Male and female flowers
The first flowers to appear on almost any squash are male — a straight stem with a flower on the end and no swelling behind it. Females appear a week or two later, recognisable by a miniature fruit at the base of the flower.
In a greenhouse or indoors there are no bees, so the female flower opens, is not pollinated, and drops. The miniature fruit yellows and falls off. This is the single most common complaint about growing squash under cover, and it is not a nutrient problem.
The fix is hand pollination. Pick a male flower in the morning when both are open, peel back the petals, and press its centre against the centre of a female flower. One male can pollinate two or three females. Do it before mid-morning, as the flowers close by afternoon.
Size and space, honestly
A courgette plant in open ground spreads over a square metre. In a bucket it cannot, so you have two options: choose a compact or bush variety and accept a smaller plant, or grow it as a cordon up a vertical support, tying the stem as it climbs.
Pumpkins and winter squash are worse — the vines run metres and the fruit is heavy. In a 10 L system, treat them as a curiosity rather than a crop.
Whatever you grow, the plant will drink far more than anything else in this catalogue. At peak, a fruiting courgette can take two litres a day from a small reservoir. Check morning and evening.
Feeding
Squash are heavy feeders and heavy drinkers. EC 1.8–2.4 through fruiting, pH 6.0–6.5. They will exhaust a small reservoir quickly, and because they drink so much the EC rises between top-ups as water leaves faster than nutrients.
Top up with plain water rather than nutrient solution, and change the reservoir every 10–14 days at peak. A courgette left on the same solution for three weeks will show pale leaves and poor fruit set.
Harvesting at the right moment
Courgettes are best at 15–20 cm (5.9–7.9 in). Leave them longer and the plant slows production while the fruit swells, and the flesh becomes watery and full of seed. Pick every two days in warm weather — the plant responds to regular picking by setting more fruit.
Winter squash and pumpkins are the opposite: leave them on the vine until the skin is hard enough that a fingernail will not dent it, and the stem has begun to cork. Harvest before the first hard frost and cure them somewhere warm and dry for a fortnight.
Saving seed: the isolation headache
Squash are insect-pollinated and cross within their species. Cucurbita pepo — courgettes, most summer squash, some pumpkins — crosses with every other pepo. Cucurbita maxima — many winter squash — is a separate species and will not cross with pepo.
Isolation is 500 metres (1,640 ft) to a kilometre. In practice, bag a female flower before it opens, hand-pollinate it with a male from the same plant, and re-bag it until the fruit sets. That is the only reliable method in a garden.
Seed must be washed free of pulp and dried thoroughly. Squash seed is viable for four to six years.