How To Control Greenhouse Temperature [Hometown Structures]

Why is temperature control in greenhouse gardening important?

Plants are fussy - and while we can do everything in our power to work with nature and not against it by planting things in season that love the heat or cold, there will always be times in owning a greenhouse where you want to control the temperature. Thankfully when I designed my greenhouse with Hometown Structures we were able to implement a lot of features that help to keep things cool in the summer and warm in the winter, but since different plants have specific temperature requirements for germination, growth, flowering, and fruiting, maintaining these conditions with every available tool is important to ensure healthy development.

Extreme temperatures can cause stress, leading to stunted growth, reduced yield, and susceptibility to diseases and pests - while on the opposite end of things consistent temperature management results in better flavor, color, and nutritional value in crops. Which means happier plants and more food in your harvest basket.

If you’re growing food in a greenhouse with a focus on keeping things low maintenance, then it’s even more important to get your temperature under control, since many diseases and pests thrive in extreme temperature conditions which cause plant stress. Maintaining optimal temperatures can help prevent disease outbreaks and precise temperature control allows for efficient use of heating and cooling systems, reducing energy consumption and costs.

What are the challenges of excess heat in a greenhouse?

High temperatures can be harmful to many plants because extreme heat causes plants to lose water faster, making them wilt and dry out. This can slow down or stop the process that plants use to turn sunlight into food, which affects their growth. Hot weather also makes it harder for plants to get nutrients from the soil, which can weaken them, can cause flowers and fruits to fall off before they're ripe, and can burn plant leaves. These conditions also encourage pests and diseases to thrive. Not to mention, to cool down plants, air conditioning systems need to work harder, which increases energy costs.

What are the challenges of excess cold in a greenhouse?

Cold temperatures can als be a big problem in a greenhouse. When it's cold, plants may grow much slower, and very cold temperatures can damage or even kill plants. Cold weather also delays the start of flowering and fruit production. Cold air holds less water, which can lead to plant diseases, and to keep plants warm, you need to use a lot of energy, which can cost a lot of money unless you use natural, energy efficient techniques.

Natural greenhouse Ventilation Techniques

Natural ventilation helps keep greenhouses healthy by letting fresh air in and old air out. But it can also help you regulate the temperature of your greenhouse. Two main parts of a greenhouse that help with this are vents on the top and sides, called ridge vents, and special side panel vents called louvered side panels. You can also strategically place doors and windows to take advantage of cross breezes.

Ridge vents are located at the very top of the greenhouse roof, while side vents are on the walls. How these vents are placed is important for good airflow. Since hot air rises, the top vents should be positioned to pull hot air out like a chimney. The side vents should be on the side where the wind usually comes from to let cool air in. Together, these vents create a draft that helps to keep the greenhouse air fresh.

Side panels with louvers have adjustable slats that let you control how much air comes into the greenhouse. By changing the angle of the slats, you can decide how much air to let in based on the weather and what your plants need. This helps you keep the greenhouse at the perfect temperature and humidity level.

Manual and automated ventilation options:

Manual ventilation involves opening and closing vents by hand based on weather conditions. While labor-intensive, it provides precise control. You can also use automated ventilation, which has sensors that monitor temperature and humidity levels, triggering the automatic opening and closing of vents. This method offers convenience and energy efficiency.

Shade Cloth To Keep Things Cool

Shade cloth is a mesh-like material that reduces solar radiation entering the greenhouse. It comes in different percentages that define how thick the material is and how much light can still get through. The ideal shading percentage depends on several factors - different plants have varying light requirements, and solar intensity varies by region.Light levels also change throughout the year. But generally, shade cloth percentages range from 30% to 90% with 30-40% being the most common.

During peak summer months, higher shading percentages may be necessary to prevent overheating. As daylight hours shorten and solar intensity decreases in the fall and winter, shade cloth can be removed or replaced with a lower percentage.

Exterior sunscreens are installed on the outside of the greenhouse to reflect solar heat before it enters. These can be painted on and typically wash off over the course of a year or so naturally. Some are also made of reflective materials like aluminum or acrylic coatings that deflect a portion of the sun's rays, preventing them from entering the greenhouse and contributing to heat buildup. Reflective sunscreens can also help protect plants from intense UV radiation.

Evaporative Cooling Systems

Evaporative cooling is a common method to reduce greenhouse temperatures, particularly in dry climates. It works by taking advantage of the cooling effect of water evaporation. Wet wall or pad systems are a popular choice for evaporative cooling in greenhouses. These systems involve a porous material, often made of cellulose or synthetic fibers, that is saturated with water. As hot air is drawn through the wet pad, the water evaporates, absorbing heat from the air and cooling it down. This cooled air is then circulated through the greenhouse.

Installation typically involves mounting the wet pads on one or more sides of the greenhouse. A water distribution system is required to keep the pads constantly wet.

Proper maintenance includes regular cleaning of the pads to prevent clogging and ensuring adequate water supply. It's essential to monitor water quality to prevent mineral buildup and damage to the pads.

Misting and fogging systems spray tiny drops of water into the greenhouse. This helps cool specific plants or areas by making the air around them humid. It can also help some plants by adding moisture to the air. But too much mist can cause plant diseases, so it's important to be careful.

Evaporative cooling systems can make greenhouses cooler, but how well they work depends on things like how humid it is, how hot the air is, and how much air is moving around. It's important to think about these things when setting up and using an evaporative cooling system.

Greenhouse Temperature Management Through Watering

Water can help cool down a greenhouse in addition to keeping plants hydrated. Using cold water to water your plants can slightly cool the soil and plants, which can help the whole greenhouse feel cooler. However, this cooling effect is small and works best when used with other cooling methods.

Drip irrigation delivers water directly to the root zone, minimizing water loss through evaporation. This reduces soil moisture levels, which can help lower soil temperature and subsequently, air temperature. Soil moisture sensors can be used to optimize watering, preventing excessive moisture that can lead to increased humidity and potential disease issues.

Wetting pathways and floors can be effective in small greenhouses or during short periods of extreme heat. However, excessive moisture can create a humid environment, which is not ideal for all plants and can promote disease development. It's crucial to balance the benefits of cooling through watering with potential drawbacks like increased humidity and disease risks. These techniques should be used in conjunction with other cooling methods for optimal temperature management.

Heating a greenhouse

Thermal mass and heat storage are effective strategies for harnessing solar energy to heat a greenhouse. By capturing and releasing heat strategically, these methods can significantly reduce reliance on traditional heating systems. You can use things like water, rocks, or bricks to store heat from the sun in your greenhouse. This helps keep it warm without using a lot of heat from other sources. These materials soak up the sun’s heat during the day and slowly release it at night.

As the greenhouse cools down at night, the thermal mass materials gradually release stored heat, warming the surrounding air. This helps to maintain a more stable temperature throughout the night.

Underground Cooling Pipes

While primarily used for cooling, underground pipes can also contribute to heat storage. During the day, excess heat can be transferred to underground pipes filled with water. The earth acts as a heat sink, storing the heat. At night, the warmer water can be circulated back into the greenhouse to provide supplementary heat.

Insulating a greenhouse

Shed greenhouse white with lots of windows and clear roof

Insulation is crucial for maintaining a stable temperature within a greenhouse, especially during colder months. Insulation acts as a barrier, preventing heat from escaping the greenhouse. This helps to maintain a warmer interior even when outside temperatures drop. By reducing heat loss, insulation helps to lower heating costs. Insulation contributes to a more stable internal temperature, reducing fluctuations that can stress plants. A well-insulated greenhouse can better withstand sudden drops in temperature.

Common insulation materials for greenhouses include:

Bubble wrap: Offers a cost-effective and lightweight solution.
Insulation blankets: Provide excellent insulation and can be easily removed when not needed.
Reflective insulation: Helps to reduce heat loss and reflect sunlight.
Foam board insulation: Offers high R-value for superior insulation.

The choice of building materials significantly influences a greenhouse's ability to retain heat. Glass offers excellent light transmission but poor insulation. Double glazing can improve insulation. Polycarbonate provides good light transmission and insulation, especially twin-wall polycarbonate. Acrylic offers a balance of light transmission and insulation, but can be more prone to scratching.

For the greenhouse frame, metal conducts heat efficiently, so insulation is crucial to prevent heat loss. Wood provides better insulation than metal but requires proper sealing to prevent heat loss.

For the greenhouse foundation, concrete has high thermal mass, storing heat during the day and releasing it slowly at night. Wood offers some insulation but may require additional measures for colder climates.

Gaps and cracks in the greenhouse structure can lead to significant heat loss. Proper sealing is essential.

Energy efficiency in greenhouse temperature control is crucial for several reasons. Efficient systems consume less electricity or fuel, leading to significant savings on energy bills. Energy-efficient systems often rely on renewable resources or consume less energy, reducing greenhouse gas emissions. Promoting environmentally friendly practices is essential for long-term sustainability. Energy-efficient greenhouses are better equipped to handle climate variations and extreme weather events.

Looking for a high quality pre-made greenhouse in Massachusetts? Hometown Structures offers the finest craftsmanship with custom designs in a wide variety of sizes perfect for the home gardener to give your plants the perfect climate to thrive in a protected environment, keep pests away from your plants, grow plants and food that don’t otherwise exist in your area/climate and extend your season with options including 8mm twin wall polycarbonate for optimal insulation, venting and windows. Every custom shed greenhouse comes with 50-Year LP Siding and 30-Year Collapse From Snow Warranty.