How to Grow Tomatoes in Greenhouse

Growing tomatoes in a greenhouse can be an excellent solution in the UK, where weather can often be unpredictable. This guide will explore why greenhouse cultivation might be your best bet for a bountiful tomato harvest, the best varieties to choose for greenhouse growing, and the proper watering techniques for your greenhouse tomatoes.

Building a greenhouse on your allotment can be a fantastic way to maximise your growing potential. It extends your growing season, allowing you to start seeds earlier and harvest crops later, but it also provides a protected environment for heat-loving plants such as tomatoes. Try to incorporate a greenhouse in the planning stage of your allotment, or leave an area free if you don’t currently have the funds to buy one.


Why grow tomatoes in a greenhouse? Advantages and Disadvantages

Growing tomatoes in a greenhouse offers numerous advantages, especially in a region with a climate like the UK. First and foremost, a greenhouse provides a controlled environment, protecting your plants from erratic weather conditions. You can manage temperature and humidity levels, making it easier for your tomatoes to thrive.

Additionally, a greenhouse extends your growing season, allowing you to start earlier in the spring and continue later into the autumn. This extended season can result in a more abundant harvest.

However, greenhouses also have a few disadvantages. They require an initial investment, and maintaining the ideal environment within the greenhouse can require ongoing effort. Furthermore, pests and diseases, if introduced, can spread quickly in a greenhouse environment. However, with careful monitoring and management, these issues can be mitigated.

Best tomato varieties for greenhouses

The choice of variety is crucial when growing tomatoes in a greenhouse. Cordon or indeterminate varieties are often preferred as they make the best use of vertical space. Here are a few recommended greenhouse varieties for the UK:

  • Sungold: A favourite among many gardeners, Sungold produces small, sweet, and tangy fruits.
  • Shirley: Shirley is a reliable early variety. It’s disease-resistant and performs well in a cooler summer.
  • Gardener’s Delight: This variety offers a classic tomato taste, producing small but flavoursome fruits.
  • Ailsa Craig: Ailsa Craig is renowned for its excellent flavour and reliably good crops.

Remember to consider factors such as disease resistance, growing time, and fruit type when choosing your variety.

Hardening off the plants

Before transplanting your tomatoes into the greenhouse, hardening them off is essential. Hardening off is the process of gradually acclimatising indoor-grown plants to outdoor conditions, in this case, the conditions in the greenhouse.

Begin this process about two weeks before you plan to move them to the greenhouse. Initially, place your tomato plants outside in a sheltered spot for a few hours each day, gradually increasing the duration over the course of 7-10 days.

Avoid exposing them to harsh wind or direct midday sun at first. This gradual exposure helps the plants adjust to the temperature fluctuations, sunlight intensity, and other conditions in the greenhouse. Hardening off is a critical step to prevent transplant shock and ensure the healthy development of your tomato plants.

How often to water tomatoes in a greenhouse

Watering is key to the successful growth of greenhouse tomatoes. Tomatoes prefer a consistent water supply and do not respond well to drying out and then being saturated.

Generally, in the summer heat, you might need to water your greenhouse tomatoes once or twice a day. In cooler weather or when the plants are still small, watering might only be necessary every two to three days. Always check the top inch of the soil; if it’s dry, it’s time to water.

Ensure you water the base of the plants to avoid getting water on the foliage, which can lead to disease. A drip irrigation system can be an effective way to maintain consistent soil moisture levels.

In conclusion, growing tomatoes in a greenhouse in the UK can be a rewarding experience. With the right choice of variety, diligent care and attention to watering, you can enjoy a fruitful and delicious harvest, regardless of the weather outside.


What month do you plant tomatoes in a greenhouse?
In the UK, you can plant tomatoes in a greenhouse as early as late February or early March, as the greenhouse environment protects the young plants from late frosts.

Why are the tomatoes in my greenhouse not turning red?
Tomatoes may not ripen and turn red due to insufficient sunlight or temperatures that are too high or too low. Ensure your greenhouse is situated in a spot with plenty of sunlight, and try to maintain a temperature of around 15-21°C.

Why are my tomato plants dying in the greenhouse?
Tomato plants can suffer in a greenhouse due to overwatering, underwatering, or lack of nutrients. Diseases and pests can also affect their health. Be sure to maintain consistent watering and feeding and inspect your plants regularly for signs of disease or pests.

Can you grow tomatoes in a greenhouse all year round in the UK?
While you can certainly extend the growing season with a heated greenhouse, tomatoes typically need temperatures between 15-21°C to fruit, which can be difficult to maintain in winter months, even with heating. Thus, growing tomatoes year-round may not be feasible.

How often do you feed tomatoes in a greenhouse?
Tomatoes should be fed regularly with a tomato fertiliser once the first fruits have been set. Typically, feeding once a week should suffice.

What happens if you don’t pinch out tomatoes?
If you don’t pinch out tomatoes, especially indeterminate or cordon varieties, they will continue to grow foliage and side shoots, which can reduce the amount of energy the plant directs towards fruit production. This can lead to fewer, smaller tomatoes.

How long does it take for tomatoes to mature in a greenhouse?
From planting, tomatoes typically take between 12-16 weeks to mature in a greenhouse. However, this can vary depending on the variety and the growing conditions.

Should I shade my greenhouse with tomatoes?
If the temperatures become too high in the greenhouse, shading can help to keep it cool and prevent scorching. However, tomatoes need plenty of light to ripen, so balance is key.

Why are the leaves on my tomato plants turning yellow?
Yellow leaves can indicate several issues, including nutrient deficiencies, overwatering, or disease. Check your watering routine, ensure you feed regularly with a balanced tomato fertiliser, and watch for signs of disease.