Ideally, a greenhouse — or the soil in a greenhouse — should be 37°F or warmer to support a garden. While it’s more difficult to reach this temperature during the coldest months of the year, it’s not impossible. Insulating your greenhouse and installing a heater are not the only heating methods available to you. There are ways to heat a greenhouse for winter gardening so you can have fresh veggies all year round.
1. Increase insulation
Insulation passively heats a greenhouse; rather than adding more heat, increasing insulation minimizes heat loss. While you can insulate the whole greenhouse structure itself, you can also focus on insulating the soil or individual plants. As long as the plants are at the right temperature, you can forgo insulating or heating the rest of the greenhouse.
Here are some ways to insulate your greenhouse, soil, or plants:
•Use bubble wrap
If you have a bunch of bubble wrap lying around, you can use it to insulate your greenhouse. Simply wrap the inside walls of the greenhouse in bubble wrap. So, the next time your Amazon package comes with a questionable amount of bubble wrap, keep it around for the winter months.
•Recycle fall leaves
Don’t have bubble wrap? No problem! There’s a cheap — even free — alternative homeowners like you can use: fallen leaves. Bags of fall leaves can be reused as insulation by pilling them up against your greenhouse walls.
•Add mulch
Among the many benefits of mulch is the insulation it provides for your soil. Mulch helps keep the soil (and your plants) warm and toasty throughout the wintertime.
Don’t think you need to spend money on fancy mulch, either. You can find free mulch even in your own backyard, such as fall leaves, grass clippings, or old paper products.
•Cover your plants
Covering your plants is one way to protect them from a freeze. Greenhouse plants can be covered in horticultural fleece (also known as gardening fleece), row covers (typically made of clear plastic), or cloches. The latter can be recycled drink bottles, old milk containers, or even mini greenhouses (hotboxes).
2. Add thermal mass
Thermal mass is the ability of a material to catch, store, and release heat energy, such as the heat from the sun. Increasing your greenhouse’s thermal mass is as simple as adding more materials with a high thermal mass. These materials are heat sinks that trap the sun’s heat in the morning and release it throughout the night.
Water, soil, clay, stone, bricks, and ceramics are some materials with high thermal mass that homeowners can easily find. Here are some ways to integrate them into your greenhouse:
•Place barrels or tanks of water, preferably black ones for maximum heat absorption, in the corners and along the north wall of the greenhouse. If you don’t have much space, even small jugs of water can help.
•Add brick or stone paths and edging. This not only adds thermal mass but also adds style.
•Store extra bags of soil inside your greenhouse.
3. Make compost
Decaying organic material releases heat as it breaks down. So, making compost inside can help keep your greenhouse warm in the winter; as a bonus, you’ll also get black gold to use in your garden. You can simply dig a trench and make a compost pile, but making a hotbed is a more useful and more aesthetically pleasing option.
Used to start seedlings in the winter, a hotbed is a raised garden bed that’s filled mostly with composting materials topped with a growing medium (such as soil). Aim for a hotbed at least 20 to 30 cm deep and maintain a 3:1 ratio of compost to soil. You’ll also need a good ratio of greens to browns. You can cover your hotbox with a cloche, row cover, or even an old window pane if you want even more heat.
4. Add a heating system
Installing a heating system is the most sure-fire way to heat a greenhouse. There are many sources of fuel, such as wood, coal, natural gas, propane, kerosene, electricity, and renewable energy (including solar energy).
