Sow outdoors
Courgettes are easy to grow from seed and can be sown outdoors in the spot where they are to grow, or you can start them off indoors in pots.
Sow two or three seeds 2.5cm (1in) deep outdoors in late May or early June and cover with cloches, jars or plastic; leave in place for two weeks, or as long as possible, after germination. Thin the seedlings to leave the strongest one.
Sow indoors
For earlier crops or in cold regions sow seeds indoors on their side 13mm (0.5in) deep in 7.5cm (3in) pots of compost from mid- to late April at 18-21C (65-70F).
If you don’t have the space to raise courgette seedlings, you can also buy young plants from garden centres in spring and these usually can be planted outdoors straight away (check with the shop when you buy them).
Two weeks before planting or sowing seed outdoors, make planting pockets 90cm (3ft) apart for courgettes or 1.8m (6ft) for summer squashes and marrows. Do this by making a hole about a spade’s depth, width and height and fill with a mixture of compost or well-rotted manure and soil. Sprinkle a general fertiliser over the soil. Plant one plant on top of each planting pocket.
For indoor-raised seedlings, plant outside on top of your planting pocket in early June, hardening off (acclimatising) before doing so. Do this by moving them into a coldframe for a week or if you don’t have a coldframe, move plants outdoors during the day, then bring in at night for a week, then the following week, leave them out in a sheltered spot all day and night.
You can also grow courgettes, marrows and summer squashes in growbags or containers (at least 45cm/18in wide). Plant one or two per growbag, or one per container.
Keep the soil constantly moist by watering around the plants, not over them. They need plenty of water, so sink a 15cm (6in) pot alongside the plants when planting out. Water into the pot and it will help ensure that water goes right down to the roots and doesn't sit around the neck of the plant, which can lead to rotting.
Feed every 10-14 days with a high potash liquid fertiliser once the first fruits start to swell.
Harvest courgettes when 10-12.5cm (4-5in) long.
Regularly picking courgettes while they are small will ensure a long cropping period.
‘Venus’ AGM: A compact courgette producing a large crop over a long season, with smooth, spine-free stems.
‘Supremo’ AGM: Its compact growing habit makes this courgette ideal for areas with restricted room.
‘El Greco’ AGM: Plants have an open growth habit, making picking easy of this prolific cropper.
‘Tiger Cross’ AGM: This is a marrow variety, producing large striped fruits, good for winter storage.
Powdery mildew: This is a common fungal disease for courgettes, especially in dry conditions when plants are under stress. You will see white, powdery patches of fungus on leaves, stems and, in severe cases, the fruits.
Remedy: Mulching and watering reduces water stress and helps make plants less prone to infection. Promptly removing any infected shoots will reduce subsequent infection. There are no chemicals to treat powdery mildew, but you can use plant and fish oils, or sulphur dust as a preventative.
Find out more about powdery mildew
No fruit, or fruit rotting when very small: This is a physiological problem, caused by the growing conditions, not a pest or disease. It is a problem when the weather in early summer is cool and this causes inadequate pollination.
Remedy: This is usually a temporary problem, and once the weather starts to improve, so will pollination. You can try to hand-pollinate plants yourself by removing a male flower (male flowers don’t have a swelling at their base) and brushing the central parts against the centre of a female flower (female flowers have a swelling at the base – this is the beginning of the fruit). But this is a bit of a hassle, and normally the plant will correct this problem itself.
Grey mould: This is a problem normally in wet conditions, and is usually worse on weak or damaged plants. The mould normally enters through a wound but, under the right conditions, even healthy plants will be infected. You will see fuzzy grey mould on affected buds, leaves, flowers or fruit. Infected plant parts eventually shrivel and die.
Remedy: Hygiene is very important in preventing the spread of grey mould. If you see grey mould, remove the infected material and destroy. Grey mould is encouraged by overcrowding, so make sure you plant your courgettes at the appropriate distance apart. No fungicides are approved for use by amateur gardeners against grey mould. Products containing plant and fish oil blends may be used, but are unlikely to have much impact.
More information on grey mould