Running electric heaters can significantly alter your energy bills. Although greenhouse shields plants from winds and rains, on a colder winter days you will need to heat it.
Bear in mind that when heating greenhouse humidity raises and to avoid it ventilation is a must. Therefore, you need to find cheap ways of heating a greenhouse structure.
1. Use a mini greenhouse inside the greenhouse
Yes, it might sound crazy but if you want to save on the energy costs you can grow the tender plants inside a mini greenhouse.
You can grow the cold loving plants that tolerate temperature of -15°F (-9°C) inside the big greenhouse. It is important that these plants are not exposed to other conditions like water logging.
2. Seal the gaps in greenhouse frame
Identify the sources of drafts in the greenhouse. Check the structure carefully. Commonly the cracks and gaps are formed in the panes and in the junctions between glazing and frame.
Reinstall broken panes, doors and vents. Use an adhesive foam strip to seal any gaps in the greenhouse frame.
3. Insulate Greenhouse with bubble wrap
Use horticultural or agricultural bubble wrap to insulate a greenhouse. It allows good light transmission and is UV stable.
Moreover, it lasts for three years. Keep in mind that larger bubbles will let more light inside the greenhouse.
Measure how much you need based on the size of the sides, roof and ends of the frame. Attach the wrap to the inside of the aluminum frame using glazing clips.
4. Compost pile releases heat inside a greenhouse
Organize a wire mesh around your compost pile. You can compost anything starting from hay, plant clippings and leaves. Also, you can place straw bales inside the greenhouse if you have enough space.
Place your compost in the middle of the greenhouse. Microorganisms in the compost break down the organic material releasing energy in a form of heat.
However, be careful with placing heaters near a compost pile as it can easily catch the flames.
5. Build a brick wall inside a greenhouse
It is known that rock or brick wall traps traps additional heat. This dense material called thermal mass collects sunlight during the day and absorbs the heat.
You can use gravel, bricks or cinder blocks. Put down a layer of thermal mass by using gravel or small stones. Place thermal mass (bricks) on or as part of the wall opposite direction to entering sunlight.
Paint all the structures in the greenhouse white so they reflect sunlight. You can arrange cinder blocks on the layer of gravel. Paint it black to increase the absorbance of heat.
6. Place a plastic gallon filled with water
Believe it or not but water can save on the greenhouse heating costs! How? Water has the highest specific heat capacity of all the liquids.
Specific heat is an amount of heat absorbed or lost by one gram of the substance to change the temperature by one degree Celsius.
So, water absorbs the excess heat in the summer to keep the temperature down. Alternatively, in winter it will hold onto the heat to keep the greenhouse warmer.
Use large barrels or gallons of water. Moreover, you can use it to reflect the sunlight into a greenhouse. You will need to organize single or multiple ponds or a water holding trench.
Place it at such an angle inside the greenhouse that sunlight reflects off of it and into the structure. This reflected light can potentially add more warmth into the greenhouse.
7. Paint a plastic gallon black inside greenhouse
You can paint the existing plastic gallon with water black and place it where there is most sunlight. Black or dark brown absorbs UV radiation and heats up the structure more quickly.
You can place a few plastic gallons painted black around the greenhouse. However, make sure you have enough space to do that.
8. Use crates of manure in the middle of greenhouse
Strategically placed in the middle of a large greenhouse manure crates can warm greenhouse by a few degrees. Similarly to compost it releases heat when broken down.
To keep the starting and seedlings warm in the winter, you can also place them on the top of the crate with manure. Once the manure has aged, you can add it to soil to enrich it.
9. Separate an area inside a greenhouse which you want to heat
This is a great idea if you grow cold loving and heat loving plants inside a greenhouse. Screen off a part of the greenhouse which you want to be heated.
Use a bubble wrap or polythene film to separate a part of the greenhouse you are going to heat. Secure it with the bricks by placing them on the ground.
10. Use an attached or lean-to greenhouse to save on heating
Building at attached greenhouse is a great way to save on energy bills. Attachment to the building allows share and exchange of heat.
A good idea is to attach a greenhouse to a chicken coop. The heat chickens produce can warm the greenhouse significantly. To find more on the advantages of a lean-to structure you can read this article.
If you have a spacious freestanding structure, then you can use the warmth of life creatures by placing them inside. For instance, you can place a rabbit’s hutch inside the greenhouse.
These were my top 10 ways to heat a greenhouse in winter without electricity. If you live in a very cold climate, you can follow this guide which tells you which heater is best for your greenhouse.