Growing your own Tomatoes in a Greenhouse or Polytunnel

Sweet, succulent and oh so delicious, vine ripened tomatoes taste like summer and they’re unbeatable in fresh salads, sandwiches and cooked dishes too. Also tomatoes are extremely healthy, much more than the shop bought version. However, tomatoes are heat loving plants that have a relatively short growing season and they can’t survive outdoors when temperatures drop in the autumn. If you want to enjoy homegrown tomatoes all year round, there is one solution though: grow tomatoes in a greenhouse!

Greenhouse tomatoes are every bit as scrumptious as tomatoes grown in the garden, but using a tomato hot house or tomato greenhouse can dramatically extend your growing season and allow you to grow fresh tomatoes longer. That said, there are some specific things to know about greenhouse tomato plant care, but we’ll cover all the greenhouse growing tips you need in this simple guide!

Benefits of growing tomatoes in a greenhouse

Growing tomatoes indoors in a greenhouse has many benefits, including season extension and pest reduction. By keeping tomatoes in an insulated and protected environment, you can grow tomatoes throughout the changing seasons and even through the winter. Plus, common tomatoes pests, like tomato hornworms and birds, are much less likely to be a problem in a greenhouse!

Since they allow you to grow tomatoes year round, greenhouses drastically increase the amount of tomatoes you can produce at home. On top of that, you’ll have more control over your plant’s environment, which can reduce the incidence of fungal diseases and other pathogens and plant pruning and trellising can be much easier in a greenhouse too!

How to plant tomatoes in a greenhouse

Unlike plants intended for the garden, tomatoes grown in greenhouses can be planted at early spring. Tomatoes can also be grown from seeds or nursery starts depending on your timeline and your budget. Tomato seeds tend to be less expensive, but tomatoes started from seed can take between 60 and 100 days to fruit.

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To start tomato seeds, use a rich, seed starting mix and plant 1 to 2 tomato seeds per cell in seed starting trays, covering the seeds with about ¼” of soil. Seeds will germinate quicker if you keep the soil moist and place a heating mat under the trays. Once the seeds have germinated and produced at least 2 sets of true leaves, transfer on your tomatoes to a larger pot or growing container.

As tomatoes mature, they can be transplanted into the soil or into raised beds, or they can be grown in individual pots. Terracotta pots and fabric grow bags work well for tomatoes, just as long as they are well draining and have plenty of drainage holes. Individual tomato plants will need at least a 5-gallon container to grow in, but larger containers will encourage tomato plants to grow more prolifically.

How to care for tomato plants

Once your tomatoes have begun to grow, caring for tomatoes in a greenhouse is quite simple, but there are a few tips to keep in mind. In particular, while pests won’t be as much of a problem in a greenhouse, indoor tomatoes will need to be pollinated by hand to ensure a good fruit set.

Hand pollination can be done either with a makeup brush or a Q-tip, or you can gently shake your tomato plants to disperse pollen amongst their plant’s flowers. When your tomato plants are in bloom, aim to hand pollinate tomatoes about every other day. Or, if you’d like to “automate” this process, you can leave the doors or windows to your greenhouse open during the day and allow pollinators and beneficial insects to do the work for you!

While pollination is definitely something to keep in mind with greenhouse tomatoes, there are a few other key growing tips that will help you grow a massive tomato harvest and maintain healthier plants too!

Lighting

Tomatoes are full sun plants, which means they need about 6 to 8 hours of bright light daily. If your greenhouse doesn’t receive enough light, you’ll need to install grow lights to keep your plants productive.

Water

Tomatoes also crave regular watering and they should be provided with about 1” of water per week. Installing a drip irrigation system can be very useful as it will automate your watering for you and it also keeps plant leaves dry, which is essential for preventing fungal diseases. If you’re hand watering tomato plants, water the plants at the soil line when the top 1 to 2” of soil feels dry to the touch.

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Temperature and humidity

Heat loving tomato plants will start producing fruit when temperatures are between 70 and 80F during the day and 60 to 65F at night. Adding insulation or installing a heater can help you moderate the temperature in your greenhouse and encourage your tomatoes to fruit earlier. Tomato plants will struggle when temperatures fall into the 50s, so you may not be able to grow tomatoes all year round if you don’t add greenhouse insulation.

It’s also important to maintain humidity levels in your greenhouse as super high humidity can cause plant issues, like edema and mildew. Installing fans near your tomatoes will strengthen your plants’ stems and also improve air flow.

Fertilizer

Tomatoes are heavy feeding plants that will need to be fertilized throughout the growing season. For best results, apply a balanced, liquid fertilizer to your greenhouse tomatoes twice a month.

Pruning and staking

Determinate-type tomatoes rarely need to be pruned or staked; however, indeterminate-type tomatoes can become massive plants that will quickly overwhelm a small greenhouse if you don’t use tomato stakes. Supporting the indeterminate tomatoes is essential in the greenhouse and outdoors too. Often, the most cost effective solution for greenhouse tomatoes is to attach plastic twine to a heavy gauge wire strung above your plants and then train your tomatoes to climb up the twine with plant clips.

Beyond staking, indeterminate tomatoes will also need to be pruned regularly to keep them from getting overgrown and to boost your harvest yields. When your plants are at least 12 to 18” high, prune indeterminate tomatoes down to one or two main stems, which makes trellising much easier. After that, pinch away tomato suckers at least once a week to redirect your plant’s energy towards producing more tomatoes!

Best greenhouse tomato varieties

Both indeterminate and determinate tomatoes can be grown in greenhouses, but what types will work best for you will depend on your growing space. Indeterminate tomatoes are more productive plants, but they take up a lot of space and they may not be ideal for small greenhouses. Determinate tomatoes produce all of their fruit in a short period of time and they don’t yield quite as many tomatoes, but these plants stay compact and they won’t overwhelm small greenhouses.

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Some of the most popular types of tomatoes to grow in greenhouses include:

  • Cherrola
  • Sungold
  • Shirley
  • Golden Sunrise
  • Sungrape

Summary

Growing tomatoes in a greenhouse is a great way to have fresh tomatoes all year round without needing to worry about garden pests. With a few growing containers and tomato seeds, you can grow cherry tomatoes, heirloom tomatoes and plum tomatoes for canning even in the depths of winter with a greenhouse. Once you discover how simple it is to grow tomatoes indoors, you may never want to grow tomatoes in a vegetable garden again!

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