How warm is a greenhouse in winter

How Warm Is A Greenhouse In Winter? 

As I step into my greenhouse on a crisp winter morning, I’m greeted by a comforting warmth that contrasts sharply with the chilly air outside. The sun’s feeble winter rays filter through the translucent walls, casting a gentle glow on the thriving greenery within. 

It’s a testament to the remarkable ability of a well-maintained greenhouse to create a cozy haven for plants even when winter’s icy grip tightens its hold.

The exact temperature inside a greenhouse can vary depending on factors like insulation, heating, and outside weather conditions. Here are the approximate temperatures: 

Optimal greenhouse temperatures vary with the seasons. During summer, maintaining a daytime range of 75-85°F (24-29°C) and a nighttime range of 60-76°F (15-24°C) is ideal. 

In contrast, the winter demands adjustments, targeting daytime temperatures around 65-70°F (18-21°C) while allowing nighttime cooling to approximately 45°F (7°C).

Join me as you explore just how warm a greenhouse can be in the depths of winter, providing a nurturing environment for my cherished botanical companions.

Top methods to keep a warm greenhouse in the winter:

Top methods to keep a warm greenhouse in the winter

1. Optimize Sunlight:

  • Ensure your greenhouse is situated in a location free from shading by trees or other structures.
  • Pay attention to changes in the sun’s trajectory during winter to prevent new obstacles from casting shadows.

2. Create Thermal Mass:

  • Use objects that absorb heat during the day and release it at night to raise the temperature.
  • Place containers of water in the greenhouse. Paint them black or add black food coloring to enhance heat absorption.
  • For larger spaces, use 55-gallon barrels filled with water and painted black.

3. Use a Germination Mat:

  • If your goal is to start spring plants early, consider using a germination mat to maintain optimal root-zone temperature and promote early growth.

4. Cover Plants:

  • Cover plants during extremely cold nights with materials like tarps, horticultural fleece, row covers, or sheets to provide extra warmth.
  • Ensure covers are kept off the plants and removed during the day to prevent excessive humidity.

5. Insulate with Bubble Wrap:

  • Attach bubble wrap to the interior walls of the greenhouse to reduce heat loss and block drafts.
  • Use horticultural bubble wrap designed to withstand UV light and with larger bubbles for better insulation.

6. Install a Heating System:

  • Electric Heaters: Electric heaters are a common choice for small to medium-sized greenhouses. They come in various sizes and types, including fan heaters, radiant heaters, and convection heaters.
  • Gas or Propane Heaters: These heaters are often used in larger greenhouses. They can provide more consistent and cost-effective heat, but proper ventilation is crucial to prevent carbon dioxide buildup.
  • Wood-Burning Stoves: In some cases, wood-burning stoves can be an efficient and sustainable heating option. They require a well-ventilated chimney system.

7. Use a Thermostat:

  • Set up a thermostat to control heating systems, saving energy by only heating when necessary.

8. Use a Thermometer:

  • Invest in a thermometer with maximum and minimum readings to monitor and adjust the temperature inside the greenhouse.

9. Choose the Right Temperature:

  • Avoid overheating by maintaining temperatures suitable for the plants you are growing.
  • Frost-free at 3°C (37°F) is the minimum, while some plants prefer 7-10°C (45-50°F).

10. Position Heaters Carefully: – Place heaters in an open, central spot, away from water, and angle them to direct airflow above nearby plants.

11. Zone Heating: – Create separate zones within your greenhouse using partitions or curtains of bubble wrap insulation to heat only the area with delicate plants.

12. Use Horticultural Fleece: – On exceptionally cold nights, layer frost-protection fleece over plants for added insulation and protection.

13. Maintain Ventilation: – Proper ventilation is crucial for preventing fungal diseases and maintaining a healthy environment. – Open vents on sunny days to release excess moisture and close them at dusk to retain warmth.

14. Heated Propagation: – Invest in heated propagators or mats to promote seed germination and root cuttings efficiently.

Here are some eco-friendly methods to heat a greenhouse:

Compost Heat Sink: Composting generates heat as organic materials decompose. To utilize this heat source:

  • Create a heat sink by digging a ditch in the centre of the greenhouse.
  • Fill the ditch with compost to significantly increase the greenhouse temperature.
  • For milder heating, use bricks or concrete in the ditch.
  • Enhance the heating ability by running pipes through the ditch, directing heat into the greenhouse.

Hotbeds with Composting Material: Hotbeds are raised beds with a layer of composting material underneath, providing natural warmth:

  • Place a layer of compost, such as straw, horse, or cow manure, beneath the planting soil.
  • The decomposing compost warms the soil and plants, preventing frost damage.
  • This time-tested method has been used for centuries.

Water Barrels for Thermal Mass: Installing water barrels in the greenhouse adds thermal mass and helps regulate temperature:

  • Water absorbs heat during the day and has a high specific heat capacity, storing a significant amount of heat.
  • As the greenhouse temperature drops at night, heat energy is released from the water, warming the greenhouse.
  • Enhance heat absorption by painting the barrels or containers black.

What Happens if your Greenhouse is Damaged in winter?

What Happens if your Greenhouse is Damaged in winter

If your structure designed for plant cultivation is compromised during the winter months, it can have several consequences, including negative effects on your plants, increased heating costs, and potential safety hazards. 

Here are some of the ramifications and steps to take if your plant-growing space is impaired in winter:

Plant Vulnerability: The most immediate concern is the potential harm to the plants inside the space. If the structure is compromised, cold temperatures, wind, and snow can harm or kill your plants. Frostbite, dehydration, and other cold-related issues can occur.

Financial Loss: Depending on the severity of the issue, you may experience a significant financial setback due to structural problems, heating equipment damage, and the value of the plants themselves.

Heating Challenges: A damaged space may have reduced insulation properties, allowing heat to escape more easily. This can lead to increased heating costs as you’ll need to work harder to maintain a suitable temperature for your plants.

Safety Concerns: Structural problems can create safety hazards, especially if there is a risk of the structure collapsing. Broken glass or damaged equipment can also pose safety risks to those working in or around the space.

Disease and Pest Risk: An impaired plant-growing space may become more susceptible to pests and diseases. Gaps or openings in the structure can allow insects and pathogens to enter more easily.

Reduced Productivity: If the issue is significant and not repaired promptly, it can disrupt your growing season and reduce the productivity of your plant-growing area.

Here are steps to take if your plant-growing space faces issues during winter:

Assess the Situation: First, assess the extent of the problem. Determine whether it is minor or major and whether it affects the structure, heating system, or plants.

Secure the Area: If there is a risk of collapse or further problems, secure the area around the plant-growing space to prevent access and ensure safety.

Rescue Valuable Plants: Save any priceless or delicate plants and transport them to a temporary shelter or another suitable site if it is safe to access the damaged space.

Repair or Replace: Depending on the severity of the issue, decide whether to restore the plant-growing area or consider alternative solutions. This will depend on your budget, the extent of the problem, and the value of the structure.

Inspect Heating Systems: To guarantee safe and effective functioning, get your heating system evaluated and repaired by a competent specialist whenever it is impacted.

Prevent Future Issues: Consider implementing measures to prevent future problems, such as reinforcing the structure, improving insulation, or using more durable materials.

Contact Insurance Provider: Contact your insurance provider to report the problem and start the claims procedure whether you have insurance coverage for your plant-growing area.

Plan for Plant Recovery: If your plants have been affected, develop a plan for their recovery or replacement in the next growing season.

Learn from the Experience: Take the opportunity to learn from the incident and implement measures to better protect your plant-growing area in the future, especially during winter.


How warm is an unheated greenhouse?

An unheated greenhouse can maintain temperatures slightly higher than the outside environment. Its effectiveness varies based on the climate in your region. In areas with mild winters and no extreme cold, an unheated greenhouse can provide sufficient protection for cold-hardy plants. However, during severe cold spells, especially in regions with sub-freezing temperatures, an electric heater is recommended to keep tender plants alive.

Do greenhouses need a heater in winter?

Yes, While not always necessary, greenhouses can benefit from supplemental heating during the winter. This is particularly important to provide adequate warmth for delicate plants when exposed to freezing temperatures. Consider using a solar-powered heater to minimize heating costs.

What is the lifespan of a greenhouse?

The longevity of a greenhouse depends on its construction materials. A wooden greenhouse can last between 45 to 60 years, while a glass greenhouse typically serves for approximately 30-40 years, contingent on proper maintenance. In contrast, modern polyethene film or polycarbonate greenhouses are more short-term, typically lasting up to 5 years. The durability of a greenhouse is influenced by factors like maintenance and the materials used.

What size heater works best in my greenhouse?

Selecting the right-sized heater for your greenhouse is crucial. Start by determining the square footage of your greenhouse and then assess the temperature difference in your region. Multiply the greenhouse’s square footage by the temperature difference, and then further multiply this result by the heat loss factor to determine the appropriately sized heater for your greenhouse.

How can I heat my greenhouse for free in the winter?

While electric heaters can be used, it’s not always the most efficient option. Greenhouses can act like convection ovens, and heating from the inside might not be ideal. Instead, consider insulating the outside walls with styrofoam panels or using solar PV panels to harness solar power for more cost-effective and eco-friendly heating during the winter.


To wrap up, in the winter, keeping a greenhouse warm is crucial for my plants. During the day, I aim for temperatures between 65-70°F (18-21°C), and at night, it cools down to about 45°F (7°C).

To make this happen, I do a few things. I put my greenhouse where it gets lots of sunlight and use water containers to trap heat. If I’m starting plants early, I use a germination mat. On really cold nights, I cover my plants to keep them warm.

Furthermore, I also use bubble wrap for insulation and have a heating system, like electric heaters, to maintain the temperature. I use a thermostat and thermometer to keep an eye on it.

Moreover, the right temperature depends on the plants I’m growing. Most need at least 37°F (3°C), but some prefer 45-50°F (7-10°C). Placing heaters in the right spot, using curtains for separate heating zones, and adding fleece on super cold nights all help. And don’t forget ventilation to keep the air fresh.

I’ve also got heated propagators for seedlings. It’s all about finding the right balance to keep my plants cozy in winter.

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