Cucumbers are tender climbing or scrambling plants, for growing in a greenhouse,
If you grow cucumbers up supports, such as bamboo canes or trellis, they take up little ground space, so are ideal in compact gardens, patio containers or small greenhouses.
Month by Month
There are many cucumber varieties to choose from, varying in fruit size, flavour, disease resistance and growing location. There are indoor varieties for growing in greenhouses, polytunnels or large cold frames, and outdoor or ridge cucumbers for growing in a sunny, sheltered spot.
Small or mini cucumber varieties produce lots of fruits, which are ready to harvest more quickly than longer ones. There are also varieties with tiny fruits (gherkins) for pickling.
F1 Hybrid varieties are generally more vigorous and productive, but seeds are more expensive. Several cucumber varieties have an RHS Award of Garden Merit (AGM), which shows they performed well in trials, so should crop reliably for you – see our list of AGM fruit and veg.
Grafted cucumber plants have recently become more readily available – these are very vigorous plants and should produce a larger crop over a longer season. They are more resistant to soil-borne pests and diseases, so are useful for growing in the same ground (such as a greenhouse border) year after year. However, grafted plants are more expensive and there’s only a limited choice of varieties.
What and where to buy
Cucumber seeds are widely available in garden centres and from online suppliers.
You can usually buy young cucumber plants or plug plants in spring, in garden centres and online. This is often a good option if you only want one or two plants. The choice of varieties may be limited though.
More vigorous grafted cucumber plants (see above) are available in spring from online veg seed/plant suppliers by mail order.
Preparing the Ground
For growing outdoor cucumbers, choose a warm, sheltered, sunny site with fertile soil. Remove any weeds and dig in two bucketfuls of well-rotted organic matter, such as garden compost, for each plant. Then rake in a general purpose fertiliser at a rate of 100g (3½oz) per square metre/yard.
Cucumbers are best sown indoors, as they can be started off earlier to get an earlier crop. Germination is also more reliable and young plants are easier to look after until they’re more resilient. They should be moved to their final growing position after about a month.
Seeds of outdoor varieties can also be sown outside in mild locations, once the soil has warmed up in early summer.
Mid-February to mid-March – if you’ll be growing them in a heated greenhouse
April – if they’ll be growing in an unheated greenhouse, polytunnel or large cold frame
Late April – for growing outdoors
Fill 10cm (4in) pots with seed compost, water well, then sow one seed in the centre of each, 1–2cm (½–¾in) deep. Position the seeds on their side to prevent rotting.
Place the pots in a heated propagator at 21°C (70°F) or on a warm sunny indoor windowsill.
Remove from the propagator once seedlings appear, which may take one to two weeks. Continue to keep the young plants warm, in bright light, and water regularly.
Sowing indoors has several advantages:
Reliably warm conditions, which should lead to better germination.
Keeps the seedlings out of reach of slugs and snails.
Protects seedlings from poor weather.
Seeds of outdoor cucumber varieties can be sown directly in their growing site in late May or early June, especially in milder parts of the UK or if the weather is particularly warm. They should be protected with cloches or fleece.
Prepare the ground as detailed above, then sow the seeds 1–2cm (½–¾in) deep and 30cm (1ft) apart. You can sow up to three seeds together in each spot, to allow for failures, then if several germinate, remove the weaker ones to leave just one strong seedling at each spacing.
Cover the sowings with cloches or fleece to keep them warm, and leave the covering in place after germination too, to help the young plants get well established and grow strongly. Protect seedlings from slugs and snails.
Indoor-sown cucumber plants or newly bought plants should be settled into their final growing site in spring or early summer, depending on where that will be:
Greenhouse cucumbers – transplant into their final growing container or a greenhouse border in late March (in a heated greenhouse) or late May (in an unheated greenhouse, polytunnel or cold frame), as long as the temperature can be kept above 12–15°C (53–59°F).
Outdoor cucumbers – harden off carefully, before being planting outside from early June, once you’re sure temperatures won’t drop below 12–15°C (53–59°F) at night. Choose a warm, sunny, sheltered spot.
Planting them is very straightforward – water well beforehand and try not to disturb the rootball, so they settle in quickly without a check in growth:
To plant in a container – choose a pot that is at least 30cm (1ft) wide and deep, and fill it with good quality potting compost. Position one plant in the centre, firming it in gently then watering generously. You can also plant two cucumbers in a growing bag.
To plant in the ground – either outdoors or in a greenhouse border or polytunnel, prepare the soil (see Preparing the ground, above) then plant 30cm apart, firming in gently and watering well.
Putting up supports
Put the supports in place at planting time – bamboo canes, wires, strings, netting, trellis or anything similar that their tendrils can twine around. They can’t cling to flat surfaces. The stems need tying in initially, and may need help later if they lose their way or come loose, especially outdoors and when laden with fruit.
With greenhouse cucumbers – insert a tall, sturdy bamboo cane up to the greenhouse roof, or attach a vertical wire or string from the roof, secured at ground level. Horizontal supports may also be required for side-shoots.
With outdoor cucumbers – build a wigwam or other structure from tall bamboo canes, or use stout netting supported vertically on upright stakes. Cucumbers will also climb up trellis or wires attached to a wall or fence.
If you leave outdoor cucumbers to trail over the ground, it’s best to lay weed-suppressing membrane or black plastic over the soil, to deter weeds. And do bear in mind that the plants and fruit are more vulnerable to pests such as slugs on the ground.
Cucumbers, whether grown outdoors or in a greenhouse, polytunnel or cold frame, need warmth and regular watering to crop well. When grown in containers, they need additional watering and feeding too.
Water little and often, to keep the potting compost or soil evenly moist. Take care to water at the base of the plants and avoid wetting the leaves, which can encourage fungal diseases.
Feed cucumber plants in containers every 10–14 days with a general liquid fertiliser.
Once they start flowering, change to a weekly tomato feed, to encourage flowering and fruiting.
Pinching out shoots
It’s a good ideal to restrict the vigorous growth of cucumbers, so they concentrate on making fruit rather than growing too large:
With greenhouse cucumbers, pinch out the growing point when it reaches the greenhouse roof. Also pinch out the tips of side-shoots two leaves beyond a female flower (which has a tiny fruit behind it). Pinch out the tips of flowerless side-shoots once they reach 60cm (2ft) long.
With outdoor cucumbers, pinch out the growing tip once plants have developed seven leaves, to encourage side-shoots. Also pinch out the tips of flowerless side-shoots after seven leaves.
Removing male flowers
Most greenhouse varieties are all-female (check seed packets for details), producing almost exclusively female flowers (with a tiny fruit behind them). These must not be pollinated, otherwise the resulting fruits will be bitter. Occasionally male flowers (without a tiny fruit behind them) may appear, in which case remove them.
Outdoor cucumber plants produce both male and female flowers. The female flowers need to be pollinated in order to produce fruit, so don’t remove the male flowers.
Temperature and humidity
In greenhouses, raise the humidity in hot weather by pouring a watering can over the concrete floor or central path, so the water evaporates. High humidity also deters red spider mites and powdery mildew.
Greenhouses can get extremely hot in summer, so put up shading to keep temperatures lower, ideally 18–25°C (64–77°F).
Fruit size varies according to the variety. In general, smaller-fruited varieties are best at about 10cm (4in) long and full-sized varieties at about 15–20cm (6–8in). The fruits should be uniformly green and firm, usually with a slightly rounded tip.
Fruits can grow rapidly, so check them regularly to get them at their best. If they turn yellowish, bulbous or soft, they are likely to be over ripe.
Cut the stem cleanly with a sharp knife or secateurs, rather than pulling. Regular harvesting encourages further fruiting.
Cucumbers are tender plants and need warm temperatures to germinate and grow strongly, and ideally 18–25°C (64–77°F) to crop well. They also need regular watering, especially when flowering and fruiting.
Although usually healthy and vigorous, they can be weakened by powdery mildew and red spider mites, especially in greenhouses and if humidity is low. Mildew-resistant varieties are available. Protect young plants from slugs and snails. Mosaic virus is a more serious problem, and affected plants should be destroyed.
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