The marrow is an easy vegetable to grow – with care you can have a very large crop in a relatively short time. Marrow, courgette, squash and pumpkin are all closely related and are grown in basically the same way. They need a sunny position, a moisture-retentive soil and somewhere out of cold winds.
Marrows 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.
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 marrow 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 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; then the following week, leave them out in a sheltered spot all day and night.
You can also grow marrows 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 that 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 should be supported off the soil on a piece of tile or glass.
Troubleshooting Growing Problems
Powdery mildew: This is a common fungal disease for marrows, 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.
No fruit, or fruit rotting when very small: This is a physiological problem, caused by the growing conditions, and 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 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 grey mould, remove the infected material and destroy. Grey mould is encouraged by overcrowding, so make sure you plant your marrows at the appropriate distance apart. No fungicides are approved for use against grey mould by amateur gardeners. Products containing plant and fish oil blends may be used, but are unlikely to have much impact.
Powdery Mildew: Appears as a white powdery deposit over the leaf surface and leaves become stunted and shrivel.
Remedy: Keep the soil moist and grow in cooler locations.
Harvest marrows as needed. If growing for show, take off all developing fruit and leave just one on the plant, so that the plant will put all its energy into ripening just one marrow.
Plant with: borage, corn, marigold, melons, nasturtium, oregano, pumpkins