How to Grow Cucumbers in the UK

Cucumbers are one of the most generous things you can grow. A single healthy plant in a greenhouse can keep a household in salad from July into autumn, and an outdoor ridge cucumber on the allotment isn’t far behind. The trick is choosing the right type for the space you’ve got, then keeping them warm and steadily watered.

The RHS cucumber guide suggests sowing indoors for an earlier crop and only sowing outside once the soil has warmed. That’s the approach here too. If you’re raising plants from seed for the first time, our guide to indoor seed sowing covers the basics.

Greenhouse or outdoor cucumbers: which should you grow?

Decide this first, because it shapes everything else.

Greenhouse cucumbers are the long, smooth ones you see in shops. They want warmth, humidity and fairly steady conditions, and they’ll climb a string to head height. ‘Telegraph Improved’, ‘Carmen’ and ‘Bella’ are all good. A greenhouse or polytunnel that stays above about 15C at night suits them best. If yours gets chilly in May, our greenhouse heating guide has a look at heaters and running costs.

Outdoor or ridge cucumbers are tougher and more compact, with shorter fruit and slightly knobbly skin. They put up with cool British summers and need no cover once established. ‘Marketmore’, ‘Burpless Tasty Green’ and ‘Crystal Lemon’ are the popular ones. They scramble along the ground or over a low frame.

New to growing your own vegetables? Start with a ridge type. They’re far more forgiving.

Greenhouse types give long, smooth fruit, while outdoor ridge types are shorter and rougher but much tougher. A ridge type is the easier start.

Best cucumber varieties for the UK

Outdoors, the British cucumber season runs roughly from late May to September. Under glass you can stretch it from April to October. These varieties all cope well here.

Greenhouse varieties

• ‘Telegraph Improved’: the old British favourite, with long, smooth fruit. It isn’t all-female, so you’ll need to pinch off the male flowers.
• ‘Carmen’: all-female, so no flower fiddling. Smooth, dark green fruit and good disease resistance.
• ‘Bella’: another all-female type, compact enough for a small greenhouse, with decent mildew resistance.
• ‘Mini Munch’: snack-sized cucumbers that fit in a lunchbox. All-female, very productive, and children love hunting for them.

Outdoor ridge varieties

• ‘Marketmore’: the most dependable outdoor cucumber. Straight, dark green fruit, and it shrugs off cool, damp summers better than most.
• ‘Burpless Tasty Green’: longer and smoother than most ridge types, without the bitterness some outdoor cucumbers have. Give it a warm, sheltered corner.
• ‘Crystal Lemon’: round, yellow and about the size of a tennis ball. Mild, crunchy and a good talking point.
• ‘Masterpiece’: an old, reliable variety with short, firm fruit. It crops early, which helps in northern gardens.

Quick comparison

If you have both a greenhouse and a bed, grow one of each. The greenhouse plant starts cropping in July and the outdoor one keeps going into September, so the harvest lasts much longer.

When and how to sow cucumber seeds

Cucumbers like warmth, stop growing in the cold and die in a frost. Sow too early and the seedlings just sit there. Sow too late and the summer runs out before the plant gets going. April is the sweet spot.

One seed per small pot, pushed in on its edge so water runs off rather than sitting on it.

How to sow

Fill 7cm pots with seed compost. Push one seed into each on its edge, about 2cm deep. Laid flat, water sits on the seed and it can rot. Water gently and keep the pots in a heated propagator at 20-25C.

At that warmth, seedlings usually appear in about a week. In a cooler room it takes much longer, and some won’t come up at all. No propagator? An airing cupboard works for germination, but move the pots to a bright windowsill the moment you see a shoot. A day in the dark is enough to make them go thin and floppy. Our full guide to sowing seeds indoors has more tips.

Sowing dates

Hardening off outdoor varieties

Ridge cucumbers need hardening off for a week to ten days before they go out. Stand them outside during the day, bring them in at night, and leave them out a bit longer each time. Pick calm, mild days, as a cold wind can scorch the leaves.

Don’t rush it. One cold night can finish young plants. Late May to early June is usually safe in most of England. In northern England and Scotland, mid-June is the safer bet.

Planting and soil preparation

Cucumbers are hungry and thirsty. They want rich soil that holds on to moisture, and a warm spot.

In the greenhouse

Use a large pot of at least 10 litres, a growbag or the greenhouse border. Mix in plenty of homemade compost or well-rotted manure first. Space plants 60cm apart. Below about 15C at night they stop growing, so keep an eye on the thermometer in late May.

Outdoors

Pick a sunny, sheltered spot, out of the wind. Dig a hole roughly 30cm deep and wide, drop a forkful of manure or compost in the bottom, then pile the soil back on top as a low mound. The mound warms up faster and drains better than flat ground. Give ridge cucumbers about 90cm each way so they have room to trail.

A cloche or cold frame over newly planted cucumbers gives them a cosy first couple of weeks. Lift it off once the plants outgrow it or the nights warm up.

Training cucumbers up strings and supports

Greenhouse cucumbers are natural climbers, and growing them upright pays off: more fruit, better airflow and no hunting through leaves on your knees.

Main stems wound up soft string, with side-shoots stopped two leaves past each fruit.

In the greenhouse

Run a wire along the roof at about 1.8-2m. Tie soft string from the wire down to the base of each plant, and as the main stem grows, twist it gently round the string. Rub off any side-shoots on the bottom 60cm of stem so the base stays clear and airy.

Above that, let side-shoots grow and pinch each one out two leaves past a fruit. When the main stem hits the wire, pinch out its tip too. From then on the plant puts its energy into fruit rather than more stem.

Outdoors

Ridge cucumbers can simply trail, but lifting them onto a low frame keeps the fruit clean and out of reach of slugs. A few canes or wooden battens about 60cm high is plenty, and the tendrils will grab hold without any tying. If you’d rather let them sprawl, put straw underneath so the fruit isn’t lying on bare soil.

Ridge cucumbers scrambling over a low frame on an allotment. Lifting the fruit keeps it clean and away from slugs.

Should you remove male cucumber flowers?

It depends on the variety, so check the seed packet before you pinch anything. Outdoor ridge cucumbers need pollinating, so leave every flower on those.

Some older greenhouse varieties, ‘Telegraph Improved’ among them, make both male and female flowers. If the female flowers get pollinated, the fruit can turn bitter and full of seeds. Telling them apart is easy: female flowers have a tiny cucumber behind the petals, while male flowers sit on a plain, thin stalk. If the packet says so, pinch the males off while they’re small.

All-female varieties set fruit without any pollination. You can usually ignore their flowers. A stressed plant sometimes produces the odd male, but the packet will say whether to bother removing it.

Feeding and watering

Watering

Keep it steady. More cucumber problems come down to watering than anything else, including bitter fruit, bent fruit and a poor crop.

Water at the base rather than over the leaves. Wet leaves in a warm greenhouse invite powdery mildew. A can with the rose taken off, or a simple drip system, does the job well.

• Greenhouse cucumbers: daily in warm weather, and large plants may want it twice a day in July and August.
• Outdoor cucumbers: every two or three days, and daily in a hot spell.
• In pots: check every day by pushing a finger 3cm into the compost. Water if it’s dry.

A mulch of straw, compost or bark helps keep the roots cool and evenly moist. Put it down in early June, once the soil has warmed up.

Water the base rather than the leaves, and keep it steady. Big swings between dry and soaked are a common cause of bitter, misshapen fruit.

Feeding

Hold off with young plants. Fresh compost has all they need, and feeding too soon gives you a jungle of leaves and very few cucumbers.

Once the first flowers open, switch to a high-potash liquid feed (tomato feed is perfect) once a week at the strength on the bottle. It’s exactly the routine you’d use for growing tomatoes.

Cucumber jobs month by month

Preventing and dealing with powdery mildew

Powdery mildew is the cucumber problem you’re most likely to meet. It looks as if someone has dusted the leaves with flour, and it usually turns up from late July. Dry roots and still, muggy air make it spread fastest.

Prevention

• Space plants 60cm apart so air can move between them
• Water at the base and keep the leaves dry
• Open greenhouse vents and doors on warm days
• Pinch out surplus side-shoots so the plant doesn’t become a thicket
• Mulch to keep soil moisture even, since thirsty plants catch it more easily

What to do

Take off the worst leaves as soon as you see it and put them in the bin, not the compost heap. The RHS powdery mildew guide has good photos if you’re unsure what you’re looking at. Late in the season, a bit of mildew on the oldest leaves won’t stop a plant cropping. Next year, choose a resistant variety such as ‘Carmen’ or ‘Marketmore’.

Common cucumber mistakes

Sowing too early

Seed sown in March often sits in cold compost and rots. The ones that do come up tend to stall. April sowings catch up within weeks, so there’s no gain in starting sooner.

Planting out before the last frost

A single cold night can kill a young cucumber. Harden plants off properly and wait for mild nights before planting ridge types outside, which in most of England means late May to early June.

Overwatering seedlings

Seedlings in soggy compost rot at the base. Water when the surface feels dry, and check every pot has drainage holes.

Forgetting the male flowers

On greenhouse varieties that need it, leaving male flowers on can give you bitter, seedy fruit. Have a quick look every few days and pinch them off while small.

Letting fruit grow too big

Monster cucumbers look great on the bench but taste watery and have tough seeds. Pick greenhouse types at 25-30cm, ridge types at 15-20cm and minis at 8-10cm. Old fruit left on the plant also slows down new ones.

Uneven watering

Bone dry one day and soaked the next is the classic route to bent, bitter cucumbers. Mulch helps, and a drip system or a friendly neighbour is worth sorting out before you go on holiday.

A stuffy greenhouse

Warm, still air brings on powdery mildew and grey mould. Open up on warm days. If you’re out at work all day, an automatic vent opener costs little and makes a real difference. Our guide to greenhouse ventilation and humidity control covers the different vent types.

Picking cucumbers

Pick when the fruit has reached full size but before any yellow creeps in. A ready cucumber is firm, dark green and slightly glossy. Dull skin or yellowing ends mean it’s past its best.

Cut cucumbers off with a sharp knife or secateurs rather than pulling, which can tear the stem.

Use a sharp knife or secateurs. Twisting or tugging can damage the stem and the fruit still to come.

When to pick

• Greenhouse types: 25-30cm for standard varieties, 8-10cm for ‘Mini Munch’
• Outdoor ridge types: 15-20cm, as they turn watery if left too long
• How often: every two or three days at the peak, which keeps the plant producing

Storing cucumbers

Cucumbers don’t keep long. A week in the salad drawer is about the limit, loosely wrapped in a paper bag rather than clingfilm. If you end up with a glut, quick fridge pickles or a cucumber relish use them up nicely.

They’re crispest picked first thing in the morning, before the greenhouse heats up.

What causes bitter cucumbers?

Bitterness comes from a natural compound the plant makes when it’s under stress. The usual causes are:

1. Pollinated fruit on older greenhouse types that should have had their male flowers removed
2. Uneven watering, especially a dry spell followed by a soaking
3. Big temperature swings, such as cold nights followed by baking hot days
4. Fruit left on too long, which can go bitter at the stalk end
5. Hungry plants that haven’t been fed

The answer is steady, unexciting care: regular watering, weekly feeding once flowering starts, no wild temperature swings and prompt picking. Modern varieties such as ‘Marketmore’ and ‘Carmen’ are also bred to be less bitter than older types.

Now you’ve got cucumbers sorted, try our guide on growing courgettes in the UK next.

Curled, pinched fruit is a sign the plant has been stressed, often by uneven watering. Those are the ones most likely to taste bitter too.

Frequently asked questions

When should I sow cucumber seeds in the UK?

In April, indoors and somewhere warm. A propagator set to 20-25C is ideal, and the seeds should be up in about a week. Push each one in on its edge so water can’t pool on it. Sow outdoor ridge types towards the end of April, ready to plant out after the last frost.

Can I grow cucumbers outside in the UK?

Yes. Ridge varieties such as ‘Marketmore’, ‘Burpless Tasty Green’ and ‘Crystal Lemon’ are bred for it. Give them full sun and shelter from wind. The fruit is shorter and rougher-skinned than greenhouse cucumbers, but it tastes just as good.

Why are my cucumbers bitter?

Stress is the usual cause, especially dry roots followed by a soaking. On some older greenhouse types, pollinated fruit can taste bitter too. Water steadily and follow the seed packet on male flowers. Ridge cucumbers need pollinating, so leave their male flowers alone.

How often should I water cucumber plants?

Every day in warm weather, and every two or three days when it’s cooler. Aim the water at the base rather than over the leaves. What matters most is keeping it steady, because swings between dry and soaked give bent, bitter fruit.

Do I need to remove male flowers from cucumber plants?

Only on greenhouse varieties where the packet tells you to. Older indoor types produce both male and female flowers, while modern all-female types rarely make any males. Outdoor ridge cucumbers need the pollen, so leave their male flowers in place.