Two weeks before planting or sowing seed outdoors, make planting pockets 90cm (3ft) apart for bush plants of summer squashes, 1.5m (5ft) for trailing plants of summer squashes, 90cm (3ft) for courgettes or 1.2m (4ft) apart for 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. The following week leave them out in a sheltered spot all day and night.
You can also grow summer squashes, marrows and courgettes 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. As they need plenty of water, sink a 15cm (6in) pot alongside the plants when planting out. Water into this and it will help ensure the water goes right down to the roots and does not 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.
The fruit of marrows and pumpkins should be supported off the soil on a piece of tile or glass.
Powdery mildew: This is a common fungal disease for squashes, especially in dry conditions when plants are under stress. You will see white, powdery patches of fungus on leaves, stems and in severe case, 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 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 (no 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 usually 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 it, remove the infected material and destroy. Grey mould is encouraged by overcrowding, so make sure you plant your squashes 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.
Read more information on grey mould
Harvest summer squashes, marrows and courgettes when the fruit is still quite small – marrows 25cm (10in) long, courgettes 10-12.5cm (4-5in).
For pumpkins, winter squashes and marrows for overwintering, let the fruit mature on the plant and remove before the first frost strikes.
Masterchef’s Greg Wallace uses a pumpkin as a bowl for a delicious squash fondue - great for parties.
‘Clarion’ AGM: Healthy plants produce a high yield of attractive cylindrical fruits that are a mottled light green. Useful for stuffing if left to grow bigger.
‘Eight Ball’ AGM: A good yield of round, green fruits; easy to see and pick from the compact, upright plants.
'Baby Bear': Flattened orange fruit and very tasty seeds.
‘Jemmer’ AGM: A hybrid offering good yield of bright, light yellow cylindrical fruits. Vigorous, healthy, upright plants with fruits that are easy to see and pick; also recommended as a courgette.
‘Peter Pan’ AGM: A uniform crop of light green, scallop-shaped fruits which should be harvested when small.
‘Sunburst’ F1: This bright yellow squash has a nutty flavour and a scalloped shape, and is best harvested when it is about 5-6cm in diameter. Grow and treat as you would a courgette.
‘Cobnut’ AGM: An early ripening butternut pumpkin. It has large, ridged fruits with a small seed cavity. Ideal for roasting or making soups.
‘Crown Prince’: A recognisable trailing squash with blue skin, orange flesh and a sweet, nutty flavour. Yields are good and it stores well over winter.
Find more AGM vegetables