How To Grow Tomatoes In A Greenhouse

how to grow tomatoes in a greenhouse

Tomatoes are delicious and will flourish in a greenhouse. They require a bit more care than some of the herbs you may be growing. You'll need to take some further steps to ensure that your tomatoes grow big and strong.

To grow tomatoes in a greenhouse, you'll need consistently warm temperature (70 - 75 degrees Fahrenheit, no lower than 60 degrees), plenty of sun, & good ventilation. Tomato plants should be staked, and soil will likely need fertilizer. Best tomato varieties for a greenhouse include: Sungold, Cappricia, Gardener's Delight, and Sweet Million.

how to grow tomatoes in a greenhouse

To start your tomato plants you will need:

  • Tomato seeds or plant
  • Stakes
  • String
  • Soil nutrients

To start your tomato plants you will need to prepare the soil by adding fertilizer and nutrients. If you are using tomato seeds you should plant them about 2 to 3 inches under the soil. If you are using pre-grown plants, you should plant the tomato plant so that the stem of the plant is underground. Put a stake next to the plant and as it grows, tie parts of the stem to the stake. This will prevent the plant from collapsing on itself. 

Tomatoes require warm and consistent temperatures, ventilation, and plenty of sun. Tomatoes grow best between 70 and 75 degrees Fahrenheit during the day and no lower than 60 degrees Fahrenheit at night.

Although humidity can be beneficial to your greenhouse, too much of it can benefit diseases more than your tomato plants. Keeping the humidity below 90% and having good ventilation so there is constant air flow and a way for hot air to escape will decrease the chance of disease multiplication and maintain a good humidity level. Some options to vent hot air out of your greenhouse can be as simple as opening a window or having an exhaust fan. The last condition to consider, is the amount of sunlight. Tomatoes require lots of sunlight so putting them close to a window or grow light will benefit the fruit.

Tomatoes plant care

Watering

The first step in tomato care is understanding how much water they need. A good rule of thumb is to start with over-watering and do not re-water until the soil is dry. You should be watering the plants every day or every other day depending on how fast the soil dries out. It is also beneficial to mist the plants. This will help distribute the water evenly, prevent you from over-watering, reduces the amount of soil on the leafs, and it aids the fruit. It is important to try to not splash the wet soil or water onto the plant leafs to prevent disease.

It is best to water the plants in the morning and stop watering 2 to 3 hours before sunset. Irrigation systems can be beneficial so you do not forget to water the plant and they will have consistent water intake. The adequate amount of water is important for tomato plant growth but water drainage is also very important. Having a pot that has holes in the bottom to let excess water out will prevent your plant from drowning in too much water.

Light

Tomatoes require lots of sunlight so putting them close to a window or under good grow lights will help your tomatoes grow. Additionally the sunlight or artificial light helps heat the plants. Since they grow best between 70 and 75 degrees Fahrenheit, the light will help the greenhouse reach that temperature.

Staking

Stakes are important to keep the plant from collapsing on itself. Many gardeners use bamboo stakes places next to the plant. As the plant grows up, tie the stalk of the plant to the stake. Tie a every half foot of the stalk.

Best tomato varieties for a greenhouse

There are two genres of tomato plants: determinant and intermediate. Determinant plants tend to take up less space and have more compact bushes. These do best in large pots and require more watering but their tomatoes all ripen at the same time and they are smaller plants in general. Intermediate tomato plants tend to grow larger and taller and will need more support from stakes or even may need cages to help support the stalks. Determinate varieties will be better for smaller spaces but they are considered to be less tasty. Intermediate varieties can get up to 10 feet tall but are typically more tasty. There is a category called miniature and dwarf tomato plants which are popular for very small greenhouses.

Some popular tomatoes especially for greenhouse use are the Sungold, Cappricia, Gardener's Delight, and Sweet Million varieties. The Sweet Million variety is a smaller variety that is best for smaller greenhouses and pots. The above varieties are great for growing in a greenhouse but many outdoor tomatoes can be grown in a greenhouse as well. If there is no heating in the greenhouse (i.e. growing the plants inside without a heat lamp) then the plants life will be extended but certain varieties will not do well in the cooler climate. Reading the plant and seed variety information is important in understanding the requirements for the variety.

preparing the soil for the best crop yield and plant health

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

Tomatoes need fertilizer and nutrients to flourish. First you need to add compost to the soil to provide nutrients. You should add the compost to the existing soil and work it in, meaning mix it really well with the existing soil. This has two practical reasons: working in the compost breaks up the soil to help root growth and health and it provides essential nutrients. Next, you should dig the hole for the tomato plant and put fertilizer in the hole before planting the plant.  Tomatoes like fertilizers with a high phosphorus level.

Again, finding the correct balance is key. For compost, in a greenhouse without natural rainfall the compost can be too powerful for the plants. If you put too much compost in or it can burn the plants. To neutralize the compost you can add leaves or hay to the compost.

To determine the best type of fertilizer, you should test the soil before adding fertilizer. The fertilizer used should have a high level of phosphorous and also contain potassium, calcium, nitrogen, and magnesium. Fertilize the tomato plants when you first plant them, once the fruit is about a third the final size, and when the tomato is picked. Apply the last two fertilizers about 4 inches from the stem to prevent burning.

Tomato plant problems

There are a few common tomato plant problems:

  • You planted them wrong: As discussed earlier, each variety will have different requirements for growing. Some will need more space or more stakes while others will be okay being close to each other. Look at the variety you planted and see how far apart they need to be planted from each other.
  • Not rotating the plants: If you plant tomatoes for consecutive years in the same area the soil will lose nutrients. This will make the tomatoes ripen unevenly, more disease, and lack of productivity. To avoid this either plant the tomatoes in a different space each year or apply the fertilizer with the needed nutrients prior to re-planting.
  • Lack of water: Tomatoes need lots of water. Refer to the tomato plant care section for more information about watering.
  • Too much water: the tomatoes will crack
  • Nitrogen high fertilizer: while this is great for the foliage, it will lead to less tomatoes grown
  • Pests or diseases

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

            Some common pests are aphids, cutworms, flea beetles, nematodes, and whiteflies. While many of these pests can be managed by proper plant care. The most common one to have to deal with are whiteflies and aphids but the other pests can have detrimental effects on your tomato plant. There are some other measures that can be taken to assure pest control:

  • Aphids: Cut off the leafs that are heavily infected by aphids. Ladybugs can be used to eat aphids or there are some insecticidal soaps that can be applied.
  • Cutworms: Can be managed by putting cardboard cones around the seedlings.
  • Flea beetles: Place sticky traps, cover young plants to protect from the beetles, or use certain pesticides if sever infection occurs.
  • Nematodes: Rotate the plants and in severe infection situations sterilize the soil (this is expensive and toxic so should be a last resort).
  • Whiteflies: Use sticky traps, ladybugs, when watering use a spray hose to get rid of the insects, or use certain pesticides.

The list of diseases is fairly long and they all have a similar solution to prevent the formation of disease. Starting with good soil and fertilizer, plucking weeds, rotate crops, remove unhealthy leaves and fruits, avoid tobacco near the plants (if you are a smoker do not smoke near the plants and wash your hands thoroughly before handling the plants), and ventilate the greenhouse. Tobacco can carry some of the common diseases which is why it is important to not have tobacco near your tomato plants. By taking proper precautions in tomato plant health it can reduce the risk of disease. Think of it like you wash your hands and take vitamin C to prevent yourself from getting sick, give your plants the nutrients they need and a clean environment to prevent them from getting sick.

How is growing tomatoes different than growing other vegetables?

Tomatoes typically need higher temperatures, 70 to 75 degrees Fahrenheit, and plenty of sunlight. While this is common of many other vegetables, it is still important to use when planning your garden. If you have a plant that needs shade then they may not pair well with tomatoes. Tomatoes also typically need more space between other plants to grow healthy and disease free. They require their own pot while other plants are able to share a pot. Also, tomato plants need stakes to avoid collapsing under their own weight. Some other vegetables do not need the supports because they are lighter.

A big difference is that you may need to pollinate the tomato plant by hand especially if grown in a greenhouse. They typically pollinate by wind but in  a greenhouse with a lack of airflow you will need to pollinate the plants by hand. To do this you can use an electric toothbrush to vibrate the plant and release the pollen or even just shake the stem lightly.

difference between growing tomatoes and other vegetates

Related Questions

Can you grow tomatoes year round?

The short answer is yes. In a greenhouse with careful climate control and soil care you can grow tomatoes year round.

Can tomato plants be overwatered?

Yes and the early signs of overwatered tomato plants are cracks in the tomato fruit and bumps on the leafs. In an extreme case, the soil will have puddles of water around the plant that do not disappear after a few hours.

When should you plant tomatoes in a greenhouse?

Traditionally, you should plant the tomato seeds 6 weeks before the last frost of the year. This is normally in April. Since you are growing in a greenhouse, frost is less of a concern so you can plant the seeds earlier than April. In fact, you can plant them year round in a greenhouse if the conditions and climate are properly maintained.

About the author

Greg Volente

Greg Volente holds a Naturalist Certificate from the Morton Arboretum, and worked for The Nature Conservancy leading environmental education programs and doing natural areas restoration. Besides gardening, he's an avid wildflower enthusiast, and loves botanizing, hiking, and backpacking.