There is plenty of confusing and misleading information about the best times and methods for sowing and growing cucumbers; this is similar for many other vegetables. In publications that I feel should know better, I often see sowing dates advised for cucumbers as February or March.

Please save yourselves a lot of trouble by ignoring such comments. Your plants would be spindly/leggy for lack of light, then too large before it’s warm enough to transplant them. You would have a lot of potting, watering and training to undertake, even before they are in the ground.

• Sow in April, or mid-spring.
• Outside, sow in late spring or early summer – in temperate climates, the later date is better.
• Seeds germinate in four to seven days, depending on the warmth and age of seeds.

Sowing conditions

Cucumber seedlings like it warm, and not too wet around the roots. You can so easily lose seedlings from overwatering – they ‘damp off’ by collapsing, literally. The stem rots from an excess of moisture.

At least damping off is rare when the conditions are warm and bright, another reason for sowing later.

• You can germinate seeds in the warmth of a cupboard because they do not need light for germination.
• Remove them as soon as you see any leaf, and keep growing them warm but in as full light as possible.

Sowing method

Seeds can simply be laid flat on the surface of a tray or module. Not a pot, because seeds and seedlings don’t need lots of compost, otherwise there is too much moisture around their little roots and they may damp off.

I recommend 3–5 cm/1.5–2 in diameter modules, with one seed per cell. Potting on then happens in two weeks time, without any root disturbance.

• The key point is that roots need air as well as moisture.
• More problems are caused by overwatering than under-watering.
• Even though cucumbers are famous for being fast-growing and moisture-loving plants, at germination and the small seedling stage they do not need much water.

Pot on?

Two weeks after sowing, when seedlings look strong, push up a module to check its compost and ensure that it’s not too tight with roots. Also check that seedlings have enough light because, if crowding close together, their stems grow long and thin.

Before that can happen, push up the module rootball and pop it into a 7 cm/3 in pot of multipurpose potting compost. Do not use soil because it would drain less freely and holds fewer nutrients.

After another week or so, and if your growing space is not yet ready for transplants, tap out the rootball from the 7 cm/3 in pot and pop it into a 10 cm/4 in pot. Then fill compost on top of the rootball, which buries the stem to give stability.

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1. Cordon cucumbers under cover

Soil preparation is the same as for any other vegetables. Spread compost in spring, after clearing the winter vegetables and before planting cucumbers, tomatoes, aubergines and so forth.

• Apply 5 cm/2 in of your finest compost, the most mature. Do not sieve it. This keeps soil in good heart for a whole year of cropping, without a need to feed.
• On sand and chalk soils, add 2 cm/1 in of extra compost to hold moisture and food for plants.
• If you want even bigger harvests than this soil treatment provides, some feeding is possible in the summer.

2. Ridge cucumbers outdoors

Transplant in the same way, except that they don’t need a support string.

Transplant size and time

Plants can be 20–30 cm/8–12 in high, preferably of a size that they have two true leaves.

Cucumber plants at transplant size have a firm and fibrous stem, part of which goes below soil level.

Transplant method

Make a hole with a trowel just a little wider than the rootball, and 5 cm/2 in deeper. Place a knotted end of your support string at the bottom of this hole, then put the rootball on top of it. Push firmly downwards, but without harming the fragile root structure.

It’s probable that compost that has been around the plant roots in the pot is partly dry, which is fine. Now that plants are in the soil, you can water more. Give a good dose at this point to make sure that all the compost around the roots is moist, and in contact with the soil which is also moist.

Spacing

The minimum is 60 cm/24 in, but plants can be 90 cm/36 in apart, especially under cover where they crop for a long season.

• In my polytunnel the middle beds are 1.25 m/4.2 ft wide and I grow two rows along them, as in the photos below.
• Outdoors, on a bed of 1.5 m/5 ft wide, I set two ridge plants across the bed.

Interplanting

This wide spacing allows for some interplanting to happen, although it’s actually not a long time before cucumber leaves cover all of the empty space between them.

One method is to set cucumbers into the remains of a harvest that will soon complete, such as the carrots you see below. After two to three weeks, once the previous vegetable is all harvested, you can spread the annual compost.

I have had success with dwarf French beans as an under plant to cucumbers. Sow the beans at the same time as your cucumbers, and transplant in the spaces in the row between them. There is not a huge harvest of beans, but the plants coexist happily for a good use of space, with the big advantage of a harvest two weeks earlier than that from bean plants outside.

Between and around cucumber plants, you can transplant French marigolds or other flowers that will not grow tall. I avoid large flower plants and also calendulas. Small is beautiful, and the seeds of dwarf marigolds are frost tender, so they do not become a ‘weed’.

• The marigolds secrete limonene which deters aphids; they also give soil cover and look gorgeous.

Support

Ridge cucumbers do not need support.

Under cover, the string that you buried in the planting hole of each cordon cucumber plant can be tied to whatever you have above. We use a wire which runs over the top of polytunnel support bars, or through greenhouse rafters. A 4 mm/0.2 in diameter wire is strong enough to support a lot of weight.

• When tying a string to the wire, don’t make it too tight because it will then be difficult to twist the plant stems around – it needs to be firm but not taut.
• Wait until plants have grown 35–40 cm/14–16 in tall before your first gentle rotation of the main stem around the string.
• I twist the stems clockwise when looking from above, but I think it works either way.

Repeat your wrapping of the main stem around its string, twice a week. Do it firmly enough that stems are quite tight around the string, otherwise a plant stem may later slide downwards when there is the weight of cucumbers on it. See below for how to support and train older cordon plants.

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I find that watering by hand gives better growth than using drip lines. Perhaps because the bed area is mostly not watered by a drip line, which actually waters only a very small area. This reduces biological activity and nutrient availability in quite a bit of the surface.

With overhead watering it’s possible to wet most of the surface. However, this usually also wets the leaves which can result in downy mildew by late summer.

1. For the first two weeks, mainly water the area just around your transplants.
2. Thereafter, water the whole bed, which will encourage roots to explore further.
3. About one month after transplanting, start to water paths as well because cucumber roots can then find moisture and food in the pathways.

How often

During late spring to early summer, I occasionally suffer problems on hot afternoons with cucumber plants that are under cover. The sun is so strong that it causes leaves to transpire more moisture than their still-developing root structure can quickly find. This causes some dieback in the main growing point, which can even stop the plant from growing any more.

Lessons from this are:

• When plants are still small, and the day brings a lot of hot sunshine, water cucumbers in the midday sun so that their still-developing roots continue to find enough moisture.
• It’s fine to wet the leaves in bright sunshine, whatever you may hear elsewhere, and on a hot afternoon this is the quickest way to help wilting plants.
• In hot climates and also on light soils, mulch the surface after transplanting with old grass, straw, seaweed etc.

How much

Give an increasing amount of water as plants grow, and above all as fruits develop. Cucumbers are 95% water and any moisture deficit will reduce the juiciness and size of fruits. In high summer, when plants are fruiting strongly and the sun is hot, water a moderate amount every day.

• In hot weather, cucumbers plus celery and lettuce are the three vegetables for which I recommend daily watering.
• Cordon cucumbers need a lot of water in summer, with so many leaves free to transpire.

Extra mulch to retain moisture

This is about laying something undecomposed on top of the surface compost. It’s worthwhile for hot and dry climates – see the photo above.

Cucumbers are like squash plants: both have wide spaces between each plant, which makes mulching easy and effective.

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How to judge readiness

Cucumbers are ready to pick at the stage you like, so pick one or two and see what you think! You are looking for the diameter to be nicely swollen without excessive fatness, the skin to be a little darker, and cucumbers to be a decent length.

• If you see any sign of fruits going yellow, or even just pale in colour, they are probably now over-ripe and old.
• The cucumbers we want and eat are unripe fruits. If allowed to grow beyond the normal eating stage, their skin goes hard and yellow, while each seed inside develops a husk.

How to pick

Use a sharp knife to cut the narrow stem between the plant and cucumber. Should you find yourself in the garden without a knife, rotate a cucumber three or four times, until the stem breaks.

When to pick and how often

In warm weather, say over 24 °C/75 °F in the afternoon, it’s worth checking for cucumbers every day, if you like them not too ripe. This is especially true for plants undercover, whereas outdoor cucumbers can often be picked every two or three days in warm weather.

A good time to harvest is early morning, so that your fruits are cool and then store better, should that be necessary. Picking at any time of day is possible.

Storing

Nature has given cucumbers a lovely wrapper of skin. They store for up to a week at temperatures below 15 °C/59 °F, and if you can keep them cooler they store for longer.

In commerce, cucumbers are sometimes wrapped in plastic to conserve moisture and keep them firm, with skin more glossy.

For home consumption this does not matter, it’s more a question of appearance. A  slightly limp cucumber is good to eat, it’s just less moist. Then, after about a week, the flavour is less sweet and the texture becomes drier.

Saving seed

Do not save seed from cucumbers of hybrid plants, because those seeds would grow random plants with few desirable fruits.

For open-pollinated varieties, cross-pollination is an issue. This never affects the flavour or quality of fruits, only the seeds inside them.

• If you are growing only one variety of cucumber, it’s safe to allow one fruit to ripen fully for seed.
• Pick in autumn when the skin is yellow and then bring inside – there is no rush to extract the seeds.
• When pale yellow and somewhat dry, cut the cucumber open and scoop out its seeds, then wash them and dry.

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Which pests are likely, and when

Aphids often arrive in spring, usually briefly and more on weak plants. Often they are greenhouse whitefly (Trialeurodes vaporariorum), and greenfly/peach aphid (Macrosiphum rosae).

It’s fine to tolerate a few aphids, and you can reduce their numbers in these three ways:

• Transplant at the correct time, not too early.
• Water correctly.
• Maintain soil biology and fertility, with no dig and compost mulch.

If worried by a profusion of aphids, which happens mostly in late spring, you can wash them off. Then in early summer you should notice predators arrive, such as hoverflies and ladybirds. From which time a population balance establishes – there are a few aphids, with a few predators. Don’t expect there to be no aphids at all.

Red spider mite (Tetranychus urticae) is a more worrying possibility.

These may multiply quickly in early summer and are then hard to control. High humidity reduces the likelihood of a major outbreak. However, an excess of humidity can cause other problems, such as downy mildew – see below.

You can buy predator insects (Phytoseiulus persimilis) – order by mid-spring. They are delivered by post, on leaves that also have a few red spider mites. Place them on cucumber leaves, following which a balance of pest and predator establishes for several plants, through the whole summer.

Two drawbacks are that the predators are expensive, and they don’t survive winter!

• As with so many pests and diseases, the best cure is prevention. I find that well-composted, no dig soil grows plants with less likelihood of spider mites.

Other difficulties

Two very different mildews are a problem – one is serious and the other less so. Both are the results of atmospheric conditions and leaf moisture levels, such that the spores do not affect random leaves. Nor do the spores survive in the soil or compost, in my experience. We compost all residues of damaged plants and, in the following season, do not notice any issues from doing this.

Powdery mildew (Podosphaera xanthii) occurs from midsummer – you notice bright white mildew on older, lower leaves. This is less of a worry than it looks, and does not prevent new growth. Prune the leaves as described above; you can then put them on the compost heap.

• Sunlight and low humidity levels reduce the powdery mildew.
• Water well, and at root level, to reduce powdery mildew.

Downy mildew (Peronospora sparsa) occurs on all leaves, including the important small ones of the main growing point. Hence it can kill plants in two to three weeks, unless dry sunshine returns.

It thrives in damp conditions and cooler nights, mostly after midsummer. We suffer it sometimes at the end of summer, when suddenly you see yellow areas on leaves, which turn brown as the mildew takes hold.

• When watering, don’t wet leaves.
• Outdoor cucumbers are at the mercy of prevailing weather conditions.
• Plants with a big infection of downy mildew are best removed to the compost heap. Then replant the ground, if there is time before your next scheduled planting – see the photo below.
• We put a lot of diseased material on the compost heaps in summer 2016 and used some of this compost in spring 2017, before planting cucumbers. In 2017 there was no downy mildew at any stage.

Cucumber mosaic virus is not too common. It causes stunted and deformed leaves, with distinctive yellow mosaic patterning. Flowering is reduced or non-existent, while any fruit that do appear are small, pitted, hard and inedible.

• My approach is to put any virus-infected plants on the compost heap, but this is not officially recommended. Virus is mostly seed-borne and should not happen too often.