How to grow cucumbers in a greenhouse(Ultimate Guide)

Several long green cucumbers hanging from a climbing vine in a greenhouse.

Growing cucumbers in a greenhouse offers several key advantages namely, the ability to extend your growing season and maintain a controlled environment for optimal growth. With the right preparation and care, cucumbers can thrive in greenhouses year-round. This guide covers everything from setting up the greenhouse to harvesting your cucumbers, offering practical tips, expert advice, and necessary precautions.

Step 1: Prepare Your Greenhouse for Cucumber Growth

A man on a ladder adjusting overhead lights in a large glass greenhouse.

The first step in growing cucumbers successfully is ensuring that your greenhouse provides the ideal conditions for them to thrive. Cucumbers need a stable environment where temperature, humidity, and airflow are carefully managed, especially during cooler months when it’s important to keep the greenhouse warm for consistent growth.

Key Considerations for Greenhouse Setup:

Temperature: Soil temperature should be at least 65°F (18°C) before transplanting. If the air is warm but the soil is cold, the plant will stunt.
Ventilation: Proper airflow is essential to prevent overheating and excessive humidity, which can lead to fungal diseases.
Humidity: Cucumbers require humidity levels between 60% and 70% during the day, and slightly higher at night (70% to 85%).

Step 2: Choose the Right Cucumber Varieties

Four-panel grid showing different smooth and bumpy green cucumber varieties.

Not all cucumber varieties are created equal, especially when it comes to growing in a greenhouse. For a higher yield and better resistance to disease, select varieties that are specifically bred for greenhouse conditions.

Recommended Cucumber Varieties:

Carmen F1: A disease-resistant variety that produces long, straight, crisp cucumbers perfect for salads.
Mini Munch F: Known for its small, sweet cucumbers, this variety provides a steady yield throughout the season.
Emilie F1: A high-yielding, medium-sized cucumber with excellent flavor and strong disease resistance.
Burpless Tasty Green F1: Produces non-bitter, long fruits that are great for fresh eating.

Step 3: Preparing the Growing Medium

Comparison of hands gardening in soil and a vertical hydroponic tower system.

If you’re growing cucumbers in soil, make sure the soil is fertile and well-draining. You can improve the soil quality by adding compost or well-rotted manure to provide nutrients when you use a greenhouse to control moisture, temperature, and growing conditions.

Soil-Based Systems

If you’re growing cucumbers in soil, make sure the soil is fertile and well-draining. You can improve the soil quality by adding compost or well-rotted manure to provide nutrients. The ideal soil pH for cucumbers is between 5.5 and 6.8.

Hydroponic Systems

Hydroponic systems are an excellent alternative to soil-based setups. They use nutrient-rich water to grow cucumbers without the need for soil. This method allows for greater control over nutrients, pH, and water levels, making it easier to optimize plant growth.

Step 4: Germinating and Transplanting Your Seedlings

Once the growing medium is ready, it’s time to start your cucumber seeds. Germinating seeds indoors provides a head start before transplanting them into the greenhouse.

Germinating Cucumber Seeds

Four small orange pots with green cucumber seedlings sprouting from soil.

Start by filling small pots with peat-free seed compost. Plant one cucumber seed per pot, placing it about 1-2 cm deep. Keep the pots in a warm area with a temperature of around 70°F to 80°F (21°C – 26°C).

Germination Time: Seeds typically germinate within 5-7 days.

After the seedlings have developed several true leaves, usually within 4-6 weeks, they can be transplanted into your greenhouse.

Transplanting to the Greenhouse

Gloved hands planting a small green seedling into dark organic garden soil.

Transplant the seedlings when they are strong enough to handle the greenhouse environment. Space the plants at least 30 cm (12 inches) apart to allow them room to grow and to ensure adequate airflow.

Be gentle when handling the seedlings to avoid damaging the delicate roots. Water them well before transplanting to help them settle in quickly.

Step 5: Supporting and Training Your Cucumber Plants

As cucumbers are vining plants, they naturally want to climb. In a greenhouse, it’s essential to use a Vertical Trellis System to support the plants and encourage vertical growth. Vertical gardening not only saves space but also improves airflow, reducing the risk of disease.

Use strings, canes, or a trellis to support the cucumber vines as they grow. Ensure that the structure is sturdy enough to hold the weight of the plant as it matures.

Pruning and Maintaining Plants

Person using orange handled scissors to prune a small green plant stem.

Pruning is essential to keep your cucumber plants healthy and focused on producing fruit. Remove side shoots that do not bear fruit and trim back any excessive growth that could block light or airflow.

Pinch the growing tips when they reach the top of your trellis to encourage lateral growth.
Regularly remove side shoots to direct the plant’s energy toward fruit production.

Step 6: Watering and Feeding Your Cucumbers

A green watering can pouring water onto the base of a young plant.

Cucumbers need a consistent supply of water and nutrients to grow and produce fruit. They are particularly thirsty during fruiting, so it’s important to water deeply and regularly.

Watering Tips

Water cucumbers at the base of the plant to keep the leaves dry. Cucumbers don’t like their roots to sit in water, so make sure the soil is well-drained.

Water deeply but infrequently to encourage deep root growth.
Avoid watering at the hottest part of the day to prevent evaporation.

Fertilization Guidelines

Cucumbers are heavy feeders, especially once they start flowering and fruiting. Start by using a balanced liquid fertilizer during the initial growth stages. Once cucumbers begin to flower, switch to a high-potassium fertilizer to support fruit production.

Apply fertilizer every 10-14 days.
Use a slow-release granular fertilizer at planting time for a steady supply of nutrients.

Step 7: Managing Pollination (If Necessary)

Cucumbers typically need pollination for fruit to set, but parthenocarpic (seedless) varieties do not. These self-pollinating cucumbers do not require bees or external pollen to develop fruit. However, seeded varieties need male and female flowers to be pollinated.

Manual Pollination Techniques

Brush Method: Use a soft paintbrush to transfer pollen from male flowers to female flowers.
Touch Method: Gently touch the male flowers to the female flowers to ensure pollen transfer.

Parthenocarpic Varieties

For parthenocarpic varieties (such as ‘Carmen F1’), no pollination is needed. In fact, pollination should be avoided to prevent bitter fruit and deformities caused by cross-pollination with male flowers from outside the greenhouse.

Caution: If your greenhouse variety is all-female (parthenocarpic), avoid pollination altogether to maintain the quality of your cucumbers.

Step 8: Managing Pests and Diseases

A yellow and black caterpillar eating a hole in a green leaf.

Pest control in a greenhouse is important because greenhouse environments can sometimes encourage pests and diseases due to high humidity and limited airflow. It’s crucial to stay vigilant and monitor your plants regularly for signs of trouble so issues can be addressed early.

Common Greenhouse Pests

Aphids and whiteflies can cause damage and spread disease. Use sticky traps to monitor pest populations and introduce beneficial insects like ladybugs to control them.
Spider mites can be a problem in dry conditions. Ensure proper humidity and air circulation to keep them at bay.

Disease Prevention

Diseases like powdery mildew and botrytis can affect cucumbers, especially in damp conditions. To prevent this:

Keep the greenhouse well-ventilated.
Prune leaves regularly to improve airflow.

Step 9: Harvesting Cucumbers

Hands using metal garden shears to cut a ripe cucumber from a vine.

Cucumbers grow rapidly, and it’s essential to harvest them at the right time to ensure the best flavor and texture. Harvesting too early or too late can lead to cucumbers that are too bitter or overripe.

When to Harvest

Mini Cucumbers: Harvest when they are about 8 cm (3 inches) long.
Full-Sized Cucumbers: Harvest when they reach 20-25 cm (8-10 inches) in length.

Growing cucumbers in a Greenhouse offers a unique opportunity to extend the growing season and maintain optimal conditions for healthy, high-yielding plants. By carefully managing temperature, humidity, and airflow, and choosing the right cucumber varieties, gardeners can enjoy fresh, crisp cucumbers year-round.

FAQs

1. Why are my cucumber leaves turning yellow?

Yellowing leaves can be a sign of nutrient deficiencies or overwatering. Ensure your plants are getting the right amount of water and nutrients. If yellowing continues, check for pests or diseases that might be affecting the plants.

2. How can I increase cucumber yield in my greenhouse?

Increase pollination efforts for seeded varieties, ensure optimal temperature and humidity levels, and prune the plants regularly to encourage fruit production rather than excessive foliage.

3. What is the best time to plant cucumbers in a greenhouse?

For heated greenhouses, plant cucumbers in late February to early March. For unheated greenhouses, wait until April when temperatures are consistently above 60°F (15°C).

4. How often should I water my cucumbers in a greenhouse?

Water your cucumbers regularly to keep the soil moist, especially when fruits are forming. Water at the base of the plant to prevent wetting the leaves, which can encourage fungal diseases.

5. How do I prevent powdery mildew on cucumbers?

Ensure proper air circulation around the plants, reduce humidity, and prune any affected leaves. Consider using fungicides if necessary, or select mildew-resistant cucumber varieties