Growing your own cucumbers in a greenhouse is a fantastic way to enjoy a longer, more productive season. If you want to learn how to grow cucumbers in a greenhouse, you’re in the right place for expert greenhouse cultivation tips.
A greenhouse gives you control over temperature, humidity, and pests, leading to a bigger and better harvest. This guide will walk you through every step, from choosing the right seeds to picking your crisp, homegrown cucumbers.
How to Grow Cucumbers in a Greenhouse
Greenhouse cultivation is perfect for cucumbers because they love warmth and consistent conditions. By following these methods, you can avoid many of the problems faced in outdoor gardens.
Choosing the Best Cucumber Varieties
Not all cucumbers are created equal, especially for greenhouse life. You need to pick types that thrive in protected environments.
* Greenhouse (All-Female) Varieties: These are specially bred for greenhouses. They produce only female flowers, which means every flower can become a fruit without pollination. This leads to higher yields and no bitter, seedy fruits. Look for varieties like ‘Telegraph Improved’, ‘Carmen’, or ‘Flamingo’.
* Parthenocarpic vs. Traditional: Parthenocarpic varieties (like the ones above) set fruit without pollination. Traditional varieties require pollination. In a closed greenhouse, you’d need to pollinate them by hand, which is extra work.
* Slicing vs. Gherkins: Decide if you want long, smooth slicing cucumbers for salads or smaller gherkins for pickling. Most greenhouse types are slicing cucumbers.
Essential Greenhouse Setup & Preparation
Before you sow a single seed, get your greenhouse environment ready. Proper setup prevents issues down the line.
First, ensure your greenhouse gets plenty of light. Cucumbers need a minimum of 6-8 hours of sunlight daily. Clean the glass or plastic panels at the start of the season to maximize light penetration.
Soil and Container Requirements
Cucumbers have a large root system and are heavy feeders. They need rich, well-draining soil.
* Soil Mix: Use a high-quality potting mix or create your own with equal parts compost, peat-free growing medium, and well-rotted manure or garden loam. The soil should be fertile and hold moisture but not get waterlogged.
* Containers: You can grow in large pots (at least 10-12 inches deep), grow bags (one plant per bag), or directly in a prepared greenhouse border. Ensure all containers have excellent drainage holes.
* Pre-Planting Feed: Mix in a slow-release organic fertilizer or a general granular feed into the soil before planting to give your cucumbers a strong start.
Sowing Seeds and Planting Out
You can start seeds indoors or directly in their final greenhouse position if it’s warm enough.
For an early start, sow seeds indoors in small pots about 3-4 weeks before you plan to plant them in the greenhouse. Sow seeds on their side, about 1 inch deep, in moist compost. Keep them at a steady 70°F (21°C) for good germination.
When your seedlings have two or three true leaves, they are ready to transplant. Harden them off for a week by placing them in the greenhouse during the day and bringing them in at night if frost is still a risk. Finally, plant them in their final positions, spacing them about 18-24 inches apart.
Daily Care and Maintenance
Consistent care is the secret to a bumper crop. Pay close attention to watering, feeding, and training your plants.
Watering and Humidity
Cucumbers are mostly water, so they need a lot of it! Inconsistent watering leads to bitter taste and misshapen fruits.
Water deeply and regularly, aiming at the base of the plant to keep leaves dry. In hot summer weather, you may need to water daily. The greenhouse should have good ventilation to manage humidity and prevent fungal diseases, but the soil itself must stay consistently moist. Using a mulch of straw or compost on the soil surface helps retain this moisture.
Feeding for Success
These plants are hungry. Once they start flowering and fruiting, they need a regular nutrient boost.
Begin a weekly feeding schedule with a high-potash liquid fertilizer, like tomato feed, as soon as the first fruits begin to swell. This promotes healthy fruit development. A balanced feed is good early on, but the switch to potash-rich feed is crucial for fruit set.
Training and Pruning Techniques
Training cucumbers upwards saves space and improves air circulation.
* Provide Support: Set up strong vertical wires, canes, or a trellis for the vines to climb.
* Tie In: As the main stem grows, gently tie it to the support with soft string.
* Pinch Out: For greenhouse varieties, pinch out the growing tip of the main stem when it reaches the top of its support. Also, pinch out the side shoots (laterals) two leaves beyond each fruit. This directs energy into the developing cucumbers.
Managing Pests and Diseases
Even in a greenhouse, problems can occur. Vigilance and early action are key.
Red Spider Mite: These tiny pests thrive in hot, dry conditions. Increase humidity by damping down paths and look for fine webbing. Introduce predatory mites (Phytoseiulus persimilis) as a biological control.
Whitefly: They gather on the undersides of leaves. Hang yellow sticky traps and consider introducing the parasitic wasp Encarsia formosa.
* Powdery Mildew: This white fungal coating appears if air circulation is poor. Ensure good ventilation, water the soil not the leaves, and choose resistant varieties. Remove badly affected leaves promptly.
* Gray Mold (Botrytis): This occurs in cool, damp conditions. Improve ventilation, avoid overcrowding plants, and remove any dead or dying plant material imediately.
Harvesting Your Greenhouse Cucumbers
Harvesting at the right time encourages the plant to produce more fruit. Don’t let them get to big.
Check plants daily once they start cropping. Harvest cucumbers when they are a good size, firm, and green. Use a sharp knife or secateurs to cut the stalk, leaving a small piece attached to the fruit. If you leave cucumbers to become over-large and yellow, the plant will stop producing new ones. Regular harvesting is essential for a continous supply.
Common Problems and Solutions
* Bitter Fruits: Caused by stress, usually irregular watering or extreme temperatures. Keep conditions consistent.
* Misshapen Fruits: Often a result of poor pollination in traditional varieties or nutrient imbalance. Use greenhouse varieties and stick to your feeding schedule.
* Yellowing Leaves: Could be a sign of overwatering, underfeeding, or a nitrogen deficiency. Check your watering routine and ensure you are feeding regularly.
FAQ: Expert Greenhouse Cultivation Tips
Q: What is the ideal temperature for growing cucumbers in a greenhouse?
A: Cucumbers need warmth. Aim for a daytime temperature of 70-75°F (21-24°C) and a nighttime temperature above 60°F (15°C). Use a greenhouse heater if needed in early spring.
Q: How often should I feed my cucumber plants?
A: Start a weekly feed with a high-potash liquid fertilizer as soon as the first fruits begin to form. Before that, the nutrients in your initial soil preparation should be sufficient.
Q: Can I grow cucumbers in my greenhouse year-round?
A: In most climates, no. They need high light levels. The main season is spring to autumn. You can extend it at both ends with heating and lighting, but winter growth is usually to slow and weak to be worthwhile.
Q: Why are my cucumber flowers falling off without producing fruit?
A: This is common with traditional varieties in greenhouses where there are no pollinators. You need to hand-pollinate them using a small brush. The simpler solution is to grow all-female, parthenocarpic greenhouse varieties that don’t require pollination.
Q: How can I improve pollination for my cucumbers?
A: If you are not using all-female varieties, you can gently transfer pollen from male flowers to female flowers using a cotton swab or small paintbrush. Female flowers have a tiny cucumber shape behind the bloom, while male flowers have a plain stalk.
By following these expert tips, you’ll create the perfect environment for your cucumbers to thrive. With attention to variety selection, consistent watering and feeding, and good training, your greenhouse will be full of crisp, delicious cucumbers for months on end. Remember, the key is consistency in their care to avoid stressing the plants.