That Terracotta Pot ‘Hack’ You Keep Seeing Online Doesn’t Actually Heat Greenhouses – Here’s What to Do Instead

Keeping a greenhouse warm in the colder months can be tricky and expensive. That's why the latest viral hack has caught my eye: a DIY clay pot heater. It uses just a terracotta pot and some tealight candles to warm up a greenhouse – an inexpensive and convenient idea. My only concern is how effective it really is at warming a greenhouse sufficiently to support the plants growing inside.

The truth is there is no single way to heat a greenhouse. For something reliable and low-effort, a lot of gardeners use electric greenhouse heaters (like this one from Amazon), but the running cost can be expensive. Others use bubble wrap to insulate a greenhouse. Now, many gardeners are giving the clay pot heaters a go, placing tealight candles under an upside down pot to radiate heat.

While it will warm the air somewhat, it's ability to heat an entire greenhouse is questionable. Here, I run through how to make one (it literally takes minutes to construct) and delve deeper into whether this hack actually works or if it's just another online fad that produces minimal results.

What is a Clay Pot Heater?

A clay pot heater is a DIY that involves an elevated upside down clay pot being heated by candles beneath.

Because clay pots have a high thermal mass, they absorb the warmth from the candles and radiate it, raising the surrounding temperature by a few degrees.

But can it really heat up an entire greenhouse? Here's all you need to know.

How to Make a Clay Pot Heater for a Greenhouse

The reason this hack is so appealing is because you only need a handful of materials to make and most gardeners will already have them lying around, so it's practically free.

You will need:

• Unglazed terracotta pots of any size, though having multiple small-medium ones are recommended. This pack of four terracotta planters from Amazon is a good choice
• Tealight candles, like these unscented tea light candles from Walmart
• A non-flammable item to hold up the pot. This could be small bricks or terracotta pot feet (from Amazon)

Constructing a Clay Pot Heater

It's as simple as elevating your terracotta pot upside down, using something like bricks or pot feet, and placing candles beneath it.

Make sure the pot is unglazed and not painted, as this will expand easily with heat and can shatter.

You want to make sure there is space between the pot and the table surface below to allow air in and keep the flame lit, otherwise the flame will be smothered and go out.

You should also block any drainage holes in your terracotta pot. You can do this by placing a terracotta saucer (like these from Amazon) over it. This keeps the heat in to then radiate and warm the surrounding area.

Does it Actually Work?

So, does it actually work to use a clay pot heater for a greenhouse? Probably not as much as the viral videos online suggest.

While there is no doubt the warmth of the candles will be radiated by the pot somewhat, the room temperature isn't likely to increase dramatically.

Candles can only generate a set amount of heat, with tealights producing 30-40 watts on average. This is not sufficient to warm a room, nor would it be to warm a greenhouse to the point it actually supports young and tender plant growth.

You may find having multiple clay pot heaters is more effective, though it still won't be as substantial as using a greenhouse heater.

Nevertheless, it can help with starting seeds indoors and providing extra warmth to nearby seedlings, at least to a certain extent. You may find a seedling heat mat (like this one from Walmart) is more effective, however.

And as a decorative feature, it is undoubtedly charming, especially if you have a seating area in your greenhouse, adding a bit of warmth to the perfect spot for an afternoon cup of tea.

If you do give this hack a go, take care not to leave lit tealights unattended.

FAQs

Are Clay Pot Heaters for a Greenhouse Safe?

It can become unsafe to have lots of open flames in a greenhouse, which is why you should keep this DIY to a minimum and simply enjoy it for its aesthetic value rather than relying on it to raise temperatures. It is possible that the clay pot can expand and shatter, too, causing a hazard. Plus, candles in a confined space without ventilation can risk carbon monoxide levels rising. These are all safety concerns to be aware of if you're considering making a clay pot heater for a greenhouse.

There are lots more effective methods to heat a greenhouse and ways to keep plants warm inside. For example, you can use a heater, seedling mat, or make a greenhouse hotbed.

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