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Squashes

This Allotment Pro editorial draft summarises the cited RHS guide. Check the source and adjust timings for local weather, soil and frost dates.
RHS source guide
Squash crop illustration

Month by month

Sow

  1. Sow indoors

    April to May

  2. Sow outdoors

    Late May to early June

Plant

  1. Plant out

    Late May to June, after the last frost

Harvest

  1. Harvest summer squash

    Mid-summer to the first frost

  2. Harvest winter squash

    Late summer to autumn, before frost

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1 - Getting Started

Squashes are tender, productive cucurbits grown for fruits in a wide range of shapes, colours, sizes and flavours. Most are varieties of Cucurbita moschata, C. maxima or C. pepo. Some form sprawling vines, while bush types stay more compact, although even these can occupy about a square metre.

All need warmth, sun, rich moisture-retentive soil and regular water. Starting seed indoors in spring gives a longer, more reliable growing season, particularly in colder districts. Once hardened off and planted after frost, healthy plants usually grow rapidly. Most fare best in the ground; compact summer types can grow in large containers.

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2 - Choosing What To Grow

Summer squashes have thin skins, are harvested young and are eaten soon after picking. Winter squashes mature fully, develop harder skins and can store for several months. Fruit forms include acorn, patty-pan, crookneck and butternut types. Match the cultivar to the available space: trailing vines may spread several metres or climb strong supports, while bush cultivars remain nearer their planting site.

Recommended varieties

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3 - Preparing The Ground

Choose a warm site in full sun with rich soil that retains moisture without becoming waterlogged. Even bush varieties can spread to about 90cm. For each plant, make a hole about 30cm wide and deep and refill it with soil mixed with garden compost or other well-rotted organic matter. In a no-dig bed, apply an organic mulch and plant through it.

Space bush growing sites at least 90cm apart and trailing plants about 1.5m apart. Summer squash can also grow in large containers filled with peat-free multi-purpose or soil-based compost, provided there is ample open space around the pot.

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4 - Sowing

Sowing indoors

Sow indoors from mid- to late April for reliable germination and an earlier, larger crop. Put one seed on its side about 13mm deep in each 7.5cm pot or module of peat-free seed or multi-purpose compost. Individual containers minimise root disturbance later. Keep at 18–21°C under a clear lid or bag until seedlings emerge, then uncover, water regularly and give bright light.

Keep young plants protected from late frost. Do not sow too early if they will become pot-bound before outdoor conditions are safe.

Sowing outdoors

Direct-sow in late May or early June after the soil has warmed. Covering prepared sites with a cloche or plastic-free fleece for two weeks beforehand can raise soil temperature. Sow two or three seeds 2.5cm deep at each site, using 90cm spacing for bush cultivars and 1.5m for trailing types. Protect seedlings with a cloche or fleece and thin to the strongest plant.

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5 - Planting

After the last frost, harden off indoor-raised or bought plants gradually. Set them into the prepared ground without disturbing the roots, firm gently, water well and retain the same 90cm bush or 1.5m trailing spacing.

Plant one summer squash in a container at least 45cm wide. Leave space around it for airflow and spreading growth; overcrowding encourages fungal disease. Tender plants may need temporary fleece if unexpectedly cold nights follow planting.

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6 - Plant Care

Watering and mulching

Squashes need regular water, especially once fruits begin swelling. Direct water onto the soil rather than foliage. A bottomless pot sunk beside the plant can deliver water towards the roots, and a short cane marks the crown when trailing stems hide it. Water early or late to reduce evaporation.

After planting, apply a thick organic mulch to conserve moisture and suppress weeds, leaving a clear gap around the stem so the crown does not rot. Insufficient water can check fruit development and encourage powdery mildew.

Feeding and ripening

Ground-grown plants in well-prepared soil often need no extra feed. Container and growing-bag crops benefit from an organic high-potassium liquid fertiliser every 10–14 days once the first fruits swell.

Place a tile, brick or board beneath large winter fruits to keep them off damp soil. Expose them to full sun where possible so their skins harden and they ripen thoroughly.

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7 - Pruning And Training

Trailing squash may sprawl freely where space permits. To control it, curve stems around a broad circle and hold them with short canes, or cut growth that strays beyond the allocated area.

Vines can also climb a sturdy arch, pergola, hazel wigwam or trellis. The structure must carry both vigorous foliage and the crop. Support individual heavy fruits in slings or netting; smaller-fruited varieties are the safest choice for vertical training.

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8 - Harvesting

Summer squashes crop from mid-summer, sometimes continuing until the first frost. Pick fruits while small, tender and thin-skinned. Frequent harvesting encourages more flowers and fruits.

Winter squashes may be eaten immediately or ripened for storage. Leave them on the vine as long as weather safely permits to improve flavour, but harvest before frost. Cut rather than pull, retaining at least 10cm of stem; a close cut leaves a soft wound that is vulnerable to storage rot.

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9 - Storing

For storage, allow winter squash to ripen fully on the plant. Cure sound fruits in sun for one or two further weeks, outdoors in suitable weather or under glass, to harden their skins. Move them inside before frost.

Store at 10–15°C in a dry, well-ventilated place, spaced so fruits do not touch. Many cultivars keep for at least three months. Inspect regularly and use any fruit that begins to deteriorate before decay spreads.

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10 - Problem Solving

Cold and frost injure these tender plants. Slugs and snails attack seedlings, while damp, crowded conditions encourage fungal problems. Warm soil, frost protection, good spacing, soil-level watering and prompt removal of damaged material reduce avoidable losses.

Common problems

Courgette, marrow, pumpkin and squash problems

Poor pollination, fruit rots, malformed fruit and leaf symptoms can share several causes. Identify the symptom before treating it and correct watering, temperature or pollination issues where relevant.

Problem source

Grey mould

Grey mould causes soft decay with fuzzy grey fungal growth, especially in cool, humid, crowded crops. Improve ventilation, avoid wet foliage and remove infected tissue hygienically.

Problem source

Slugs and snails

Slugs and snails can destroy emerging seedlings and chew young foliage. Check beneath pots and sheltering debris, protect vulnerable plants and use wildlife-friendly controls.

Problem source