DIY Frost Guards for Your Greenhouse: A Simple Winter Heating Trick
- Apr 28
- 2 min read
Updated: 2 days ago
When temperatures drop in winter, keeping your greenhouse warm without electricity can be a challenge. But there's a surprisingly simple and budget-friendly solution: clay pot frost guards powered by candles.
How It Works
These homemade heaters work by trapping and slowly releasing the heat generated from candles placed under an inverted clay pot. The setup creates a small but effective heat source that can raise the temperature inside your greenhouse by 3–4°C—just enough to protect your plants from frost.
What You’ll Need
Unglazed clay pots (avoid painted or varnished ones)
Candles with strong wicks and long burn time
Grave candles are the most commonly used because of their durability
Tea lights work well in smaller spaces, like cold frames (each generates about 40 watts of heat)
A non-flammable surface to place the candles
Optional: a stand or bricks to raise the clay pot for better airflow and heat distribution
Make sure the vent hole of the clay pot stays open so the flames don't go out. For a standard-sized greenhouse, two frost guards with two to three candles each should do the trick.
Extra Tip: Insulate Smartly
Line your greenhouse with bubble wrap insulation—it helps retain heat while still allowing sunlight to reach your plants.
A Note on Sustainability
While this method is effective, it’s not the most eco-friendly. Many grave candles are made from mineral or palm oil and come in plastic containers, leading to waste and recurring costs. If you're concerned about sustainability, look for candles made from vegetable-based waxes. They burn cleanly, produce no soot, and their packaging is often compostable. Just keep in mind that they might not be easy to find, so it’s wise to stock up in advance.
Final Thoughts on the DIY greenhouse frost guard
Unlike electronic frost guards with thermostats, these DIY greenhouse frost guards don’t turn on automatically. Keep an eye on the weather forecast so you know when to light them. With a little preparation, this simple method can be a great way to extend your growing season—no power required.
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