How to grow and care for watermelon plants

Can you grow watermelons in the UK?

Watermelon can be grown in the UK but needs a long season of heat and sunshine, along with rich soil and ample moisture. It's therefore best to grow watermelons in a greenhouse or polytunnel, ideally in open soil which you can enrich with plenty of organic matter.

For the best chance of success at growing watermelons in the UK, choose a variety that's bred to grow in cooler climates, such as 'Mini Love'. An early-fruiting watermelon variety may produce fruit as early as August. Watermelon plants are frost-tender and last for one growing season, so you’ll need to sow or buy fresh seed each year.

How to grow watermelons

Grow watermelons in moist but well-drained soil in a sheltered, sunny spot. For best results, grow in a greenhouse or polytunnel. Water regularly and feed weekly with a high potash fertiliser. To create a bushy, productive plant, pinch out the growing tip of the plant once five to six true leaves have formed, then thin subsequent side shoots to allow four to develop. Pinch out the tips of these four once six leaves have formed. Harvest with a sharp knife when you tap the fruit and it sounds hollow.

Where to grow watermelons

For the best chance of success, grow watermelons under cover in a greenhouse or polytunnel. If you want to take your chances outside, choose a sheltered spot in full sun. It's possible to grow watermelons in pots but you will need to water and feed them more regularly than those growing in the ground, and consistent watering is key to getting a good crop. For pots, choose a compact-growing variety such as 'Little Darling F1' and plant it in a large container at least 35cm high and wide, using good quality, peat-free potting compost, along with some organic matter such as well-rotted manure.

How to plant watermelons

Sow watermelon seed into peat-free seed compost from mid-April to early May, and keep in a heated propagator set to between 18ºC and 21ºC. Pot on into individual pots when the seedlings are large enough to handle. Alternatively, buy ready-grown, young watermelon plants. Transplant them into larger pots and grow on in a warm spot such as a conservatory or greenhouse. If growing watermelons outside, wait until the last frosts have passed (typically early June) before planting out. Harden off the plants over a couple of weeks first, standing them outside for increasing periods of time to acclimatise them to the outdoors. Then plant in deep, fertile soil, enriched with well-rotted manure or garden compost.

If growing in a greenhouse or polytunnel, there's no need to harden off plants. Simply plant them into your greenhouse border when the plants are a good size, ideally with plenty of well-rotted manure or home-made compost to enrich the soil.

Watermelon plants can be left to trail along the ground or trained upwards onto a sturdy support. If the latter, fix this support in place when planting, so as not to disturb the rootball later on, and tie stems into the support frame as they grow.

How to care for watermelons

If training your watermelon plants to grow vertically, tie their stems into their support frame as they grow – they are not self clinging. Then, as the fruits develop and become large, you will need to support them individually otherwise the stem may collapse under the weight. Old bras and t-shirts are excellent for this, simply attach them to the support frame and let the developing fruit rest in the 'hammock' of material.

Attention to watering is especially important when growing watermelons, as an evenly moist soil is essential to ensure good fruit quality, size and flavour. Pay particular attention to watering once the fruits have started to form.

Feed with a liquid fertiliser that is high in potash, such as tomato fertiliser, diluted as directed. Apply weekly from when the first fruits start to develop.

How to prune watermelon plants

To encourage fruiting side shoots to be produced, first pinch out the growing tip of the plant once five to six true leaves have formed. Then thin subsequent side shoots to allow four to develop and pinch out the tips of these four once six leaves have formed.

Pests and diseases of watermelons

Watermelon plants growing under cover are more likely to suffer from problems than those growing outside. Aphids and red spider mite are pests that are most likely to occur under cover. Inspect regularly and act early before pests take hold. Biological controls work well under protection and are environmentally friendly. Help prevent attack with companion planting: strong-smelling marigolds or basil to deter pests, and nectar-rich flowers to attract beneficial predators.

When to harvest watermelons

Harvesting watermelons when fully ripe is important to enjoy their sweetest flavour. The toughness of the skin is a good indicator – press it with your fingernail and, if it leaves a mark, the fruit isn’t yet ripe. Or tap the fruit – it will give off a hollow sound when ripe. Then cut the fruit from the plant using a sharp knife.

Watermelon varieties to grow

Watermelon Little Darling F1 – a compact variety that ripens quickly, bearing delicious small oval fruits with sweet and juicy flesh. Each plant produces up to four watermelons. Best grown in a greenhouse or polytunnel. Height x Spread: 45cm x 120cm

• Buy watermelon 'Little Darling F1' from Suttons

Watermelon 'Sunlove' – up to four yellow-fleshed fruit are produced on plants that are less abundant in leaf than some, so are easier to manage. H x S: 40cm x 4 m

• Buy watermelon 'Sunlove' from Suttons

Watermelon ‘Mini Love’ – early cropping variety, producing fruit from late summer. Produces up to six large fruit per plant. H x S: 40cm x 4 m

• Buy watermelon 'Mini Love' from Thompson & Morgan