How to Grow Cucumbers in the UK

Grow cucumbers under cover or outdoors in a warm, sheltered position. Choose a greenhouse variety for a longer protected season or an outdoor ridge type bred to crop after planting out in early summer.

The RHS cucumber guide recommends indoor sowing for an earlier crop and outdoor sowing only after the soil warms. This guide covers variety choice, sowing, training, feeding, watering and flower management. Start with indoor seed sowing if you are raising plants from seed.

Indoor vs outdoor cucumbers: which type should you grow?

Cucumbers fall into two distinct categories in the UK, and choosing the right type for your growing space is the most important decision you will make.

Indoor (greenhouse) cucumbers produce long, smooth-skinned fruit. They need warmth, humidity, and consistent conditions. Indoor varieties include Telegraph Improved, Carmen F1, and Bella. They grow as climbing plants trained up strings or canes, reaching 1.8m or more. A heated greenhouse or polytunnel kept above 15C at night gives the best results. Our greenhouse heating guide covers heater types and running costs for maintaining overnight warmth. These plants produce 20-25 fruits per season.

Outdoor (ridge) cucumbers are tougher, more compact plants. They produce shorter, rougher-skinned fruit with a slightly different flavour. Ridge varieties tolerate cooler UK summers and need no protection once established. Popular choices include Marketmore, Burpless Tasty Green, and Crystal Lemon. They grow as trailing plants along the ground or over a low frame, yielding 10-15 fruits per plant.

If you are new to growing your own vegetables, start with outdoor ridge types. They are more forgiving and need less daily attention than greenhouse plants.

Best cucumber varieties for the UK

Not all cucumber varieties suit British conditions. The UK growing season runs from late May to September outdoors, and April to October under glass. Choose cultivars bred for cooler climates.

Indoor (greenhouse) varieties

• Telegraph Improved - the classic British greenhouse cucumber. Long, smooth fruit up to 35cm. Heavy cropper, producing 20-25 fruits per plant. Needs training up strings. Not an all-female variety, so you must remove male flowers.
• Carmen F1 - all-female variety. No need to worry about removing male flowers. Produces smooth, dark-green fruit 25-30cm long. Disease-resistant. The best choice for heated greenhouses.
• Bella F1 - another all-female type. Compact growth habit suits smaller greenhouses. Good mildew resistance. Fruits slightly shorter at 20-25cm.
• Mini Munch F1 - produces small, snack-sized cucumbers 8-10cm long. Ideal for lunchboxes. All-female. Very productive. Children love picking these.

Outdoor (ridge) varieties

• Marketmore - the most reliable outdoor cucumber for UK gardens. Dark-green, straight fruit 20-25cm long. Strong disease resistance. Handles cool, wet summers better than most varieties. Produces 10-15 fruits per plant.
• Burpless Tasty Green - long, smooth fruit without the bitterness common in outdoor types. Grows to 25cm. Good flavour. Needs a warm, sheltered spot for best results.
• Crystal Lemon - unusual round, yellow fruit the size of a tennis ball. Mild, crisp flavour. Vigorous trailing plant. A conversation starter.
• Masterpiece - an old, dependable UK variety. Short, firm fruit. Crops early. Good for northern gardens with shorter seasons.

Variety comparison table

Gardener’s tip: Grow one indoor and one outdoor variety. The greenhouse plant starts cropping in July. The outdoor plant follows in August. Together they extend the harvest window by 4-6 weeks.

When and how to sow cucumber seeds

Timing is critical with cucumbers. They are tropical plants that refuse to grow below 12C and suffer permanent damage from frost. Sow too early and seedlings stall in cold conditions. Sow too late and the plants do not have enough season to produce a worthwhile crop.

Sowing method

Sow cucumber seeds on their edge, not flat. This prevents water sitting on the broad seed surface, which causes rot before germination. Use 7cm pots filled with seed compost. Push one seed per pot 2cm deep, placed on its narrow edge. Water gently and place in a heated propagator at 20-25C.

Seeds germinate in 5-7 days at this temperature. Germination slows significantly below 18C and stops below 12C. If you do not have a propagator, an airing cupboard works for the germination phase. Move seedlings to a bright windowsill as soon as they emerge. For more detailed advice, see our full guide to sowing seeds indoors.

Key sowing dates

Hardening off outdoor varieties

Before planting ridge cucumbers outside, harden them off over 7-10 days. Place pots outdoors during the day and bring them in at night. Start with 2-3 hours of outdoor exposure and increase daily. Cucumbers resent cold wind more than most vegetables, so choose calm, mild days for the transition.

Warning: A single night below 5C can kill cucumber seedlings. Do not rush to plant out. In most of England, late May to early June is safe. In northern England and Scotland, wait until mid-June.

Planting and soil preparation

Cucumbers are hungry, thirsty plants. They need rich, moisture-retentive soil and a warm position. Prepare the ground well before planting.

Indoor planting

In the greenhouse, plant cucumbers into large pots (10 litres minimum), grow bags, or directly into a prepared border. Mix plenty of homemade compost or well-rotted manure into the soil before planting. Space plants 60cm apart. Maintain a minimum night temperature of 15C for best results. Below 12C, growth stops and plants become vulnerable to disease.

Outdoor planting

Choose a sunny, south-facing position sheltered from wind. Dig a planting hole 30cm deep and wide. Fill the bottom with well-rotted manure or compost, then mound soil on top to create a slight hill. This warms the root zone and improves drainage. Space ridge cucumbers 90cm apart to allow their trailing habit room to spread.

A cloche or cold frame over newly planted outdoor cucumbers gives them a warm start. Remove it once the plants outgrow the cover or when night temperatures stay above 12C.

Training cucumbers up strings and supports

Indoor cucumber plants need vertical support. They are natural climbers and produce far more fruit when grown upright. Training maximises light exposure, improves airflow, and makes harvesting simple.

Greenhouse training

Attach a horizontal wire or bar across the top of the greenhouse at 1.8-2m height. Tie a length of soft twine from the wire down to the base of each plant. As the main stem grows, twist it gently around the string. The plant grips the string with its tendrils. Remove side-shoots from the bottom 60cm of the stem to keep the base clear and airy.

Above 60cm, allow side-shoots to grow and produce 2 fruits each. Pinch out the growing tip of each side-shoot after 2 leaves beyond the fruit. When the main stem reaches the overhead wire, pinch out its growing tip. This directs the plant’s energy into fruit production.

Outdoor training

Ridge cucumbers can trail along the ground, but training them over a low frame or A-frame keeps fruit clean and reduces slug damage. A simple frame made from bamboo canes or wooden battens 60cm tall is enough. The plant’s tendrils grip the frame naturally. Alternatively, grow through a mulch of straw to keep fruit off bare soil.

Should you remove male cucumber flowers?

Follow the seed packet because flower handling depends on the variety. Outdoor ridge cucumbers need pollination, so leave male and female flowers in place.

Some traditional greenhouse varieties produce both male and female flowers and may form bitter, seedy fruit if pollinated. Female flowers have a small cucumber-shaped swelling behind the petals; male flowers sit on a plain stem. Remove males only when the variety instructions say to do so.

All-female varieties are bred to produce fruit without pollination and normally need no flower removal. Stress can occasionally trigger male flowers, so check the packet or breeder’s guidance before acting.

With a traditional indoor variety whose instructions require male-flower removal, check plants regularly and pinch off males while they are small.

Gardener’s tip: Look behind the petals. A tiny green cucumber marks a female flower; a plain stem marks a male. Keep or remove the male according to the variety instructions.

Feeding and watering

Watering

Cucumbers are 95% water. Consistent moisture is the single biggest factor in fruit quality. Irregular watering causes bitter fruit, misshapen cucumbers, and reduced yields.

Water at the base of the plant, never over the leaves. Wet foliage in a warm greenhouse is a direct invitation for powdery mildew, the most common cucumber disease. Drip irrigation or a watering can without a rose works best.

• Greenhouse cucumbers: water daily in warm weather. In peak summer, large plants may need watering twice daily.
• Outdoor cucumbers: water every 2-3 days in normal conditions, daily during hot spells above 25C.
• Container-grown plants: check daily. Push your finger 3cm into the compost. If it is dry, water immediately.

Mulching around the base with straw, well-rotted compost, or bark chips helps retain moisture and keeps the root zone cool. Apply a 5cm layer after the soil has warmed in early June.

Feeding schedule

Do not feed young cucumber plants. The nutrients in fresh compost are sufficient until flowering begins. Over-feeding young plants creates lush foliage but delays fruit production.

Start feeding with a high-potash liquid fertiliser (such as Tomorite or Chempak No.4) once the first flowers open. Apply weekly at the dilution rate on the bottle. The same feeding approach works well for growing tomatoes.

Month-by-month cucumber calendar

Powdery mildew prevention and treatment

Powdery mildew is the most common cucumber disease in UK gardens. It shows as white, powdery patches on the upper surface of leaves. It spreads fastest in warm, dry conditions with poor airflow, which sounds contradictory but the fungus thrives when leaves are dry and nights are cool.

Prevention

Prevention is far easier than cure:

• Space plants 60cm apart for good airflow around the foliage
• Water at the base, never over the leaves
• Ventilate the greenhouse well on warm days. Open doors and vents to keep air moving.
• Avoid overcrowding. Pinch out excess side-shoots so light and air reach all parts of the plant
• Mulch the soil surface to maintain even moisture levels. Drought-stressed plants are more susceptible.

Treatment

If mildew appears, act fast. Remove and bin badly affected leaves immediately. Do not compost them. The RHS powdery mildew guide has detailed identification help.

A weekly spray of one part milk to nine parts water on both leaf surfaces can slow the spread. This is a traditional remedy backed by university research showing milk proteins have antifungal properties. It will not cure a severe infection, but it helps contain mild outbreaks.

Mildew-resistant varieties like Carmen F1 and Marketmore offer some built-in protection and are worth choosing if mildew has been a problem in previous seasons.

Common mistakes when growing cucumbers

Sowing too early

Cucumber seeds sown in March sit in cold compost and rot before they germinate. Even if they survive, the seedlings stall in low temperatures. April is early enough. The plants grow so fast in warm conditions that a March sowing gains you nothing by midsummer.

Planting outdoors before the last frost

One cold night finishes cucumber plants. Hardening off is not optional. Wait until night temperatures stay above 10C before planting ridge varieties outside. In most of England, that means late May to early June.

Overwatering seedlings

Young cucumber seedlings sitting in waterlogged compost develop root rot within days. Water when the compost surface feels dry, not before. Good drainage in pots is essential. Make sure every pot has drainage holes.

Forgetting to remove male flowers

On indoor varieties, leaving male flowers causes pollination. Pollinated fruit turns bitter and seedy. Check plants every 2-3 days and remove male flowers before they open fully. This is the single most common reason for bitter greenhouse cucumbers.

Letting fruit grow too large

Large cucumbers look impressive but taste watery and develop tough seeds. Pick fruit at 20-25cm for standard varieties and 8-10cm for mini types. Regular picking signals the plant to keep producing. Leave one overripe cucumber on the vine and the plant stops setting new fruit.

Inconsistent watering

Alternating drought and flood causes misshapen, bitter fruit with hollow centres. Cucumbers need steady, even moisture throughout the growing season. Mulching and drip irrigation help maintain consistency, especially during holiday absences.

Poor ventilation in the greenhouse

Warm, stagnant air inside a greenhouse is a recipe for powdery mildew and grey mould. Open vents and doors on warm days. An automatic vent opener is a worthwhile investment if you are at work during the day. Our guide to greenhouse ventilation and humidity control covers the full range of vent types and how to maintain the 60-70% humidity cucumbers prefer.

Harvesting cucumbers

Pick cucumbers when they reach full length but before they start to yellow. A ripe cucumber feels firm, looks dark green, and has a slight sheen. If the skin turns dull or the ends start to yellow, the fruit is past its best.

Use a sharp knife or secateurs to cut the fruit from the stem. Do not twist or pull, which damages the plant.

Harvest guidelines

• Indoor varieties: pick at 25-30cm for standard types, 8-10cm for Mini Munch
• Outdoor ridge varieties: pick at 15-20cm. Ridge cucumbers left too long become watery
• Frequency: harvest every 2-3 days in peak season. This keeps the plant producing
• Daily check: in August, a healthy plant can produce a new cucumber every 1-2 days

A single indoor cucumber plant produces 20-25 fruits over the season. Outdoor ridge types yield 10-15 fruits per plant. Regular picking is the key to hitting these numbers. A plant left with ripe fruit stops producing new flowers.

Storing fresh cucumbers

Fresh cucumbers store poorly compared to other vegetables. Keep them in the fridge for up to one week. Do not wrap tightly in cling film, which traps moisture and accelerates decay. A loose paper bag in the fridge salad drawer works best. For a longer-term option, make pickles or relish.

Gardener’s tip: Harvest cucumbers in the morning when they are cool and crisp. Afternoon-picked fruit in a hot greenhouse has already lost some moisture and will not store as well.

Why Carmen F1 suits UK greenhouse growers: This all-female variety reduces flower management and has an RHS Award of Garden Merit. Follow the seed supplier’s instructions because stressed plants can occasionally produce male flowers.

What causes bitter cucumbers?

Bitter cucumbers are the most common disappointment for UK growers. The bitterness comes from cucurbitacin, a natural compound that increases when the plant is stressed. Several factors trigger it:

1. Pollination of all-female varieties - male flowers pollinating indoor types causes bitter, seedy fruit
2. Irregular watering - drought followed by heavy watering concentrates cucurbitacin in the fruit
3. Temperature swings - cold nights below 12C followed by hot days above 30C stress the plant
4. Over-mature fruit - cucumbers left on the vine too long develop bitterness, especially at the stem end
5. Nutrient deficiency - underfed plants produce stressed, bitter fruit

The fix is consistent care: steady watering, regular feeding, stable temperatures, and prompt harvesting. Choose modern F1 varieties like Marketmore and Carmen, which have been bred with lower cucurbitacin levels than older open-pollinated types.

Now you’ve mastered cucumbers, read our guide on growing courgettes in the UK for the next step.

Frequently asked questions

When should I sow cucumber seeds in the UK?

Sow indoors in April at 20-25C. Seeds germinate in 5-7 days at this temperature. Sow on their edge to prevent the seed sitting in water, which causes rot. For outdoor ridge varieties, sow indoors in late April and plant out after the last frost in late May.

Can I grow cucumbers outside in the UK?

Yes, ridge varieties grow well outdoors in sheltered spots. Choose Marketmore, Burpless Tasty Green, or Crystal Lemon for outdoor growing. They need a sunny, south-facing position with wind protection. Outdoor cucumbers produce shorter, rougher-skinned fruit than indoor types.

Why are my cucumbers bitter?

Bitter fruit usually follows stress or pollination of greenhouse cucumbers. Water consistently and follow the seed supplier’s flower-removal instructions. Outdoor ridge cucumbers need pollination, so leave their male flowers in place.

How often should I water cucumber plants?

Water daily in warm weather, every 2-3 days in cooler periods. Cucumbers are 95% water and need constant moisture. Water at the base, never over the leaves. Inconsistent watering causes misshapen fruit and encourages bitter compounds to develop.

Do I need to remove male flowers from cucumber plants?

Remove male flowers only from greenhouse varieties that require it. Traditional indoor types may produce both flower sexes, while modern all-female types rarely produce males. Outdoor ridge cucumbers need pollination, so do not remove their male flowers.