Cucumber Growing Masterclass

, written by Benedict Vanheems gb flag


Cucumbers are one of the most prolific vegetables you can grow – and a freshly picked garden cuke has to be the crunchiest, juiciest thing you’ll ever enjoy!

So let me share what I’ve learnt over the years, including when and how to start cucumbers, the best supports to use, the one thing you can do to guarantee vigorous plants, and my secrets to exceptional fruits.

What Type of Cucumber to Grow?

There’s a wealth of cucumbers to choose from: gherkin types whose smaller, firmer fruits hold up well to pickling; slicing cucumbers for salads; snacking cukes for the lunchbox; and quirky customers like lemon-shaped cukes, or even yellow ones!

Most varieties have a vining growth habit, but there are also compact, bushier types perfect for containers. There are cucumbers for greenhouse or tunnel-growing, and others for growing outside. Modern breeding has even given us varieties tolerant of cooler summers – just the job for those of us with decidedly iffy climates!

Here’s my first pro tip: pick a cucumber that makes growing it easy! Select varieties offering at least some resistance to common diseases like powdery mildew or cucumber mosaic virus. And secondly, opt for a parthenocarpic cucumber.

Female cucumber flower
Many cucumber varieties are all-female and don't need to be pollinated

Gynoecious and Parthenocarpic Cucumbers

This mouthful of a word describes flowers that don’t need to be fertilized to set fruit – no bees required. Fruit set is guaranteed and, because no pollination is needed, the fruits are almost completely seed-free.

Most parthenocarpic varieties are also gynoecious – meaning they produce mainly female flowers. And, since female flowers form the fruits, that can only mean one thing: more to pick! If a variety is described simply as ‘all-female’ it’s gynoecious, and almost certainly parthenocarpic too.

Gynoecious and parthenocarpic varieties are hybrids – the result of crossing two parent varieties – so seeds can be on the pricier side, but the vigor, reliability and long cropping period they promise more than compensates.

Humidity dome on a heat mat
A heat mat can speed up germination of warmth-loving cucumbers

How to Sow Cucumbers

Cucumbers grow very quickly, and in ideal conditions take as little as two months to go from seed to the first fruit, so there’s no rush to start them early in the season. I aim to sow three to four weeks before my last frost date to have sturdy young plants ready once conditions are warm enough to transplant them. If you’re not sure when your frost dates are likely to be, take a free trial of our Garden Planner which includes frost dates and recommended growing dates for your location.

Bear in mind that cucumbers grow best when night-time temperatures are consistently above 50ºF (10ºC) and daytimes a lot warmer than that. This is a warm-season crop that really dislikes the cold!

Before sowing, soak your cucumber seeds in lukewarm water overnight, for no longer than 12 hours. This helps to break down the tough seed coat, which should speed things along and improve the overall germination rate. Rinse them thoroughly after soaking to remove any residual toxins from the seed coat. Sow promptly, because the seeds are now awake and primed for germination! For more tips on getting your seeds to germinate, check out our Seed-Starting Masterclass.

Sow cucumber seeds into small pots, or plug trays with large cells. Some gardeners sow two seeds per pot then remove the weakest seedling if they both germinate, but given their cost I prefer to sow one per pot so I don’t waste any seeds. Make a little hole with your finger, pop the seed in then cover to a depth of around half an inch (1cm). Remember to label the pot.

Cucumbers germinate fast when temperatures are in the range of 70-80ºF (21-26ºC), so in all but the warmest climates you’ll probably have to start yours indoors in spring. A warm windowsill is fine but a heat mat will gently warm the potting mix from below and coax seeds to sprout quicker, within about a week.

Cucumber seedling
In summer or in warmer regions you can sow cucumbers direct where they are to grow

Growing Cucumber Seedlings That Will Thrive

Keep your seedlings on a warm, sunny windowsill then move them into a greenhouse, hoop house or cold frame before they get too big, bringing them back inside on chilly nights.

If the roots fill their pots or plugs before it’s time to transplant, just pot them on into a larger container. You can continue stepping plants up into progressively bigger pots whenever you need to, using a quality, all-purpose potting mix.

In warmer regions, or as spring tips into summer, you can sow seeds direct into their final growing positions, but you may prefer to start them off in pots to enable a head start and to keep fragile seedlings safe from pests like slugs or cucumber beetles.

Ideally, we want to transplant indoor-sown cucumbers during a spell of milder weather, and most definitely after any risk of frost is long gone. But before then, plants need ‘hardening off’, or acclimatizing to their new home. Put plants outside somewhere reasonably sheltered (or into a greenhouse, tunnel or cold frame) for increasingly longer over the course of a week or so – a few hours at first, a little longer the next day and so on, until it’s time for the big day.

Planting cucumbers
Install supports when planting to keep fruits off the ground and improve airflow around the plants

How to Plant Cucumbers

Cucumbers put out lots of growth and need rich, fertile soil to support this. Prepare beds with rich organic matter such as compost or well-rotted manure, and then for an extra boost to encourage that initial surge of growth, rake some chicken manure pellets into the top layer of soil.

Cucumbers are best grown on supports to keep them up off the ground. This reduces the pest risk, improves airflow around plants so there’s less chance of disease, and allows more sunlight to reach the foliage, which helps to power growth. The simplest way to support vining cucumbers in a greenhouse is using sturdy string, secured at the top to the greenhouse frame. You could also use trellis or A-frame-style supports, but I love how easy string supports are to set up and manage.

When it’s time to plant, soak the plants’ rootballs for an hour or two, dig holes for them, then carefully remove each plant from its pot. To hold it in position the strings can be either loosely tied to the base of the stem, or looped beneath the rootball as it’s planted. Handle plants with care as the roots and stems are delicate and can easily snap.

Space plants about 12-18 inches (30-45cm) apart to make the most efficient use of space. So long as the vines are properly supported, pruned and watered, this fairly close spacing is absolutely fine.

Watering cucumbers
Plenty of water is essential for good cucumber yields

Watering and Feeding Cucumbers

Cucumbers are vigorous growers, and the fruits are up to 96% water, so the one thing you can do to ensure both strong growth and plentiful fruits is to keep them well-watered. Push a finger into the soil every day or two to check how moist it is at root level, and if it’s anywhere close to dry, give plants a really good, deep water. Try to avoid wetting the foliage, especially if you’re growing under cover, because moist, humid conditions can encourage disease.

Add a thick mulch of any kind of organic matter – straw, leaves, bark chippings, compost – to slow evaporation from the soil and keep the roots cool and moist. If plants don’t get enough water, leaves will quickly go dry and crispy, growth might stall and fruits may develop a bitter taste or grow misshapen, so consistent, plentiful watering is the one need that absolutely must be met.

Well-prepared soil will get cucumbers off to a flying start, but once they start flowering begin applying a high-potassium organic fertilizer to encourage more of those flowers and fruits. I water on a liquid tomato feed every two weeks, or you could opt for top-dressing of a granular fertilizer that can then be lightly forked in.

Cucumber vines
Pruning cucumber vines helps improve airflow to keep plants healthier

How to Prune Cucumber Vines

Pruning cucumbers is very similar to vining tomatoes. Cucumber leaves, fruits, tendrils, and side shoots or suckers all form at the same intersections right the way along the main stem. As I grow my cucumbers fairly close together, I remove all side shoots, but if you space plants further apart you have the option of leaving the lowest side shoot or sucker to grow. This can then be secured to its own support, effectively creating a double-headed vine that acts like two separate plants.

Removing excess foliage will improve airflow and make it easier to spot fruits that may otherwise lurk among dense foliage – and that’s an important consideration to ensure those fruits keep coming! I like to cut off the lowest leaves as they become tired and inevitably tattered, which reduces the risk of disease, and remove any growth that seems overcrowded higher up too.

Once vines reach the top of their supports you can either pinch off the growing tip, or let the stem flop back down and develop sideshoots that will produce more fruits.

Cucumbers use their tendrils to grab hold of supports as they grow upwards, but I like to help vines sit snug in their string supports by carefully weaving them into place. This does need a delicate hand to avoid snapping. Do this often, as the vines grow.

The very first fruits are often weirdly shaped, and traditional, open-pollinated varieties can struggle early in the season if it’s still quite cool, so you may decide to remove flowers until plants are more established and the weather’s warmer.

Cucumber harvest
Keep picking cucumbers to keep them coming!

Harvesting Cucumbers

Pick fruits while they are still young, firm, and bright green. The best way to harvest fruits is to cut them from the vine with a bit of stalk attached – don’t try to yank them off or you’ll risk pulling away the whole plant! If you can, harvest in the morning while the fruits are still firm from the cool of the night.

Check daily and pick promptly to encourage plantst to produce more fruits. Leave cucumbers to get too big and overripe or, worse still, begin to go yellow, and the plants will slow down as they’ll think they no longer need to produce more seeds to create the next generation – a good reason to be meticulous in finding and picking every last fruit. With cucumbers it really is a case of picking often to keep ’em coming!

Sometimes cucumbers can be bitter, but peeling them and removing the stem end helps

Bitter Cucumbers and the Burps!

Occasionally, fruits can develop a bitter taste. This is caused by the compound cucurbitacin, which plants release more of when they’re stressed, for instance from lack of water or nutrients or if temperatures are too low or very high. It can also happen when female flowers are pollinated, so remove any male flowers if you have them.

Cucurbitacin also makes us burp, so if you’ve suffered bitter fruits – or the burps – in the past, try growing a so-called burpless variety which naturally produces less cucurbitacin. And, of course, water copiously. If you do find a bitter-tasting fruit, try cutting off the stem end of the fruit and peeling it, which should remove most of the bitter parts.

Striped cucumber beetle
Cucumber beetles can be kept under control by picking them off by hand

How to Ward Off Cucumber Beetles

Bitter tasting fruits can also attract cucumber beetles – both spotted and striped types - which feeds on plants, transmitting a range of diseases and bacterial wilts as they do. To make your plants less attractive to the beetles grow bitterness-free varieties, and try starting seedlings off under cover where you can protect them. Keep the plants under insect mesh for as long as possible, until flowers start to form or they need to grow up and out, by which time plants will be more robust. Beetles can be picked off and squashed, knocked off and gathered – even vacuumed up, if you don’t think that’s too cruel!

Powdery mildew
Powdery mildew can be kept at bay using a dilute milk spray

Powdery Mildew on Cucumbers

Powdery mildew covers leaves in a white fuzz, reducing their ability to photosynthesize and stalling growth. As well as choosing resistant varieties, keep plants well-watered and ensure good airflow to avoid an attack getting out of hand.

If mildew strikes, act quickly to pick off the worst-affected leaves then use a milk spray. Mix one part milk ( it has to be animal milk) to three parts water, and spray at the very first sign of infection, taking great care to cover every leaf surface – top and bottom. It’s believed that the proteins in the milk work with sunlight to create hostile conditions for the fungi. It doesn’t last though, so it’s worth repeating this simple treatment every 10 days to guard against another flare-up.

Ben with cucumber slices on his eyes
Ben recommends cucumber slices for youthful looking eyes!

Grow Even More Cucumbers

As cucumbers age they can start to lose their mojo. I find one sowing’s enough in my cooler climate, but if you enjoy warmer summers or a longer growing season you may find that plants simply run out of steam long before the end of summer. You can alleviate this by making repeat sowings about once a month to replace the oldest plants, swapping out the tired old guard with keen, fresh plants to reinvigorate things.

Of course, it’s easy to feel overwhelmed with cucumbers – once they get going, they’re relentless! But there are so many ways to enjoy them: drop them into drinks or make a cucumber water to cool down on a hot day; pop them on your eyes to freshen up; enjoy in salads of course; whizz them up into smoothies or a gazpacho soup, or transform them into very moreish pickles.

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