How to grow cucumber

Buy fresh seed of a downy-mildew-resistant variety from a registered dealer, in a sealed, labelled packet. Downy mildew is cucumber's number-one killer, and a resistant variety is the cheapest protection you can buy against it.

Pick land that has not grown cucumber, pumpkin, melon, squash or watermelon for the last 2–3 years. These are all one family — the cucurbits (the cucumber family) — and growing them on the same ground season after season lets the beetles and diseases that attack them build up in the soil. Moving to a fresh spot breaks that cycle.

Choose a warm, sunny, well-drained spot. Cucumber roots rot in soggy ground — if water pools there after rain, build raised beds or ridges so it drains away.

Dig the bed loose and deep — about a spade's depth (20–30 cm) — and break up the clods, so roots and water move down easily.

Work in plenty of well-rotted manure or compost — dark, crumbly, no strong smell. It feeds the soil all season and helps it hold the even moisture cucumber needs. Fresh manure burns young roots and carries weed seeds, so use it only when it is well rotted. Your recommendation gives the amount for your field.

Put the trellis up in the week before sowing, or on sowing day — while you can still walk the bed freely. Once the vines run, it is too late to build around them.

Set strong posts down each row and run wire or strong string between them, about 1.5–2 m tall — head height — because cucumber climbs fast and tall.

Add strings or netting for the vines to grip. Cucumber climbs with little curly threads called tendrils, and they need something thin to grab onto.

Make it sturdy. A vine loaded with fruit and wet leaves is heavy, and a weak trellis that collapses in a storm takes the whole crop down with it.

Sow only when the soil is warm — at least 13 °C. Cold, wet soil rots the seed before it can sprout. If the mornings are still cold, wait a week — cucumber grows so fast it soon catches up.

Mark your stations at the final spacing: rows about 1.5 m apart (roughly one and a half strides) with stations about 40 cm apart (two hand-spans) along the row. This wide spacing gives every vine sun and moving air — crowded vines get mildew.

Drop 2–3 seeds per station, about 2–3 cm deep — as deep as the top joint of your finger, no deeper. Cucumber seed is small, and pushed in too deep it may never reach the surface.

Cover and firm the soil gently so each seed sits snug in moist earth, then keep the bed evenly moist (never soaked) until the seedlings appear — this takes about 4–10 days.

You sow a few seeds per station as insurance against gaps; you will thin down to the single strongest plant once they are up (see the thinning task).

Thin about 10–15 days after sowing, once the seedlings have their first one or two true leaves and you can see which is strongest.

At each station, keep the single healthiest, sturdiest seedling and remove the rest.

Snip or pinch the extras off at ground level — don't pull them out, or you tear the roots of the one you are keeping.

Water gently afterwards to settle the soil back around the plant you kept.

Walk the bed twice a week from about 5 days after sowing, looking closely at the young seedlings — especially the soft new leaves and the base of each stem.

Cucumber beetles: look for small beetles — about the size of a grain of rice — that are yellow-green and either striped or spotted, on the leaves and stems, and ragged round holes chewed in the young leaves. They also spread a wilt disease, so don't shrug off even a few.

Cutworms: look for seedlings cut clean off at ground level, lying on the soil in the morning. Scratch the soil near a cut plant to find the fat, grey, curled-up caterpillar that did it.

Damping-off: look for seedlings that suddenly flop over with a thin, dark, water-soaked pinch at the base of the stem, usually in wet patches, with whole groups collapsing together.

Write down what you find and where. If beetles or cutworms are taking plants, act now (open the matching pest guide). If seedlings are damping off, ease off the watering and improve drainage — it thrives in soggy soil.

Start once the vines begin to run, about 2 weeks after sowing, and keep at it every 5–7 days — cucumber grows fast and gets away from you quickly.

Lead the main vine up the trellis and tie it loosely at intervals with soft string, in a loose figure-of-eight so the string cushions the stem instead of cutting into it.

Guide the curly tendrils (the little grabbing threads) onto the strings or wire so the vine can hold its own weight up off the ground.

Pinch out the small side-shoots — the laterals, the branches growing out low on the main vine. Opening up the base lets air through and keeps the lowest fruit off the ground.

Never let the vine flop back onto the soil — sprawling leaves stay wet and are the first to catch mildew.

Feed about 3–4 weeks after sowing, once the vine is running well but before it is covered in flowers.

Put the nitrogen your recommendation gives in a band — a line about a hand-span (20 cm) to the side of the plants — never on the stems or over the roots, where it burns.

Feed onto moist soil (after watering or light rain) and water it in, so it soaks down to the roots instead of gassing away into the air.

Keep the fertiliser off the leaves — grains on wet leaves scorch them. Wash your hands afterwards, and keep fertiliser away from food, water and children.

Water every 2–3 days from about 2 weeks after sowing onward — more often in heat or on sandy soil that dries fast. Aim for roughly 25 mm of water a week (a good soaking, not a daily splash).

Keep the soil evenly moist down to the roots — never bone-dry, never waterlogged. Push a finger in, and water before the top few centimetres go completely dry.

Water at the base of the plant (drip, or a can at the roots), not over the top — wet leaves invite downy mildew.

Water in the cool of the morning so the plant goes into the heat of the day full, and the leaves dry off quickly.

Walk the crop twice a week and turn the leaves over — most trouble starts on the underside.

Downy mildew (the big one): look for angular yellow patches on top of the leaf, boxed in by the veins so they look square rather than round. Turn the leaf over and in damp weather you may see a grey-purple fuzz underneath. It spreads upward from the older leaves — act at the very first patch.

Aphids: look for clusters of tiny soft green or black insects on the growing tips and leaf undersides, sticky leaves, and curled new growth. They also carry virus, so don't let them build up.

Whitefly: shake a plant — if a cloud of tiny white flies lifts off, you have whitefly. They cluster under the leaves and, like aphids, spread virus.

Red spider mite (in hot, dry spells): the leaves look finely speckled and dusty or bronzed, with fine webbing on the undersides and growing tips. The mites themselves are almost too small to see.

Cucumber mosaic virus: look for mottled light-and-dark (mosaic) leaves, puckered and distorted, on stunted plants. There is no cure — pull out and remove badly affected plants (this is called roguing) so aphids don't carry the virus to the rest.

Write down what you find. At the first sign of downy mildew, protect the crop (see the tips); for aphids, whitefly and mites, act while their numbers are still low.

From the first flowers, learn to tell them apart: male flowers sit on a thin stalk and open first; female flowers have a tiny cucumber swelling behind the petals. Bees must move pollen from the male to the female.

Do not spray insecticide on or near open flowers, and never in the morning bee hours when the bees are working. If a pest forces you to spray, do it late in the evening when the flowers are closing and the bees have gone home, and choose a bee-safe product.

Give bees a reason to visit — avoid blanket spraying and leave a little flowering growth nearby. More bee visits mean more, straighter fruit.

Some special greenhouse varieties set fruit without bees. If that is what you are growing you can skip the bee worry, but open-field crops depend on them.

Keep watering every 2–3 days right through flowering — never let the plants wilt, not even for one hot afternoon.

Keep the moisture even — the same steady damp each time. It is the wet-then-dry swings that ruin fruit, even more than being a little dry overall.

Water at the base, in the cool of the morning, so the leaves dry fast and the bees have dry flowers to work.

In real heat, water more often — hot, dry air empties the plant fastest at exactly the moment the fruit is trying to set.

Start picking about 6–7 weeks after sowing (around 45 days), then pick every 2–3 days — cucumbers double in size fast, and 'just right' turns into 'too old' in a couple of days.

Pick a fruit when it is firm, an even deep green, glossy-skinned, and at the size your variety should be — the seeds inside are still soft, just how you and the market want it.

Cut the fruit off with a knife or secateurs, leaving a short stalk. Don't yank it — pulling tears the vine, and the wound lets in disease.

Pick in the cool of the morning when the fruit is firm and full of water, and get it straight into the shade.

If it fails — the fruit has gone dull, is yellowing, or the belly has swollen (the seeds have hardened) — it is over-mature and bitter. Pick it off and throw it out (or compost it) anyway, because leaving it on the vine tells the plant to stop fruiting. Then pick more often — every 2 days — so it doesn't happen again.

From your first pickings (about 6 weeks after sowing), feed potassium (K) every 7–10 days through the harvest run — the amount is in your recommendation.

Band it or water it in at the base of the plants, on moist soil, and never onto wet leaves.

Keep the water steady and even alongside the feed — K and water work together to keep fruit firm and sweet. A thirsty plant cannot use the food you give it.

Wash your hands after handling fertiliser, and keep it away from food, water and children.

Keep walking the crop twice a week and turning leaves over, even while you are busy picking.

Downy mildew: the same angular yellow patches boxed in by the veins, with grey-purple fuzz underneath in damp weather, spreading up from the older leaves. Stay ahead of it with a protectant spray in warm, humid spells.

Powdery mildew (tell them apart): look for white, powdery, flour-like patches on top of the leaves. Downy is yellow-and-angular with fuzz underneath; powdery is white-and-dusty on top. It worsens in warm days with humid nights.

Fruit flies: look for small sting marks or oozing spots on the young fruit, and fruit that then rots or drops with maggots inside. Pick up and destroy any fallen or stung fruit so the maggots don't breed on.

Act at the first sign. When you spray: cover up, spray in the cool with the wind behind you, keep it off the fruit you will pick, and respect the pre-harvest interval — you are picking every few days, so mind the wait between spraying and picking.