Updated at: 23-03-2023 - By: Sienna Lewis

If you know when to plant your vegetables in a greenhouse, you can have a productive vegetable garden all year long, beginning in February. One major benefit of greenhouse farming is that planting can begin in January and continue until December. Vegetables can be grown year-round, regardless of the weather, if a greenhouse is heated.

Growing vegetables in a greenhouse requires more than just knowing when to start planting seeds. You also need to think about the seasons and divide plants into hardy, cold-season, and warm-season varieties. Knowing what plants can survive by studying the planting zones in your state is also useful. Zone 1a experiences annual minimum temperatures of -60°F to -55°F, while zone 13b experiences average highs of 75°F to 80°F.

How To Know When To Start Growing Vegetables In A Greenhouse

Due to the greenhouse’s ability to accommodate both cool- and warm-season vegetation, planting season for vegetables can begin as early as February in states like Colorado. Knowing your planting zone and the typical weather patterns in your area will allow you to begin growing vegetables at the appropriate time. Moreover, because you’ll be working inside a greenhouse, you’ll be able to control the environmental factors.

Classify vegetables

Hardy vegetables

Even in a greenhouse, winter gardening is dangerous, but hardy, frost-tolerant crops can be started in December or January. Even so, some Oregon gardeners said that there were vegetables that could survive a severe frost. Beets, spinach, leeks, kale, turnips, carrots, radishes, Brussels sprouts, and Swiss chard are all examples of cold-hardy plants.

Greenhouse Grown Tomatoes - Learn How To Grow Tomatoes In A Greenhouse

The best time to start transplanting frost-tolerant crops is in February or March after you have hardened them off by gradually exposing them to outdoor conditions. When planted in the ground in January, onion bulbs can survive quite cold temperatures. Semi-hardy vegetables thrive in the greenhouse during the cool season and are perfect for those who live in colder climates.

Cool-season vegetables

At the start of March, the greenhouse is ideal for growing cruciferous vegetables like broccoli, cauliflower, cabbage, and lettuce. Light frost is also not a problem for parsley and celery. To get the best results from hardening off and transplanting these vegetables, do so in April.

The second crop of cool-season vegetables can be started in July and August, and then transplanted in late August or early September if you live in a temperate region. They’ll be better able to handle the cooler weather of autumn if you do this. They can be harvested now through early next spring as well.

Warm-season vegetables

In March and April, the greenhouse can be used for growing warm-season crops like tomatoes, squash, eggplant, legumes, peas, cucumbers, peppers, and corn. Keep in mind that late-spring frosts are possible in some locations, so it’s best to plant these crops in the middle of April or the beginning of May. If you want to grow vegetables for the warm season, you need to make sure the greenhouse isn’t too cold.

Know your seasons

Late winter to mid-spring

From late winter to early spring, greenhouse cultivation of hardy plants can begin. The use of a heated propagator allows for the early planting of a wider variety of plants. As an added bonus, mid-spring is a great time to plant fast-growing, tender vegetables.

Late spring to late-summer

Summer vegetables should be planted in the late spring or early summer so that they can be hardened off after the first frost. By midsummer, you should be able to harvest summer crops and throw away overripe cucumbers. It is possible to start a new harvest of lettuce, baby carrots, and salad leaves in a greenhouse by sowing them in late summer.


Certain herbs and vegetables, such as parsley and calabrese, can be started indoors in the fall. Overwintering is ideal for many crops, including peas. Fall is a great time to plant leafy greens in Maine, and early August is a good time to plant cruciferous vegetables.

Is Year-Round Greenhouse Planting Possible?

Because of the ability to regulate the environment inside the greenhouse, vegetables can be grown there year-round. Planting of cold-hardy crops can begin as early as February without the need for artificial lighting in some states like Colorado. Most plants are best started in greenhouses and then transferred to outdoor locations once they have matured.

Then, in March or April, you can start sowing warm-season crops and harvesting cold-tolerant ones. May is a good month for harvesting leafy greens and for transferring indoor-grown vegetables to outdoor beds. Even so, if you want to keep your warm-season crops from wilting in the heat this June and July, you’ll need some sort of cooling system.

Because of the shorter days between November and January, supplemental lighting may be necessary in August and September for winter gardening. All things considered, you want your plants to be ready for harvest by November or December so that you can continue to pick intermittently all through the winter. As an added bonus, a greenhouse may be able to keep your vegetables frost-free during the winter months, depending on where you live.

Where should you SOW your Tomato seeds?

The benefits of an unheated greenhouse to elongating the growing season are well-known. When it’s below freezing outside in the late winter, the greenhouse will be a tad warmer than the outside air.

The temperature must be above 10°C (50°F) for tomato seeds to germinate and for the seedlings to develop normally. In addition, your tomato plants are extremely vulnerable to temperatures of 4°C (39°F) or lower. When your tomato plants are young, you should never let the temperature in your greenhouse drop below 10 degrees Celsius for an extended period of time.

So, if it’s going to be frosty outside, you can’t plant tomatoes in your unheated greenhouse. Tomatoes, if grown in an unheated greenhouse, must be planted after the last date of danger of frost in the area has passed.

The extra five weeks of growing time and five weeks ahead of schedule in planting may sound excessive, but trust me on this. Okay, so let me break down how exactly this works.

We’ve established that after the last predicted frost dates, you can plant tomato seeds indoors in a greenhouse. With an unheated greenhouse, this is the earliest harvest you can expect.

You Should Know! It takes about 5 to 6 weeks for tomato seeds to germinate and grow into sturdy seedlings ready for transplanting.

Tomato seeds should be started indoors about 5-6 weeks before the first frost in your area. As soon as the danger of frost has passed, you can bring your tomato seedlings inside the cold greenhouse. Because the last frost isn’t supposed to happen until the first week of April, I start my tomato plants indoors in late February.

How to Grow Tomato Seedlings Indoor?

  • Get a plug tray to start your tomato seeds in. The dome on the LOVEDAY Seed Starter Trays (See Price) maintains high humidity, which is essential for speedy germination.
  • Compost should be filled into the seedling trays and lightly pressed to level it. Use a general-purpose compost or seed-starting mix to fill the space. (I’ve had good luck with Espoma Seed Starter, but you can use anything you like).
  • Tomato seeds should be planted on top of the compost and then covered with another half an inch to an inch of compost.
  • Wet the compost down so that it is just damp (don’t drown it!) and cover it up.
  • The optimal range for tomato seed germination is between 70 and 80 degrees Fahrenheit (21.1 and 27 degrees Celsius). Using a heat mat to warm the bottom of the seedling trays will significantly increase the rate of germination for your tomato seeds if the temperature in your home is below 64 degrees Fahrenheit. If you’re interested in the cost, I use and recommend the iPower Seedling Heat Mat.
  • Make sure you have a grow light set up above your tomato seed tray. Try out the widely-recognized BESTVA LED Grow Light (Check Cost). It’s great for starting seeds and can even be used to cultivate tomatoes in the house. Tomato seedlings need to have this Grow Light placed 12 to 24 inches above them.
  • You should switch off the Grow Light for the first few days of germination. Once your tomato seeds have germinated, they need about 18 hours of artificial light per day.
  • Transplant your tomato seedlings inside your unheated greenhouse after the last frost date has passed, usually after 5 weeks.

Check out this comprehensive Greenhouse Tomato Guide for more information on growing tomatoes in a greenhouse.

What is the Perfect Time to sow Tomatoes Seeds?

Tomato seeds should be started indoors about five to six weeks before the last date of frost in your area. The primary goal of indoor seed-starting is to cultivate strong, disease-resistant plants from the start.

After the last frost dates for your region have passed, you can move the seedlings into your unheated greenhouse.

Can I directly Sow Tomato Seeds Inside my Greenhouse?

In your unheated greenhouse, tomato seeds can be sown directly. If that happens, you will be at least 5 weeks behind schedule.

When the last frost is over, the greenhouse temperature may even be a tad higher than 10 degrees Celsius (50 degrees Fahrenheit). Tomatoes are heat-loving plants, and the ideal germination temperature is between 70 and 80 degrees Fahrenheit (21-27 degrees Celsius), so this is still too cool for the seeds to germinate.

It will take time for your greenhouse tomatoes to germinate and develop into robust seedlings, which will set back your anticipated harvest dates.

It is possible to successfully cultivate tomato plants from seed by increasing the greenhouse’s temperature to a level at which the seeds can germinate.

What can I do to extend my Growing Season Even More?

Heating your greenhouse in the late winter and ensuring that your greenhouse plants are getting at least 8 hours of sunlight each day will allow you to extend your growing season even further.

If not, greenhouse tomatoes will need an extra 2–4 hours of lighting per day. You should use the BESTVA LED Grow Light (See Price) I described earlier. The optimal placement for this light is 24 inches above your greenhouse tomatoes.

What Happens If You Plant Tomatoes Early or Too Late? 

Timing is crucial when growing tomatoes in an unheated greenhouse. If you take a wrong turn, there are so many environmental factors that will work against your tomatoes.

Tomato growers are divided over the above questions. While simultaneously leading to poor judgment.

Planting Tomatoes Too Early In Your Unheated Greenhouse:

Poor, leggy plants are the result of planting seedlings too early (likely in late January or early or late February, when light intensity is low and not enough to grow tomatoes).

There will be fewer tomatoes at the end of the season as a result of this. The seedlings’ development will be stunted, and they won’t reach full size. They will show signs of not getting enough light by having leaves that are too pale.

Because of this, you’ll need to take measures such as heating the greenhouse and providing supplemental artificial lighting if you want your greenhouse tomatoes to thrive.

Planting Tomatoes Too Late In Your Unheated Greenhouse:

In an unheated greenhouse, you can plant tomatoes late if you don’t mind a shorter growing season.

You see, the length of your growing season will decrease proportionally if you plant tomatoes late inside your unheated greenhouse. If you’re expanding to meet consumer demand, this will severely cut into your bottom line. It stands to reason that you’ll maximize your earnings by getting your tomatoes to market as quickly as possible during the peak demand period.

Can I heat my Greenhouse for Free ?

Yes, you can warm your greenhouse without using any expensive fuel, as there are numerous methods for doing so.

Including thermal mass within your greenhouse, for instance, can aid in maintaining an ideal temperature inside. During the day, when the sun is at its zenith, the thermal mass will soak up heat and store it, and at night, when the sun has set, it will radiate that heat back, keeping the temperature stable.

Compost that has been allowed to decompose can be used in your greenhouse to both increase thermal mass and improve air quality. The compost’s decomposition heat will aid in keeping your greenhouse at a comfortable level. The greenhouse’s temperature can also be maintained using solar heaters.

I mean, you can keep your greenhouse toasty warm without running up expensive utility bills in a few different ways. You can learn more about this subject by visiting the following links:

  • Inexpensive methods of heating a greenhouse
  • Solar Panels for Heating a Greenhouse

Do I need Greenhouse Ventilation During Winter?

Greenhouses require ventilation during the warmer summer months. There is no way to prevent the greenhouse tomatoes from suffocating in the absence of adequate ventilation.

Your Guide to High-Wire Tomato Growing - Greenhouse Grower

What about the winter, though?

During the late winter, if the sun is shining brightly and staying up until noon, the greenhouse temperature can rise dramatically. For this reason, I insist that you put in place an efficient mechanical ventilation system for your greenhouse tomatoes. If you’re interested in a do-it-yourself greenhouse ventilation system, you should read this in-depth article.

  • Automatic, do-it-yourself greenhouse ventilation system for under fifty dollars.

Do You Want to learn more about Growing Greenhouse Tomatoes?

This article will teach you everything you need to know about growing tomatoes in a greenhouse.

The following are covered in depth in this guide.

  • Site Evaluation for a Tomato Greenhouse.
  • Choosing Which Types of Tomatoes to Plant
  • Expanding Soil
  • High-Density Planting of Tomatoes in a Greenhouse
  • Indoor Tomato Crop Timetable
  • Greenhouse tomatoes have specific needs for moisture, acidity, and heat.
  • Developing a Rough Skeleton for Seedlings
  • Seedling Transplantation in a Greenhouse
  • What Kind of Soil Should Be Used to Cultivate Tomatoes in a Greenhouse?
  • Greenhouse tomato training, pruning, and pollination

Honestly, I think this is the best resource out there because it covers everything. It’s a lot of reading, but the information is valuable.

Please consider subscribing to our newsletter if you have a moment to do so. We promise to keep you informed as we discover new and exciting facts about greenhouse agriculture.

Tomatoes plant care


Learning how much water tomatoes require is the first step in caring for them. Start by overwatering, but wait to water again until the soil is completely dry. Depending on how quickly the soil dries out, you may need to water the plants every day or every other day. Misting the plants can also help. As a result, the soil won’t get as caked on the leaves, you won’t have to water as often, and the fruit will benefit. To avoid spreading disease, it’s best to avoid getting wet soil or water on the plant’s leaves.

The plants should be watered in the morning and again about two to three hours before sunset. In order to ensure that your plants receive a steady supply of water, an irrigation system may be useful. Tomato plants require an adequate amount of water, but water drainage is also crucial to their development. A plant can be saved from drowning in excess water by using a pot with drainage holes.


Tomatoes thrive in bright, indirect light, so position them near a window or use quality grow lights to maximize their exposure to sunlight. The warmth of the sun or artificial light is also beneficial to the plant’s growth. Since their optimal temperature range is between 70 and 75 degrees Fahrenheit, the light will assist in getting the greenhouse to that range.


In order to prevent the plant from toppling over on itself, stakes are required. Bamboo stakes are commonly used in gardening, and many gardeners place them right next to the plant. The plant must be tied to the stake as it grows taller. Connect every half a foot along the stalk with a knot.

Best tomato varieties for a greenhouse

Two types of tomato plants exist: determinant and intermediate. Reduced space requirements and bushier growth patterns are common characteristics of determinant plants. However, their tomatoes ripen simultaneously even though the plants are smaller and do better in larger pots. Tomato plants at the intermediate level typically grow to be larger and taller, requiring more support from stakes and possibly even cages. Despite their superiority in confined spaces, the taste of determinate varieties is generally discounted. Even though the tallest intermediate varieties can reach 10 feet in height, they tend to be the most flavorful. Miniature and dwarf tomato plants are widely grown in urban and suburban spaces with limited greenhouse space.

Sungold, Cappricia, Gardener’s Delight, and Sweet Million are some of the most well-liked tomato varieties for use in greenhouses. Sweet Million is a dwarf variety well-suited to containers and smaller greenhouses. Although the aforementioned tomato varieties thrive in a greenhouse setting, many outdoor varieties are also suitable for greenhouse cultivation. It’s true that some plant varieties won’t thrive in the cooler temperatures if you don’t heat the greenhouse (by bringing them inside and not using a heat lamp). It is crucial to read the plant and seed variety information in order to comprehend the necessities of the variety.

How do you prepare the soil for the best crop yield and plant health?

In order to grow and produce fruit, tomatoes require fertilizer and other nutrients. To start, amend the soil with compost to increase its nutrient content. When adding compost to existing soil, it is recommended to “work it in,” or thoroughly incorporate the compost into the soil. Working in the compost serves two useful purposes: it aerates the soil, which promotes healthy root development, and it supplies vital nutrients. The next step is to fertilize the soil in the prepared planting hole for the tomato plant. Fertilizers with a high phosphorus content are ideal for tomato plants.

Finding that sweet spot is essential. Compost, on the other hand, can be too potent for plants in a greenhouse devoid of natural rainfall. Too much compost can be harmful to plants. Add some leaves or hay to the compost to make it more neutral.

Before applying fertilizer, soil should be tested to determine the best kind to use. The fertilizer should include not only phosphorous, but also potassium, calcium, nitrogen, and magnesium at high concentrations. Fertilize the tomato plants when first planted, again when the fruit is about a third of its final size, and again right before harvest. If you want to avoid burning the plant, keep the last two fertilizers a good four inches away from the stem.

Tomato plant problems

Several common issues can arise with tomato plants:

  • They didn’t grow because you planted them incorrectly; as we’ve established, different varieties have different needs. Some people will feel uncomfortable in close quarters, while others will be fine. Consider the variety you planted and how much space it required between plants.
  • Failure to rotate crops can lead to nutrient loss; for example, planting tomatoes year after year in the same spot. In addition to causing uneven ripening and an increase in disease, this will also reduce tomato yields. This can be avoided by rotating the tomato patch each year or by applying a nutrient-rich fertilizer just before planting.
  • Caused by a deficiency in water: tomatoes have high water requirements. For tips on how often to water your tomato plants, see our dedicated care guide.
  • Insufficient water causes tomatoes to split.
  • While a high nitrogen fertilizer is beneficial for the plant’s foliage, it will reduce yields of tomatoes.
  • Insects and/or pathogens

What do you do if you find pests or disease on the tomato plant?

Aphids, cutworms, flea beetles, nematodes, and whiteflies are just a few of the common pests. However, many of these pests are controllable through attentive plant maintenance. Whiteflies and aphids are the most common pests, but all of them can cause damage to your tomato plant. Further steps can be taken to guarantee pest control, including the following:

  • To get rid of aphids, remove any severely infested leaves. Aphids can be eliminated by using ladybugs or an insecticidal soap.
  • Cones made of cardboard can protect young plants from cutworms.
  • Sticky traps can be set out, young plants can be covered, and if the infestation is severe, specific pesticides can be used to get rid of flea beetles.
  • Avoid nematodes by rotating your plants and, if necessary (because it’s expensive and toxic), sterilizing your soil.
  • Sticky traps, ladybugs, a spray hose while watering, and specific pesticides can all be used to get rid of whiteflies.

Quite a few diseases are covered, and while their treatments may differ slightly, they all share an emphasis on disease prevention. Tobacco should be kept away from plants (if you smoke, don’t do it near the plants, and wash your hands thoroughly before handling the plants), and the greenhouse should be well-ventilated. Why you shouldn’t put tobacco anywhere near your tomatoes: Tobacco is a known disease carrier. A healthy tomato plant can be kept disease-free with some preventative care. Give your plants the nutrients they need and keep their environment clean, just like you would if you were trying to keep from getting sick by washing your hands and taking vitamin C.

How is growing tomatoes different than growing other vegetables?

Tomatoes prefer warmer conditions, around 70 to 75 degrees Fahrenheit, and a lot of sunlight. Although this is true of many different types of vegetables, it is still useful information to have when organizing your garden. Tomatoes might not be the best companion plant for a plant that prefers to be kept in the shade. Tomatoes, like many other plants, thrive best when given plenty of room to do so. While some plants can share a pot, these ones need to have their own. As an additional precaution against topple-over, tomato plants require stakes. Some vegetables are too light to require the supports, and these are among them.

The main distinction is that greenhouse-grown tomatoes may require manual pollination. Although they are normally wind-pollinated, when grown in a greenhouse with inadequate ventilation, human intervention is required. You can do this by gently shaking the stem of the plant or by using an electric toothbrush to vibrate the plant and release the pollen.

When to Plant Tomatoes in Your Greenhouse

Sowing Time? A greenhouse means you can start seeds whenever you like. In all seriousness, though, most gardeners aim to grow tomatoes outdoors in the summer.

Finding the “last frost date” for your area is the first step because it provides an approximation of when the threat of winter frost has passed. You can use that to figure out how far in advance you should plant your tomato seeds. You can find the correct last frost date to use by entering your location into one of several online resources. To avoid the risk of a very late surprise frost and because tender plants appreciate giving the ground an extra week or so to warm up, you should start your seeds six weeks before that date and plant the seedlings outdoors between a week and ten days after the last frost date. Seeds are typically sown in the United Kingdom between the first week of March and the last week of April. For information on when to plant and when to harvest various plants and vegetables, please refer to our greenhouse growing guide.

The real benefit of having a well-lit, heated greenhouse is that you can sow your seeds whenever you like, regardless of the season. That doesn’t mean you can start planting seeds right now and have ripe, red tomatoes for New Year’s Day, though. Tomato plants in general require a lot of care, but those grown in cooler climates require even more, and that starts with picking the right plants. In most home greenhouses, where space is at a premium and temperatures can vary, “determinate” varieties, also known as bush tomatoes, are the best option because they are more resilient, better suited to late summer, fall, and winter planting, and take up less space. Determinate tomato plants bear their fruit all at once, unlike indeterminate tomato plants, which bear fruit throughout their growing season (and do especially well in the warm, sunny months). In order to have a steady supply of greenhouse tomatoes throughout the cold months, staggered planting dates should be used. Many people believe cherry or plum tomatoes are the best indeterminate for indoor growing, but it’s important to note that they will grow much taller and will need sturdy support for the vines if grown in a greenhouse. While indeterminate tomato plants tend to yield more overall, determinate varieties typically produce more fruit per unit area. Before we get into the nuts and bolts of planting seeds and caring for plants, it’s important to note that growing “off-season” tomatoes in a greenhouse during the winter’s shorter days (with less natural sunlight) and in colder weather requires greater attention to maintaining proper temperatures and humidity, and positioning plants so they receive as much sunlight as possible (supplemented by grow lights, if necessary).

Growing Tomatoes from Seeds

Plants from the garden center are a less labor-intensive option for kickstarting an indoor tomato garden, but starting with seeds and seeing the first sprouts is more exciting. For those who have never tried it, the extra effort is well worth the reward of seeing their seedlings flourish into full-grown plants. Furthermore, when growing from seed, you’ll have access to a wider selection of varieties.

Even before you see any flowers, leaves, or tiny sprouts, you’ll have to make a crucial decision: which tomatoes to grow. We’ve covered the distinction between determinate and indeterminate types; your choice will depend on your greenhouse’s size and the fruits you prefer to grow. The best varieties for greenhouse growing are usually clearly marked by seed companies and websites; some popular suggestions include Roma VF, Tumbling Tom, and Red Alert for bush plants, and Alicante, Gardener’s Delight, and Shirley for indeterminate plants that will be cordoned (more on that later in the article).

Your work in choosing seeds and preparing them for planting is now complete. The steps are the same whether you intend to keep the plants in pots inside, transfer them to grow bags, or transplant them into the ground inside your greenhouse or outside. Let’s begin with the fact that you’ll need to start the seeds in containers.

Growing Tomatoes in Pots

Some green thumbs follow the lead of commercial operations and germinate their seeds in tiny cell packs for home use. There’s nothing wrong with that, but the seedlings will do better in smaller pots that are 7.5-10 cm in height and wide enough to accommodate their growing roots. Add soilless potting mix, seeding compost, or multipurpose compost to almost fill the pots, leaving about 1 cm of space at the top, and scatter a few seeds near the pot’s center. The majority of the seeds will germinate if you plant only three to five in each container. Put a light layer of soil mix or compost over the seeds and gently press down to ensure good contact with the soil. Put a label on each container indicating the plant’s name and when it was planted.

Next, locate a spot in your greenhouse that gets at least four hours of sunlight daily and put the pots there. The seeds will germinate more rapidly if exposed to more light and heat, so the grow mats and grow lights we suggested are essential. Covering the pots with plastic wrap is another option for maintaining the desired cooking temperature. However, if you opt for the plastic shortcut, remember to take it off as soon as you notice the first sprouts. There is a high risk of “damping off” disease, a fungal infection that can kill your plants if insufficient air reaches them.

Your seeds will rot if you water them too much. Simply sprinkling water into the containers will re-wet the topsoil when it dries out. In about two weeks, you should see seedlings, and in about six to eight weeks, they should be ready to be transplanted into their own, larger pots. During this time, make sure the seedlings have plenty of fresh air by opening a window or running a small fan, and if the greenhouse gets chilly at night, consider covering the seedlings with horticultural fleece to keep them toasty.

The seedlings are ready for transplanting when they are 2-3 cm in height and have a few true leaves. Handle each plant by its leaves as you plant it in its own pot, and dig its roots as deeply as possible into the compost or potting mix. A plant can be moved to its “final” pot, grow bag, or the ground once it has reached a height of about 20 cm. Do not transfer plants to their final outdoor location until the weather is sufficiently warm; in the UK, this is typically around the middle of May.

Don’t skimp on size if you intend to grow tomatoes in containers throughout the season. When a plant finally outgrows its “final” pot, it’s a major undertaking to repot it. A six-liter (or larger) pot is suitable for smaller varieties like bush plants or cherry tomato vines, while a ten-liter (or larger) pot is required for indeterminate varieties. If you’re not using specially designed containers like Airpots, you’ll need to drill lots of tiny holes in each pot so the roots can get some air. Some containers, such as pagodas and watering cans, are more like ornamental garden features. It doesn’t matter as long as the plants have enough room to root and grow.

Tomatoes need plenty of space and bright light, so that’s where you’ll put them. But you should also make sure the containers are set up in a way that will allow you to give the plants some sturdiness. Cages or trellises can help bush tomatoes, too, but vining types absolutely need some kind of support system.

Growing Tomatoes in Grow Bags

In the 1970s, growing tomatoes in grow bags along the inside of a greenhouse’s borders became popular as a way to avoid “using up” the soil in the ground or exposing plants to potential diseases and pests in the soil. They went out of style for a while but have recently made a comeback as people realize what a great way it is to grow tomatoes indoors (or outside, to make the most of a brief growing season).

Ready-to-use grow bags are the most convenient option because they include compost that has been modified to function without the drainage holes typically found in the bottom and sides of pots. But if you’re going to plant directly into compost bags or make your own bags, it’s a good idea to puncture the bottom of the bag in a few places to help the water drain out. Grow bags made of porous material are another option, as they allow for optimal drainage and ventilation for your tomato plants. Use your hands to separate any clumps of compost inside the bag, and then unfold the top slots (or make your own). To avoid damaging the roots of your small tomato plant, you should soak the pot in water for an hour before making room for the plant and its root ball with a trowel. It’s important to dig the hole deep enough so that the top of the root ball fits inside the bag and can be hidden by a light layer of compost. Plant carefully, patting down the topsoil and the plant, and watering thoroughly. Keep in mind that as the plants grow, their roots will spread throughout the bag. There shouldn’t be more than two plants in a 60-liter grow bag, and no more than three in a 75-liter bag. A grow bag support frame, which slides under the bag and has slots for canes or poles to support the plants as they expand, can be a useful investment.

Can you grow tomatoes all year in a greenhouse? - Simplify Gardening

Compost for Growing Tomatoes

Several distinct composting options are currently available. Multipurpose compost can be used for both seeds and plants, while seeding compost is low in nutrients and potting compost has everything your plants will need as they grow. Using the “right” compost at each stage of your plants’ development is the best strategy, but it can get pricey. Buying grow bags and using the compost inside of them is a more cost-effective option than buying separate bags. When most commercial growers use the same quality of compost, you know it must be fine. Many experts recommend using homemade compost for tomato plants, so don’t be shy about digging into your compost pile.

Cordon Tomatoes

Despite its common use as a synonym for “indeterminate,” “cordon” actually refers to the main stem of an indeterminate tomato plant when it develops without side shoots. You might be wondering how a plant could possibly expand without the aid of branches. Sowing seeds and tending to plants is necessary. But first, a quick refresher course in biology.

The roots, the main stem (which grows from the roots), and the leaf stems (also called “trusses”) which grow out from the main stem are the most important structural parts of a cordon tomato plant. Flowers and fruits develop atop the leaf stalks. Indeterminate varieties, as they develop, produce numerous lateral shoots, or “suckers,” either above or below the main stems of the leaves. If left unchecked, the shoots will develop into new “main” stems or produce even more side shoots, depleting the plant of resources needed to produce fruit. So, the best tomatoes come from plants that have been pruned (or cordoned) so that they have just one main stem. This is accomplished by periodically removing the side shoots, which can be pinched off with your thumb and forefinger. If you check on your plants once a week, you will be able to spot the side shoots in their early stages and remove them with ease. Leave the leaf stems above the shoots alone, and you’ll end up with a single tall vine with many tomato-bearing leaf stems.

Stopping Tomatoes

A cordon tomato plant will continue to grow and grow, diverting nutrients to the new growth the whole time, but it will never reach a height that would allow Jack to climb up and find the Giant’s gold unless you stop it. The technique of stopping tomatoes (also known as topping tomatoes) makes this a breeze.

When a plant has developed four to six leaf stems (the number depends on the height of your greenhouse and how well the plant is doing), you should cut the main stem at a point two leaves above the top leaf stem to stop its upward growth. The plant will then devote its full resources to developing new red tomatoes on the existing trusses.

When growing a determinate variety, you won’t have to prune out unwanted growth.

Feeding Your Tomatoes

The tomato plants in your greenhouse won’t need much of anything in the way of special care or feeding. After the first tomatoes have started to set, switch to a high-potash, high-potassium “tomato plant” fertiliser, but during the initial stages of plant growth, use a nitrogen-rich liquid fertiliser once every week or two (follow the instructions on the container to determine the optimal feeding schedule).

A sick plant should not be fed; in fact, starvation is recommended until the plant shows signs of recovery. Furthermore, salts build up in the compost when liquid fertilizer is used. Two times during the plant’s life cycle, you should forego feeding it and instead provide it with a lot of extra water to help flush out the salts.

Watering Your Tomatoes

An average greenhouse tomato plant requires about a liter of water a day, more in very hot and sunny weather and less in very cold and cloudy weather. Watering plants lightly every day is preferable to soaking them once every few weeks. The latter will cause the skins of the tomatoes to crack or split.

Observing the soil and the tomato plants is the best way to determine if they require watering. Leaves shouldn’t be wilting and soil should be moist from the surface to a depth of about 5 cm. Lack of moisture in the soil and wilted or dark green leaves on plants are telltale signs of a water shortage. Soggy soil and pale (almost yellow) leaves, on the other hand, are indicators that your plants are getting too much water.

Tomato Diseases and Pests

Tomatoes grown in a greenhouse are more disease-resistant than those grown in the open. However, two common pests in greenhouses can cause significant damage to your tomato plants.

  • Red spider mites, which thrive in the protected greenhouse environment, are not visible to the naked eye but can be identified by the telltale signs of mottling, bronzing, or speckling on the upper leaf surfaces. Phytoselius persimilis, a predatory mite, can be purchased at a garden center and will eat the red spider mites. This should be done immediately, and water should be misted onto the underside of the leaves (where the mites nest) on a regular basis. Pesticides won’t work on red spider mites, but they will kill the beneficial bugs.
  • Whitefly: Whiteflies emerge in the spring, first appearing as tiny (1.5 mm), scaly crawlers and then maturing into small white moths. Whiteflies are frequently a problem in greenhouses, so prevention is of the utmost importance. The first step is to release the parasitic wasp encarsia formosa into the greenhouse in early April, where it will feast on the nymphs. Hang sheets designed to trap adult flies near your plants later in the month. Unfortunately, whiteflies have developed resistance to many common pesticides, and your tomatoes can soak up even the ones that still work. Tomatoes grown in greenhouses are still susceptible to the same pests and diseases that plague outdoor crops. If you have a problem with aphids, you can grow marigolds near your tomatoes to attract hoverflies, or you can use one of several chemical sprays. Disfigured, mottled yellow leaves are a telltale sign of the mosaic virus, which is also a serious problem in the United Kingdom. If you remove the leaves from the plants and the greenhouse right away, wash your hands thoroughly afterward, and give the sick plants lots of food and water, they should bounce back quickly.

Related Questions

Can you grow tomatoes year round?

The quick answer is yes. Tomatoes can be grown all year round in a greenhouse with the right climate control and soil maintenance.

Can tomato plants be overwatered?

Yes, and cracks in the tomato fruit and bumps on the leaves are the earliest signs of overwatered tomato plants. Saturated soil will have puddles around the plant that don’t drain after a few hours.

When should you plant tomatoes in a greenhouse?

Typically, tomato seeds should be planted around six weeks prior to the expected date of the last frost in your area. As a rule, this takes place in the month of April. Planting the seeds earlier than April is possible because of the greenhouse’s protection from frost. In fact, if the greenhouse’s environment is controlled, they can be planted at any time of year.


The main benefit of greenhouse gardening is that it allows you to be productive all through the year. But when is the right time to plant seedlings for a greenhouse vegetable garden? Planting and sowing can begin as early as February in states like Colorado.

If you are familiar with your planting zone, growing seasons, and crop types, you can grow anything in a greenhouse. The greenhouse can be used as a shelter from frost or to get an early start on planting vegetables indoors before the weather is favorable outside.