A Greenhouse Grower’s Guide to Cucumbers

How to Grow Cucumbers in a Greenhouse

Growing cucumbers in a greenhouse is a rewarding experience that can yield a bountiful harvest of crisp, delicious fruits. Greenhouses provide an ideal environment for cucumbers, offering protection from pests and allowing for extended growing seasons. Cucumbers need lots of sunlight so make sure you position your greenhouse so that it allows at least six hours of direct sunlight through the day. This controlled setting enables gardeners to cultivate cucumbers with greater success than outdoor growing, especially in the UK's variable climate.

The two most popular groups of cucumbers are ridge cucumbers and greenhouse cucumbers. Ridge cucumbers, named for the small ridges along their length, are typically grown outdoors and tend to be smaller than greenhouse cucumbers.

In Britain, growing ridge cucumbers can be very difficult because they don’t respond well to temperate climates. Although some determined gardeners do have success with outdoor cucumbers, cucumbers grow far better in a warm, humid surroundings.

Greenhouse cucumbers, on the other hand, are the typical cucumbers you’d find at the supermarket or your nan’s sandwiches. They’re bigger than their ridged counterparts and completely smooth. As well as this they tend to be juicier and sweeter, which is why they’re more commonly sold than ridge cucumbers.

As a result of all these factors, most greenhouse growers opt for greenhouse cucumbers, as opposed to ridge cucumbers, and we recommend attempting a crop of ridge cucumbers only if you’re very experienced.

TOP UK CUCUMBER VARIETIES

Variety	Type	Key Benefits
Bella F1	All-female	Mildew resistant, thrives in unheated greenhouses
Burpless Tasty Green	Ridge	No pollination needed, beginner-friendly
Carmen F1	All-female	High yield, cucumber mosaic virus resistance
Passandra F1	Mini	Short crisp fruits, perfect for small spaces

Choosing the right variety makes all the difference. All-female F1 hybrids produce the highest yields in greenhouses—no male flowers means every flower produces fruit. For beginners, start with Bella F1—its mildew resistance gives you crucial wiggle room when learning optimal ventilation.

Ridge varieties like Burpless Tasty Green work both outdoors and in greenhouse borders, offering flexibility if temperatures fluctuate. For confined spaces, Passandra's compact fruits maximize productivity in smaller greenhouses.

How to Germinate Cucumbers

Germinating cucumber seeds is arguably the most challenging part of growing cucumbers, and while getting the seeds to take can be tricky, given the right conditions good quality seeds should germinate quickly. The most important aspect is making sure that the compost you use gives the seeds the conditions they need to grow. Warm, moist, nutrient-rich compost will give your cucumber seeds everything they need to germinate.

Most cucumber growers plant their seeds quite early in the year. If it’s a warm year, planting as early as March or April will give you the longest possible cropping season. Earlier than March the greenhouse will still be too cold, but if you hold off, you’ll yield a smaller crop.

By following these steps, you should see your seeds germinate within weeks:

1. Take a small flower pot, fill it with multipurpose, peat-free compost and press the seeds into the compost. They should be buried around 1 cm deep in the compost.
2. Soak the pot in water for around 12 hours, until the compost is completely saturated and damp throughout.
3. It is important that the pots are kept very moist and humid. We recommend placing a clear plastic bag over the pot to retain as much moisture as possible.
4. The compost needs to be kept warm. Some growers opt to put the compost in an airing cupboard or near a boiler, while others find that a sunny windowsill is warm enough. Heat mats are the best possible solution, however, as they can maintain a constant temperature of around 20°C which is ideal for your seeds.
5. After a week or so, seedlings should start emerging from the compost. When this happens, move the pots to an area that gets a good amount of sunlight, such as a windowsill.

GROWING CALENDAR: TIMING IS EVERYTHING

Month	Task	Critical Notes
Late March	Sow seeds	Use heated propagator (20°C); one seed per pot
Mid April	Transplant seedlings	When 2-3 true leaves appear; soil temp must be 18°C+
May	Train vines	Set up strings; pinch out growing tip at 60cm
June-August	Peak harvest	Harvest every 2-3 days; mist plants on hot days
Early July	Succession sow	Second crop for extended autumn harvests

Timing matters with cucumbers. Sow too early and weak light produces leggy seedlings. Sow too late and you miss peak growing season. For heated greenhouses, sow from late March; for unheated, wait until mid-April.

The secret to extended harvests? Succession sowing. Plant a second batch in early July to keep fresh cucumbers coming through October. Don't rush transplanting—cucumber roots hate disturbance, so move them only when they've developed 2-3 true leaves and nights stay above 12°C.

Transferring the Seedlings into a Greenhouse

When the seedlings have germinated, they don’t require the same level of constant heat. As they reach around 3” tall, they should be strong enough to survive being re-potted into their permanent positions. Cucumbers thrive in compost that is full of nutrients and organic matter, so a homemade compost that is dense in vegetable matter is perfect. Similarly, they need plenty of water to grow to their full potential, so keeping them well watered should be a priority. Like any plant, however, waterlogging can lead to root rot and other problems, so we recommend potting the adult cucumber plants in containers as opposed to the bare ground, as this makes monitoring water levels much easier.

Cucumbers do well in direct sunlight, and the more light they get, the faster they will grow. Because they are climbing plants, it’s a good idea to use garden canes and twine to support the growing stem and keep it upright.

VERTICAL TRAINING TECHNIQUES

Mastering the vertical.

Greenhouse cucumbers need vertical training to maximize space and yield. Set up your system before plants reach 30cm tall.

How to Train greenhouse Cucumbers

The single-stem method produces the cleanest, most disease-resistant plants. Remove all side shoots that develop in leaf joints along the main stem, except for 2-3 shoots you'll allow to develop between 1-1.2m up the plant. This balances energy and extends harvest season.

For maintenance-free training, try spiral plant supports or A-frame trellises, both available in our greenhouse accessories section. These eliminate weekly training sessions while still keeping plants vertical.

Troubleshooting: Beat Common Cucumber Problems

Prevention beats cure with greenhouse cucumbers. Most problems stem from three environmental factors: temperature fluctuations, humidity imbalance, and poor ventilation.

CUCUMBER PROBLEM SOLVER

Problem	Symptoms	Quick Fix
Red Spider Mite	Fine webbing, stippled leaves	Daily misting, introduce predatory mites
Powdery Mildew	White powdery patches on leaves	Improve ventilation, remove affected leaves
Cucumber Mosaic Virus	Yellowing, mottled leaves, stunted growth	Remove plants, disinfect greenhouse, plant resistant varieties
Bitter Fruits	Fruits taste bitter, often curved	Consistent watering, maintain 18-24°C temperature

Red spider mite thrives in dry conditions—maintain 70-80% humidity to prevent infestations. Mist plants regularly and add an automatic greenhouse misting system during heatwaves.

Combat powdery mildew with proper spacing between plants. Aim for 45cm minimum between plants to create airflow. Open vents early in the day to avoid humidity spikes that trigger infection.

For organic prevention, neem oil applied bi-weekly works against multiple pests. For robust plants that resist illness naturally, apply seaweed extract monthly—it contains trace elements that strengthen plant cell walls.

Harvesting and Storage

PERFECT PICKING: BEYOND THE BASICS

Harvest cucumbers when they reach ideal size but before seeds fully develop—typically 15-20cm for slicing varieties, 7-10cm for mini types. The perfect cucumber should be:

Firm with no soft spots

Uniform dark green colour

Straight with no bulging ends

Harvesting Techniques that Prevent Damage

Always use sharp scissors or pruners to cut fruit—never pull or twist. Leave 1cm of stem attached to prevent rot entry points. Harvest in morning when fruits are most crisp and hydrated.

EXTENDING FRESHNESS: STORAGE SECRETS

Fresh-picked cucumbers last twice as long when properly stored:

For continuous harvests, pick every cucumber when ready—even ones you don't need. Left unpicked, mature fruits signal the plant to slow production. Regular harvesting keeps plants producing for weeks longer.

As the season continues, you should have a good crop of juicy, big cucumbers, but harvesting them can be a challenge in and of itself. Unlike most crops where the vegetables become ready at roughly the same time, cucumbers will come to fruition over the course of the season. Some cucumber plants may produce vegetables within a couple of months and will continue to grow more throughout the season.

Cucumbers should be picked regularly and early, as this directs more energy to the developing cucumbers, therefore speeding up the growing process and ultimately yielding a bigger crop over the course of the season.

ESSENTIAL GREENHOUSE EQUIPMENT FOR CUCUMBER SUCCESS

The right equipment transforms cucumber growing from constant maintenance to simple success: