Learn How to Grow Tomatoes in a Greenhouse. This comprehensive guide covers everything from choosing the right varieties to managing pests and diseases for a bountiful harvest.

How to Grow Tomatoes in a Greenhouse

Growing tomatoes in a greenhouse offers numerous advantages over outdoor cultivation in the UK, including extended growing seasons, protection from unpredictable weather, and better control over environmental factors. This guide provides a comprehensive overview of how to successfully grow delicious tomatoes in your greenhouse.

Choosing the Right Tomato Variety

Selecting the appropriate tomato variety is crucial for greenhouse success. Consider these factors:

• Growth Habit: Determinate (bush) varieties are more compact and suitable for smaller greenhouses, while indeterminate (vine) varieties require significant support and pruning but typically produce larger yields over a longer period. Popular indeterminate varieties include ‘Moneymaker’, ‘Sungold’, and ‘Gardener’s Delight’. Determinate varieties like ‘Roma’ or ‘San Marzano’ are good for smaller spaces and making sauces.
• Disease Resistance: Opt for varieties resistant to common greenhouse tomato diseases like blight, fusarium wilt, and verticillium wilt. Check seed packets or plant descriptions for disease resistance codes (e.g., F1, F2, V, TMV).
• Taste and Usage: Choose varieties based on your taste preferences and intended use (e.g., salad tomatoes, cooking tomatoes, cherry tomatoes).

Preparing the Greenhouse

Before planting, thoroughly clean your greenhouse to eliminate potential pests and diseases. This involves:

• Washing Surfaces: Use a horticultural disinfectant to clean glass, staging, and pots.
• Checking Ventilation: Ensure adequate ventilation to prevent excessive humidity, which can lead to fungal diseases. Consider installing automatic vent openers.
• Soil Preparation: Use a high-quality potting compost specifically formulated for tomatoes, or prepare your own mix with equal parts loam, peat-free compost, and perlite or vermiculite for good drainage.

Sowing and Transplanting

• Sowing Seeds: Sow tomato seeds indoors in seed trays or small pots approximately 6-8 weeks before the last expected frost. Maintain a temperature of around 20-25°C for germination.
• Pricking Out: Once seedlings have developed their first true leaves, transplant them into individual pots.
• Hardening Off: Gradually acclimatise the seedlings to greenhouse conditions by placing them outdoors for increasing periods each day for about a week before transplanting them into their final growing positions.
• Transplanting: Transplant tomato plants into grow bags, large pots, or directly into the greenhouse soil when they are about 20-30cm tall. Space plants according to the variety’s growth habit (typically 45-60cm apart for indeterminate varieties).

Providing Support and Training

Indeterminate tomato varieties require support to grow vertically. Options include:

• Canes: Insert sturdy canes into the soil near each plant and tie the main stem to the cane at regular intervals.
• String Supports: Suspend string from the greenhouse roof and tie it loosely around the base of the plant, winding the plant around the string as it grows.
• Tomato Cages: Enclose plants in wire or plastic cages for support.

Regular pruning is essential for indeterminate varieties to encourage fruit production. Remove side shoots (also known as suckers) that grow between the main stem and the leaves.

Watering and Feeding

• Watering: Water regularly, especially during hot weather, keeping the soil consistently moist but not waterlogged. Water at the base of the plant to avoid wetting the foliage, which can promote fungal diseases.
• Feeding: Begin feeding tomato plants with a liquid tomato feed once the first flowers appear. Follow the manufacturer’s instructions for dosage and frequency.

Pollination

Tomatoes are self-pollinating, but greenhouse environments can sometimes hinder pollination. You can assist pollination by:

• Gently Shaking Plants: Gently shake the plants a few times a week to release pollen.
• Using a Soft Brush: Use a soft brush to transfer pollen from one flower to another.
• Improving Air Circulation: Good air circulation helps to disperse pollen.

Pest and Disease Management

• Common Pests: Watch out for common greenhouse pests such as whitefly, aphids, and red spider mites. Use biological controls (e.g., predatory mites) or insecticidal soap to manage infestations.
• Common Diseases: Prevent fungal diseases by ensuring good ventilation and avoiding overwatering. Treat infected plants with a fungicide. Blight can be a major problem, particularly if there are outdoor tomatoes nearby.

Harvesting

Harvest tomatoes when they are fully coloured and slightly soft to the touch. Gently twist the fruit from the stem. Regular harvesting encourages further fruit production.

FAQ:

Q: How often should I water my greenhouse tomatoes?

A: Water deeply when the top inch of soil feels dry, usually every 1-3 days depending on weather conditions.

Q: What is the best temperature for growing tomatoes in a greenhouse?

A: Aim for a daytime temperature of 21-24°C and a nighttime temperature of 13-16°C.

Q: How do I prevent blight on my greenhouse tomatoes?

A: Ensure good ventilation, avoid wetting the foliage, and consider using a blight-resistant variety. Remove any affected leaves immediately.

external_links:

• https://www.rhs.org.uk/vegetables/tomatoes/growing-in-greenhouse (Royal Horticultural Society guide to growing tomatoes in a greenhouse)
• https://www.thompson-morgan.com/how-to-grow-tomatoes-in-a-greenhouse (Thompson & Morgan guide to greenhouse tomato cultivation)