Grow tomatoes in the greenhouse – Complete Guide

Tomatoes are popular in every season and can be found on our dining table for almost every occasion. For this reason, there is also great interest in growing tomatoes not only in summer months. This gets possible with the help of planting tomato plants in greenhouses, regardless of whether it is a huge or just a mini greenhouse. This in-depth article will give you all the information you need to know about how to grow tomatoes in your greenhouse, what to watch out for and when you can expect your first harvest. 

What are the ecological requests for growing tomatoes in a greenhouse?

For successful growth in greenhouse cultivation, climatic factors such as temperature, humidity, light, and air movement should be adjusted very well. Do not forget that these factors are in close relationship with each other and have to be in harmony. That’s why you should know, which conditions you have to create for your greenhouse tomatoes to grow healthy and in time. In this guide, you will get all kinds of information to start growing your tomatoes in the greenhouse.

If you don’t have a greenhouse yet and want to set up one, then also take a look at: Setting up a greenhouse – what to know before starting

What botanical properties do greenhouse tomatoes have?

In open field cultivation, the tomato roots grow to a depth of 100-150 cm and strongly to the sides, but in greenhouse cultivation, it spreads to 40-60 cm and grows 40-100 cm in depth. Wether it is growing tomatoes in a small or large greenhouse, up to three-quarters of the roots are in the 0-20 cm upper part of the soil. Nearly a quarter of it is in about 20-50 cm depth and the rest is deeper than 50 cm. 

The herbaceous body is initially round, soft, and hairy. As it ages, it hardens and gains an angular structure. The flowers of tomatoes grown in the greenhouse are formed in clusters. The inflorescences show simple (single) or double (forked) branching. In some varieties, you can also see mixed clusters.

The best tomatoes to grow in the greenhouse

In order to make good use of the space for tomatoes in the greenhouse, one chooses tall-growing varieties, so-called stick tomatoes, which are attached to stakes, spiral tomato sticks or strings. If you want to get seeds for the next year from your harvested tomatoes, you should choose non-seed varieties and make sure that they are only fertilized by themselves, because hybrid varieties / crosses would split into many different offspring in the next year.

Recommended tomato varieties (stick tomatoes) for the greenhouse are, for example, ‘Berner Rose’ (pale red beefsteak tomato), ‘Tigerella’ (round variety, flamed red), Pannovy F1 hybrid (red, round-fruited tomato), San Marzano tomatoes (red bottle tomatoes) , ‘Dolcevita’ F1 hybrid (red cocktail tomato) and ‘Yellow Pearshaped’ (pear-shaped, yellow cocktail tomato).

Growing periods in greenhouse tomato cultivation

Before we start growing tomatoes in our greenhouse, we have to know when we have to do which step. Therefore, we have to differentiate between single- and double-crop.

A single crop means a one-time production within a calendar year and generally starts with sowing seeds in August to September and continues until June to July. In this production method, heating is required.

Double crop cultivation means growing tomatoes twice in a calendar year, namely in autumn and spring. Seed sowing for autumn production in double-crop cultivation starts in the second half of July and early August, production ends in January-February. Seed sowing for spring production is done between December and January and the production continues until July and ends when the field tomato is released. In double-crop cultivation, which is preferred for heating savings, it may be necessary to heat the greenhouse at the end of autumn and the beginning of production in spring.

What are the temperature requirements for growing tomatoes in a greenhouse?

We already talked about warmth in the greenhouse above. It is the most important environmental factor affecting vegetative growth, inflorescence development, form, number of flowers, and fruit quality. Tomato is a warm and hot climate vegetable. When the temperature drops between -2 and -3 degrees, you can be sure, that the plant dies completely. Too much humidity and heat cause diseases to occur in the plant, and hot and dry winds cause flower loss. 

The temperature must be 16-19 degrees for normal development in tomatoes. It has been determined that if the temperature drops below 13 degrees, ripening is delayed and the crop is very low. Tomato flower powders continue to germinate at 10 and higher degrees, best at around 27 degrees and continue to fertilize and develop as desired. The ideal fertilization temperature is between 17-27 ° C. You have to know that, if the temperature is below or above the desired degrees, it results in the ripe fruits not being browned.

However, a tomato is a plant that does not like excessive heat. Tomato plants need different temperatures at different stages of their development. Besides, there should be a difference between day and night temperatures, so it is wrong to keep the day and night temperatures at the same level. A temperature difference between day and night temperature is required, provided that it is not more than 6-7 ° C.

Lighting for the tomatoes in the greenhouse

It is wrong to consider temperature and light as two separate factors. It is necessary to lower the temperature towards the lower limit in the periods when the light is low and to increase the temperature towards the upper limit in the periods when the light is high.

How to prepare the soil to grow greenhouse tomatoes?

Like cucumbers, the best preparation for tomatoes is to plow the soil deeply. In autumn, plow the soil deeply with a plow. The second time, it is made with plow again and tempered in spring. Then break the clod by using a rake, worshiper, or disc harrow. Since tomato is a deep-rooted plant, if an impermeable plow base is formed in the culture areas, the soil can be cultivated with a chisel.

What are the soil requirements of tomatoes grown in greenhouses?

The soil requirement of the tomato is simple. Tomatoes can be grown in any soil, from sandy to clay. Deep, permeable, loamy soils with good water holding capability and rich in humus and nutrients are ideal soils. It yields early in sandy loam soils. It is very resistant to socks. The most suitable soil reaction is around a pH value of 6.5. This should be resistant to low soil acidity.

Growing seedlings for greenhouse tomatoes

Starting work with a healthy seedling of a good variety seed constitutes half of the success in vegetative production in the greenhouse. Starting with unhealthy seedlings, first of all, comes back as a loss of seed, time, and effort.

There are four important conditions for obtaining healthy seedlings:

• Using healthy seeds from a good variety
• Using a good seedling mortar
• Choosing the seed planting and seedling container appropriately
• To make the seedling care correctly

You can either grow the seedlings yourself or obtain them from private companies that produce seedlings for commercial purposes.

Preparing the greenhouse for planting tomatoes

Before you start planting your first tomatoes in the greenhouse, make sure that you prepare your greenhouse first. 

Start with the complete removal of the plant residues, if you have already grown something in it before. 

Especially in old greenhouses, the soil should be cultivated with subsoil and the plow base should be broken. The plow base is closely related to the physical structure of the soil. Especially in heavy character (clayey) soils, it occurs in a shorter time. Due to the continuous cultivation of the soil at the same depth, a hard layer of 10-15 cm thickness is formed starting from the lowest tillable layer of the soil. In the soil where the plow base has formed, the roots of the plant cannot pierce this layer, and the irrigation water may accumulate in this layer and cause root rot in the plant. 

Furthermore, in greenhouses with elderly and soil salt problems: The soil should be irrigated several times in the form of ponds and the greenhouse litter should be thoroughly washed.

The soil should be disinfected if disease and pest problems were seen in the previous growing period. You should consider spraying the soil by chemical means as a last resort. The most practical way today is solarization. Soil solarization is the process of eliminating soil diseases and pests by covering the soil surface with transparent PE and raising the soil temperature with solar energy. The application period is June, July, and August when the sunlight is high. 

Before solarization, the soil should be applied as deeply as possible while it is annealed, the surface should be covered with a thin transparent PE cover so that there is no gap and all the ventilation of the greenhouse should be closed. 

Planting tomatoes in a greenhouse

If we have taken all of the above points into account, we can finally plant our tomato plants. After sowing, seedlings are ready for planting between 30-45 days. This is depending on the conditions and the nature of the seedling growing container. In a seedling ready for planting, the first inflorescence bud has appeared. 

After the soil preparation process in the greenhouse is completed, water the soil for the last time. The planting places are prepared according to the single-row or double-row planting style, but the double-row planting style has some advantages:

• Lighting and ventilation are better
• Movement between the rows of plants is easier, cultural processes are easier
• Since one side of the plant rows will be worked on, the soil crushing and therefore the compression of the roots is less

Planting can be done flat, and I recommend preparing the planting places in the form of a high pillow. The reason for doing this is that if the high pillow-shaped plantings are prepared, the soil will be warmed better and the excess water will drain more easily.

An important point during the preparation of the planting spots:

Regardless of the direction of the greenhouse, the direction of the plant rows must be in the north-south direction. Thus, the shading of the plants to each other is reduced.

Planting in single crop and autumn cultivation:

Since the air temperature is high during planting, the seedlings can be expected to grow a little more in the seedling, but care should be taken not to let the seedlings get into the paint.

How to hang greenhouse tomatoes

After planting, the plants are observed, when the leaves begin to lighten, it means it is time to hang the plants. This discoloration is a sign that the seedlings are now taking root in the environment. This corresponds to approximately 1.5-2 weeks after planting.

You can hang the tomatoes in the greenhouse by tying them with plastic ropes to the wires passed in parallel over the planting rows. The length of the hanger ropes should be prepared considering this if the plant will be hung up in the following periods. The hanging rope is tied to the plant body in a way that a finger will enter between the body and the rope, taking into account that the trunk will become thicker in the future. You can also consider fixing it to the body with the help of a hanger clip. 

How to prune tomatoes grown in greenhouses?

Pruning your greenhouse tomatoes is done primarily to:

• establish the vegetative-generative growth balance in the plant
• increase the light-exposed surface of the plant
• increase the air movement between the plants themselves and each other
• prevent the proliferation of disease and harmful factors in the plant
• remove the leaves that have become consumers rather than producers

Shoot Pruning

Therefore, a bunch of pruning is done on the tomatoes. The first one is Shoot Pruning. In this process, you will clean the shoots emerging from the leaf seats, inflorescences, leaf blades, and root neck. There should be no shoots other than the main stem of the plant. The most important of these shoots are the ones that we call the seat that emerge from the place where the leaves meet the stem. 

If the plant is grown without seat shoots:

• the plants take the appearance of a bush
• generative growth slows down (since nutrients are used by the side shoots)
• lighting and air movement are reduced
• disease and pest reproduction become easier
• cultural processes become difficult

For these reasons, taking a seat in greenhouse tomatoes is a mandatory procedure. Seat retrieval should be done in the morning when the plant’s turgor capacity is high (breaking is easy) and is 4-5 cm tall. Taking the seats is done by manually tipping the bolt left and right and tearing it off. If the seat is taken when it is smaller, the eyes will not be blunted, but the exile may come out again. If it is too late, such shoots can be cut with a cutting tool.

Leaf Pruning

When the height of the plant exceeds about 120 cm, it is necessary to clean regularly to accelerate the frying of the ripe fruits and to ensure air movement. Leaf removal is done either by clearing the cluster with fried fruits or the leaves under the cluster of standard size. You can do this cleaning process with a sharp knife without leaving any protrusion from where the petiole joins the stem. Otherwise, disease factors can enter from the leaf stalk part left. 

The other leaf pruning on other parts besides pruning the lower leaves is the pruning known as “window opening”. This pruning is done in the form of removing a part of the leaves completely or in half by cutting the leaves that shade each other, prevent the clusters from seeing light, and restrict air movement. It is called this because it looks like opening a window.

Flower and Fruit Pruning

Flower-Fruit Pruning is done to increase the number of fruits. In this form of pruning, when the clusters grow a little more than the size of the hazelnut after the fruit is attached, the fruits other than the fruits to be left are cut and cleaned.

Tip-Pruning

Cutting the growth tip of the tomato plant and stopping the growth is called Tip-Pruning. Two months before the growth is desired to finish, the growth tip of the plant is cut by leaving two leaves on the last cluster. These left two leaves both protect the last cluster from sunburn and nourish it. Thus, vegetative growth is terminated and fruits ripen.

Pollination and fertilization of greenhouse tomatoes

Tomato flowers have an erect flower structure. In other words, male and female organs are on the same flower. Although it has a self-pollinating structure in natural conditions, high relative humidity, insufficient air movement, and lack of insect activity in greenhouse conditions (due to the closed environment of the greenhouse) cause inadequate pollination and fertilization. For this reason, it is necessary to help the flowers of tomatoes grown under greenhouse conditions to be pollinated. For this purpose:

• Using a vibrator: The vibrator is a battery-powered vibrating tool. 2-3 times a week, between 10 and 15 o’clock, the plants are wandered and the clusters are touched for 1-2 seconds to help pollinate.
• Bumblebee (Bombus Terrestris): This is the most effective solution. These bees are produced by private companies and marketed in cardboard boxes. According to the size of the greenhouse, the number of hives is determined. Their lifespan is about 6-8 weeks. When bees visit the flowers, they help in pollination.

In these two methods, you should keep the temperature inside the greenhouse at least at 13 ° C for live pollen dust and active female organ activity, otherwise, the necessary benefit will not be obtained.

For fertilization, you can use organic manure. The first one is given when the fruits reach a size of a hazelnut. When it lies in the fruit, the other half is given between the furrow.

Watering greenhouse tomatoes

In tomato cultivation, you have to avoid watering them as much as possible until the first fruits appear on the plants. Until this stage, it is satisfied with the lifeline given during planting. Hoeing is important for this. Irrigation can be done if needed.

After the first fruits appear, irrigation becomes important. Sufficient irrigation is done in the right periods according to the soil structure and the characteristics of the selected type. Finally, after the harvest begins, irrigation should be done after each harvest.

Time to harvest the tomatoes of your greenhouse

You will be able to harvest your first tomatoes approximately in 4.5-5 months after sowing under ideal conditions. How much you will harvest depends on:

• the growing period
• the climate arrangement of the greenhouse
• the number of plants in the area 
• the applied cultivation method

Considering all the information given in this article, you won’t have a lot of trouble starting to grow your tomatoes in the greenhouse. Good luck and keep your green thumb!