How to grow cucumbers

A cucumber left to sprawl covers a great deal of ground, sits its fruit on damp soil, hides them under leaves, and gets mildew from the bottom up because nothing dries. The same plant on a net, a trellis or a string takes roughly a quarter of the space, and every problem in that list gets smaller.

The fruit are cleaner and straighter, because a hanging cucumber grows down rather than curving around whatever it is lying against. They are far easier to find, which matters more than it sounds — a missed cucumber turns into a marrow and stops the plant. And air moves through the foliage, which delays mildew by weeks.

Cucumbers climb with tendrils and mostly do it themselves; they need a net or strings rather than a smooth pole. Put the support in at planting, not after.

The photograph below is a commercial polytunnel with plants trained up strings, which is the same principle at a larger scale. In a garden, a panel of wire mesh leant against a fence does the job.

Like all the cucurbits, cucumbers want warmth rather than merely the absence of frost. Our calendar puts direct sowing two weeks after the last frost, which is later than most packets suggest and produces better plants — seed in cold ground rots, and a seedling that is chilled sulks for a fortnight.

If you start them early, start them in something you can plant whole: a soil block, a coir pot, a paper pot. Cucumber roots resent disturbance more than most, and a plant tipped out of a plug and teased apart loses more time than it gained.

Feed the ground well before planting. This is a plant that builds a lot of vine in a short time and it is genuinely hungry.

Water steadily and generously — a cucumber is mostly water and a plant that dries out reliably makes bitter fruit. Mulching pays for itself here.

Most cucumbers carry separate male and female flowers, and an insect has to move pollen from one to the other. The female is the one with a tiny cucumber already formed behind the flower. If it is not pollinated, that tiny cucumber yellows, shrivels at the tip and drops — which looks like disease and is not.

Early in the season a plant often produces a run of male flowers first. That is normal and needs no action. In cool, wet or windy weather bees do not fly, which in a maritime climate is the commoner cause. You can hand-pollinate in the morning: pick a male flower, strip the petals, and dab it into an open female.

Then there is the case that catches people out. Many modern greenhouse varieties are all-female and parthenocarpic — they set fruit without pollination at all. For those, pollination is actively unwanted, because a pollinated fruit becomes seedy, swollen and bitter. That is why some seed packets tell you to keep bees away, which reads as bizarre advice until you know why.

So check the packet. If it says all-female, parthenocarpic or seedless, do not hand-pollinate and do consider growing it under cover. If it says nothing, assume it needs insects.

Bitterness in cucumber comes from cucurbitacins, compounds the plant produces under stress. The two reliable triggers are irregular water and temperature swings — a plant that dries out and is then soaked, or a hot spell after cool weather.

It concentrates at the stem end and just under the skin, which is why the traditional remedies work: cut an inch off the stem end, and peel it. If only part of a fruit is bitter, that is the part.

Prevention is the same short list as everything else on this page: steady water, mulch, and enough feeding that the plant is never checked.

Older varieties are markedly more prone than modern ones — many current varieties are bred low-cucurbitacin or burpless, and if bitterness is a recurring problem in your garden the simplest fix is a different variety rather than a different technique.

One cucumber left to mature tells the plant its work is finished and production slows sharply. In a sprawling plant under big leaves that happens easily, which is another argument for growing them where you can see them.

Pick every day or two at peak. A cucumber goes from perfect to overgrown in a couple of warm days, and an overgrown one is watery, seedy and dull.

Pick by size rather than by calendar — pickling varieties at two to four inches, slicers at six to eight, and any of them smaller if you like them that way. Nothing is lost by picking early.

Cut with a short stem rather than pulling. Pulling tears the vine, and cucumber vines are more brittle than they look.

Powdery mildew arrives late in the season and is effectively inevitable outdoors. White dusty patches on older leaves spread upward. Airflow delays it, base watering delays it, removing the worst leaves keeps the plant going — but by the time it takes hold you will usually have had the crop.

Downy mildew is the more serious one where it occurs: angular yellow patches bounded by leaf veins, with grey growth beneath in damp weather. It moves much faster than powdery mildew and resistant varieties are the real answer.

Cucumber beetles chew seedlings and flowers and, more importantly, transmit bacterial wilt — a plant that wilts suddenly and completely, without recovering overnight, has usually got it and cannot be saved. Row cover over young plants is the effective protection, but it has to come off at flowering unless the variety is parthenocarpic.

And the one that is not a problem: broad leaves flagging in full midday sun and recovering by evening. That is normal transpiration in a large-leaved plant. Only worry if it is still wilted in the morning.