Cucumis sativus

Cucumbers come in two kinds that need opposite treatment at flowering: remove the male flowers on greenhouse types, leave them on outdoor ones. In Scotland, cover is often what separates a marginal harvest from a reliable one.

Under glass or in a polytunnel a cucumber is one of the most productive plants you can put in a small space. Outdoors in the open the crop depends much more on the weather.

Choosing a type

Greenhouse (indoor) varieties are grown under glass, in a polytunnel or in a coldframe, and crop from mid-summer to mid-autumn; most are all-female varieties, bred so that the plant sets no seed. Outdoor (ridge) varieties suit a sunny, sheltered spot and have a shorter, more weather-dependent season. Mini and gherkin types have smaller fruit. The type you choose decides your sowing calendar, your spacing and what you do at flowering time.

Preparing the ground

Dig in two bucketfuls of garden compost or well-rotted manure a few weeks before planting, or mulchA layer of material spread over the soil around plants to suppress weeds, retain moisture, and improve soil structure as it breaks down. Full definition → the surface for a no-digA growing method that avoids turning the soil over, building fertility instead by adding organic matter on the surface. Full definition → bed. Outdoor ridge cucumbers do better on a mounded ridge, which helps shed excess water and avoids the waterlogging that root rot needs. In containers, use a pot at least 30cm wide and deep, or a standard growing bag with two plants.

Sowing

GraftedJoining a chosen fruiting variety onto a separate rootstock, so the tree grows the fruit of one plant on the roots of another. Full definition → plants are an alternative to sowing seed: they are more vigorous and more resistant to soil-borne disease, but cost more and come in a limited choice of varieties. Grafted Vegetable Plants in Scotland → covers when they are worth the extra cost.

Sow indoors: mid-February to mid-March in a heated greenhouse, or April in an unheated greenhouse, polytunnel or coldframe; plants for outdoors can be sown indoors from late April. Sow one seed on its side, 1-2cm deep, in a 10cm pot at around 20-21°C. GerminationA seed sprouting: breaking dormancy and putting out its first root and shoot, given the right warmth and moisture. Full definition → takes a week or two; keep seedlings warm, well lit and watered, and move them to their final position after about a month, once growing strongly.

Outdoor varieties can also be sown direct, late May or early June, three seeds to a station, thinned to the strongest seedling, and covered with clochesA small, portable clear cover placed over an individual plant or short row to trap warmth and keep off wind, rain and pests. Full definition → or fleeceA lightweight, breathable fabric laid or draped over plants to trap a little warmth and keep off frost, wind and some flying pests. Full definition →.

Planting CalendarTime cucumbers around the 12°C thresholdGreenhouse from late May, outdoor only once temperatures are reliably above 12°C.
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Planting out

Move greenhouse cucumbers to their final position from late May (late March if the greenhouse is heated). Harden outdoor plants off first, then plant them out from early June, once local temperatures are reliably above 12°C. That often comes later and less reliably in Scotland than in milder parts of the UK, so treat early June as the earliest realistic date rather than the target, and lean on a polytunnel or unheated greenhouse wherever one is available.

Spacing depends on how you grow them: 30cm apart for ground-planted cucumbers (RHS), while Gardener's World splits it by method: about 60cm apart for a greenhouse plant trained up a support, 45cm for a trained outdoor plant, and 90cm if you let an outdoor plant sprawl. Teagasc allows roughly 2.5 square metres per sprawling ridge plant. Water well before and after planting, firm gently, and watch for slugs straight away.

Supports

Growing vertically keeps fruit clean and saves ground space. In a greenhouse, train the main stem up a tall bamboo cane or vertical wire/string reaching the roof. Outdoors, use a wigwam of canes, netting on upright stakes, or a trellis against a wall or fence. If you'd rather let a plant trail on the ground, lay a weed-suppressing membraneA permeable fabric laid over soil to block weeds while still letting water and air through, often planted through with holes cut for each plant. Full definition → underneath first to keep the fruit clean and stop it rotting where it touches wet soil.

Growing Up on an Exposed Scottish Plot → covers which structures hold up in wind, and how to anchor a tall support properly.

Varieties

Carmen and Marketmore carry the RHS Award of Garden Merit on their own plant pages, a UK-wide award rather than a Scottish one. Lili is listed with the AGMThe RHS's Award of Garden Merit: a UK-wide trials award for reliable performance, not a Scotland-specific recommendation. Full definition → in the RHS growing guide, but its plant page shows no award.

'Emilie', 'Mini Munch' and 'Delistar' are also listed with AGM in the RHS guide, none carrying a Scotland-relevant trait beyond the three picks below. Gardener's World also names F1The first-generation offspring of two specific, deliberately chosen parent plants, bred for a predictable, uniform result but not worth saving seed from. Full definition → Bella, which it says can be grown in an unheated greenhouse and has good tolerance to powdery mildew, though it has no RHS listing.

★ Our pick for Scotland

CarmenAGM

Greenhouse, long straight fruit, good disease resistance

High-yielding greenhouse variety with good disease resistance.

Why this one: A high-yielding greenhouse cucumber with long, straight, mild-flavoured fruit and good disease resistance, best grown under glass. It may still be susceptible to cucumber mosaic virus and powdery mildew, so water carefully and keep an eye on the leaves.

Also worth considering

MarketmoreAGM

Outdoor/ridge, medium fruit, dark green

The RHS's outdoor AGM pick, also named by Gardener's World as a ridge cucumber with short, dark fruit.

Lili

Greenhouse/outdoor, predominantly female flowers, reliable crop of large fruit

Suits an unheated greenhouse or outdoors in warmer areas, so one variety covers a polytunnel and open ground where the 12°C outdoor-planting threshold is unreliable. Predominantly female flowers mean less male-flower-spotting to do. It is listed with the AGM in the RHS growing guide, but its plant page shows no award.

Best Cucumber Varieties for Scotland → compares all named cucumber varieties head-to-head, with the practical detail that doesn't fit in a summary card.

Care

Keep the soil or compost evenly moist; greenhouse and container plants may need watering daily in hot spells. Water at the base rather than over the leaves, ideally in the morning, to keep the leaves dry. Sinking an empty plant pot into the ground beside each plant and watering into that gets moisture to the roots directly. Mulch around the base with compost or well-rotted manure, leaving a gap right at the stem to avoid rot. Ground-planted cucumbers rarely need feeding unless the soil is poor; container plants do best fed every 10-14 days with a general liquid fertiliser, switching to a high-potash feed such as tomato food once flowering starts.

A watering can filling an empty pot sunk into the soil beside a cucumber plant, directing water straight to the roots
A pot sunk beside the plant sends water straight to the roots, not just the surface.

Pinching outRemoving the soft growing tip of a stem to stop upward growth and make the plant branch out sideways instead. Full definition →: on greenhouse plants, pinch out the growing point once it reaches the roof, pinch side-shoot tips two leaves beyond a female flower, and pinch flowerless side-shoots once they reach 60cm. On outdoor plants, pinch the growing tip once the plant has seven leaves, and pinch flowerless side-shoot tips at the same stage.

Male flowers: remove, or leave alone? This is the decision most worth double-checking. Greenhouse/all-female varieties must NOT be pollinated: remove any male flowers that appear, or the fruit turns bitter and full of seed. Outdoor/ridge varieties are the opposite: leave every flower alone, since insects pollinating both male and female flowers is necessary for fruit to develop. If an outdoor plant is under a cloche or frame, open it during the day so pollinators can reach the flowers.
Fingers removing a male cucumber flower on a plain stem from a greenhouse plant to prevent pollination
A male flower removed from a greenhouse cucumber, since pollination turns the fruit bitter.

In a greenhouse, raise humidity in hot weather by pouring a full watering can over the floor or path, keep the temperature between 18-25°C where you can, and use shading to stop it overheating.

Harvesting

Ripens from mid-summer to mid-autumn under cover, about 12 weeks after sowing, with a shorter outdoor season that depends on the weather. Mini cucumbers are ready at about 8cm long, small-fruited varieties around 15cm, and full-sized types at 20-25cm. Cut the stem cleanly with a sharp knife or secateurs rather than pulling, once fruit is uniformly green and firm with a slightly rounded tip. Check every few days, since fruit grows fast: left too long, cucumbers turn yellowish, bulbous and soft, and regular picking is what keeps the plant producing more.

Cucumbers are best eaten fresh, but will keep for a few days in the fridge.

Common problems

  • Slugs and snails damage seedlings, particularly in damp weather.
  • Powdery mildew shows as a white, dusty coating on leaves and can weaken plants; water carefully, and note that resistant varieties are available.
  • Glasshouse whitefly feeds on sap and excretes sticky honeydew that leads to sooty mould.
See more problems
  • Red spider mite causes mottled leaves and is a particular problem in greenhouses with low humidity.
  • Cucumber mosaic virus is one of the most common plant viruses, spread by aphids. It causes yellow mottling, distorted leaves and stunted growth, and affected plants should be destroyed rather than treated.
  • Root rot takes hold in waterlogged soil; a mounded ridge or free-drainingSoil that lets water pass through quickly rather than pooling, so roots aren't sitting in wet ground after rain. Full definition → site for outdoor plants helps avoid it.
Garden MythsWhat's true about growing cucumbers?Every common claim checked: what holds up, what the sources argue over, and what has been tested and found false.
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Common questions

Should I remove the male flowers from my cucumber plant?

Depends on the type: remove any male flowers on a greenhouse/all-female variety, since pollination makes the fruit bitter, but leave every flower alone on an outdoor variety, which needs insect pollination to fruit at all. See also: Cucumber Myths →

Why is my cucumber bitter and full of seeds?

Often a greenhouse all-female variety that has been pollinated: check for and remove any male flowers straight away, since on this type pollination can make the fruit bitter. See also: Cucumber Myths →

Can I grow cucumbers outdoors in Scotland without any cover?

You can, but the 12°C threshold for planting out is often later and less reliable here than in milder parts of the UK. A polytunnel or unheated greenhouse makes it a far safer crop.

Is cucumber spacing the same whether I train it up a support or let it sprawl?

No. Gardener's World gives about 60cm for a trained plant under cover, 45cm for a trained outdoor plant and 90cm for a sprawling one, and Teagasc gives a sprawling outdoor ridge plant about 2.5 square metres. The RHS figure for ground-planted cucumbers is a single 30cm. See also: Cucumber Myths →

More on cucumbers

Sources

Show the 3 sources
  • RHS: greenhouse vs outdoor/ridge distinction, soil prep, sowing method and temperature, transplant timing and the 12C outdoor threshold, spacing, supports, watering, mulching, feeding, pinching out for both types, the critical male-flower-removal-vs-pollination distinction between greenhouse and outdoor types, harvesting method and fruit-size guide, six named AGM varieties, powdery mildew, red spider mite, cucumber mosaic virus, whitefly, slug risk
  • BBC Gardeners' World: greenhouse/outdoor sowing calendar and the male-flower-removal rule; spacing broken down by growing method (60cm greenhouse, 45cm outdoor trained, 90cm outdoor sprawling) that RHS states only as a single 30cm figure; supplies a harvest-timing figure in weeks (about 12) that RHS doesn't give; names Marketmore and F1 Bella (unheated greenhouse, good tolerance to powdery mildew)
  • Teagasc: sowing timing, germination temperature and the pollination distinction between glasshouse all-female and outdoor ridge types; outdoor ridge spacing as an area figure (2.5 square metres per plant) rather than linear spacing; adds ridging as a specific outdoor soil-prep step against waterlogging, and precise indoor pruning detail (leaving the first 100cm of stem bare, side branches stopped 30cm from the ground)