RHS Growing Guides

How to grow marrows

Our detailed growing guide will help you with each step in successfully growing Marrows.

  1. Getting Started
  2. Choosing
  3. Sowing
  4. Planting
  5. Plant Care
  6. Pruning and Training
  7. Harvesting
  8. Storing
  9. Problems
1

Getting Started

Getting Started
Choosing
Section 1 of 9

Marrows are the mature fruit of certain Cucurbita pepo cultivars. The immature fruit of the same or similar cultivars is called courgette. They are one of the most popular vegetables to grow, and just one plant will provide you with a succession of tender, tasty courgette fruits from mid-summer through into early autumn.

These tender plants are easy to grow from seed, usually sown indoors in spring, for transplanting outdoors in early summer. They can also be sown outdoors in early summer.

Courgettes like a warm, sunny, sheltered spot, rich soil and regular watering, and form large vigorous plants. They can also be grown in containers if space is limited.

There are many varieties to choose from, with fruits in various shades of green or yellow, sometimes striped, and either long or spherical. You can pick the fruits at any size, but the flavour and texture is best when they are small and tender. Regularly harvesting encourages plants to keep on cropping. If left, courgette fruits will quickly grow into marrows. The flowers are also edible.

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2

Choosing

There are many courgette varieties to choose from – some making large trailing plants, ideal if you have plenty of space, while others are bushy and compact, great in small veg plots or containers.

The fruits vary in appearance too – you can choose from various shades of green or yellow, striped or plain, long or spherical, and large leaves can be green, mottled or silvery. Many varieties are ornamental as well as productive.

All courgette varieties like similar growing conditions – lots of sun, warmth and moisture. Most varieties form quite large plants over the course of the summer, needing at least a square metre/yard of ground space. Still, they are prolific croppers, so just a couple of plants is usually enough for a family.

Spine-free varieties make harvesting easier, while disease-resistant varieties are a good choice in regions prone to damp or humid summers.

For the most reliable varieties, look for those with an RHS Award of Garden Merit (AGM), which means they have performed well in RHS growing trials.

What and where to buy

Courgette seeds are widely available from garden centres and online seed stockists.  

Young plants are also available in spring from garden centres and online suppliers, ready for planting outside after the last frost. These are ideal if you don’t have the time or space to grow from seed, but you may find the choice of varieties is fairly limited.

Related RHS Guides
Buying: mail order plants

Recommended Varieties

Marrow — bush type

Showing 3 out of 4 varieties
3

Sowing

Courgettes are easy to grow from seed. They are best started off indoors in pots, but you can also sow them outdoors in early summer, especially in warmer regions.

Sowing indoors

For an earlier crop or in colder regions, start courgettes off indoors in April or early May. Germination also tends to be more reliable indoors, as warmth is needed.

Sow the seeds individually on their side, 13mm (½in) deep, in 7.5cm (3in) pots of moist seed compost. Then place in a heated propagator, greenhouse or on a sunny windowsill enclosed in a clear polythene bag. The seeds need 18–21°C (65–70°F) to germinate.

Once seedlings appear, take the pots out of the propagator or remove the bag.

Sowing indoors keeps the seedlings out of reach of slugs and snails until they’re larger and more robust.

Related RHS Guides
Vegetable seed sowing

Sowing outdoors

You can sow seeds outdoors in late May or early June, once the soil warms up. Prepare your sowing site by digging in lots of home-made garden compost or well-rotted manure, to about the depth and width of a spade’s blade.

Then sow two or three seeds in the centre, 2.5cm (1in) deep, and water well. Cover with a cloche or fleece, and leave in place for two weeks, or as long as possible, after germination. If more than one seed germinates, remove the smaller, weaker seedlings to leave just the strongest one. Space additional sowing sites at least 90cm (3ft) apart.

Germination outdoors may be less reliable than indoors, and seedlings are more vulnerable to slugs and snails, so protect them if possible. Outdoor-sown plants will usually start cropping later than those sown earlier indoors.

Related RHS Guides
Soil preparation

4

Planting

Young, well-rooted courgette plants grown from seed indoors should be ready for planting out in early summer, once all danger of frost is past.

You can also buy young plants from garden centres and online suppliers in late spring and early summer.

Courgettes are tender plants and need to harden off (acclimatised to outdoor conditions) before they’re planted outside. Do this by putting them in a cold frame for a week. If you don’t have a cold frame, place them 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.

Courgettes like a warm, sunny position. Prepare the planting site by digging lots of well-rotted manure or garden compost into an area roughly the width and depth of a space’s blade. Then sprinkle a general purpose fertiliser, such as Vitax Q4 over the soil at a rate of two handfuls per square metre/yard.

Carefully remove the young courgette plant from its pot, without disturbing the roots, and plant it into the centre of your prepared site. Firm it in gently, then water well. Space additional plants at least 90cm (3ft) apart.

Protect young plants from slugs and snails.

Planting in a container

You can also grow courgettes in large containers in a warm sunny spot. Compact or bush types are the best choices. This is an ideal option if you have limited space.  

Plant one young courgette plant into a container that’s at least 45cm (18in) wide, filled with soil-based or multi-purpose compost. Then sprinkle a handful of general purpose fertiliser, such as Vitax Q4 over the compost. Water the plant in well, and continue watering regularly.  

Growing bags are also suitable for courgettes, and can accommodate one or even two compact plants.

Transplanting indoor grown marrow seedlings to a growbag

5

Plant Care

Watering

Courgettes are thirsty plants and need regular watering, especially if growing in a container. Aim to keep the soil consistently moist. During hot spells, plants may even need watering daily.

When you water, try not to wet the leaves, as this can encourage fungal diseases, such as powdery mildew.
Top tip

Sink a 15cm (6in) pot into the ground alongside your courgette plant and water into it, so the water goes directly down to the roots. The moisture doesn’t then sit around the neck of the plant, which can lead to rotting.

Related RHS Guides
Collecting rainwater

Feeding

To boost fruiting, especially with plants in containers, feed every 10–14 days with a high potash liquid fertiliser once the first fruits start to swell.

Mulching

Lay a thick layer of mulch over the soil around courgette plants to help hold moisture in the ground and deter weeds. Use garden compost or well-rotted manure, but leave a gap around the base of the stem, to prevent rotting.

6

Pruning and Training

Remove any leaves that become tatty or are affected by powdery mildew. This helps to expose the fruits to the sun and makes finding them easier when harvesting.

7

Harvesting

Harvest courgettes when small, tender and full of flavour, at 10–12.5cm (4-5in) long. Regular picking while the fruits are small will ensure a long cropping period. 

You can also harvest the flowers, to add colour to salads or to fry or stuff with soft cheese. It’s best to choose male flowers (without the small fruit behind), so you don’t reduce fruiting.

8

Storing

Courgettes are best eaten freshly picked, but will keep in the fridge for up to a week.  

They can be frozen, ideally after blanching in boiling water, which helps to preserve their colour and texture. 

They can also be made into chutney and other preserves.

9

Problems

Storing
Guide Start
Section 9 of 9

Slugs and snails can eat seedlings and young plants, and sometimes flowers and young fruits too, especially in damp weather.

Powdery mildew is a fungal disease that forms a white powdery coating on the leaves, which dry out and shrivel, hindering the plant’s growth. Avoid wetting the leaves to stop powdery mildew from forming.

Not seeing any fruit or fruit rotting when very small is usually caused by cool weather in early summer, which results in inadequate pollination.

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