How To Grow Tomatoes In A Greenhouse – Step By Step!

There is nothing that compares to the fresh taste of your own homegrown tomatoes! If you live in a cooler climate like I do which is a  growing zone 3 with a short growing season, growing tomatoes in a greenhouse is a must to have any kind of crop of tomatoes, especially if you like to grow enough to can and make sauces with. 

This article will show you how to grow tomatoes in a greenhouse using tomato seedlings. We will cover how to prepare your soil and when to plant your tomatoes in a greenhouse. Tips for fertilizing, supporting, and how to prune tomato plants for the best yields. I will talk about common tomato diseases and lastly harvesting your tomato crop!

Why Grow Tomatoes In A Greenhouse?

The main reason to use a greenhouse to grow tomatoes in is so that you can provide a longer growing season for tomatoes that require a warm and longer growing season if you live in a colder growing zone.

You can help control the environment that they will be growing in by adding in more heat if need be earlier on before the heat of summer hits and also in the cooler fall weather. 

Your plants will also be protected from strong winds and damage from hail storms which will set the plants back and interfere with good crop yields.  

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When To Plant Tomatoes In Your Greenhouse

When to plant tomatoes in your greenhouse will depend on a couple of factors. The highs and lows of your greenhouse temperature and whether or not you have a heated greenhouse. 

Tomato seedlings can safely be planted in your greenhouse once the night temperatures stay at a steady 7 degrees celsius, 45 Fahrenheit, or warmer. This could be in early April if your greenhouse temperatures are steady. If the nighttime temperatures are dropping a bit below and you are itching to get your tomatoes out in the greenhouse you will need to use a heater to keep it warm enough at night so you don’t risk losing your tomatoes to frost. 

I highly suggest that you invest in a greenhouse thermometer that will tell you what your greenhouse temperature reaches during the day as well as what the temperature drops down at night. This is the best way to know the exact temperatures that your greenhouse reaches so you will know when you can safely plant your tomato seedlings in your greenhouse. 

This is a good greenhouse thermometer that I started with that will give you the high and lower temperatures of your greenhouse. It is also a good idea to keep a greenhouse journal with these temperatures written down to refer to year after year. I write down the dates, the temperature it drops to outside of the greenhouse, and what the temperature goes down to inside my greenhouse and the daytime highs. That way I know that if it goes down to -5 at night, inside the greenhouse stays above zero. 

Choosing Tomatoes To Grow In A Greenhouse

Really any tomato plant will grow in a greenhouse and do well with the extra heat when living in a cooler growing climate. The main factor that will determine what variety of tomatoes you will grow in your greenhouse will be the size and height of your greenhouse.

If you have a smaller-sized greenhouse you will want to choose tomato varieties that are either vine-growing which are called indeterminate tomatoes or smaller compact bush tomatoes called determinate. You can also grow a variety of cherry tomatoes that grow in baskets and hang down that you can hang from hooks above in your greenhouse. Visit your local nursery and read the tags of the tomato varieties that they have growing for your area. 

You can also grow tomatoes in large pots or grow bags in your greenhouse and place them where it works best for your greenhouse. 

I have a large greenhouse so I have done many different types of tomatoes. At the end of my tomato row, I plant a couple of Sweet 100’s which are vine tomatoes that produce tons of small clusters of sweet tomatoes. I plant bush beefsteak tomatoes down the rest of my tomato bed. I also have a hanging tomato basket that bears lots of cherry tomatoes. All have done very well in my greenhouse. 

Growing Tip: Be sure to write down the tomato varieties you have chosen to grow in your greenhouse/garden journal. Document how they grew and produced so that you know if you want to grow them again next year.  

Where To Plant Tomatoes In A Greenhouse

A few things to consider when deciding where to plant your tomatoes in a greenhouse. Tomatoes need a lot of direct sunlight so if there is a sunny spot in your greenhouse that gets full sun throughout the day that may be your deciding factor. 

Tomato plants get very large and will take up a lot of space. Tomato plants will need at least 18-24 inches apart for growing space. They will require some staking and spacing out for good air circulation throughout the plants. Where in your greenhouse will be the best spot to also provide support? You may need to use the ceiling frame for tying. 

Will you be using large pots or a grow bag for growing your tomatoes or will you be putting down a permanent bed on the ground? Will you be placing companion plants in front of your tomato plants? These are the things to keep in mind when growing your tomatoes in a greenhouse. 

How To Prepare Soil For Tomatoes In A Greenhouse

Whether you are using large pots for growing greenhouse tomatoes or placing your tomato seedlings into a prepared bed you will need to get the soil ready and amend it. Tomatoes do well in fertile soil for maximum growth and production. So While our tomato seedlings are still growing at home or at the Nursery we can start to get our soil ready.

I like to work my soil a bit as it gets compacted over the winter months and I like it a bit softer to work in and allow my tomato roots to easily grow down and around.

I use this soil test kit to get an idea of where I am with soil nutrients. I add a bit of steer or mushroom manure for nitrogen if it looks like I am low when I do my test. Be sure to only add a bit of this as too much nitrogen will curl or burn your tomato leaves. I’ve had it happen before. 

If your soil looks like it needs a boost a good thing to add is a mix of manure, peat moss, vermiculite, and compost. If you can’t get these items individually your local nursery probably carries bags of this already mixed and ready to go. It’s a good way to enhance your soil with nutrients and water-holding amendments. 

If I have my own compost ready to go I will top dress with that but I usually don’t have enough compost to go around with all my gardens. 

When I plant my tomato seedlings I will add other nutrients into that hole at the time of planting. 

Hardening Off Tomatoes 

If you have started your tomato plants from seeds and have them growing indoors you will need to slowly adjust them to the temperatures of your greenhouse.

Start by placing them in the greenhouse for a couple of hours at a time and don’t place them in the direct hot sun in the greenhouse. This will wilt them and possibly even burn the young leaves. Gradually build up to a full day in the greenhouse and then your tomato plants will be accustomed to your greenhouse temperatures. 

If you have bought tomato plants from your local nursery then the plants will already be hardened off and ready to plant in your greenhouse. 

Supplies needed for growing tomato plants in a greenhouse

• Supportive Garden Stakes – works to hold the main stem of your tomato plant as it grows upward and gets heavy
• Tomato Cages – useful for supporting and holding up leaves of bush tomato plants
• Tomato Clips – helpful for clipping onto stems to hold upright 
• Velcro Garden Tape – soft reusable velcro tape that you can cut to the size needed for many uses
• Hand Trowel – needed for digging deep holes for your tomato seedlings
• Tomato Fertilizer – a must for short growing seasons for healthy plants and high yields

Planting Tomatoes In a Greenhouse – Transplanting Tomato Seedlings

Now that we have our soil ready, and our tomatoes are hardened off, the temperatures are suitable, it is time to plant tomatoes in the greenhouse!

Before I start digging my tomato holes I like to place my plants along the bed and measure out to get an idea of how things are going to look with the spacing. If I am happy with that I will start digging the tomato holes. 

To achieve nice healthy tomato plants we need to do a couple of things.

• Step One: First of all, we need to dig our holes deep, tomato plants like to be planted deep! Planting tomato seedlings deep will help them to form more roots along the buried portion of the tomato stem helping them to grow better.
• Step Two: After my tomato holes are dug, I sprinkle in some extra nutrients. Bone meal to help get the roots of the plants off to a good start. Organic tomato/vegetable granular fertilizer so they get the good growing nutrients and micronutrients they need. I work this into the soil in the hole that I have dug with my hand trowel.
• Step Three: My next step is to add some water to the holes. We want to make sure our tomato seedlings will have a good drink of water to get them off to a great start after transplanting them. 
• Step Four: Gently remove your tomato seedling from its container. If the roots are all bound up, gently loosen them apart. 
• Step Five: We are going to remove the bottom lower leaves of the tomato seedling and place them into our dug hole up to the next set of tomato leaves. Cover the hole back up with the outside dirt and gently pat it down around the base of your plant.

I find I get the best results with my tomatoes by following this system. Your tomato plants should be good for a couple of days before they need watering again. Check the moisture content with your hands by digging down a bit below the topsoil level. 

Watering Tomatoes In A Greenhouse

For the next couple of weeks after transplanting tomato plants, I like to hand-water them. They are still small enough that they are not consuming a lot of water yet so I want to control how much water they are getting and I find it enjoyable! You will need to keep the soil moist but not soggy. 

Once the tomato plants start really growing and the days are getting warmer I like to set up drip lines to make it more hands-off and put them on a timer to ensure that the tomato plants are getting enough water throughout the day on those sunny days when the temperatures rise in the greenhouse. If you have a larger-sized greenhouse having a drip line in place helps cut down on the amount of time spent watering during the hot season. 

So how much water do greenhouse tomatoes need? It’s hard to say the exact amount of water your tomatoes will need. You can’t tell just by looking at the top of the soil surrounding the plant so it is best to dig down into the dirt a couple of inches around the outside of your tomato roots to get an idea of how the moisture content feels there.  

In the heat of summer, I have my drip lines running in the morning and in the evening as well. When the temperatures drop in the fall I go back to watering just once a day. 

If you need more help deciding your soil moisture levels then a soil moisture meter will help give you the reading of your moisture. It will tell you if your soil is wet or dry and give you a more accurate decision of whether or not you should water your tomato plants.

How To Support Tomatoes In A Greenhouse

From my experience of growing tomatoes, I have had to stake and support all of them. Even the bush-type tomatoes. They just get too big and I have had some of the tomato branches split from the heavy weight of tomatoes when not supported. There are a few different ways to help support your greenhouse tomatoes and I have used a variety of these ways throughout the season.

Vertically On Stakes

A common way to support growing greenhouse tomatoes is to use a strong tall stake.  As the tomato plant grows ties or velcro garden tape can be used to train the main stem up along the stake supporting it. 

Growing Tomatoes In A Greenhouse Tips

• Keep the greenhouse well-ventilated during the hot season. This can be done by making sure all doors and windows are fully opened so that a crosswind can vent through your greenhouse. If you can’t see the leaves on your plants moving a bit when it’s windy out then you need to set up another window or vent. 
• Set up an automatic drip system for your plants. Doing this is such a time saver in the heat of the summer and ensures that your plants will get that extra watering throughout the day to keep them from wilting during the heat.  
• Trim off yellowing or moldy leaves from plants and remove them from the greenhouse.
• Fertilize regularly to ensure optimal growth and production

FAQs About How To Grow Tomatoes In A Greenhouse 

How do I start tomatoes from tomato seeds? 
I have an article on starting tomato seeds indoors that you can read and follow step by step so that you can save money and have your own tomato seedlings to plant. 

How long will tomato plants live in a greenhouse? This depends greatly on your climate. I can only speak for a zone 3 climate. If you can heat your greenhouse in the spring and fall you can have a growing period of up to 8 months. 

More helpful Greenhouse Growing articles to read for tips and step-by-step growing!

• Too cold to grow basil outside in your climate? Learn all the tips for growing basil in a greenhouse here!
• Grow green beans in a greenhouse for high yields!
• How to grow cucumbers in a greenhouse for a longer growing season!

Happy planting!

Don’t forget to pin this post to your favorite gardening board so that you can come back to it when you are ready to grow tomatoes in a greenhouse!