How to Grow Cucumbers: Heat, Water, and Bitter Fruit

Two things end most cucumber crops, and both are avoidable. Cold soil at the start, which rots seed and stalls transplants, and inconsistent water later, which makes the fruit bitter and misshapen.

Everything else about cucumbers is fairly forgiving.

Bush or vining

The packet says which, and it decides everything downstream.

There is also a split by use: slicing cucumbers for eating fresh, pickling types which are shorter and blockier, and burpless or seedless greenhouse varieties, which are thin-skinned and usually parthenocarpic — they set fruit without pollination, which matters under cover where bees cannot reach.

Timing and sowing

Soil temperature is the gate. Above 60°F to germinate at all, 70°F to do it well. Below that, seed sits and rots.

Cucumbers dislike root disturbance, so sow direct where the season allows. If you must start indoors, sow only about three weeks before planting out, use biodegradable pots, and plant the whole pot — a root-bound cucumber seedling sulks for weeks after transplanting and is usually overtaken by one sown later straight into the ground.

Sow an inch deep, two or three seeds per station, thinning to the strongest.

Soil, water and mulch

Cucumbers are hungry and thirsty. Dig in plenty of compost or well-rotted manure before planting.

Then the part that decides fruit quality: water deeply and consistently. An inch or two a week, delivered as two or three deep soakings rather than a daily sprinkle, always at the base and ideally in the morning.

Mulch two to three inches deep. This is what holds the moisture steady between waterings, and steadiness is the whole point.

Support

Vining cucumbers grown up a trellis give straighter fruit, far less powdery mildew because the foliage dries within an hour of rain, no rot where fruit sat on wet soil, and about a fifth of the footprint.

Put the structure in at planting. Driving stakes beside an established cucumber spears the roots, and cucumber stems are brittle enough that lifting a sprawling vine onto a support breaks them. Cucumber trellis designs covers the shapes that work.

Male flowers, female flowers, and no fruit

This is the most common panic, and usually nothing is wrong.

Cucumbers produce male flowers first, often for one to two weeks before any females appear, and males typically outnumber females by around three to one all season. Male flowers sit on a plain thin stalk. Female flowers have a tiny immature cucumber behind the petals — once you have seen it, it is obvious.

So: flowers with no fruit for the first fortnight is the plant working normally.

If female flowers form and then shrivel and drop, that is a pollination problem. Hand-pollinate by brushing pollen from a male flower onto the centre of a female with a small paintbrush, or plant flowers nearby to bring bees in — the logic in plants that repel mosquitoes works in reverse here.

Very high temperatures also cause flower drop, and there is nothing to do but wait.

Feeding

Balanced feed until the first fruit sets, then switch to high potassium — the same principle as feeding tomatoes. Nitrogen after fruiting starts gives you an enormous vine carrying very little.

Containers need feeding far more often, because nutrients wash out with every watering. See growing cucumbers in containers.

Picking

Pick at the size on the packet, every day or two. In peak season a cucumber can go from ready to oversized in 48 hours.

The reason to be strict about it: a single fruit left to mature and set seed signals the plant that it has reproduced, and production slows or stops. Consistent picking is what keeps a plant cropping for weeks rather than days.

Cut with snips rather than pulling, leaving a short stub of stem.

The problems worth recognising

White powdery coating on leaves — powdery mildew. Airflow and vertical growing prevent most of it.

Yellow, mottled leaves and stunted growth — cucumber mosaic virus, spread by aphids. No cure; remove the plant and control aphids.

Sudden wilting of a healthy plant — bacterial wilt, spread by cucumber beetles. Also incurable. Remove it, and manage the beetles next season.

Misshapen, pinched fruit — incomplete pollination, or inconsistent water.

Hollow centres — erratic watering again, or over-large fruit left too long.