How to grow cucumbers in a greenhouse: tips & advantages
Cucumbers are heat-loving plants and since our UK summers can be unreliable, to say the least, they are often grown undercover in a greenhouse, both at home and by commercial growers. Read on to find out how to grow cucumbers in a greenhouse and what varieties are best.
Cucumbers (Cucumis sativus) are popular with home-growers and for good reason, as their delicious fruits can be produced for months on end if given the right conditions. With cucumber varieties available for growing outdoors or undercover this article will cover which varieties are suitable for growing in a greenhouse and how to look after them to get the best harvest.
Benefits of growing cucumbers in a greenhouse
With our variable summers, many gardeners choose to grow their cucumber and tomatoes (Solanum lycopersicum) in a greenhouse. Providing protection from the elements, especially at night, a greenhouse can either be warmed by just the sun or with a supplementary heat source as well. Even an unheated greenhouse can provide precious warmth early on in the season, meaning that cucumber plants can get a 2 to 3 week head-start over those planted outside. With additional heating or when using a hotbed, a heated greenhouse can mean cucumbers can be planted even earlier in April, giving months of growing time ahead. However, greenhouses do not just provide the opportunity for earlier plantings but can extend the season into October as the temperatures begin to dip outside.
Grown vertically in a greenhouse, cucumbers require strings or canes to be tied into as they grow. Not only is growing cucumbers vertically a space-saving method, but it can increase air circulation, which can help prevent disease and make harvesting the fruits easier. For more information on how to support cucumbers, you can read our article on cucumber trellis here.
Even with good ventilation, at the height of the summer greenhouses can become too hot and reach temperatures over 45 °C. To avoid heat stress and scorching of the foliage, damping down, shading the cucumber plants with white fabric and even the whole greenhouse, may become necessary.
When grown in a greenhouse or polytunnel, cucumbers are protected from wet weather, which when prolonged, can lead to fungal diseases occurring. However, other cucumber diseases can still be a problem and preventative measures may need to be taken. Pests can also be an issue when growing undercover, especially aphids (Aphidoidea) which can transmit disease, but can be dealt with by introducing predatory ladybirds (Coccinella septempunctata) and lacewing larvae (Chrysoperla carnea).
Benefits at a glance:
- Longer growing season, due to earlier planting
- Protection against wind, rain and hail
- Space-saving method of growing vertically
- Controllable temperature by shading and damping down
- Pest control by introducing beneficial insects
Cucumbers do not have to be grown in a greenhouse, as they can also thrive when grown outdoors in a sunny and sheltered location. By growing outdoor cucumber varieties, they can be grown either directly in the ground, in pots or even in raised beds.
The best cucumber varieties for greenhouses
There are many cucumber varieties available to grow that can differ in habit, fruit size, colour and even shape. However, when growing cucumbers in a greenhouse or polytunnel it is worth growing cultivars bred for growing under cover, as they tend to be more prolific and have increased resistance to the most common greenhouse diseases. Here are some of the best cucumber varieties for growing in a greenhouse:
- ‘Burpless Tasty Green F1’ : Forming long ridge-type fruits up to 30cm in length, this cultivar produces delicious non-bitter fruits that can be harvested around 60 days after sowing.
- ‘Carmen F1’ : Long, slender and straight fruits up to 40cm in length. Good tolerance against mildew and cold weather. Awarded the RHS Award of Garden Merit.
- ‘Emilie F1’ : Producing heavy yields of green fruits harvested at 20cm long this hybrid cultivar has been awarded the RHS Award of Garden Merit. Good disease resistance and superbly flavoured fruits.
- ‘Mini Munch F1’ : Heavy yields throughout the season of small fruits harvested when 8cm or longer. Superb flavour and crunchy. Awarded the RHS Award of Garden Merit.
- ‘Socrates F1’ : Prolific small fruits harvested when 15cm long. Bitter-free taste and an excellent flavour. Awarded the RHS Award of Garden Merit.
- ‘Telegraph Improved’ : An improved version of the long-grown heirloom variety. Long and smooth-skinned green fruits up to 30 – 40cm, with a mild and crisp flavour.
Tip – For something unusual, why not try growing the round and yellow ‘Lemon Cucumber’ , which is best suited to growing in a greenhouse. To learn more about growing this exotic-looking lemon cucumber you can read our separate article here.
How to plant cucumbers in a greenhouse
When grown in a heated greenhouse, cucumber seeds can be sown 1 to 2cm deep in individual pots from late February to March, for an unheated greenhouse it is best to wait until April to begin sowing. Requiring a temperature of 21°C to germinate, cucumber seeds are often sown in a propagator to provide this warmth. You read more on how to sow and grow cucumbers in our article here.
Once the young cucumber plants are large enough, they can be potted on or planted out into a trench in a heated greenhouse from late March, or in an unheated greenhouse in late May. Cucumbers prefer a rich and fertile soil and benefit from being fed during the growing season. On planting, a slow-release granular fertiliser can be added to the soil, which will help provide the nutrients to encourage strong and healthy growth. Our Plantura Tomato Food is ideal, as it contains the necessary nitrogen, potassium and phosphorus and will feed the plants for up to three months.
- Perfect for tomatoes, chillies, courgettes, cucumber & more
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When growing cucumbers in a greenhouse, it is advisable to provide good air circulation between the plants, which can help prevent disease. Planting at a minimum spacing of 45 to 50cm and if space allows, even more, is recommended. On planting, canes can be inserted into the soil or strings hung from the roof to train the vines upwards. Water thoroughly and keep the soil moist, but not wet.
Good companion plants
Companion plants are those that can be grown together for mutual benefit and not compete against each other. Companion plants for cucumbers include those that are light feeders and that are not part of the same Cucurbitaceae family of plants.
Tomatoes are often grown in a greenhouse as they prefer similar growing conditions to cucumbers. They can be grown together in a greenhouse, but to stop them competing for each other’s nutrients and space it is advisable to plant them in separate areas away from each other.
Companion plants for cucumbers can include:
- Borage (Borago officinalis) and marigold (Calendula)
- Lettuce (Lactuca sativa)
- Fennel (Foeniculum vulgare) and dill (Anethum graveolens)
- Onion (Allium cepa) and garlic (Allium sativum)
Polyculture or mixed culture gardening doesn’t just work outside in the garden, it can be beneficial inside a greenhouse as well. To learn more about polyculture gardening and its many benefits you can read our specialist article here.
Cucumber plant care in the greenhouse
Whether grown outdoors or in a greenhouse, cucumbers need to be watered and fed regularly throughout the growing season. Depending on the variety grown and space available, it can be beneficial to pinch out the growing tip and remove side shoots, for more information on this you can read our separate article.
Watering and fertilising cucumber
Cucumbers prefer a moist, but well-drained soil and regular watering is a must to prevent the soil from drying out. Where possible, harvested rainwater is recommended as well as adding a layer of mulch that will help conserve moisture and also help prevent weeds.
In late summer, once the slow-release fertiliser applied at the time of planting has run out, cucumber plants can be fed with a liquid feed. Easier to apply, since it does not have to be worked into the soil around the plant’s root, the plants can be fed at the same time as watering. A liquid tomato fertiliser such as our Plantura Liquid Tomato Food is perfect to use and can be used weekly until the end of the season.
- Perfect for tomatoes & other vegetables
- Liquid fertiliser for healthy plant growth & an abundant harvest
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Cucumber diseases that can affect cucumbers in a greenhouse
Good ventilation is key for growing in any greenhouse, as if unventilated, the humid warm air can quickly become stagnant and encourage fungal diseases. Here are some of the most common cucumber diseases that can affect plants when grown in a greenhouse:
- Cucumber Mosaic Virus
- Cucumber wilt caused by Fusarium and Verticillium fungi
- Cucumber downy mildew (Pseudoperonospora cubensis)
- Cucumber powdery mildew (Podosphaera xanthii and Erysiphe cichoracearum)
- Grey mould (Botrytis cinerea)
- Sclerotinia disease (Phomopsis sclerotioides)
If cared for correctly, cucumber can produce impressive yields for weeks on end. Learn more about how to harvest and store your cucumbers here.