A Guide to Growing Vegetables in a Greenhouse

In our guide to growing vegetables in a greenhouse, we will see that growing vegetables in a greenhouse offers UK gardeners the chance to extend their growing season, protect plants from unpredictable weather, and achieve bountiful harvests. Whether you’re new to greenhouse gardening or looking to refine your techniques, this comprehensive guide will help you get the most out of your greenhouse. We’ll cover the best vegetables to grow, recommended varieties, plant care, pest management, and harvesting tips.

Why Grow Vegetables in a Greenhouse?

A greenhouse provides a controlled environment where you can manage temperature, humidity, and light levels, offering several advantages:

1. Extended Growing Season: Start plants earlier in the spring and continue growing later into the autumn and winter.
2. Weather Protection: Shield plants from frost, heavy rain, and strong winds.
3. Pest and Disease Control: Reduce the risk of pests and diseases that typically affect outdoor gardens.
4. Optimised Growing Conditions: Create the ideal environment for plant growth with controlled heat, light, and ventilation.

Best Vegetables to Grow in a Greenhouse

In the UK, a greenhouse can support a wide range of vegetables. Here are some of the best choices:

Tomatoes

• Varieties: ‘Gardener’s Delight’, ‘Alicante’, ‘Sungold’, ‘Moneymaker’
• Care:  need plenty of light and warmth. Water regularly and feed with a high-potassium fertiliser once fruit starts to set. Provide support with stakes or trellises.
• Pests: Watch out for aphids, whiteflies, and spider mites.
• Harvesting: Pick tomatoes when they are fully coloured and slightly soft to the touch.

Cucumbers

• Varieties: ‘Telegraph’, ‘Marketmore’, ‘Mini Munch’
• Care: Maintain high humidity and keep the soil consistently moist. Provide support for climbing varieties.
• Pests: Common pests include cucumber beetles, aphids, and spider mites.
• Harvesting: Harvest when cucumbers reach the desired size. Pick regularly to encourage continuous production.

Peppers (Sweet and Hot)

• Varieties: ‘California Wonder’, ‘Bell Boy’, ‘Jalapeño’, ‘Habanero’
• Care: Peppers thrive in well-drained soil with consistent moisture. Feed regularly with a balanced fertiliser.
• Pests: Watch for aphids, spider mites, and thrips.
• Harvesting: Harvest when peppers reach full size and colour. Picking regularly encourages more fruit production.

Aubergines

• Varieties: ‘Black Beauty’, ‘Long Purple’, ‘Thai Green’
• Care: Maintain temperatures above 20°C and provide consistent moisture. Support plants as they grow.
• Pests: Common pests include aphids, whiteflies, and spider mites.
• Harvesting: Harvest when fruits are glossy and firm, but before they start to soften.

Salad Greens

• Varieties: ‘Lollo Rosso’ (lettuce), ‘Rocket’, ‘Mizuna’, ‘Swiss Chard’
• Care: Grow in trays or directly in the greenhouse soil. Keep the soil moist and harvest leaves regularly.
• Pests: Slugs, snails, and aphids can be problematic.
• Harvesting: Pick leaves when they are young and tender for the best flavour.

 

Planting and Care

Proper planting and ongoing care are essential for a successful greenhouse garden. Here’s how to ensure your vegetables thrive:

Soil Preparation

1. Soil Quality: Use high-quality, well-draining compost or soil. Add organic matter such as well-rotted manure or compost to improve fertility.
2. pH Level: Most vegetables prefer a slightly acidic to neutral pH (6.0-7.0). Test your soil and amend as necessary.

Watering

1. Consistency: Water plants regularly to keep the soil evenly moist. Avoid waterlogging, which can lead to root rot.
2. Timing: Water early in the day to reduce evaporation and allow plants to dry before nightfall, which helps prevent diseases.

Feeding

1. Fertiliser: Use a balanced fertiliser to provide essential nutrients. For fruiting plants like tomatoes and peppers, switch to a high-potassium fertiliser once they start to flower.
2. Frequency: Apply fertiliser according to the manufacturer’s instructions to avoid over-fertilisation.

Ventilation

1. Airflow: Maintain good airflow to prevent heat buildup and reduce humidity levels, which can lead to fungal diseases.
2. Vents and Doors: Open vents and doors during the day and consider using fans if necessary.

Pruning and Training

1. Tomatoes: Remove side shoots (suckers) and train plants to grow vertically using stakes or trellises.
2. Cucumbers: Train climbing varieties to grow up trellises or nets to save space and improve light exposure.
3. Peppers and Aubergines: Prune to remove dead or diseased foliage and to promote air circulation.

Common Greenhouse Pests and Diseases

Our guide to growing vegetables in a greenhouse would not be complete without considering pests and diseases that can destroy all of your hard work. Even in the more controlled environment of a greenhouse, pests and diseases can be a problem. Here are some common issues and how to manage them:

Aphids

• Identification: Small, soft-bodied insects found on the undersides of leaves.
• Control: Introduce beneficial insects like ladybirds or use insecticidal soap.

Whiteflies

• Identification: Tiny white insects that fly up when plants are disturbed.
• Control: Use yellow sticky traps and introduce natural predators like Encarsia formosa.

Spider Mites

• Identification: Tiny red or yellow mites, often causing fine webbing on plants.
• Control: Increase humidity and use miticides or natural predators like Phytoseiulus persimilis.

Botrytis (Grey Mould)

• Identification: Grey, fuzzy mould on leaves, stems, and fruit.
• Control: Improve air circulation, remove affected plant parts, and use fungicides if necessary.

Powdery Mildew

• Identification: White, powdery spots on leaves and stems.
• Control: Ensure good ventilation, avoid overhead watering, and use fungicides or natural remedies like neem oil.

Harvesting Tips

Knowing when and how to harvest your vegetables ensures the best flavour and quality:

Tomatoes

• Timing: Pick when fully coloured and slightly soft.
• Storage: Avoid refrigerating tomatoes, as it can affect their flavour.

Cucumbers

• Timing: Harvest when they reach the desired size. Overripe cucumbers can become bitter and seedy.
• Storage: Store in a cool, humid place but not in the fridge.

Peppers

• Timing: Harvest when they reach their full size and colour. Sweet peppers can be harvested green or left to mature to red, yellow, or orange.
• Storage: Store in the fridge for up to a week.

Aubergines

• Timing: Harvest when the fruits are glossy and firm. Overripe aubergines can become bitter and tough.
• Storage: Store in a cool place, but not in the fridge.

Salad Greens

• Timing: Harvest leaves as needed, starting from the outer edges. Regular harvesting encourages continuous growth.
• Storage: Wash and store in the fridge in a perforated bag.

Additional Growing Tips

1. Succession Planting: To ensure a continuous supply of fresh produce, sow seeds for fast-growing crops like salad greens and herbs every few weeks.
2. Companion Planting: Grow plants that benefit each other together. For example, basil planted near tomatoes can improve their flavour and repel pests.
3. Soil Health: Rotate crops and add organic matter to maintain healthy soil. Avoid planting the same crops in the same spot year after year to prevent soil-borne diseases.
4. Mulching: Apply mulch to help retain soil moisture, suppress weeds, and regulate soil temperature.
5. Season Extension: Use shade cloth or greenhouse paint to reduce temperatures during hot days and extend the growing season into autumn with heaters or insulation.

Conclusion

As you can see from our guide to growing vegetables in a greenhouse, growing vegetables in a greenhouse in the UK offers numerous benefits, from extending the growing season to protecting plants from adverse weather conditions. By selecting the right varieties, providing proper care, and managing pests effectively, you can enjoy a bountiful and continuous harvest of fresh, home-grown vegetables. Whether you’re a seasoned gardener or just starting, these tips will help you make the most of your greenhouse.