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.
Month by Month
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.
Marrow — bush type
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.
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.
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.
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
When you water, try not to wet the leaves, as this can encourage fungal diseases, such as powdery mildew.
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.
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.
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.
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.
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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