeydew-type melons never slip, so go by colour and scent.

Melons build up their sugar on the plant, so leave them there until they are properly ripe.

In a cool climate, choose small-fruited, early cantaloupe or netted melons. Charentais, Ogen and similar varieties ripen fastest and are the most forgiving. Large winter or honeydew melons need a longer, hotter season.

Watermelons are a different plant altogether, Citrullus lanatus, and need even more warmth. They are a gamble without a greenhouse in most of Central Europe and the UK.

Powdery mildew shows as a white coating on the leaves and is worse when plants are dry at the roots. In a dry greenhouse, red spider mite can speckle the leaves. Cucumber mosaic virus causes yellow-mottled, stunted plants and can't be cured, so remove affected plants.

Gummy stem blight and Fusarium wilt can make stems rot or plants collapse; keep the stem base dry and rotate. Slugs attack young plants.

Poor fruit set is usually a pollination problem, especially under cover. Hand-pollinate if you see few bees.

Melons belong to the cucumber family with cucumbers, courgettes and squash. Leave three to four years before any of them grows in the same bed again.

Mixed-planting tables pair melons with sweetcorn, beans or nasturtiums. We found no good evidence behind these pairings; they are tradition. In a greenhouse, melons are often grown alongside cucumbers, which like similar warmth, but the two share pests and diseases.

What matters more is space and light: don't let taller crops shade your melons, and keep them apart from other cucumber-family crops in your rotation.