How Do I Grow Cantaloupe Melons in a Greenhouse?

In cool temperate climates, growing cantaloupe melons in a greenhouse or polytunnel is the most reliable way to get a good harvest. Melons are subtropical plants that need warmth, long growing seasons, and plenty of sun — conditions that are only consistently available outdoors in the warmest regions. A greenhouse extends the season, protects from cold nights, and creates the warmth melons need to ripen their fruit fully. With the right management of training, pollination, and ventilation, greenhouse melons can be one of the most rewarding crops you grow.

Sowing and planting out

Sow melon seeds individually in 9 cm pots of seed compost in April or early May, ideally on a heated propagator at 21–25°C. Germination is rapid at this temperature — usually within four to five days. Grow on in a warm, light greenhouse or on a windowsill. Pot up into larger containers as roots fill the pot. Plant into the greenhouse border or large containers (at least 30 litres) from late May to early June when night temperatures in the greenhouse remain above 10°C. Space plants 60–90 cm apart.

Training the vines

Train the main stem vertically up a cane or string tied to the greenhouse structure. When the main stem reaches five or six leaves, pinch out the growing tip to encourage lateral shoots. Allow four to six lateral shoots to develop and train them horizontally along supporting wires. Pinch out the tip of each lateral two leaves beyond where a fruit is setting. This creates a structured, manageable plant with good air circulation and concentrates energy into fruit development.

Hand-pollination and fruit support

Hand-pollinate female flowers mid-morning using a male flower or small paintbrush. Thin to two to three fruits per plant once they have begun to swell. As fruits reach tennis-ball size, support each one in a small net bag (an old stocking or onion bag works well) tied to the training wire — this prevents the weight of the developing fruit pulling the vine down or snapping it. Keep the greenhouse well ventilated throughout to reduce disease pressure.