Step-by-step guide to growing Marrows and Courgettes

Best harvested before they reach their maximum size, marrows are among the easiest vegetables to grow. With minimal care and cultivation, you can have a very large crop in a relatively short time. Picked while young and tender, they make a pleasant hot vegetable dish; left to grow to full size, they are less tasty but ideal for storing for winter use. The flesh of mature marrows is often used for jam-making, and the bright yellow flowers can also be eaten.

One of the hardiest of the large and varied cucurbit family, which also includes cucumbers and melons, the vegetable marrow is a squash. There is considerable confusion in the use of names, which seem to vary from country to country. In the United States, marrows are considered as one type of summer squash; in Britain, the term marrow often includes varieties which might be called squashes.

The baby marrow, 7.5-10 cm (3-4”) in size, is known in France as courgette and in Italy as zucchini, both names now being common in Britain, and is especially delicious when eaten at this size. Although so-called courgette varieties of marrow are available, in fact the fruits of any marrow can be eaten small; the bush varieties are perhaps more prolific in their production of potential marrows. Courgettes, if left on the plant and not picked when small, will eventually be no different from an ordinary marrow.

Most marrows are cylindrical in shape, with rounded ends, and green, creamy white or green striped skins, but there are also many novelty varieties available to gardeners. Custard marrows, sometimes called Scalloped Summer Squash, which may be white or bright yellow, are shaped like thick round cushions with scalloped edges, and are very ornamental in appearance.

The variety Little Gem has small, perfectly round fruits, and Vegetable Spaghetti, as its name implies, has flesh which when cooked is very similar in appearance to spaghetti.

The marrow plant has the trailing habit, bristly stems and leaves of the cucurbit family. Marrow plants are normally divided into two categories, according to habit of growth. The trailing variety will produce 3-5 m (10-15’) stems if unchecked, but is usually confined by pruning to about 1.2 m (4’). The so-called bush marrow is not strictly speaking a bush, but it has a truncated main stem. Occupying about 60 cm (2’) square, it is much more suitable for the smaller garden. Three or four plants of either type will be adequate for most households, as each plant is capable of producing up to six large marrows, or approximately 2 kg (4 lbs) of baby marrows.

Training and Pollination

The tips of the main stems of trailing varieties can be pinched out if they have not produced sideshoots; wait until they are about 60 cm (2’) long. As the trailing stems can grow to a length of 5 m (15’) you may have to keep pinching out the growing tip of the subsequent sideshoots to keep the plant’s size under control. These main stems can be trained by inserting short pegs into the soil on either side of the stems at intervals of 60 cm (2’). Stop the sideshoots at the seventh leaf to keep them at a reasonable length.

To train trailing varieties vertically up supports, take out the growing point of the main stem when the required height is reached, and then that of the sideshoots. Also trained up the support, to keep them in bounds. Some growers stop the sideshoots at one leaf beyond the fruit. Sometimes the sideshoots need stopping with or before the main stem. The fruits of varieties trained vertically should be no larger than a grapefruit, or the weight of the crop may pull the plant and support down. You can rig up elaborate net pouches to support very large marrows grown vertically, but it is much easier to train these sorts along the ground.


In general, marrow pollination can be left to insects. This method cannot be depended on in inclement weather; if it is very cold, wet or windy while the plants are flowering, natural pollination is less likely to be successful. Hand pollination is the best method in these conditions, particularly if you want to have early marrows for picking. Marrows under glass should always be hand pollinated. Female flowers have an embryonic marrow behind their yellow petals, and a cluster of squat, yellow lobes. Male flowers have a prominent central core, bearing yellow pollen. When the plant first begins flowering, only male flowers will appear. Do not be worried; female flowers will follow. To hand pollinate, take a male flower and remove its petals; push the core into the centre of a female flower. For the highest success rate, use a different male for each female flower. As soon as the fruit has set, the petals quickly fall off and the fruit will begin to swell.

Growing under glass

If grown in a heated greenhouse, trailing marrows sown in late winter should be ready for harvesting in late spring. The vines are usually grown in the borders, while early tomatoes are grown on the staging. Prepare the marrow stations by filling a hole 45 cm x 45 cm x 30 cm deep (18” x 18” x 12” deep) with a mixture of equal parts loam and well rotted manure. Train the leading shoot up to the roof and pinch it out when it reaches the greenhouse ridge, in much the same way as indoor cucumbers. Pinch out the fruiting laterals one leaf beyond the embryo fruit. Remove any flowers that form on the main stem, and do not allow more than four marrows per plant, if the fruit are growing to full size. As the young fruit develop, support them with net pouches or bags fixed to overhead wires. Once the plants are fully grown, you may have to thin out some of the foliage, to allow enough light into the greenhouse for the tomatoes.

For early summer marrows, set out young greenhouse-raised plants in mid-spring under cloches. They can also be grown in deep cold frames; remember to open the frames on warm sunny days so plenty of air can circulate around the plants. Try to maintain a temperature of 19°C (65°F)—it must not fall below 13°C (55°F).

Harvesting and storing

Cutting normally begins in midsummer, and continues through mid-autumn. Marrows are at their best when eaten no more than 25 cm (10”) long, and when the thumb will pierce the skin easily. If you allow marrows to grow to enormous sizes, the flavour will deteriorate, and the flesh will become dry and full of seeds. Courgettes are picked when 7.5-10 cm (3-4”) long. Do not let them get much bigger than this, or they will lose their flavour.

Harvesting the fruit when it is young encourages the plant to produce more fruit. Since marrows tend to be heavy croppers, and the baby ones are more flavourful, this is a sensible procedure. For winter storage, conserves, and pickling, let a few marrows grow on to full size. Allow a plant to produce only one very large marrow, and it is better to reserve a few plants especially for this purpose.

Marrows harvested when fully ripe, at the end of the season in autumn, will store right through winter under cool, dry conditions. 7°C (45°F) is the minimum temperature for storing marrows, but 10°C (50°F) is better.. Slated shelves in a dry outhouse or cellar are ideal, or they can be hung out of the way, individually, in nets. Never store marrows touching one another, or they may rot in store.

Exhibition tips

Gone are the days when mammoth but tasteless marrows were shown at exhibitions, and prizes were awarded to the heaviest entries. According to the Royal Horticultural Society Show Handbook, the judges are to look for young, tender, shapely fruit of any colour, with the individual fruit as uniform as possible.

Although botanically fruit, marrows and courgettes are always shown as vegetables. They are considered separate entries, but the same criteria apply to both, and the maximum number of points awarded to either is ten.

Three marrows are usually shown in collections, and two in single dishes. They should be no longer than 30 cm (1’). These are always staged directly on the show bench. Because they tend to roll about, it is a good idea to keep the fruit secure by placing tiny wooden wedges under them. Twelve courgettes are shown in collections, and six in single dishes. Because they are smaller, they are more presentable when displayed in shallow baskets or flat dishes. Because marrows and courgettes lose their freshly picked look very quickly, they should be harvested at the last possible moment.

Pests and Diseases 

Slugs: these are particularly fond of young seedlings and in bad cases can completely decimate the crop. Feeding chiefly after dark, they attack the plants both below and above the soil. During the day, they hide away in cool, moist places. Their favourite haunts are decaying vegetable matter, moist, heavy, sour soils, or even alkaline soils that are rich in humus and moisture.

It is very difficult to eradicate slugs in heavily infested areas, because they are able to cast off poisons or irritants which may fall upon them by excreting slime. To be completely effective always repeat an application of slug pellets on successive nights. As long as slime trails continue to appear on the soil near the plants, your marrow seedlings are still at risk.

An alternative to using slug baits is to set traps very near the affected plants. Use wet sacks, heaps of damp vegetable refuse or shallow dishes of diluted stale beer and sugar. Make sure that the traps are inspected daily, and the captured slugs destroyed.

Greenfly: these pests are doubly damaging to marrows. Besides physically sapping the strength of the plants, they are responsible for transmitting viral infections, particularly cucumber virus, which is also found on a variety of ornamental plants, such as aster, dahlia and delphinium, amongst others. The symptoms of aphid infestation are pale green to yellowed, puckered and distorted leaves and growing points. Control by spraying with liquid derris, bioresmethrin or malathion as soon as greenfly is evident; alternatively, dust with derris powder.

Powdery mildew: this is a fungal infection, the symptoms of which are powdery, white coatings on the leaves and, less often, similar coatings on fruit. The infection is associated with poor cultivation, particularly insufficient moisture at the roots, and lack of air. Plants weakened from drought are most susceptible, so the best precaution is to make sure your marrows never run short of water. If powdery mildew appears, dust the infected plants with green sulphur or dinocap every two weeks, or benomyl every three to four, until the symptoms disappear. Remove badly infected leaves altogether.

Red spider mite: these can be troublesome in hot- dry weather; the main symptoms of red spider mite infestation are leaves turning speckled grey-green and then bronze. In bad cases the leaves wither and fall prematurely, and they and the stems are sometimes covered with a fine, silky webbing. If your marrows are growing in a greenhouse, fumigate with azobenzene. Outdoors, control is more difficult, particularly as some strains of red spider mite have developed a resistance to commonly used insecticides. Both indoors and out, cut off and burn all infested leaves, and step up the application of water, both to leaves and roots, as this helps to control these pests.

Grey Mould (Botrytis cinerea) the symptoms of this fungal infection are fluffy grey growths on the stems, fruit, particularly the blossom end, and leaves. The disease is usually associated with cold, wet, close conditions and over-watering, so the best precaution is to make sure enough light and air are able to reach the plants, and never allow them to become overcrowded. Remove the remains of the flower from the end of a fruit as soon as it has obviously set. In case of a botrytis infection, control with benomyl. Remove and burn badly infected plants and, if necessary, cut away some of the foliage from remaining plants so air can circulate freely.

Cucumber mosaic virus: the leaves of plants infected with mosaic virus show mottling in the form of yellow lines and rings; the whole plant then rapidly shrivels up and dies. The fruits may also become mottled light and dark green, and the shoots stunted. As there is no effective control for the virus, and it is carried by greenfly, the best prevention is to control greenfly. If any plants show signs of mosaic virus, dig them up and burn them immediately; do not leave them on the compost heap, or the infection will spread.

Collar rot: this affects cucumbers as well as marrows, and is usually associated with excessively wet conditions. The plants are attacked by soil-borne organisms at or slightly above ground level. Leaves wilt, the stems darken, and the plants eventually die. The best precaution against collar rot is to ensure that the soil is well drained and aerated. Plants which are not too badly damaged may be saved by removing all decaying tissue and dusting the infected area with captan, and top dressing around the stem to encourage the growth of new adventitious roots. In ten days top dress again. Badly infected plants should be pulled out and destroyed, and the soil around adjacent plants treated with captan or benomyl.

Gummosis: although cucumbers are more vulnerable to this fungal disease than marrows, marrows can occasionally be infected. Those grown in a greenhouse or frame, in cold, wet conditions are most likely to suffer. The main symptoms are large sunken, oozing spots on the fruits, dark in colour. The spots eventually become covered with dark spores and occasionally small spots appear on the stem or leaves. Keeping the greenhouse or frame warm and well ventilated is a good preventive measure. Control gummosis by spraying with captan or zineb; destroy all diseased fruit. Disinfect the greenhouse or frame before replanting.

Anthracnose: like gummosis, this is mainly a disease affecting cucumbers, but marrows, especially the young plants, occasionally become infected. The leaves of infected plants will have small pale patches which quickly turn pale brown with a yellowish ring round them, growing bigger until the whole leaf dies; stems are sometimes affected. Remove and destroy badly damaged plants. Spray the remaining plants with one part lime sulphur to sixty parts water with a spreading agent, such as a few drops of liquid household detergent. Make sure that the greenhouse is well ventilated, and wash down the whole of the inside with diluted formalin when it is empty or between crops. Marrows grown in cold frames or under cloches also need plenty of air circulation.


05. September 2013 by admin
Categories: Vegetable Gardening | Tags: , , | Comments Off on Step-by-step guide to growing Marrows and Courgettes


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