Growing Tomatoes in a Greenhouse
Most gardeners will tell you that few things can beat the outstanding, fresh taste of home-grown tomatoes in the summer. Luckily, with a greenhouse you are not limited to the summer months; you can grow delicious tomatoes whenever you want. Tomatoes can be picky plants, but with a little bit of practice anyone should be able to produce their own supply of these mouth-watering delights year-round.
Starting Out
In order to grow the best tomatoes possible, it is important that you give your plants a healthy start. Begin by purchasing seeds developed especially for greenhouse use (readily available in seed catalogs,) which will help you to avoid some common greenhouse problems. Start the seeds in warm conditions, preferably under grow lights and on heat mats, and allow them to develop for a couple weeks before transplanting. Eventually, you'll want the plants to be in very large containers (at least ten gallons in size) so that they will have adequate room to grow. Be sure that any containers you use have been sanitized with a mild bleach solution to prevent the spread of disease. Also, use fresh soil instead of last year's, which could possibly pass diseases to your plants. One common problem with greenhouse tomatoes is Blossom End-Rot, a condition that is caused by a calcium deficiency. To compensate for this, be sure to add an additional calcium source to your soil such as bone meal.
Choosing a Location
Tomatoes should only be placed in a greenhouse that is already healthy. If you notice any pre-existing problems with disease or pests, treat these problems before exposing your tomato plants to them. Tomatoes are prone to bugs such as white fly, which can ultimately lead to their detriment. You can minimize these problems by simultaneously planting herbs such as basil and lavender in the greenhouse that will help to deter these pests. Be sure that your tomato plants are placed in a sunny spot that will be near a heat source during cold weather.
Lighting
Often times the reason that tomatoes will not grow during the winter is that they do not have enough natural light. Because of this, supplemental lighting is almost always required throughout winter months. High-pressure sodium lights should be used for tomatoes because they encourage flowering and fruiting. For best results with tomatoes, lights should be used up to 16-18 hours per day. Make sure to use a light with the proper wattage for the area you wish to use it in.
Heating
If the proper temperature is not maintained within the greenhouse, the tomatoes will fail to produce. You should plan on keeping the greenhouse above 60°F, but below 90°F. In most areas, this will require some heating during cold weather. It is important to get a heater that puts out the proper amount of BTUs for your greenhouse so that the temperature will stay in the proper range. You can use our online heater calculator to find a heater that will suit your needs.
What are the Ideal Conditions for Greenhouse Tomatoes?
Tomatoes grow in relatively warm temperatures, making them the perfect greenhouse crop. Compared to outdoor tomato cultivation, growing in a controlled greenhouses increases yields and quality, reduces pests and diseases, and increases the growing season.
Tomatoes are one of the most popular vegetables (well, fruit…) in the world. So, it’s no surprise that they’re one of the most common crops in commercial horticulture. In fact, in 2020, over 185 million kgs were grown globally, on over 5 million hectares.
Tomato plants have a relatively short growing season, contrasted by a high demand year-round. Which is one of the main reasons growers around the world choose to grow tomatoes in a greenhouse.
The ability to control the temperature, humidity level, and lighting, allow growers to provide ideal growing conditions throughout the year. In most of the world, this wouldn’t be possible without a controlled environment.
Optimal Growing Conditions for Tomato Crops
Greenhouse cultivation has many benefits, but not without challenges. Cultivating tomatoes in a closed environment requires growers to create the optimal growing conditions, rather than rely on the weather.
This guide will help you provide the ideal tomato growing conditions. It’s important to remember, however, that specific conditions may differ between different tomato varieties.
Ideal Temperature for Tomato Greenhouse
Maintaining the right temperature is one of the most basic functions of greenhouse, regardless of how technological or advanced it is.
Providing optimal temperatures allows the plants to take in and break down nutrients as efficiently as possible. This leads to faster growth and fruit development. If conditions are too cold, or too warm, the plants will experience stress, which affects growth, as well as quality. In a temperature-controlled environment, there’s no reason to reach temperatures outside of the ideal range.
The ideal temperature for tomato cultivation is between 21-27°C (70-82°F). This range is also best during pollination. These temperatures are considered optimal for day time. During the night, tomato crops may enjoy lower temperatures, reaching 16-18°C (62-64°F).
Tomato plants grow best within this range, meaning they will exhibit the quickest development, largest yields, and highest fruit quality. However, depending on the variety, they may be able to grow well between 15-32°C (59-89°F).
The ideal temperature to germinate tomato seeds is between 18-29°C (65-85°F).
Ideal Temperatures for Tomato Cultivation:
Day time – 21-27°C (70-82°F)
Night time – 16-18°C (62-64°F)
Seed germination – 18-29°C (65-85°F)
How to Maintain Optimal Temperatures for Tomatoes
Maintaining the right temperature for tomatoes differs from greenhouse to greenhouse. Some greenhouses are located in warmer climates than others. So, while most greenhouses require heating, some actually need cooling to reach the ideal range.
You can use ducts, heat pumps, boilers, chillers, HVAC, or other forms of air conditioning depending on your local climate.
Ideal Humidity for Tomato Greenhouse
Humidity, like temperature, has a major impact on tomato plants’ growth, development, yield and quality. In order to reach full potential, it’s important to maintain the right relative humidity level, or VPD range.
Outside of the ideal range, plants will struggle to perform physiological tasks, such as taking in nutrients or performing photosynthesis.
When humidity is too high, the tomato plants won’t be able to evaporate water through their stomata. This stops them from being able to take in more water and nutrients from the soil, inhibiting development.
Low humidity, on the other hand, will lead to water stress. In this case, the stomata close, in order to retain water. This has a similar effect, in which the plant shuts down important processes, slowing down growth and development.
It’s also important to note that many common diseases and mildews develop in high humidity, including botrytis and powdery mildew. So, maintaining ideal humidity levels also protects against diseases and reduces crop loss.
The optimal relative humidity level for tomatoes is between 60-85% RH. However, you can improve growth further by dialing in different relative humidity set points for night and day.
During the day, tomato plants may enjoy higher humidity levels of 80-85% RH. However, during the night, when the plants are less active, humidity levels of 65-75% are ideal.
The ideal relative humidity level for pollination is around 70%. In higher humidity, pollen may stick together, making it harder to disperse. In lower humidity, the plants’ stigma tends to dry out, reducing its ability to collect pollen.
In terms of VPD, the ideal range for tomatoes is generally between 0.5-0.8 kPa. However, higher VPD levels may be better during later developmental stages, such as flowering. In these stages optimal VPD levels can reach 1.2 kPa.
Ideal Relative Humidity & VPD for Tomato Cultivation:
Day time – 60-85% RH
Night time – 65-75% RH
Pollination – 70% RH
VPD – 0.5-1.2 kPa
How to Maintain Optimal Humidity for Tomatoes
It’s important to note that tomato crops, like all plants, release water vapor. So, in fact, they increase the humidity levels around them. In a closed environment, this will inevitably lead to high humidity.
Humidity is a complex issue. There are numerous factors that impact it. So it may be difficult to predict relative humidity levels at all times, throughout the growing space. Some factors that directly affect humidity include temperatures, grow lights, irrigation systems and airflow.
In most cases, greenhouse growers will need to reduce humidity, rather than increase it. There are two main methods to do so – through heating and ventilation, or through dehumidification.
Heating and venting is the traditional way greenhouse operators deal with humidity. It involves opening up windows and vents, in order to let the humid air out.
However, releasing air from inside and introducing outdoor air affects the conditions inside. In most cases, the air outside is cooler, meaning it lowers the temperature inside the greenhouse. That means you need more heating to compensate for the heat loss.
Heating and venting may be useful and even efficient when weather outside is fair. However, this method is highly inefficient in cold, humid, or rainy conditions, requiring a lot of additional heating just to maintain temperatures. Additionally, this method might not work in high humidity or rain, leaving growers with no solution.
So, in most climates, the only way to fully control humidity and ensure ideal conditions, is to use dedicated dehumidifiers. Dehumidification systems that are designed for greenhouse use provide the most comprehensive and energy efficient way to control humidity. In fact, using DryGair has been found to save an average of 50% on total energy consumption, compared to ventilation.
Use Air Circulation to Further Improve Conditions
Another important part of humidity control is air flow. While maintaining an overall ideal humidity level is crucial, conditions can vary throughout the greenhouse. Most importantly, humidity may be higher between densely placed plants, or inside the foliage.
These pockets of humid air are known as microclimates. They can be detrimental to tomato plants, slowing down growth and leading to disease outbreaks. This is especially problematic with grown tomato plants, due to the high amounts of foliage.
Different types of tomato crops may be more at risk from this issue, such as determinate tomatoes with many side shoots. However, indeterminate varieties aren’t risk-free, and still require comprehensive humidity control.
Maintaining constant air movement helps disperse these microclimates. But not all airflow is equally effective.
Air circulation is a type of airflow in which the air is circulated throughout the entire space. As opposed to simple horizontal or vertical fans, air circulation doesn’t create multiple competing airflow directions. Rather, it creates cohesive air movement. This doesn’t just disperse humid microclimates, but also creates uniform conditions throughout the entire space.
All DryGair units include a patented air circulation module that ensures ideal conditions at all points in the greenhouse. This is a critical part of tomato cultivation, significantly reducing common disease outbreaks, such as botrytis.
Additional Tips for Greenhouse Tomato Cultivation
Creating ideal growing conditions is key to producing large yields of high-quality tomatoes.
However, there are additional things you can do to further improve growth, prevent diseases, and save money by reducing energy costs.
Avoid Wet Surfaces
Some of the most common molds and mildews require water in order to develop. So, the most effective way to avoid these detrimental diseases is by avoiding the presence of water in your greenhouse.
There are two ways in which free water reaches the greenhouse. First, is through irrigation. When plants are watered from above, some of the water remains on the leaves and fruit. Under these conditions, disease development and spreading are very likely.
To prevent plants from getting wet, water or add the nutrient solution straight to the soil or potting mix.
The second way in which water appears in the greenhouse is through high humidity. When relative humidity reaches 100%, water starts to condense on various surfaces, including railings, equipment, and even on the plants themselves.
However, proper humidity control and air circulation prevent this condensation from occurring.
Keep Space Between Plants
High humidity and wet plants become increasingly problematic the more crowded the greenhouse is. When plants overlap, they prevent air from flowing between the leaves and increase the amount of moisture within the foliage. This makes it incredibly difficult to maintain ideal humidity levels between the leaves, where it matters most.
So, in order to be able to control conditions, it’s important to have enough space between plants.
Of course, this can work both ways. Proper dehumidification reduces the overall humidity level and provides powerful air circulation, allowing you to decrease the space between plants. It’s all about creating the right balance for your growing facility.
Use Insulation to Prevent Heat Loss
Saving energy is one of the biggest challenges of controlled environment agriculture. This has quickly become a burning issue over the past year. Fortunately, there are ways to save a lot of energy.
One of the simplest and most effective ways to save energy is by insulating the greenhouse and using thermal screens.
Traditionally, growers open the greenhouse in order to release moisture. However, this method was developed before commercial dehumidifiers were readily available.
These days, using dehumidification, greenhouse operators can keep the facility closed and insulated, and extract humidity from inside. This has several benefits, as it not only saves a lot of energy (50% on average), but also helps growers maintain ideal growing conditions, leading to larger yields, higher quality tomatoes, and less diseases and pesticide use. This has several benefits. It saves a lot of energy (50% on average). But also helps growers maintain ideal growing conditions, leading to larger yields, higher quality tomatoes, and less diseases and pesticide use.
Interested in dehumidification for your growing facility? Please feel free to contact our experts for a free consultation.
Lowest Temperature To Grow Tomatoes
Tomatoes are the most popular home garden vegetable to grow. With a veritable plethora of tomato varieties, from heirloom to cherry, and every size and color imaginable, it’s no wonder. A suitable tomato plant can be found to grow in almost any climate and environment. The warmest growing temp for tomatoes and the lowest temperature to grow tomatoes are the eternal conundrum for the home gardener. Tomato temperature tolerance varies depending upon the cultivar, and there are many.
Tomato Plants and Temperature
Most tomatoes are warm season plants and should only be planted after the danger of frost has passed. Tomato temperature tolerance for extreme heat or cold snaps is of extreme importance to the development of blossoms and subsequent fruit set.
Blossom drop will occur in the spring if daytime temperatures are warm but night temps drop below 55 F. (13 C.). In the summer when temperatures soar over 90 F. (32 C.) with nights over 76 F. (24 C.); again, the tomato plant will suffer damage to immature fruit or loss of flowers.
Additionally, when nights become too warm, the pollen grains of the tomato flower begin to burst, thwarting pollination, hence no fruit set. This is doubly true when the air is saturated with relative humidity.
The growing temp for tomato seedlings should be maintained at constant temps of between 58-60 F. (14-16 C.), whether starting in the greenhouse or indoors, and then not transplanted until the last frost has passed.
Cold Hardy Tomatoes
There are specific tomato varietals bred for cold hardiness which will tolerate conditions at or below 55 degrees F. (13 C.). The best choices for colder climates are short to mid-season tomatoes. These tomatoes set fruit not only in cooler temps, but also reach maturity in the shortest number of days; around 52-70 days. One of the most popular is called Early Girl, but there are many different cold hardy varieties to choose from.
Some examples of hybrid tomatoes for cool climates are:
Celebrity
Golden Nugget
Husky Gold
Orange Pixie
Oregon Spring
Siletz
Heirlooms varieties include:
Bush Beefsteak
Galina
Glacier
Gregori’s Altai
Grushovka
Kimberly
Legend
Manitoba
New Yorker
These are just to name a few. A little research should turn up a dizzying list to choose from.
Heat Tolerant Tomato Varieties
Just as there are those of us who live in cooler climates, there are also those who live where temperature conditions run to the more extreme heat index. There are tomato varieties bred for those conditions as well.
Some examples of hybrids which are heat tolerant are:
Heirlooms include:
Tomato Frost Protection
Besides planting cold hardy tomato varieties, some tomato frost protection may be provided by using plastic “mulches” or covering which will trap the heat to keep the fruit warm if temps drop below 55 F. (13 C.). Dark plastic coverings will raise the temps by 5-10 degrees while clear warm the tomatoes by up to 20 degrees. This may be just enough to save the tomato crop.
