Cucumber

About

Cucumbers come in two kinds that want quite different treatment, and buying the wrong one for your situation causes most of the trouble people have with them.

Greenhouse cucumbers are the long smooth ones. Modern varieties are all-female and set fruit without pollination, which is why they have no seeds worth mentioning. They need warmth and shelter and they crop heavily.

Ridge cucumbers are the shorter, rougher, often prickly outdoor types. They need insects to pollinate them, they tolerate a British summer without glass, and they taste more strongly of cucumber.

The male flower rule that circulates as universal advice applies to one of these and not the other.

Appearance and character

A vine climbing by coiled tendrils, with large triangular lobed leaves that are rough and slightly bristly. Left to itself it trails across the ground; given support it climbs to 2 or 3 m.

Flowers are bright yellow and five-petalled. On most varieties male and female flowers appear separately on the same plant, and the female is easy to identify by the miniature cucumber behind the flower.

Fruit ranges from 8 cm pickling gherkins to 40 cm greenhouse types, in smooth, ridged, spined and warted skins. Yellow, white and round varieties exist, including the lemon cucumber, which looks nothing like a cucumber and tastes exactly like one.

The characteristic flavour and the cool texture both come from very high water content, at around 96 per cent.

Where it is from

South Asia, most probably the Himalayan foothills of northern India, where the wild ancestor still grows and where cultivation goes back at least three thousand years.

The plant is built for warm humid monsoon conditions with abundant water and rich soil, and every requirement follows from that. It has no drought tolerance worth the name, no frost tolerance at all, and an appetite for water and nutrients that surprises people used to easier crops.

Cucumbers reached Europe via Greece and Rome, where Tiberius reportedly demanded them year round and had them grown in wheeled frames moved to follow the sun.

How it grows

A tender annual. Seed germinates in warmth at around 20 deg C in under a week, and the plant crops within twelve weeks of sowing.

Sow seed on its edge rather than flat, which reduces the chance of rot, in individual pots to avoid disturbing the roots later. Cucumbers dislike transplanting and a checked plant sulks for weeks.

Greenhouse types are trained up a single vertical string or cane, with the growing tip pinched out at the roof, and side shoots stopped two leaves beyond each developing fruit. Ridge types are left to sprawl or given netting, and the main shoot is pinched after six or seven leaves to encourage branching.

Picking drives production. A cucumber left to mature fully signals to the plant that it has reproduced, and cropping slows or stops. Cut fruit while it is firm and before it fattens.

Fruit forms fastest in warm weather, and a plant can go from flower to picking size in about ten days in July.

Through the seasons

Spring is sowing. Greenhouse varieties from March in a heated propagator, ridge varieties from late April indoors or late May outdoors. Plant out only once nights are reliably above 12 deg C.

Summer is the crop. Water daily under glass, feed weekly once fruit sets, train and pinch, and pick every two or three days. Shade the greenhouse glass lightly in midsummer, since intense direct sun scorches the leaves.

Late summer brings powdery mildew, which usually ends the season. Keep plants watered and ventilated to delay it.

Autumn finishes them. Clear the plants once cropping stops, and remove all debris from the greenhouse, since pests overwinter in it.

Care difficulty

Moderate. Cucumbers are hungry, thirsty and fussy about temperature, and none of that is difficult so much as demanding of consistency.

Water is the main thing. A cucumber plant in a greenhouse in July may need watering twice a day, and any check produces bitter, misshapen fruit.

Warmth is the second. These plants stop growing below 15 deg C, and a cold week in June sets them back further than the same week would set back a courgette.

The third is knowing your variety, since the pruning and pollination rules differ completely between greenhouse and ridge types.

Watering

Water very frequently and consistently. This is one of the thirstiest crops in a British garden.

Under glass in hot weather, daily is the minimum and twice daily is common. Outdoors, water thoroughly every two or three days in dry spells.

Use tepid water rather than cold. Cucumbers are tropical and cold water at the roots checks growth, which matters most under glass where the difference is greatest.

Water at the base and keep the leaves dry, since wet foliage encourages powdery mildew.

Irregular watering is the direct cause of bitter and misshapen fruit. Steady moisture matters more than volume.

Mulch the soil to hold moisture, and damp down the greenhouse floor on hot days to raise humidity, which cucumbers like and red spider mite does not.

Warning signs, diseases and pests

Powdery mildew is close to inevitable by late summer. White powdery patches spread across the leaves and the plant declines. Water the roots well, ventilate generously, remove the worst leaves, and grow resistant varieties. A milk and water spray at one part in nine has some effect. Treat it as the natural end of the season rather than a failure.

Red spider mite is the greenhouse pest that ruins crops. Leaves become finely speckled and dull, then bronzed, with fine webbing between the stems. It thrives in hot dry air, so damping down the floor and misting suppress it. Biological control with Phytoseiulus persimilis works well.

Slugs and snails take young plants outdoors.

Whitefly cluster under the leaves and coat everything in sticky honeydew.

Cucumber mosaic virus mottles and distorts the leaves and stunts the plant. There is no cure, it is spread by aphids, and affected plants should be removed.

Bitter fruit has three causes, separated in the troubleshooting section.

Fruit that yellows and drops when small usually means the plant is short of water or has set more fruit than it can carry.

Growing environment

Full sun outdoors. Under glass, very intense midsummer sun scorches the large soft leaves, so light shading from June to August helps.

Warmth is the requirement that matters most. The productive range is 20 to 30 deg C, growth stalls below 15, and frost kills. In Britain, greenhouse and polytunnel crops are earlier, longer and far more reliable than outdoor ones.

Soil should be rich, moisture-retentive and free-draining, with plenty of well-rotted manure or compost dug in. Cucumbers are gross feeders and reward preparation.

Humidity suits them, which is the opposite of most greenhouse crops and the reason cucumbers and tomatoes are an awkward pairing under the same roof. Tomatoes want dry air; cucumbers want it damp.

Supports go in at planting. Vertical strings, netting or canes all work.

Feeding

Feed weekly with a high-potassium tomato fertiliser once the first fruit starts to swell. Container and growbag plants may need it twice weekly.

Prepare the bed with plenty of organic matter before planting, since a cucumber takes far more out of the soil than most vegetables.

Do not start feeding before fruit sets. Early nitrogen produces a mass of leaf.

Magnesium deficiency, showing as yellowing between the veins on older leaves, is common on heavily fed plants. Correct it with Epsom salts.

Troubleshooting

Bitter fruit. Three possible causes. Irregular watering or temperature stress is the commonest. On all-female greenhouse varieties, pollination by a stray male flower makes seedy bitter fruit, which is why those flowers are removed. And saved seed that has crossed with an ornamental gourd can produce dangerous levels of bitterness, so bin any strongly bitter fruit.

Should I remove the male flowers? Only on all-female greenhouse varieties. Ridge cucumbers grown outdoors need their male flowers to set fruit at all.

Misshapen or curved fruit. Uneven watering or poor pollination outdoors.

White powder on the leaves in August. Powdery mildew. Water the roots, ventilate, and accept the season is ending.

Speckled bronzed leaves with fine webbing. Red spider mite. Damp down the greenhouse and introduce biological control.

Small fruit yellowing and dropping off. Water shortage, or the plant is carrying more than it can support. Water more and thin the fruit.

Plant stalled and sulking after planting out. Cold, or root disturbance. Cucumbers hate both. Fleece it and wait for warmth.