Growing advice - Courgette and Marrows

Courgettes and Marrows (Cucurbita pepo) are also known as vegetable marrows or summer squashes. They are trailing annual plants that can trail for several metres or form a compact bushy plant with a spread of about 90cm (3ft). They have cylindrical fruit growing to around 30cm (12in) long and 13cm (5in) in diameter. Courgettes are tender-skinned varieties of marrows that are harvested young. The skins may be green, yellow, white or striped. Some are round, others have flattish edged fruits. Spaghetti marrows have a hard skin, but when cooked, the flesh resembles spaghetti. Generally all fruits are cooked, the flowers can also be cooked or eaten raw. Courgettes and marrows are warm season crops and need temperatures of between 18C and 27C (64F-81F) for successful cropping. They require no added nitrogen fertiliser, as this will encourage lots of leaf growth and little fruit.
How to Sow for Best Results

From April onwards, marrows and courgettes can be started off in 7.5cm (3in) pots, and grown indoors. Place two or three seeds, on their side, about 25cm (1in) deep per pot, which is filled with moist compost.

The compost should be moist, but definitely not wet. Wet compost (which can even be the case straight from the bag) will be cold and reduces the oxygen that the seeds need to germinate. It may even stop the seeds germinating at all. If the compost is too dry this will also cause problems. If this is the case, sprinkle a small amount of warm, clean tap water over the compost and leave it to soak in thoroughly. When the compost has absorbed the water, take a small handful and squeeze it in your fist. If water drips out it is too wet, so leave it for a short while in a well ventilated spot to dry off. If it holds together when you open your hand, it's just about right. You can now fill your pot with the moist compost and you don't have to water it again before you sow the seed. Check the compost for dryness regularly. If this is the case, add a little clean water from below, being careful not to over water. Too much water can kill seedlings, as it can spread "damping off fungi" and encourage other moulds and diseases.

After they have germinated, thin out the seedlings to remove the weakest, leaving the strongest. Seeds germinate best if kept at 20C (68F). The night temperature should be no lower than 16C (60F). This night temperature should be maintained for four to six weeks after the seedlings have been planted out (follow in situ instructions after planting out). Therefore plant out when all frost has passed and use cloches or floating mulches to maintain the temperature.

From late May the seed can be sown in situ, when all risk of frost has passed and the soil temperature is at least 16C (60F). Prepare holes at least 30cm (12in) wide and mix in plenty of well rotted garden compost or farmyard manure. Mound the planting hole up slightly as this will help with the plants' drainage. When planting the seed, place them on their sides about 25mm (1in) deep. Sow two or three seeds per mound, and after the seeds have germinated remove the weakest plants, leaving the strongest. Space them about 90cm (3ft) apart. In cold areas protect the young plant and seedlings with floating mulches or cloches. A thick mulch should also be applied to help retain water and increase the general soil and atmospheric conditions around the plant.

Trailing stems may be grown up strong supports or trained round in circles at ground level using wire hoops to peg the stems down. Feed with a high potash liquid feed every two weeks. Keep an eye out for slugs and snails, especially when the plants are young. If they become a problem, use a recommended proprietary brand of slug and snail bait. Try to avoid watering from above as this may lead to fungal problem especially in warm weather. Pick off any badly affected leaves and spray with a recommended proprietary brand of fungicide.
Harvesting Your Crop

Cut courgettes when they are about 10cm (4in) long. Marrows can be cut from about six to eight weeks from planting, but this will depend on the size you like your marrows. Always handle marrows and courgettes with care as they can bruise. Cut them with a short stem and check the plant regularly for fruit. Regular cutting will produce more fruit.

Flower and therefore fruit development is sometimes a little erratic at the start of the season. Generally the first flush of flowers will be mainly female. Female flowers have a small swelling (embryonic fruit) behind the petals. Most pollination is done by insects, but if fruit is failing to set, the female flowers can pollinated by hand.

To pollinate by hand, take a male flower and remove all its petals and press it against the centre of the female flower. Pollen can also be transferred using a fine paint brush, taking pollen from the male stamen and brushing it lightly over the female stigma.

Marrows and courgettes generally don't store for very long so cut and use the fruit within a few weeks. Spaghetti marrows will keep for a few months, but are better cooked and eaten fresh.

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