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Marrows are tender plants and love warmth, sun and plenty of water. They can quickly grow into large plants, producing sizeable fruits in a relatively short time. Marrows are essentially large courgettes, but their skin can be ripened until it becomes hard, so the fruits can be stored for later use. Both marrows and courgettes are the same botanical species (Cucurbita pepo), but marrow varieties are particularly bred for cropping when the fruits are larger and for their ability to store.

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There are several marrow varieties to choose from, although any courgette variety will produce marrows if you leave the fruits to grow. There are trailing types that can spread over several metres, and bush types that are slightly more compact, for smaller gardens or containers. Marrow fruits are traditionally green and usually striped lengthways, although there are yellow-skinned varieties too.

For the most reliable varieties, look for those with an RHS Award of Garden Merit (AGM), as these performed well in our trials – see our list of AGM fruit and veg (135kB pdf) and our Recommended Varieties below. You may also find marrows growing in the veg areas of the RHS gardens over the summer months, so do visit to compare varieties and pick up growing tips.

What and where to buy

Marrow seeds are readily available from garden centres and online seed stockists. In spring, you may also find young marrow plants on sale in garden centres and online. These are useful if you don’t have the time or space to grow from seed, but the choice of varieties may be limited. If you buy after the last frost, they can usually be planted out straight away – although do check with the seller to make sure they have been hardened off.

Choose a warm, sunny location for marrows, where you can space plants at least 90cm (3ft) apart for bush varieties and 1.5m (5ft) apart for trailing varieties. Prepare each sowing/planting site by digging in lots of home-made garden compost or well-rotted manure, to the depth and width of a spade’s blade. Ideally do this a few weeks before sowing or planting out, to allow the soil to settle. Alternatively, if you're practising no-dig, mulch

Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings. the soil at each site ahead of sowing or planting directly into the mulch.

Marrows grow readily from seed in warm conditions. They are best started off indoors in spring, where they can be kept reliably cosy and protected from slugs and snails, but you can sow them outdoors too, after the last frost.

Sowing indoors

For a longer cropping season or more reliable results in colder regions, start marrows off indoors from mid- to late April.

Sow the seeds into 7.5cm (3in) pots or a modular tray filled with moist peat-free seed compost

Seed compost is a free-draining compost formulated for germinating seed. It often contains a mix of fine materials including sterilised loam, coir, coarse sand or grit. It contains low levels of nutrients, as high levels could damage seedlings. . Position the seed on its side, 1.5cm (½in) deep, sowing one per pot/module, to minimise root disturbance when planting out later. Water in, then keep at 18–21°C (65–70°F) in a heated propagator

A heated propagator is a portable heated structure with a vented lid and adjustable, constant, thermostatic temperature control. It provides a warm, humid environment to help seeds germinate and cuttings to root quickly. . Alternatively, place on a warm sunny windowsill and cover with clear plastic bags until the seedlings

A seedling is a young plant grown from seed. appear. Keep young marrow plants indoors until after the last frost, in a warm, bright spot and water regularly. For more sowing tips, see our guides below.

Sowing outdoors

You can sow marrow seeds outdoors in late May or early June. If possible, warm the soil for a couple of weeks ahead of sowing, especially in cooler locations, by covering the ground with cloches or plastic-free fleece. The soil should be at least 13°C (56°F) for successful germination

Germination is the process by which a seed develops into a new plant. It starts with the seed coat absorbing water, expanding and splitting, which allows oxygen and water into the seed so its food reserves can be broken down and used by the embryo for growth. The first root (called the radicle) pushes into the soil to anchor the new plant in place and start absorbing water and nutrients. The first shoot (called the plumule) then grows upwards, out of the soil, towards the light. .

Sow two or three seeds in the centre of each prepared site, 2.5cm (1in) deep, then water well. Cover with cloches or plastic-free fleece

A soft, fibrous, translucent material laid over or around plants hastening their growth and protecting them against weather and pests. Heavier grades of fleece give about 2°C of protection from frost. It is usually used without supporting hoops. , and leave in place for as long as possible after germination. If more than one seed germinates per sowing site, remove the smaller, weaker seedlings

A seedling is a young plant grown from seed. to leave just the strongest one.

Germination outdoors may be less reliable than indoors, and the young seedlings are vulnerable to slugs and snails, especially in damp conditions. Outdoor-sown marrow plants will usually start cropping later than those sown earlier indoors.

Young marrow plants grown from seed indoors should be ready for planting out in early summer, once the soil has warmed up. If you haven’t grown your own from seed, you can simply buy young marrow plants in late spring and early summer.

Harden off young plants to gradually acclimatise them to outdoor conditions and make sure your planting sites are prepared in advance (see Preparing the ground above). Then gently remove each young marrow plant from its pot, without disturbing the roots, and plant into the centre of your prepared sites. Firm them in, then water well. Protect the young marrow plants from slugs and snails, especially in damp weather.

Planting in a container

Marrows generally crop best in the ground, but compact or bush varieties can also be grown in a large container. Just bear in mind that plants will need regular watering and feeding to swell the large fruits. Also make sure there is plenty of space around the outside of the container, so the marrow plant can spread out its large leaves. Overcrowding and poor air circulation encourage fungal diseases.

Choose a container that’s at least 45cm (18in) wide, fill it with peat-free soil-based or multi-purpose compost

Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. , then plant one young marrow plant in the centre.

Watering

Marrows need regular and generous watering, especially when flowering and fruiting, and when growing in containers. Aim to keep the soil or potting compost

Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. consistently moist. During hot spells, plants may need watering daily, and this is best done early in the morning or in the evening so the moisture doesn't simply evaporate.

Use rainwater from a butt if possible, and when you water, try not to wet the leaves, as this can encourage fungal diseases such as powdery mildew. For more water-wise advice, see our guides below.

Mulching

Cover the ground around marrow plants with a thick layer of mulch

Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings. to help hold moisture in the soil, reduce the need to water, and deter weed germination

Germination is the process by which a seed develops into a new plant. It starts with the seed coat absorbing water, expanding and splitting, which allows oxygen and water into the seed so its food reserves can be broken down and used by the embryo for growth. The first root (called the radicle) pushes into the soil to anchor the new plant in place and start absorbing water and nutrients. The first shoot (called the plumule) then grows upwards, out of the soil, towards the light. . Use garden compost or well-rotted manure, but leave a gap around the base of the stem, to keep dampness away, which could cause rotting.

Feeding

Marrows growing in the ground don’t generally need feeding, unless the soil is very poor. But if you want particularly large fruits for exhibition, or are growing marrows in containers, then it’s worth feeding regularly – apply a high potassium organic liquid fertiliser, such as tomato feed, every 10–14 days once the first fruits start to swell.

Looking after fruits 

Place a tile or wooden board under developing marrows to lift them off damp soil and help to prevent rotting. To ripen a marrow’s skin for storage, ensure the fruit gets plenty of sun, and carefully turn it occasionally to expose the underside.

If you want to produce giant marrows for shows or competitions, keep just one marrow on the plant, removing any others that start to form, so the plant puts all its energy into growing just one large fruit. Regular watering and feeding with a potassium-rich organic fertiliser, such as tomato feed, will also help to increase fruit size.

Remove any leaves that become tatty or are affected by powdery mildew. This helps to expose the marrows to the sun, to ripen the skin.

Marrows can be harvested from mid-summer, at 20–30cm (8–12in) long, for use straight away. The flowers are also edible. Harvesting marrows regularly encourages plants to produce further fruits, and in warm, damp weather these can grow rapidly. Later in the season, the fruits can be left to reach full size and mature on the plant, for storing. Harvest the last marrows before any frosty weather arrives.

Marrows for storing should be left to fully ripen in the sun until the skin is hard. But bring them indoors well before any frost. Place them in a cool, dark, frost-free place, such as a garage, where they should keep for a month or two. Check them regularly for signs of deterioration or rot.

Marrows are tender plants, so can be damaged or killed by cold weather or frost. In early summer, plants may produce no fruit or the fruits may rot when very small – this is caused by cool weather, leading to poor pollination, but should remedy itself once the temperatures improve. Marrow plants can also be affected by various fungal diseases, and slugs and snails may eat young plants, flowers and young fruits. See Common problems below for advice on how to spot and tackle these issues.