Top Of The Crops - Cucumber

Welcome to Top of the Crops! Today, in this cucumber growing guide, you will learn everything that there is to know about growing cucumber in a polytunnel. The team at First Tunnels love the taste of all our freshly harvested cucumber straight from our polytunnels.

How to Grow Cucumber (In a Polytunnel)

Cucumbers are a useful crop for home growers. Just one or two plants will often produce an abundance for a typical family to enjoy throughout the summer months. 

Key Information

The cucumber is the fruit of  Cucumis sativus, usually referred to as a vegetable. This is a vining plant which belongs to the same family as melons, squash, courgettes and pumpkins, watermelons, and several gourds. 

Cucumbers can be grown outside across much of the UK but they will often do best in a greenhouse or polytunnel garden, where they will get the warmth they crave. There are numerous named varieties to choose from. 

When to Grow Cucumber

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

The Preferred Conditions for Growing Cucumber

If you would like to grow cucumbers then one of the first things to think about is where precisely they could grow well in your garden.  To grow this crop successfully you need to understand the cucumber growing conditions that they require – especially when it comes to sunlight, water and soil. 

Cucumbers need a position in full sun that is as warm and sheltered as possible. Some varieties are best suited to being grown outdoors in a sunny location, while others are best grown under cover in a greenhouse or polytunnel. 

These are fairly hungry and thirsty plants that will do best in a fertile and humus rich soil or growing , that you have amended with plenty of organic matter. The soil or growing medium should be moist yet free draining. 

Consistent moisture is important throughout the cucumber growing season but problems can arise if waterlogging occurs. 

Cucumbers will do best when temperatures are between 18 and 25ºC. in the summer. In a greenhouse or polytunnel you may need to take steps to keep temperatures down and humidity up. 

When deciding where to grow cucumbers, you will also need to remember that they require some form of support. Choosing an appropriate support structure for these plants is important. 

What You Will Need to Grow Cucumber

To grow cucumbers you will need:

  • cucumber seeds or plants.

  • a suitable cucumber growing area (in-ground, raised beds or containers)

  • seed trays, small pots or soil blocks if sowing indoors. 

  • A trellis or other support structure for the cucumbers to climb. (Fortunately you do not need to buy one and can often make your own using reclaimed materials and/or upcycled items.)

Preparing the Ground

If you are growing cucumbers in the ground then it is important to make sure that the soil is in good shape before you sow or plant your cucumbers. Top dress the area with plenty of homemade compost or other organic matter and ensure that there is not competition from weeds. 

How to Grow Cucumber

Cucumbers can be grown from seed, or purchased as starts or young cucumber plants. Cucumbers are generally easy to grow from seed and this is the more affordable option. 

Sowing Cucumber Seeds

Cucumber seeds can be sown indoors or directly where they are to grow. The former is generally the better choice in the UK as when sowing outdoors you may struggle to get good germination rates and may encounter pest problems with the young and vulnerable plants outdoors. 

However, outdoor varieties can also be sown outside in mild locations as soon as the soil has warmed reliably. 

Sowing indoors

When you will sow cucumber seeds indoors depends on where they will ultimately be placed. 

  • Cucumbers to be grown undercover in a heated greenhouse can be sown between the middle of February and the middle of March. 

  • Cucumbers for unheated greenhouse or polytunnel growing are typically sown in April. 

  • Cucumbers that will be transplanted outside are usually sown in late April. 

Typically, one seed will be sown in the centre of 10cm pots filled with a seed starting potting mix. Soil blocks can also be used.  The seeds should be sown around 1-2cm deep, on their sides to reduce the chances of rotting. 

The seeds should be placed on a warm, sunny windowsill in a heated room, or in a heated propagator set to 21ºC. They should germinate within a week or two and should be removed from the propagator if one was used and grown on in a bright, warm location, with frequent watering, for the next month or so. 

Sowing outdoors

While, as mentioned above, it is not usually the best option, you can direct sow cucumber seeds outdoors in milder areas, or when the weather is particularly warm. You can direct sow cucumber seeds between late May and mid June. 

Though note that cloche protection will usually be required to provide the temperatures required for successful germination. 

Sow three seeds at stations around 30cm apart, close to your support structure (see below), as germination can be patchy. Then thin to leave the strongest seedling at each station if more than one seed germinates successfully. 

How to Plant Cucumbers

Cucumbers sown indoors will be ready to plant out into their final growing positions after a month or so, as long as the temperatures can be kept above around 12-15ºC. in your chosen cucumber growing location. Remember to harden off indoors grown cucumbers before placing them outdoors. 

Plant cucumbers in the ground around 30cm apart, firming them gently into place and watering them in well. Mulch around the plants with organic matter upon planting. 

If you wish to grow cucumbers in containers, place your young cucumbers into pots that are at least 30cm wide and deep, filled with a good quality, peat-free potting mix. 


Before planting, make sure that you have appropriate trellis or other support structures in place. While cucumbers can be allowed to trail on the ground, it is better to grow them vertically because it saves space, and keeps the fruits safe and out of harm's way. 

Stems should be tied in to supports at first, but should be able to self-cling with their tendrils as they grow. 

Removing Male Flowers

Some greenhouse/ polytunnel varieties should produce only female flowers.  If male flowers appear on these types (these don't have little fruits forming behind them) they should be removed or when the female flowers are pollinated, the fruits can be bitter. 

Outdoor varieties of cucumber, however, should produce both male and female flowers. The female flowers on these varieties do need to be pollinated to produce fruit and so on these types, the male flowers should not be removed. 

Care Tips for Growing Cucumber

Make sure that you water consistently to keep the soil or growing medium moist but not waterlogged at all times. Regular watering is essential for cucumbers to crop successfully. Remember that more watering will be required when cucumbers are grown in containers. 

It is best to feed cucumbers every couple of weeks with a balanced, organic liquid plant feed such as compost tea. Once flowering starts on the plants, switch to a weekly feed with a potassium-rich solution such as comfrey tea to encourage healthy flowering and fruiting. 

Pinching out is also a good idea on cucumber plants. This involves nipping off the growing tips of the plants and nipping off side shoots to focus the plants on fruiting rather than on foliage growth. 

With cucumber growing in a greenhouse or polytunnel you should nip off the growing tip when it reaches the top of the structure, nip out side shoots two leaves beyond a female (fruit forming) flower,  and nip off the ends of side shoots without flowers once they are around 60cm long. 

With cucumber growing outdoors, nip off the growing tip of plants once they have around 7 leaves to encourage bushiness, and nip off the tips of side shoots without flowers after these have developed around 7 leaves. 

How to Harvest Cucumber

Cucumbers in a greenhouse or polytunnel will usually ripen from the middle of summer through to the middle of autumn. Outdoors, harvests will be later, shorter and more variable – dependant very much on the weather in a particular year. 

What the cucumbers will look like and how large they will be will depend on the variety you are growing. Make sure you know what to expect so that you can harvest them when they are at the best size and what they should look like at the ideal harvesting time. 

When removing the cucumbers from the vines, use a knife or a pair of secateurs to cut the stem just above the fruit cleanly, rather than pulling them from the plant. 

Storing Cucumber

Cucumbers are best used fresh from the garden in a range of recipes or pickled for preservation if they are of the pickling kind. You can keep cucumbers in the fridge in a sealed container for a week or two but they will not keep for long. 

Common Pests and Problems 

Cucumbers can encounter issues with powdery mildew, and red spider mites when grown under cover. Slugs and snails can destroy young plants. Other than this, however, cucumbers usually don't encounter serious problems as long as they are grown correctly, in the right location. 

Just look out for mosaic virus, which is a more serious issue. If you see this then the plants should be removed and destroyed immediately to prevent its spread. 

Advice for Buying Cucumber Seeds/ Plants

There are many different varieties to choose from, so make sure you know what you want before making your decision. Select AGM varieties for tried and tested options that work well in the UK. 

Top Tips for Growing Cucumber in a Polytunnel

  • Select varieties suited to indoor growing and provide the right support. 

  • Raise humidity by wetting surfaces during hot weather.

  • and ensure good ventilation to keep temperatures down below 25ºC. 


Best way to grow cucumbers
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Gould, M., (2023) 15+ Cucumber Recipes That Aren’t JUST A Salad. Delish. [online] Available at: [accessed 13/12/23]

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