Tomatoes grow in relatively warm temperatures, making them the perfect greenhouse crop. 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.

While most tomatoes are grown traditionally in an open field, greenhouse tomatoes are an ever-expanding portion of the market, due to the success of these high-tech, high-density operations, particularly in Mexico and Canada. In the United States, greenhouse and protected growing continues to climb. Pennsylvania, Michigan, Missouri, and Ohio boast the largest numbers of greenhouse operations.

Temperature

Maintaining the right temperature is one of the most basic functions of greenhouse, regardless of how technological or advanced it is.

For daytime cultivation, tomatoes flourish between 21°C and 27°C (70°F–82°F). At night, they prefer it cooler—ideally 16°C to 18°C (62°F–64°F). Germination, that critical first act, thrives between 18°C and 29°C (65°F–85°F).

But temperature needs aren’t static—they flex with the greenhouse’s geographic location. Heating might be vital in northern climates, while cooling becomes a priority in hotter zones. Greenhouse can use Heat pumps, boilers, HVAC systems, chillers depending on the local climate.

Humidity & VPD

Tomatoes don’t just care about heat—they’re picky about moisture too. Relative humidity (RH) should float between 60–85% by day, 65–75% by night, and land at a solid 70% for pollination. Too damp, and diseases creep in. Too dry, and pollination flops. High humidity causes pollen grains to clump like wet flour—zero dispersal. Too low, and stigmas dry out like old toast. Striking balance is everything.

Vapor pressure deficit (VPD), that lesser-known but crucial metric, should rest between 0.5–1.2 kPa. Keeping humidity stable doesn’t just help fruit set—it’s your strongest weapon against disease. Remember, moisture is a pathogen’s playground.

Planting Timeline

With a heated greenhouse, you’re good to sow seeds from late February through mid-March. No heat? Start seeds indoors mid-March, then shift them outside post-frost. Tomatoes love the light—give them 21°C to 27°C during the day and keep it above 10°C at night for steady growth. Just beware: dip below 15°C or shoot above 32°C, and flowering and fruiting will stall.

Hydration: Not Too Little, Not Too Much

The volume of water needed by tomato plants for optimal growth and production varies with the season and size of the plants. Young seedlings (transplants) usually need about two fluid ounces (50 ml) per plant per day, while mature plants need two to three quarts (2L) per day. On average, 90% of the water taken up by the plant is used for transpiration (cooling), and the remaining 10% is used for growth.

Inadequate amounts of water lead to wilted plants, and wilted plants are not productive. Prolonged water deficits can lead to permanent wilting, which can result in the death of the growing tips of the plant.

Space is Not a Luxury—It’s a Necessity

Crowding creates a jungle of problems. Stagnant air. Damp leaves. Trapped humidity. Give each plant breathing room—3.5 to 5 square feet, ideally. Use trellises with two transplants per container, spaced 16 inches apart within rows and 5 feet between them. Cables and support lines are essential—guide vines upward, let air circulate freely, and manage the canopy for optimal health.

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. 

Orientation and Wind: The Architecture of Efficiency

Orientation of the greenhouse is a compromise for wind direction, latitude of location and type of temperature control. Single greenhouses with latitude above 40°N should have ridge running east to west to allow low angle light to enter from side rather than ends. Below 40°N the ridge of single greenhouses should be oriented from north to south, since the angle of sun is much higher. This orientation permits the movement of shadow of the gutter across the green house. The location and orientation of the greenhouse should avoid falling of shadow on the adjacent greenhouses. To avoid the shading effect from one green house to another greenhouse these should be oriented East to West. However, the wind direction and latitude are also to be considered. 

Air inside a greenhouse doesn’t behave like the breeze outside. The airflow sinks towards the soil under the effect of negative buoyancy, while the airflow rises around the canopy due to the effect of positive buoyancy. Therefore, the densest point of the airflow occurs slightly above the tomato canopy (H ≈ 11 cm), and the average wind speed value is 0.28 m/s, while the average wind speed value at the bottom of the tomato is only 0.12 m/s, which easily leads to the aggregation of pathogen microorganisms. In conclusion, due to the existence of tomato canopy, different airflow layers will be formed in the greenhouse, which interact with each other to form complex airflow circulation in the greenhouse. 

Location and Lighting

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.

Often 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.