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The colder months bring frost, freezing nights, and slower growth. Knowing how to heat a greenhouse in winter can decide whether your plants thrive or struggle. Here’s what you can do.
How to Keep Greenhouse Warm in Winter
Don’t let winter slow your crop production, let alone damage it. Keep these few techniques in mind to maintain a productive greenhouse:
Seal in the warmth with insulation
A greenhouse is like a warm cup of tea—if it’s not covered, heat can slip in gaps. This is where insulation comes in.
Bubble wrap and polycarbonate panels are great options. They trap tiny pockets of air, acting like a second layer of skin over your greenhouse. Apply to the walls and the roof, and don’t leave gaps at corners or around frames. Even small openings can let out a surprising amount of heat.
Doors and vents are also among the sneaky culprits for heat loss. Add weather stripping or a draught seal around edges to stop warm air from escaping.
Don’t forget the floor, as cold from the ground can pull the temperature down fast. Go for insulation boards, thick mats, or layers of reclaimed wood under raised beds this time. Your plants will feel it too—the roots stay warmer, and seedlings are less likely to stall in growth.
Add extra heating
Sometimes insulation isn’t enough on its own, especially during hard frost, so pair it with a heater. Your best option includes an electric heater with a built-in thermometer. It won’t overheat the space or waste energy when it’s already warm.
If your greenhouse isn’t near mains power, paraffin or gas heaters are a great alternative. They put out enough heat to warm bigger greenhouses, but ventilation is crucial. You want the heat but not a build-up of fumes, and a small fan can help with this.
The roots need warmth, too; use heat mats or soil cables to keep the soil at a steady temperature. Combined with good insulation, the roots stay warm, and your plants can stay growing.
Attach your greenhouse to a nearby structure
The idea is to position the greenhouse near a shed, garage, or the side of your house. Walls hold heat, and by sharing that mass with your greenhouse, you reduce how the air inside cools at night.
If you can, position the greenhouse on the south or southwest side of the building. That way, it picks up sunlight during the day and the wall radiates stored heat back after sunset.
With this approach, you may not run extra heaters and just take advantage of the heat that’s already there.
Place water barrels
Another trick that works is using water as a heat buffer. Line at least one or two inside or outside. During the day, the water will absorb sunlight and absorb that heat. When the sun goes down, it will slowly release the warmth back into the greenhouse.
The bigger the barrel, the more heat it can hold. Alternatively, paint the barrels dark or black to absorb more heat. Position them near the centre or along walls where airflow will carry the warmth around.
Winter Growing in a Greenhouse
Kale, spinach, winter lettuce, as well as parsley and chives, will do well as long as the soil doesn’t freeze solid. Mix fast-growing crops in with slower ones—for instance, baby spinach between kale.
Try using raised beds, pots, or planters. They heat up faster in the sun and cool down slower at night. Move pots around to the warmest spots if there’s a sudden frost, or cover seedlings. And again, pairing this with a heat mat or soil cable under your pots gives you a mini microclimate.
Round-up
Knowing how to heat a greenhouse in winter doesn’t have to be complicated. Keep the warmth inside with insulation and add a heater if it gets really cold. It’s optional, but you may also use walls or water barrels to hold heat for your plants. Do these, and your plants will keep growing even through the frostiest nights.
Read this guide next: Greenhouse Ventilation: The 5 Essential Aspects to Consider
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