Forget Pricey Heaters: Warm Your Greenhouse In Winter For Free With Something You Already Have

Your DIY backyard greenhouse is supposed to make growing plants year-round possible. However, that often requires help from equipment like heaters. While you can spend over $200 on electric heaters, water is basically free. Thanks to the power of the sun, water's high specific heat capacity, and a few plastic barrels, you can create thermal mass heaters for your greenhouse.

There is a science behind how a container of water can save your plants from frostbite. As it absorbs heat from the sun during the day, the water's temperature increases, creating a hot tub of stored energy. The water slowly releases its warmth as the day's temperature cools down, which in turn makes it an effective heater. Using water as a thermal mass for heating is budget-friendly, and it is a great way to winterize your backyard greenhouse. However, it can be less effective on cloudy or low-sunlight days.

For these DIY heaters, you'll need a few 55-gallon drums filled with water. That's typically the standard size of a backyard rain barrel. It's best to buy a black one or spray paint yours black to increase sunlight absorption. If you're working with a smaller greenhouse, you can also use smaller containers so you still have sufficient room. Place the barrels in areas of the greenhouse that receive direct sunlight, since solar energy heats the water. These barrels will become hot spots, and you can put your heat-loving plants on and near the containers so they get more warmth. That's it — the water and sun do all the work.

The more barrels, the more chances you have for a warmer greenhouse. However, it's important to note that a 55-gallon drum filled with water weighs over 400 pounds, and they will take up a lot of floor and vertical space. You can stack the barrels (before filling) on top of each other as a way to organize your greenhouse to maximize space. But only if they won't block ventilation or create more shade for your plants. Or perhaps use the barrels as table legs to create a bench for more potted flowers and produce. This way, the drums become a part of the greenhouse's ecosystem.