How to Grow Courgettes from Seed (Cucurbita pepo)

A courgette is a pumpkin picked as a baby. Leave the same fruit on the plant for a month and you have a marrow; leave the plant to its own devices and it will bury a family in fruit by August. That generosity is the whole story of growing courgettes from seed: they are among the easiest and fastest vegetables in the garden, and the only real mistake is sowing too many of them.

Cucurbita pepo is the same species as the Halloween pumpkin, the patisson and the ornamental gourd, and it behaves like one — frost-tender, hungry, thirsty and enormous. Give it warmth to start, a bucket of compost to root into and a knife every other day, and one plant will produce 15 to 20 fruits between July and the first frost. This guide covers when to sow, why the first flowers never set fruit, how to keep the plants picking until October, and which of the 25 varieties in our summer squash range suit a bed, a trellis or a pot on the balcony.

• Sow April–May indoors in pots, late May–June direct once the soil is warm, up to early July for a late crop
• Germination 5–8 days at 20–25 °C; the seed rots in cold, wet compost
• Spacing 90 cm between bush plants, 60 cm for climbers up a post, one plant per 40-litre pot
• Harvest July–October at 10–20 cm long, every two days — picking is what keeps the plant flowering

Courgette, zucchini, marrow or patisson?

They are all the same plant. Courgette is the French name and zucchini the Italian one for a fruit picked immature; a marrow is either a courgette left to swell or a variety such as Alberello di Sarzana bred to be eaten large. Patisson (scallop or custard squash, such as Custard White and the colour mix) is a flat, fluted C. pepo picked at the size of a saucer, and Early Summer Crookneck is the bent-necked yellow type Americans grew before the courgette arrived. Round varieties — Tondo di Nizza, the Round Zucchini F1 mix — are picked at tennis-ball size for stuffing, and yellow Gold Rush F1 and organic Yellowfin F1 taste identical to green but are far easier to spot among the leaves.

Two summer squashes in our range are a different species altogether. Tromba d'Albenga and Rugosa Friulana are Cucurbita moschata, the butternut's family: trailing plants with long, curved, seedless-necked fruit that are eaten young like a courgette or left to ripen into a keeper. They need a longer, warmer summer, so treat them as a greenhouse or south-wall crop north of the Loire. Everything else below applies to all of them.

When to sow courgettes

Courgettes die at the first touch of frost and sulk below 10 °C, so the sowing date is set by the last frost in your garden, not by the calendar. Sow indoors three to four weeks before you expect to plant out — mid-April to early May for most of Britain and the Netherlands — and the plants will be exactly the right size when the soil warms. A March sowing on a windowsill gives a leggy, pot-bound plant that spends June recovering, while a mid-May sowing overtakes it by July: the same lesson applies to cucumbers, and it is the one most beginners learn the hard way.

Direct sowing works well once the soil holds 15 °C, which in an open bed usually means late May or early June. Sow two seeds per station under a jam jar or cloche and remove the weaker seedling. A last sowing in the first week of July gives young, mildew-free plants that carry the harvest through September into October, when the spring-sown ones are exhausted — the varieties tagged for July in our range (Tondo di Nizza, the early Courgette Mix, both patissons and organic Partenon F1) are the ones bred for it. Later than that and the plant runs out of season before it runs out of flowers.

Planting out: a bucket of compost per plant

A courgette does not need a well-prepared bed so much as a well-prepared hole. Dig out a spade's depth, tip in a full bucket of garden compost or well-rotted manure, mix it with the soil and plant on the slight mound that results, so water drains away from the stem rather than pooling round it. On a no-dig bed you can skip the digging entirely: a fresh 10 cm layer of compost is the best courgette soil there is, and the plant's huge leaves will smother any weed that thinks about coming through the cardboard.

Space bush varieties 90 cm apart — a plant that looks lonely in June is a metre across by August. Climbing types such as Black Forest F1 and the organic Ola Escaladora are the answer for small gardens: tie the main stem to a stout post or trellis and they take a third of the ground, keep the fruit clean and off the slugs, and are easier to pick. In pots, give each plant at least 40 litres; the compact Patio Star F1 was bred for exactly this and stays under 60 cm wide. Harden off for a week first, and keep fleece handy for the first fortnight — a cold night in early June does not kill a courgette, but it stops it for ten days.

Sowing and growing courgettes, step by step

1. Sow one seed per pot, on its edge Push a single seed 2 cm deep into a 9 cm pot of moist seed compost, standing on its narrow edge so water runs off the flat faces instead of sitting on them — the commonest cause of a rotted, unsprouted seed. One seed per pot, because courgette roots hate being disturbed.
2. Keep it warm, then bright At 20–25 °C the seed is up in five to eight days; at 15 °C it takes three weeks and half of them rot. Once the leaves show, move the pot off the heat to the brightest, coolest place you have, or the stem stretches — see our guide to leggy seedlings.
3. Plant out after the last frost When the plant has two or three true leaves and roots showing at the base of the pot, plant it out into its compost pocket at the same depth it grew, never deeper. Water in well and put a cloche or fleece over it if nights are still below 10 °C.
4. Water at the base, deeply, twice a week A cropping courgette drinks 10 litres or more a week. Water the soil, not the leaves: wet foliage invites mildew, and a sunken pot or a cut-off bottle beside the stem gets the water to the roots. Mulch with compost or straw to hold the moisture in.
5. Feed once the fruit starts coming In a well-composted bed the plant needs nothing more; in a pot, give a high-potash tomato feed every fortnight from the first fruit. Too much nitrogen gives a plant the size of a car and no courgettes.
6. Pick small, pick often Cut the fruit with a knife at 10–20 cm, every second day, flower still attached if you like — small courgettes have the flavour, and the plant keeps flowering only as long as no fruit is allowed to ripen. Miss a week and the one hidden under the leaves becomes a marrow that tells the plant its work is done.

Flowers but no fruit? Read the flowers

A courgette carries two kinds of flower. Males stand on a long, thin stalk and do nothing but shed pollen; females sit on a tiny, unmistakable courgette that swells only if a bee — or you — moves that pollen across. The first flush of flowers on a young plant is almost always entirely male, which is why the plant appears to bloom for a fortnight and produce nothing. Be patient: the females follow once the plant has a few big leaves, and a garden with bees in it does the rest.

In a cold, dull or wet week bees stay home and the small fruit yellows and rots from the tip — poor pollination, not disease. Hand-pollinate on any morning bees are scarce: pick a male flower, strip its petals and dab the pollen into the centre of an open female. If that sounds tedious, grow organic Partenon F1, a parthenocarpic variety that sets fruit without pollination at all — the reason it is the courgette for early tunnel crops, covered balconies and cold Junes.

Bush or climbing?

Whichever you choose, mix an early F1 with an open-pollinated variety: the hybrid starts the harvest a week or two sooner, and the open-pollinated plant is the one whose seed you could, with care, save. With care is the operative phrase — see the last mistake below.

Common mistakes

• Sowing a whole packet. Two plants feed a family of four; six feed the street and exhaust the cook. Sow spares, keep the best two, give the rest away.
• Sowing in March. A courgette on a windowsill for eight weeks is a wreck by planting time. Count back three to four weeks from your last frost and sow then.
• Laying the seed flat. Water sits on a flat seed and rots it. Sow on its edge, one to a pot, and do not overwater until it is up.
• Watering from above. Wet leaves plus warm nights equals powdery mildew by August. Water the roots, mulch the soil and pull off the first whitened leaves.
• Letting one become a marrow. A single ripening fruit switches the plant from flowering to seed-setting. Pick everything, including the ones you do not want.
• Saving seed casually. C. pepo crosses freely with pumpkins, patissons and ornamental gourds within bee range, and the next generation can carry the bitter, genuinely toxic cucurbitacins of the gourd parent. Save courgette seed only from a single variety grown in isolation, as our seed saving guide and the pumpkin guide both explain — otherwise buy fresh.

Frequently asked questions

Why are my courgettes bitter?
Cucurbitacin, the same compound that makes a cucumber bitter, but in courgettes it can reach dangerous levels. A faintly bitter fruit from a stressed, drought-hit plant is harmless; a strongly bitter one, especially from home-saved or unknown seed, has usually crossed back towards its wild gourd ancestry and should be thrown away, plant and all. Taste a sliver raw before you cook a batch from a new plant.

Can I grow courgettes in a pot?
Yes, and on a sunny balcony they crop well. Use a 40-litre pot or larger, a compact variety such as Patio Star F1 or Tondo di Nizza, water daily in summer and feed weekly. Smaller pots dry out faster than the plant can drink, and the fruit aborts.

Why do the small courgettes rot at the tip?
The female flower was not pollinated, so the fruit is being abandoned. It happens in cool, wet spells when bees are grounded and on young plants that have not yet produced male flowers. Hand-pollinate for a week, or choose the parthenocarpic Partenon F1. If the whole fruit softens after a wet spell, remove it and improve airflow.

Can I sow courgettes in September?
No — the plant needs a warm, frost-free 10 to 12 weeks from sowing to a worthwhile harvest, and with the days shortening a September sowing is killed by frost before it flowers. September is for picking the last fruit, letting one plant's fruit swell into marrows to store, and clearing the mildewed plants to the compost heap. Sow winter salads in the space and courgettes again in April.

Courgettes ask for three things — warmth to start, compost and water in the middle, and a knife every other day at the end — and repay them more generously than any vegetable you can sow. When the plants finally collapse with the first frost, compost them, move the cucurbits along the rotation, and sow next year's from fresh seed. Browse the full courgette and summer squash range, the wider Cucurbita pepo, pumpkin and winter squash collections and our organic squash seeds, everything else in vegetable seeds, or read on through our growing guides and the beginner's guide to growing vegetables from seed.