How to control the temperature in the greenhouse – ways to create an optimal microclimate for plants

Temperature influences the growth of greenhouse crops. The plant has three important temperature points (cardinal) — minimum, optimal, and maximum for the best growth.

Each plant species has an optimum temperature range. Also, the same plant has different optimum temperatures for vegetative growth and flower development.

What is the best temperature for greenhouse crops

Most crops grow better if the day is warmer than the night, given satisfactory humidity and airflow. However, if the night is too warm or too cold, it damage crops than the day temperature. Therefore, the day and night temperatures difference (DIF) is essential for horticultural ornamental and greenhouse crops for growth habit and flowering time.

If the temperature is below the minimum level, growth slows, flowering is delayed, and the color of leaves and flowers intensifies.

Seed germination, growth and development, and photosynthesis are greatly affected by temperature — above the maximum level and cause premature smaller flowers, smaller leaves, reduced stem diameters, and diminished coloring.

Typically, the optimum air is 60-70°F, and for plants, the optimum is 50-75 °F. Heating the bottom of the benches that support the plants increases the rate of germination. Each crop varies in its heat requirements for germination.

The growth rate increases until 95 °F are reached. When the maximum temperature exceeds 95 °F, the growth rate drops quickly and stops completely because enzymes are deactivated.

Many plants rely on temperature sensing to control flowering time as well. For example, winter annuals germinate in the summer, overwinter, and flower in the spring. These types of plants typically require a cold treatment (of varying lengths and intensity) before flowering.

Here are some examples. However, the greenhouse owner can maximize the operation by identifying the correct temperature for each crop.


– State extension vegetable & small fruit crops specialist, West Virginia University.

– Vegetable crops production guide for the Atlantic provinces.

– Growing cannabis indoors: getting started.

Are temperature and humidity exclusive

No, they are not. Every time you adjust the temperature, you’re going to affect the humidity and vice versa.

Monitoring and managing both are crucial for managing pests and disease.

It is not just the air; plant temperature is also essential for higher yield. Plants affect how slow or fast a crop can grow. At optimum, the plant can get rid of its moisture.

Consistency throughout the Greenhouse is important to be managed equally. Otherwise, little pockets of high humid, hot air in certain parts of the greenhouse create microclimates.

How can growers maintain the temperature and humidity in their greenhouse

Heating devices will maintain the temperature within that range during periods of cold weather. However, do not undersize your heating capacity. You may not need all your heaters much of the year, but if you undersize your system, you may lose your entire crop during the coldest nights of winter.

The basic heating system

It consists of a fuel burner, heat exchanger, distribution system, and controls. Heat delivery to the crop is by convection and radiation.

– Heating by hot water or steam. Hot water or steam can be produced using boilers—then hot water or steam transported throughout the greenhouse in pipes.
– Heating by hot air. The most popular fans used in Greenhouses are the HAF (Horizontal Airflow Fans). Fuel is burned to heat air that is then distributed by fans around the greenhouse.
– Moveable night-time insulation. Cloth or film curtains can be positioned above the crop or near the roof to retain heat near the crop. The insulating material used during the night can be the same material used for shading during the day.

High temperatures can be detrimental to plant growth. It can cause such problems as thin, weak stems or, as in tomatoes, stick trusses, reduced flower size or, as in tomatoes, flower fusion and boat formation, delayed flowering, poor pollination, and fruit set. Also, flower bud and fruit abortion. Therefore, having a cooling system is also essential.

Passive cooling systems

– Shading. Shade cloth or shade paint/whitewash, besides regulating the light intensity, can also help cool the greenhouse.
– Ridge Vents. Vents in the roof of a greenhouse that allows hot, interior air to escape.
– Roll-up Side Walls. This can be used in flexible glazing (polyethylene film) single-bay greenhouses where the side walls can be rolled up several feet, allowing a natural horizontal flow of air over the plants.
– Cooling Towers. Water-cooled pads at the top part of tall towers cool the surrounding air. The cooled air then drops, displacing warmer air below.
– Removable Roof. Recent greenhouse designs can include a roof that retracts entirely for natural ventilation.

Active cooling systems

– Fan and Pad. “Evaporative cooling” where air from the outside is pulled through porous, wet pads. The heat from the incoming air evaporates water from the pads, thereby cooling the air—this helps increase the relative humidity in the greenhouse.
– Fogging Systems. This system gives better uniformity since the fog is distributed throughout the greenhouse and not just near one end, as with the fan and pad system.
– Air Conditioning. Too expensive for most greenhouses.

Future optimal microclimate Greenhouses — Controlled Environment Agriculture (CEA)

CEA can range from simple shade structures, growth chambers through greenhouses to full indoor or vertical farms. Using advanced technology and data, light, temperature, relative humidity, carbon dioxide (CO2) around the leaves can be monitored for the plants to thrive. To deliver sustainable solutions for high-value crops.

Within a crop production environment, plants can be grown using different methods. By far, the most popular method is hydroponics. An automated hydroponics system can measure water conditions: pH, electrical conductivity, temperature, level, and flow.

Indoor farming, Vertical farming, Greenhouse, Protected cropping, and Automated Plant growing system are different growing environments for CEA. Control systems can be very simple or very complex.

An automated plant growing system is a computer-controlled system that manages the environment in which plants are grown. This is done to find a solution to some of the challenges growers face, such as reducing labor needs and improving efficiency.

Hydroponics is the cultivation of plants by using mineral nutrient solutions, in water, without soil. To make sure plants grow optimally with sufficient CO2 concentration, a hydroponic CO2 controller is an ideal solution.

Hydroflow CO2 Controller is a CO2 controller for grow rooms. It regulates the CO2 level automatically and precisely.

CO₂ controller for grow room and greenhouse
CO₂ controller for grow room and greenhouse

The Best An automated hydroponic system is a closed-loop system that provides all the nutrients required for plant growth. It uses recirculating water, air pumps, and misting nozzles to provide an optimal environment for plant growth.

The Grow Room Climate Controller is an excellent way to control the climate in your grow room. The Greenhouse Environment Controller is also an excellent choice for your greenhouse environment.

Fully automated plant growth systems are the most advanced CEA environment. It continues to grow your plants for months without any further maintenance, completely self-regulating water, nutrient concentration, pH level, light. The system will also give feedback on CO2 level, humidity, and temperature with grow room climate controllers and the Internet of Things (IoT) network. This helps farmers to grow plants and vegetables in remote areas, deserts and save labor.