Cucumis sativus, Cucurbitaceae family
From their origins in the Himalayan foothills, cucumbers are now grown and appreciated all over the world. There is a range of cucumber types and this lesson does not comprehensively cover all of them.
I concentrate on what some call the European or English cucumber. They grow best in warmth above about 21 °C/70 °F of an afternoon, and they need support.
Because they are grown vertically, I refer to them here as cordon cucumbers. The fruits have a soft skin and some seeds. They are harvested before the flesh becomes fibrous, when the cucumbers are 30–40 cm/12–16 in long.
Also in this lesson we look at ridge cucumbers. ‘Ridge’ refers to soil ridges on which the plants used to be grown. Their fruits are 12–20/5–8 cm long and often prickly, with a tougher skin compared to cordon cucumbers.
I describe growing them outside, because in climates with summer daytime temperatures above about 18 °C/64 °F this works really well. They can give a large harvest for just the period of high summer, before fading quickly in autumn.
Cucumbers can be sliced and diced for salads, and pickled to eat later. They come in a range of lengths, giving you many choices when choosing seed. The smallest are gherkins – prickly skinned mini cucumbers that pickle well.
- Another variation is fruits of the Mexican sour gherkin which are colloquially called ‘cucamelon’ (Melothria scabra). They are harvested at grape size and look like mini watermelons, hence the name.
I was disappointed when growing them because, from a large and leafy plant, the fruits were hard to find for just a small harvest. The flavour is not as described in the seed catalogue, being more sour than delicious, and fruits are best pickled.
- Something different and highly worthwhile, though not edible, is loofa, ‘vegetable sponge’ (Luffa aegyptiaca).
Grow them in the same way as cordon cucumbers, trained up a string – the photo below gives you an idea of harvest. One plant gave me four loofa of decent size, in the polytunnel. In a temperate climate I would not grow them outside, because they are of subtropical or tropical origin. See this YouTube video: Peeling a loofa.
- Days from seed to first harvest: 60–75.
Cucumber seeds sownCucumbers ready to harvestMid-spring, under cover – cordon varietiesUnder cover – early summer to early autumnMid to late spring under cover – ridge varietiesOutside – midsummer to very early autumnIn warm climates, early summerThrough late summer and autumn
- Best climate is warm or hot, humid, not too windy.
Why grow them
Feedback from my customers in the local town of Bruton suggests there is little flavour in cucumbers available in most supermarkets. My customers say things like, ‘These cucumbers taste just like they used to!’
Homegrown cucumbers have a fuller and richer flavour, and they are sweeter and juicier from being fresh.
- Plants are just so productive. From one sowing, you can harvest up to 10 kg/22 lb of cucumbers from one ridge plant, over a six to eight week period. While cordon plants crop for over three months, giving 30–40 large cucumbers.
Cucumbers you may be buying
Commercial growing is mass production, of high volumes at low prices. My ‘premium price’ of £1 wholesale for a long cordon cucumber, compares to the standard 70p wholesale price. For a small-scale producer, even £1 for a large and graded fruit barely covers the time needed to grow them, let alone the costs.
- Like most vegetables now, mass-produced cucumbers are grown in soil with not much life.
- Many are not even grown in soil. A common method for under cover production is hydroponic, with roots grown in media such as rock wool.
- Rock wool is manufactured from basalt rock and slag, a waste product from the production of steel and copper.
- A computer-controlled pump pushes water and a programmed, varying collection of nutrients to roots in the rock wool.
If you believe that food is just a collection of nutrients, then you won’t mind eating vegetables grown hydroponically. Many tomatoes are also grown in this way.
However, I suspect that a big deficiency in hydroponic harvests, which has not been mentioned until recently, is of microbes – tiny life organisms that vegetables automatically collect from the soil they grow in. Plus micronutrients and complex organic minerals that we know little or nothing about – partly because science cannot measure them, has not tried to, or does not mention – such as polyphenols and other antioxidants.
- With no dig soil, the count of healthy microbes is increased, which probably affects the flavour as well.
- Having said that, we do not notice consistent differences between flavours of vegetables from my dig and no dig beds. They both receive a decent dose of homemade compost every year!
Pattern of growth
All vegetables of the cucurbit family need a roughly equivalent amount of warmth to grow well. Therefore you can sow seeds of cucumber and squashes at the same time, from mid-spring under cover. Earlier sowings are possible but rarely worthwhile, in my experience.
Cucumbers have an amazing ability to convert warmth and moisture into rapid growth, even at Homeacres where afternoon temperatures outside are usually below 23 °C/73 °F.
- In high summer, cucumber plants make new leaves and fruit very rapidly, from mid-June to mid-August, the two hottest months of summer.
- Then in late summer we see more disease, and growth weakens through autumn until plants are killed by frost or sometimes downy mildew.
- Cordon plants under cover usually crop for a month longer than ridge plants outside.
Male and female flowers, bitterness
38 years ago I grew my first cordon cucumbers in a polytunnel. The variety was Telegraph which is open-pollinated, and grows both male and female flowers. Female flowers grow on the end of baby cucumbers.
Within two months there were some lovely fruits. I picked and ate the first one, feeling so proud, but it was disgusting and I spat it out. I was bitterly disappointed!
It turned out that my market garden mates were growing all-female hybrids (F1). With these varieties, bitterness is not an issue because they have almost no male flowers.
- The easiest way to avoid bitterness is not to grow open-pollinated cordon cucumbers such as Telegraph and Telegraph Improved.
- For ridge cucumbers you do not need to worry about the male flowers – they do not cause bitterness.
It puzzles me that all-female cordon plants do actually have some male flowers, therefore there is some pollination happening. It’s necessary, because without seeds the fruits do not develop correctly.
There are parthenocarpic varieties that do not need pollination, but most F1 hybrids do not fall into that category.
I could find out more by growing a plant of Telegraph again, but cannot discover whether, if I grew it among hybrid cucumbers, it might cause bitterness in them. Do insects fly from its male flowers to the hybrids’ female flowers, and affect flavour?
Sorry if I am confusing you, but there is little agreement about the best procedure.
A swollen stomach and wind can happen after eating cucumber – I have suffered this. I eat a lot of cucumber in the warm days of summer, and here is my method for making them more digestible:
- Prepare cucumber two hours before eating – cut off half of the skin or more, slice thinly and sprinkle with salt.
- A lot of liquid drains away.
- This softens and sweetens the cucumber and improves digestion.
Suitable for containers/shade?
Shade is not ideal because cucumber plants thrive in warmth and full light, nonetheless it is possible. Container growing certainly works, as long as you keep up with watering, and to some extent feeding, especially later on. The photos below give an idea of what you can do from one pot.
- Another option is to grow a ridge variety in a large pot, allowing enough space around the pot for the trailing stems and fruits.
Types and varieties
When choosing a variety, be careful that you select the type which is appropriate for your desired growing method.
- You can grow ridge cucumbers under cover, but they would be a lot of work to grow up a string.
- Cordon varieties have mostly been bred to grow in warmth and do not thrive outside.
Cordon vertical growth, under cover
In the UK at least, most current varieties of long, green cordon cucumbers are hybrid, apart from Telegraph.
Hybrid cordons are quicker and easier to grow. Breeding has given us varied fruit sizes, with excellent flavour. There are also lovely heirloom varieties for fruits of a different colour, size and shape.
- Carmen F1 is currently the best hybrid variety for a season-long output of fine cucumbers with top flavour.
- Mini Munch F1 grows fat fruits no longer than 10 cm/4 in – a lot of them.
- Passandra, Petita, Melen and Socrates (all F1) grow half-size, smooth-skinned cordon fruits, say 20 cm/8 in long.
- Burpless Tasty Green F1 grows long cucumbers claimed to be sweeter than other varieties, but I am not convinced about this, good as they are.
- Iznick F1 is something different, a small-fruited variety suitable for growing in a container
Ridge sprawling plants outside
- La Diva F1 cucumbers have an almost smooth skin and plants are prolific. You can also grow them as cordon.
- Tanya has great flavour – fruits are 20 cm/8 in, often with a tapering end and knobbly skin.
- Marketmore (sometimes called Marketmore 76) grows mostly straight fruit of 20 cm/8 in length, with knobbly skin.
- Crystal Lemon grows round, yellow fruits best picked small, say 5 cm/2 in diameter. Crystal Apple is similar. They can be cordon or ridge, more worthwhile as ridge. The terms lemon and apple relate to the fruits’ shape and size, not to their flavour.
- Cornichon de Paris needs picking regularly, when fruits are just 2.5 cm/1 in long. Best grown under cover and can be grown as a cordon.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
- For the first two weeks, mainly water the area just around your transplants.
- Thereafter, water the whole bed, which will encourage roots to explore further.
- About one month after transplanting, start to water paths as well because cucumber roots can then find moisture and food in the pathways.
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.
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.
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.
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.
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.
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.
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.
This is quick and simple. Use a knife or sharp trowel to cut through the main stem just below where it begins to root into the soil. By season’s end, there has usually been a steady weakening of the lower stems and root structure in the darker and cooler conditions, making them easier to remove.
Take the whole plant to your compost heap and either cut it into pieces or simply squash it down. It’s less important to cut up than, for example, broad beans and tomatoes, whose stems are tougher.
Following removal of under cover cucumbers, rake the surface level, water thoroughly, and then all is ready to transplant vegetables for cropping through winter.
Outdoors you may have already interplanted some vegetables. Otherwise you can follow cucumbers with any of spring onions, spring cabbage and garlic.