When to sow squash and pumpkins

Squash and pumpkins come from warm climates and die at the first touch of frost, so everything revolves around the last frost date. In the UK and most of Germany, Austria and Switzerland that means sowing indoors from mid-April to mid-May and planting out from mid to late May, once the nights stay mild.

Don't start too early. Squash seedlings grow fast and are ready to plant after about three to four weeks, with two or three true leaves. Plants that sit in small pots for longer get leggy and root-bound and often stall after planting out.

You can also sow straight into the bed from late May to early June. Cover the spot with fleece or a cloche for a week or two beforehand so the soil warms up. Direct-sown plants catch up surprisingly quickly, but in a short or cool summer the fruit may not ripen in time.

Sow one seed per 3–4 in pot, pushed in on its edge about 0.8–1.2 in deep. Keep the pots at 68–77°F, on a warm windowsill or in a propagator; at that temperature seedlings appear in about a week, while at 61°F they take more than two weeks. Squash dislike root disturbance, so don't prick them out: sow them straight into their own pots.

Harden the plants off for a week or so before planting out. Choose the sunniest, most sheltered spot you have. Squash are hungry plants (Starkzehrer) and like rich, moisture-holding soil that doesn't sit wet, so dig a generous amount of compost or well-rotted manure into each planting hole. The edge of a compost heap is a classic spot.

Give bush varieties 35–39 in each way and trailing varieties at least 59 in; big trailing types can easily cover 79 in or more. In a 120 × 80 cm raised bed that means one plant. Put it near a corner and let the vines trail over the edge and across the path, or train a small-fruited variety up a sturdy trellis.

On cold May nights, below about 50°F, cover young plants with fleece. Slugs love the tender seedlings, so check for them every evening for the first few weeks.

Squash need plenty of water, especially once the fruit starts to swell. Water the soil, not the leaves, and water deeply rather than a little every day. Sinking a pot or cut-off bottle next to each plant helps the water reach the roots. A thick mulch after planting keeps the soil moist; leave a gap around the stem.

Plants in rich garden soil usually need no extra feed. In containers, or if you are after very large fruit, give a high-potassium liquid feed every 10 to 14 days once the first fruits swell.

As fruits ripen, lift them onto a tile, board or bit of straw so they don't rot where they touch damp soil, and make sure the leaves don't shade them completely.

Winter squash are harvested fully ripe, from about August to October depending on variety and summer. Leave them on the plant as long as you can for the best flavour, but bring them in before the first frost. A ripe squash has a hard skin you can't easily dent with a fingernail, and the stalk has turned dry, woody and cracked.

Cut each fruit with at least 4 in of stalk attached and carry it by the body, not the stalk. A snapped or very short stalk leaves a soft spot where rot gets in.

Before storing, let the skin harden for one to two weeks somewhere sunny and warm, outdoors in dry weather or in a greenhouse. Then store the squash in a single layer, not touching, somewhere airy and dry at 50–59°F. Most winter squash keep for at least three months, the best keepers for six months or more. Check them regularly and use any with soft spots first.

Most garden squash belong to three species. Cucurbita maxima includes Hokkaido or Red Kuri, Crown Prince and the giant pumpkins. These cope best with a cool summer and are the safest choice in Central Europe and the UK.

Cucurbita pepo covers classic Halloween pumpkins, acorn and spaghetti squash, the Styrian oil pumpkin and, harvested young, courgettes. Cucurbita moschata includes butternut and the Muscat pumpkins: deep orange, fine-textured and sweet, and they store well, but they need the most warmth. Give them your warmest spot and don't plant them out before late May.

Powdery mildew is almost certain from late summer: a white, floury coating on the leaves. Dry roots make it worse, so keep watering in dry spells. Late in the season it does little harm to fruit that is already well grown.

Slugs and snails are the main danger in the first weeks after planting out. Grey mould can rot fruit and stems in wet weather.

Never eat a squash or courgette that tastes bitter. The bitterness comes from cucurbitacins, which can cause serious poisoning. Garden varieties are bred to be free of them, but home-saved seed can cross with ornamental gourds, and stress can occasionally trigger bitterness. If you save seed, keep in mind that varieties of the same species cross readily.

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

The best-known pairing is the "three sisters": sweetcorn, climbing beans and squash, a traditional growing system from the Americas. It works as a way of sharing space, but don't expect big yields of all three in a small bed. Other companion tips for squash, such as nasturtiums, are tradition with little evidence behind them.

The practical rule: give squash the room they need, and keep them away from other cucumber-family crops in the rotation.