Can I Grow Watermelon in a Cool Climate or Short Season?

Watermelon is a tropical crop that evolved in warm, dry conditions. In temperate climates — northern Europe, much of the UK, northern North America, highland areas — the default answer from many gardening guides is "no." But many gardeners in these climates do successfully grow watermelon by choosing the right varieties, extending the season with structures and warming the soil. It is harder than growing watermelon in a warm climate, but entirely possible.

Choose an early-maturing, small-fruited variety

Full-size watermelons take 80–90 days from transplanting and need sustained summer heat. In a cool climate you do not have that. Choose varieties bred for short seasons — typically 65–75 days from transplanting, with small to medium fruits (1.5–4 kg). Look for varieties described as "early," "short season" or "northern" in seed catalogues. Varieties like Crimson Sweet, Sugar Baby, Blacktail Mountain and Golden Midget are often recommended for cooler climates. These ripen faster and tolerate cooler conditions better than full-size tropical types.

Black plastic mulch to warm the soil

Lay black plastic mulch (polythene sheet) over the growing area two to three weeks before planting to absorb solar heat and warm the soil. Watermelon roots in warmer soil grow faster and the plant establishes more quickly. Soil temperature at root depth should be at least 21°C before planting. Under black plastic in a sunny position, soil warms four to six degrees above ambient, which can be the difference between a plant that establishes readily and one that sulks for weeks.

Season extension with structures

A polytunnel, glasshouse or even a large cold frame adds two to four weeks to the effective growing season and raises temperatures significantly. In the UK, polytunnel-grown watermelon is reliably achievable; open-ground growing in southern England requires the warmest summers. Start plants indoors in early May and transplant under cover in early June after hardening off.

Manage fruit load for faster ripening

In a short season, limit each vine to one or two fruits. Fewer fruits ripen faster and reach higher sugar levels before the first autumn cold. Remove any additional fruitlets beyond your two best when they are tennis-ball sized.