How to Grow Cucumbers: A Practical Guide from Seed to Harvest

Cucumbers are surprisingly easy to grow once you've got them through the early stages and into warm growing conditions. They're often thought of as greenhouse plants, but there are varieties that grow perfectly well outside, and compact types can be a great choice for large pots on a sunny patio.

The important thing is knowing what type you're growing. Some cucumbers are bred mainly for greenhouse conditions, while outdoor varieties are happier dealing with the slightly less predictable British summer.

We grow cucumbers in plenty of warmth and give them regular water once they get going. They're hungry, productive plants, and it's surprising how quickly a small seedling can turn into something that needs support and starts producing fruit.

If you're short of space, don't immediately rule them out. A cucumber growing upwards from a large container takes up relatively little patio space, particularly if you choose a suitable compact variety.

When to Sow

Cucumbers can be sown from March to May.

For greenhouse growing, you can start from March somewhere warm. For plants that will eventually grow outside, I prefer sowing during April or early May.

There's very little advantage in starting outdoor cucumbers ridiculously early. They grow quickly once conditions warm up, and an April-sown plant can soon catch up with an older seedling that's spent weeks sitting around somewhere cold.

Cucumber seeds need warmth to germinate. A propagator is useful, but a warm windowsill can work perfectly well.

If you're planning to grow them outdoors, remember that cucumbers are tender. Wait until the danger of frost has passed and nights are becoming reliably warmer before planting them outside.

How to Sow

Cucumber seeds are large and easy to handle.

I prefer sowing them individually into small pots rather than putting several into a seed tray. Cucumbers grow quickly and don't particularly appreciate having their roots disturbed unnecessarily.

Fill small pots with seed compost and sow one seed about 1–2cm deep.

You'll sometimes see cucumber seeds sown on their edge. You can do this, although the most important things are warmth, moisture and not burying them too deeply.

Water gently and keep the pots somewhere warm, ideally around 20–25°C for germination.

Keep the compost moist but not soaking wet. In good conditions, seedlings can appear within 5–10 days, although some may take a little longer.

Once they've germinated, move them into plenty of light while keeping them warm.

Cucumber seedlings soon become substantial plants, so be prepared to give them more room.

Growing Seedlings On

Once cucumber seedlings start growing, they don't tend to hang around.

Keep them somewhere warm and bright and water when the compost begins to dry.

As the roots fill their pots, move the plants into slightly larger containers. Try to disturb the root ball as little as possible.

If they're destined for the garden or patio, harden them off gradually over a week or two. Put them outside during the day when conditions are suitable and bring them back under cover initially.

Cold winds and chilly nights can quickly check young cucumber plants.

By planting time, you should have sturdy plants with several healthy leaves rather than enormous specimens already trying to take over the windowsill.

Growing Cucumbers Outdoors

Outdoor cucumbers need your warmest, sunniest and most sheltered position.

Wait until the danger of frost has passed before planting them out. Depending on where you garden, this will usually be from late May into June.

Choose free-draining, fertile soil and add some organic matter before planting if your ground is poor.

Allow plenty of room between plants if you're letting them trail across the ground. Alternatively, train them upwards against a trellis or other sturdy support.

Growing vertically has several advantages. It saves space, keeps fruit away from wet soil and makes the cucumbers much easier to spot when you're harvesting.

Start guiding young stems onto the support before they become a tangled heap.

And don't be discouraged by a cool start to summer. Outdoor cucumbers sometimes seem to sit doing very little until the weather warms, then suddenly decide to grow everywhere at once.

Growing Cucumbers in Outdoor Pots

Cucumbers can grow very successfully in pots, making them a useful crop for patios and smaller gardens.

The first thing I'd say is don't use a tiny pot.

Cucumbers produce a lot of growth and fruit from one plant and need enough compost to support it. For a compact cucumber, I'd use a container of at least 30cm across, with something around 20–30 litres giving the roots a much better reserve of moisture and nutrients.

Grow one plant per large pot rather than trying to squeeze several together.

Use good-quality multipurpose compost and make sure the container has plenty of drainage holes.

Put the pot in a warm, sunny, sheltered position and provide support from the start. A trellis, canes or sturdy climbing frame can all work.

Choose a variety suitable for outdoor container growing. Compact varieties are particularly useful because you can train the plant upwards and get a good crop without giving up a large area of patio.

The main challenge with containers is watering. A mature cucumber in a pot can use a surprising amount of water on a warm summer day, so check the compost regularly.

Supporting and Training

Cucumbers naturally produce long stems that want to scramble.

You can let outdoor plants trail across the ground if you have plenty of room, but in a smaller garden I much prefer growing them upwards.

Provide sturdy support and loosely tie or guide the main stem as it grows.

Side shoots can generally be allowed to develop on outdoor cucumbers, although very vigorous growth can be shortened if the plant is becoming unmanageable.

Training doesn't need to become complicated. You're mainly trying to keep the plant supported, open and somewhere you can actually find the cucumbers.

One thing I've learnt with climbing vegetables is that putting the support in before you desperately need it is considerably easier than trying to untangle a mature plant afterwards.

Watering and Feeding

Cucumbers need regular watering, particularly once plants are flowering and producing fruit.

Try to keep the soil or compost consistently moist rather than allowing plants to become bone dry and then soaking them.

Water around the base of the plant rather than continually soaking the foliage.

Cucumbers are also hungry plants.

Once flowering and fruiting begin, container plants in particular will benefit from a high-potash liquid feed, used according to the instructions on the product.

There's no benefit in feeding tiny seedlings heavily. Wait until the plants are established and actively growing.

A cucumber that's warm, properly watered and adequately fed can be remarkably productive.

Flowering and Pollination

This is one area where knowing your variety really matters.

Traditional outdoor ridge cucumbers commonly produce male and female flowers, and insects transfer pollen between them. Female flowers are easy to recognise because they have a tiny cucumber-shaped swelling behind the flower.

Don't worry if the first few flowers don't produce cucumbers. Early flowers are often male.

Many modern greenhouse cucumbers are all-female or predominantly female varieties and can produce fruit without pollination.

With some greenhouse varieties, pollination is actually undesirable because it can affect fruit quality.

Always check the instructions for your chosen variety. Don't automatically remove male flowers or try to pollinate flowers without knowing which type you're growing.

For traditional outdoor varieties, bees and other insects will normally take care of pollination.

If small fruits begin developing and then yellow and drop off, poor pollination can sometimes be responsible, although cold weather or plant stress can have a similar effect.

Harvesting

Start harvesting cucumbers when they've reached a useful size for the variety.

Don't wait for every fruit to become enormous.

Mini cucumbers are supposed to be picked small, while traditional outdoor cucumbers will naturally grow considerably larger.

Regular picking encourages the plant to keep producing more.

Use a knife or secateurs to cut the fruit rather than pulling and twisting it from the plant. Cucumber stems can be surprisingly easy to damage.

During warm weather, check plants frequently. Cucumbers have a remarkable ability to hide behind a leaf and go from nearly ready to how did that get so big? in what feels like two days.

Pick fruit while it's young, firm and fresh.

Keep plants watered and fed and they can continue producing through summer.

Common Problems

Slugs and Snails

Young cucumber plants are very attractive to slugs and snails.

Keep a close eye on newly planted outdoor cucumbers, particularly during damp weather. Once plants are larger they can cope with some leaf damage, but a young plant can disappear remarkably quickly.

Powdery Mildew

A white powdery coating can appear on cucumber leaves, particularly later in summer.

Keep plants properly watered and give them enough room for reasonable airflow. Older leaves can be removed if they're badly affected.

Small Fruits Turning Yellow and Falling Off

This can happen because of poor pollination, cool weather, irregular watering or general plant stress.

If you're growing an outdoor variety that needs pollination, make sure insects can reach the flowers.

For greenhouse varieties that produce fruit without pollination, check growing conditions rather than assuming pollination is the problem.

Wilting Plants

Cucumbers naturally lose a lot of water through their large leaves and can wilt dramatically during hot weather.

Check the soil before assuming something more serious is wrong. Container plants in particular can dry out very quickly.

If they're wilting repeatedly every day, the pot may simply be too small to hold enough moisture.

Yellowing Leaves

A few older yellow leaves are normal.

Widespread yellowing can be caused by overwatering, poor drainage, lack of nutrients or cold conditions.

Look at the whole plant and how it's being grown before automatically adding more feed.

Cucumbers do need more attention than something like a radish, but you don't need a greenhouse or a huge garden to grow them.

Choose an outdoor or suitable compact variety, give one plant a decent-sized pot and train it upwards.

Keep the water and feed coming once it starts cropping and you can get a surprising number of cucumbers from a very small patch of patio.