Cucumber

Cucumis sativus is a tender annual vine in the cucurbit family, domesticated in South Asia, related to melons and squash and behaving like them: a big-leaved, rapidly running plant with hollow stems, coarse hairy leaves and tendrils that coil around anything thin. It sets fruit quickly and expects to keep setting, which is why a picked vine out-produces an unpicked one several times over.

Garden varieties fall into three overlapping kinds. Slicing cucumbers are the blocky, medium-thick-skinned fruits bred for the salad plate. Pickling types are smaller, crisper and thinner-skinned, bred to hold their shape in a brine, and they produce prolifically over several flushes. Burpless or English types are long, smooth, nearly seedless vines usually grown in a greenhouse or on a sunny trellis, with skin tender enough that fewer people find them disagreeable.

Cucumbers are the most cold-sensitive of the common summer vines, and they resent root disturbance. Sow directly in the prepared bed once all frost danger has passed and the soil is at least 65°F, ideally 70°F, at a depth of half an inch in firm, moist ground; germination takes three to ten days in warm soil and can take three weeks in cold, wet ground, and a seed that sits there often simply rots. In short-season climates, start three seeds in a cell or peat pot three weeks before that date and set them out with the roots intact, but do not expect the transplant to grow until the weather does.

Space generously or train upward. A hill of three plants needs four to six feet in every direction if the vines run on the ground. Trellised, single-stem plants go twelve inches apart in the row with a three- to four-foot aisle, which converts a sprawling fifteen-by-fifteen patch into a narrow fence. Dark plastic or a fabric mulch a week before sowing warms soil enough to plant early.

Give cucumbers the sunniest, most sheltered corner you have, six to eight hours of direct light, because shade produces thin, pale, slow vines, and wind tears big leaves off trellised plants. Soil should be loose, deep and loaded with compost, around pH 6.0 to 6.8; a cucumber is a heavy feeder that puts out a lot of topgrowth in a hurry, so work in a few inches of finished compost before sowing and top-dress it again midseason rather than relying on synthetic feed alone.

Then water like the fruit is mostly water, because it is. One to two inches a week at soil level, deep and frequent enough that the ground stays evenly damp, is the difference between sweet, straight fruit and bitter, curved, hollow-ended ones. Drought stress concentrates cucurbitacin, the compound that makes the skin and blossom end bitter, and it also stops fruit set entirely. Drip lines or soaker hoses under mulch do the job better than sprinklers, which wet the foliage and feed mildew.

Train vines onto something with thin, grabbable members: stock panel or cattle panel arched over the bed, a six-foot fence, or string hanging from an overhead trellis that the plants climb. Trellising lifts fruit off the ground for straight, clean, unblemished cucumbers, opens airflow that slows disease and turns a sprawling crop into one you can pick without finding it. Tie main stems loosely as they climb, and support heavy fruit with a loop of fabric so the stem does not tear; the vine's tendrils handle most of the climbing themselves.

Flowers come in an order that surprises new growers. A cucumber plant makes male blooms first, sometimes for a week or two before any female appears, and each female flower has an unmistakable tiny fruit at its base. Bees must carry pollen from male to female, so a vine that flowers but sets nothing usually lacked pollinators on the mornings the blossoms opened, not that it lacked flowers.

Check daily once fruit appears, and every other day at minimum through the flush. Slice-pick at six to eight inches for most slicers, two to four inches for picklers, before the skin dulls and the seeds swell: a cucumber left to grow big and yellow tells the plant its reproduction is finished, and production slows sharply, while a vine picked hard keeps making flowers and fruit for weeks. Cut the stem with pruners or a knife rather than twisting and pulling, which damages the brittle vine and the roots.

Harvest in the cool morning when fruit is firm and crisp, and get it into the shade fast. Cucumbers keep about a week in the crisper at 50 to 55°F; colder shelves and a cold car trunk pit the skin and leave water-soaked flesh, and they also go soft quickly beside ethylene-producing apples and tomatoes. Process pickles within a day of picking for the crispest results.

Late summer almost always brings powdery mildew, a white, talc-like coating that spreads over the leaves and quietly shuts the vine down. Prevention is worth more than any spray: grow resistant or tolerant varieties, space and trellis for airflow, water at the roots, and act at the first white spot by removing badly coated lower leaves and applying a labeled fungicide or a potassium-bicarbonate spray on a schedule. Downy mildew, angular leaf spot and aphids follow the same cultural logic of airflow, clean residue and rotation.

The most lethal pest is smaller than the damage suggests. Spotted and striped cucumber beetles chew seedlings and holes in leaves, and worse, they transmit bacterial wilt, which collapses a vigorous vine to the ground in two days. Floating row cover over young plants until the first female flowers open keeps beetle numbers low; remove it when pollination is needed. Bitter fruit is stress, not disease.