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.
Powdery Mildew: Appears as a white powdery deposit over the leaf surface and leaves become stunted and shrivel.
Remedy: Keep the soil moist, grow in cool locations, and spray using plant and fish oils or sulphur-based controls.
More info on 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: Can be a problem in densely sown crops, especially ‘cut and come again’ veg crops. Seedlings suddenly collapse. 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: Sow thinly and when conditions are warm. 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 seedlings, plants and 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.
More info on Grey mould
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.
‘Tiger Cross’ AGM: This is a striped marrow variety, producing high yields of large striped fruits, good for winter storage. Claimed to be Cucumber Mosiac Virus tolerant.
‘Badger Cross’ AGM: F1 hybrid. Later bush variety of small, good shape with dark striped fruits. Claimed Cucumber Mosaic Virus tolerance.
‘Clarita’ AGM: An early cropping F1 hybrid. Offers high yield of pear-shaped, green-white fruits. It needs cutting when small.
‘Minipak’ AGM: A later bush variety with small dark striped fruits.