Cucurbit
How to grow cucumbers
Cucumis sativus
Cucumbers need warmth, rich compost and constant moisture. Choose the type first: all-female greenhouse varieties for long, smooth fruit under glass, or ridge varieties for a sheltered, sunny spot outdoors. Sow indoors at 20 to 25 °C in April, plant under glass in late May or outside in early June, train the stem up a string or trellis and never let the roots dry out. Top-dress from the first flowers and cut the fruit young.
- Hardiness
- Tender, greenhouse types need 20°C+
- Position
- Full sun under glass, or a warm sheltered spot outdoors
- Soil
- Rich, moisture-retentive, free-draining
- Ideal pH
- 6.5 to 7.0
- Water
- High, constant moisture, warm water under glass
- Feeding
- Heavy feeder
Sowing and planting cucumbers
WhenSow Mar to Apr (glass) or May (outdoor); plant out Jun; harvest Jul to Sep
Starting off
Sow indoors, one seed on its edge 1 to 2 cm deep in a 9 cm pot at 20 to 25 °C, germinating in 3 to 7 days: late March to April for a heated greenhouse, late April to May for outdoors. Plant out under glass in late May, outdoors in early June once nights stay above 12 °C. Pinch outdoor types at 6 to 7 leaves to encourage side shoots.
Spacing and planting
Greenhouse cordons 45 cm apart in the border or one per 25 cm pot or growbag, trained up a string to 2 m; outdoor ridge types 45 cm apart in rows 90 cm apart up a trellis, or 90 cm apart to trail. Plant on a slight mound. One plant crops in a 30 cm pot.
Varieties worth growing
- Carmen F1
- All-female greenhouse cucumber with full-length fruit and strong resistance to powdery mildew, so it crops into September.
- Passandra F1
- All-female mini cucumber, picked at 15 cm. Heavy crops, good disease resistance, and a sensible size for a small household.
- Marketmore
- The dependable outdoor ridge cucumber: dark, slightly spiny fruit, and it copes with a cool summer better than most.
- Burpless Tasty Green F1
- Long, thin-skinned fruit that never needs peeling. Grows outdoors up a trellis or in an unheated greenhouse.
- Crystal Lemon
- Round, pale yellow fruit the size of an apple, crisp and mild. A vigorous outdoor plant that sets well in a British summer.
Cucumbers month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Nothing to do.
- February
Nothing to do. Order seed.
- March
Sow late in the month only if you have a heated greenhouse to plant into.
- April
Sow in 9 cm pots with heat: mid month for an unheated greenhouse, the last week for outdoor types.
- May
Pot on if roots fill the pot. Plant in the greenhouse in the last week. Harden off outdoor plants.
- June
Plant outdoors early in the month. Tie the main stem to its string or trellis. Top-dress pots at the first flowers and border plants late in the month.
- July
Cut fruit every two days. Pinch side shoots two leaves beyond a fruit. Damp down the greenhouse.
- August
Keep picking. Give pots their second top-dress six weeks after the first. Stop the main stem when it reaches the roof. Watch for mildew and spider mite.
- September
Last fruits. Outdoor plants finish with the first cold nights.
- October
Clear the plants and bin diseased foliage. Empty pots and wash down the greenhouse.
- November
Nothing to do.
- December
Nothing to do.
Feeding cucumbers
A hungry, thirsty plant that crops in proportion to how steadily it is fed and watered. A rich base at planting, then the same dry fertiliser as a top-dress from the first flowers, and nothing once the nights turn cold.
A balanced feed, leaning to high-potassium once fruiting; never let it dry out or the fruit turns bitter.
Feeding plan
Planting in pots or growbags, late May
Fruit & Vegetable Fertiliser 4-5-6
5 g per litre of compost, mixed through. A 30 cm pot holds about 15 litres, so 75 g (5 x 15).
Planting in a border or outdoor bed
Fruit & Vegetable Fertiliser 4-5-6
100 g/m² forked in with a bucket of garden compost per plant. In late June add 50 g/m² round the plants and water it in.
At the first flowers and once more at least six weeks later, pots and growbags
Fruit & Vegetable Fertiliser 4-5-6
2 to 4 g per litre of pot volume scattered on the compost and watered in: 30 to 60 g for a 15 litre pot (2 to 4 x 15). The label gives no interval for top-dressing pots, so stop at these two. Border and bed plants have had the label's season limit of 150 g/m² (100 + 50) and get no more.
Only if older leaves yellow between the veins
Kieserite (magnesium sulphate)
2 g per litre of water drenched onto the roots: 20 g in a 10 litre can. Repeat once after three weeks if it persists.
Mid September onwards
Nothing
Growth has stopped; feed left in cold compost is wasted.
Signs to watch
Bitter, misshapen fruit
Water stress or pollination by a male flower, not nutrition
Water evenly and remove male flowers on all-female types
Older leaves yellow between the veins
Magnesium locked out by potash feeding or cold roots
Epsom salts spray and warm water
Young leaves yellow with green veins
Iron chlorosis on alkaline compost
Chelated iron
Pests, diseases and problems
White powdery coating on the leaves from midsummer, older leaves first
Powdery mildew, worst on plants that are dry at the root in still, humid air
Keep the compost evenly moist, ventilate, and cut off the worst leaves. Choose a resistant variety such as Carmen F1 or Passandra F1 next year.
Leaves finely speckled pale yellow, then bronzed, with fine webbing under glass
Glasshouse red spider mite, which thrives in hot, dry air
Damp down the greenhouse floor daily in hot weather and mist under the leaves. Introduce the predatory mite Phytoseiulus persimilis as soon as you see speckling.
Clouds of small white insects fly up when the plant is touched; leaves sticky and sooty
Glasshouse whitefly
Hang yellow sticky traps to spot them early and introduce the parasitic wasp Encarsia formosa from late spring, before numbers build.
Leaves mottled yellow and green, puckered and stunted; fruit small, pitted and bitter
Cucumber mosaic virus, carried by aphids and on hands and knives
There is no cure. Pull and bin the plant, wash hands and tools, deal with aphids promptly and grow a resistant variety.
Stem turns soft and brown at soil level and the whole plant wilts
Stem and root rots in cold, wet compost
Plant on a slight mound so water drains away from the stem, water around the plant rather than onto it, use tepid water under glass and fresh compost each year.
Small fruits turn yellow from the tip and shrivel before they develop
The plant is carrying more fruit than it can feed, often after cold nights or a check to the roots
Remove the withered fruitlets, keep watering and feeding steady, and the next flush will set normally. On young plants take off the first few fruits so the plant builds leaf first.
Harvest and rotation
Harvest and storage
Cut greenhouse types at 25 to 30 cm, outdoor ridge types at 15 to 20 cm, 10 to 12 weeks from sowing, while the end is still rounded; use a knife and check every 2 days, as fruit left on stops the plant. A greenhouse plant gives 15 to 25 fruit, an outdoor one 8 to 12. They keep a week in the fridge; small ridge types pickle well.
Rotation and companions
Rotation: cucurbit group with courgette, squash and melon, 3-year gap outdoors; change greenhouse border soil or use fresh growbags every year.
Good to knowTrain up supports; on all-female greenhouse types remove the occasional male flower (small, no fruit behind it) to avoid bitter, seedy fruit.
Growing cucumbers in pots
Cucumbers crop very well in pots, and under glass a pot is better than tired border soil. Give each plant a 30 cm pot (about 15 litres) of fresh peat-free multipurpose compost, or grow two to a growbag, and fix the string or cane before planting. A plant in full leaf in July can drink 3 to 4 litres a day, so check morning and evening; a saucer helps in hot weather. For a patio, a ridge type such as Marketmore up a 1.5 m wigwam against a warm wall is the reliable choice.
Cucumbers: common questions
Can you grow cucumbers outside in the UK?
Yes, if you grow an outdoor ridge variety such as Marketmore in a warm, sheltered, sunny spot. Sow indoors in late April, plant out in early June once nights stay above 12 °C, and train the plant up a trellis. Long greenhouse varieties rarely do well outside.
Should I remove male flowers from cucumbers?
Only on greenhouse varieties that are not all-female, where pollinated fruit turns bitter and seedy. All-female types produce almost no male flowers. On outdoor ridge cucumbers leave the male flowers alone, because those plants need pollinating to set fruit.
Why are my small cucumbers turning yellow and dying?
The plant has set more fruit than it can support, so it sheds the youngest. Cold nights, dry compost and hunger all make it worse. Pick off the yellow fruitlets, keep the watering steady, top-dress if one is due, and the plant will set again within a fortnight.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.