How to Grow Tomatoes in a Greenhouse – 6 Tips

How to Grow Tomatoes in a Greenhouse

A greenhouse grown tomato bursts with flavor and color. Without a doubt, there are definite benefits to cultivating this delicate crop in a protective environment. In this article, we will explore how to grow tomatoes in a greenhouse.


6 Tips for Growing Tomatoes in Your Own Greenhouse


One of the main crops I chose to plant in a greenhouse was tomatoes. My state regularly suffers from sudden spring and early autumn frosts combined with a short growing season, so greenhouse cultivation gave me the freedom I needed to grow juicy tomatoes without worrying about the fickle attitude of Mother Nature.

Within my greenhouse, I was able to gain multiple harvests of tomatoes with only minimal effort.


1. When Should I Plant Tomato Seeds in a Greenhouse?

Cheery tomato seeds in a plant starter pot

Will you be gardening in a heated or unheated greenhouse? Do you have proper greenhouse lighting? These are major questions that you’ll need to consider when deciding when to plant tomato seeds in a greenhouse.

I had two greenhouses. One had an HVAC system and lighting. Within its confines, I could easily start and grow tomato plants 365 days a year because I had complete control of the lighting and temperature.

My other greenhouse was an unheated greenhouse with no electronic lighting, but sunlight flooded through the plastic sheeting of the greenhouse. Within that structure, I had to start tomato seeds in the late spring after all danger of frost has passed.

I would sow my tomato seeds indoors in the middle of March and then transplant the seedlings to the greenhouse. However, in my state, I would wait until the first of April to start tomato seeds inside the unheated greenhouse. I wanted to ensure sufficient light and warmth to give the plants a good start.

Remember, in order for tomato seeds to germinate they require a soil temperature of at least 50 degrees Fahrenheit. I could easily achieve that by starting my tomato seeds in a sunny window of my home but I needed to wait a little longer to start the seeds outdoors in the greenhouse.


2. When to Plant Tomato Plants in an Unheated Greenhouse

Tomato seedlings in a container with a garden marker

Tomato seedlings are easily damaged at temperatures of under 39 degrees Fahrenheit. I wanted to ensure that the frost date had passed in my geographic region so my seedlings would not be damaged in my unheated greenhouse.

If you plant your tomato plants in your unheated greenhouse in April or May then you’ll enjoy harvests from July into October.

In my climate-controlled greenhouse, I planted tomatoes in both the early spring and autumn to guarantee a year-round yield.

Ensure that your tomato seedlings stand at least eight inches tall with tiny flowers just starting to open when you move the tomato pots into your unheated greenhouse.

When planting seedlings in the greenhouse, try to space them at least one and a half feet to two feet apart. If you are placing pots in your greenhouse then space the containers about two feet apart to promote ample growth and air circulation to prevent the development of fungal infections.


3. What Size Pots for Tomatoes in a Greenhouse?

Tomatoes growing in fabric grow bags

When growing tomatoes in a greenhouse, I will plant the tomatoes directly in the raised beds of the greenhouse and I will also use pots or grow bags.

Pick pots that measure 24 inches deep by at least 12 inches across. You can use plastic or clay pots. I prefer plastic because they are more lightweight so easier to move inside the greenhouse.

To save money, you can plant your tomato plants in five-gallon buckets. Just remember to make drainage holes in the bottom of the bucket.

Fabric grow bags have become an economical, easy way to grow tomatoes. The vigorous root system of the tomato plants hit the side of the grow bag and automatically self-prune instead of circulating the pot. The self-pruning caused by the bag ensures the root system to offshoot and produce fibrous hairs which encourage whole plant health.

I have to admit, I am in love with grow bags. They are easy to move and promote airflow. Many of the grow bags even have small handles so I can easily pick up the tomato plants to rearrange the interior of the greenhouse.

The only drawback to bags for tomatoes is that in the extreme heat of summer, the plant’s root system dries out quickly so you’ll have to water more often.

I use a grow bag that will hold from 15 to 26 pounds because I believe they provide the best room for optimum growth. Never use grow bags that are too small or the plant will become top-heavy and topple over. The grow bags are so lightweight that they do not adequately weigh the plant down in the upright position if there is ample top growth.


4. How to Pollinate Tomatoes in a Greenhouse

Tomato flowers ready to be pollinated

Tomato flowers depend on air movement and the wind for pollination. Inside a crowded greenhouse with other plants, there is extraordinarily little wind to create pollination. You can mechanically pollinate the tomato plant flowers or you can maintain bee hives in the greenhouse.

The tomato plant has both male and female parts to ensure pollination. Without a pollinator, tomato plants will self-pollinate about 20 to 30 percent of their flowers. Simple gravity will pull the pollen from the plant’s flowers and as the pollen falls it pollinates lowering flowers. Also, walking by the tomato plants and accidentally bumping them can assist with pollination.

I have successfully used fans and air blowers in my greenhouse to pollinate the tomato flowers.

You can also hand pollinate by swiping the flowers with a paintbrush or feather. Many people opt to use a combination of pollination methods to ensure that you have an ample crop of tomatoes.

Artificial pollination of greenhouse tomatoes flowers with a paintbrush


5. How Long Can a Tomato Plant Live in a Greenhouse?

When grown outdoors, a tomato plant will live only a single season which spans from six to eight months. However, grown indoors you can easily nurture the plant to live much longer. If you maintain the perfect growth conditions during the year, you can easily get a tomato plant to live for two to five years depending on the variety.

Any deficit in the greenhouse shortens the life of a tomato plant such as a lack of water, improper sunlight or nutrient-poor soil. Diseases and pests will also impact the lifespan of the plant.

Unfortunately, one thing to consider is that just because a tomato plant will grow for two to five years does not mean it will look fabulous or continue to produce an ample crop. Tomato plants can quickly become lanky and flowering diminishes. The number of tomatoes produced takes a nosedive.

If your aging tomato plants look less than ideal and are producing poorly it’s time to consider digging them up and replacing them with young, healthy plants.

Hydroponically grown tomato plants usually grow better and produce more tomatoes than plants grown in soil. You can expect a hydroponically grown tomato to look healthy and continue production for eight to 11 months. In some situations, a hydroponically-grown tomato plant will look fantastic and produce well all the way until it reaches two years of age.

One way to extend the life of your tomato plants is to remove the tomatoes before they fully ripen on the plant. Pluck a tomato when it appears half green and half pink which indicates the tomato is no longer taking nutrients from the plant.


6. Picking Between Determinate and Indeterminate Tomato Plants

Indeterminate tomato plants

If you want a tomato plant with a long-life span, then avoid the determinate tomato plant which is a bush type of plant. It will only grow to two or three feet tall and produce fruit for four to six weeks. Once the determinate tomato plant stops producing tomatoes then it immediately dies.

When you do not have a great deal of space in your greenhouse then you might want to consider growing determinate tomato plants and then just replace them as they reach the end of their lifespan which is what most commercial farmers do.

A single determinate tomato plant is an impressive producer with many producing up to 10 pounds of tomatoes before dying. They are a great type of tomatoes to grow in cooler climates where the growth cycle is short because you’ll be able to attain an ample crop in a short time.

I like to grow determinate tomato plants in my unheated greenhouse because I can produce a lot of tomatoes in a short time period.

In a heated greenhouse, indeterminate tomato plants are ideal because they will continue producing fruit throughout their lifespan so you can enjoy tomatoes year-round.



When learning how to grow tomatoes in a greenhouse, you’ll have to first determine if you will be using a heated/cooled greenhouse or an unheated greenhouse. With the optimum growing conditions, you can grow and harvest tomatoes year-round. Unfortunately, with an unheated greenhouse, you will only have one season to enjoy tomato production.

About Kimberly Sharpe 8 Articles
Based in Florida, Kimberly Sharpe has worked as a full-time freelance writer since 2006. She writes for numerous online sites and publications in a wide array of industries such as gardening, home design, DIY, real estate, home remodeling, lighting, cultivation methods, and more. Gardening, hydroponics, and outdoor design are hobbies she is passionate about in her spare time.