Heating Your Greenhouse During Winter with (Almost) Zero Costs!

Greenhouses are a time-tested way to extend your growing season, provide ideal conditions for plants that love warm weather, or keep right on gardening straight through the winter. A properly designed hoophouse can keep your plants warm and happy using nothing but the power of the sun.

But despite the efficiency of sunlight, greenhouses may need an extra heat source in the wintertime. This can turn into a tricky problem: heating is often expensive, and that’s because no matter what you use for fuel or energy, there is a cost associated with it.

Luckily, there are many ways to effectively and reliably heat a greenhouse in the wintertime for no additional cost at all if you are clever.

in what follows I’ll tell you about several proven methods for doing so that will save you a fortune and help keep your plants alive in the coldest conditions.

A Good Greenhouse Will Have Lots of South-Facing
Windows

In the northern hemisphere, like the US for instance, you’ll want the windows, skylights, and other transparent surfaces of the greenhouse facing south so they can take in the maximum amount of full-value sun possible. That will result in a considerably higher temperature during the day.

Weatherize Properly

Greenhouses benefit from “winterization” in the same way that your home or barn does: spend time in your greenhouse running down every gap, crack, nook, cranny, and crevice that’s letting any amount of air in or out. Then seal them with a tube of caulk, weather stripping, trim, or anything else that’s required to stop the draft.

Once that’s done, give the windows and skylights, or any other transparent surfaces, a good cleaning until they’re crystal clear. Dirt and grime will impair the transmission of light, which means a lower overall temperature inside.

Insulate if Needed

If you live in a cold, northern climate, or you’re just coping with a brutally cold winter, insulation can help make the difference inside your greenhouse.

You can use corrugated plastic paneling, foam board panels, bubble wrap, or any other insulating material to help stop the cold from creeping in.

Obviously, there is a limit to the efficacy of insulation; you don’t want to insulate over the windows, or else you will stop sunlight from getting in…

Otherwise, walls, floors, ceiling panels, and every other surface can and should be insulated if you can do so effectively.

You’d be wise to install the insulation in a semi-permanent fashion that’s easy to remove when the weather warms up; it’s possible to overdo it and make the interior too hot when the mercury climbs again!

Haul in Hot Ashes

An old-school technique that really works. If you’ve got a fireplace, fire pit, or wood-burning stove, you can carefully shovel out the ashes once the fire has died down, or scrape some out if it’s still burning, load them into a steel pail, and then set that out in your greenhouse.

As you might imagine, these ashes will still be quite hot and radiate out a lot of heat, dramatically increasing the temperature inside. Simple as that!

But there are a few drawbacks to this method, too…

For starters, you’re only going to get ashes from burning wood or other fuel, meaning this is only a value proposition if you use wood, not gas, as fuel for heating and cooking.

Second, that bucket will get really hot, possibly hot enough to set other materials on fire. Placing the bucket safely is paramount.

Lastly, take great care that there are no embers or chunks of other flammable material in the ashes that might cause sparks, setting your plants or something else on fire.

Use Hot Rocks

If you like the idea of using radiant heat but think the hot ashes idea is just too risky, you can use this trick. Most large rocks have a significant thermal density, meaning they absorb a lot of heat and then radiate it slowly over time.

Either leave the rocks inside the greenhouse in direct sunlight where they will be warmed, or leave them outside on a dolly or cart for the same purpose, moving them inside the greenhouse at night when temperatures start to plummet. They won’t get so hot that they are a fire risk, but they will warm things up for sure.

The only real drawback with this method is that it’s not enough for coping with ferocious cold, and you’ll be hauling heavy rocks around if you don’t leave them inside.

Place Hot Water Barrels and Pipes

When you were a little kid, did your parents ever give you a hot water pack when you were chilled or sick? If so, you know the heating value of water.

Now, chances are you aren’t going to run any sort of hot water system out to your greenhouse. One way or the other, that would defeat our no-cost objective! But what you can do is use containers of water, painted black, in the same way that you would use stones.

A black water barrel, or even a few black buckets, warmed all day by the sun, will radiate out a surprising amount of heat after the temperature starts to fall.

If you’ve already got the containers, you’ve got everything you need besides a little black paint. Just remember to position them so they get lots of sunlight!

Make Compost Inside

Every gardener loves compost. It’s one of the very best things you can make for your plants.

Whether you have an in-ground garden, raised beds, or lots of containers, this all-natural, nutrient-rich stuff is just the ticket for giving your plants the food they need and also improving soil structure.

And as every seasoned gardener knows, compost takes time to make. That’s because there are many biological processes of decomposition that must occur to make it.

One of the outputs of those processes is heat. That’s right: a compost pile that is decomposing properly will emit a significant amount of warmth!

Note, though, that bigger piles emit correspondingly more heat; a little bucket won’t make much difference in a large greenhouse.

Light Candles

Even a few such candles can make a significant difference in your greenhouse’s internal temp

There are obvious concerns with this approach, though: burning candles are a significant fire hazard, especially if you aren’t around to intervene if one gets knocked over or something bumps into it.

If you want to use candles for warming up your greenhouse during winter weather, consider placing them in tall, metal containers and keep them well away from anything flammable.

Install Solar Panels to Run Electric Heaters

If you already have a good solar power system, you can rely on it to run a small space heater. Yes, even small space heaters gobble up tons of energy. On average, one uses about 1,500 watts of electricity.

Trying to power one directly with solar panels will be a big commitment, so you’re better off hooking up the heater to a battery system for the purpose…

For folks who live in the coldest climates, especially ones that don’t get lots of sunshine, this might be the only way to keep the interior of the greenhouse livable for your plants.

The good news is that with proper insulation and taking care to ruthlessly eliminate drafts even a small heater can do a great job.

If you don’t have solar panels already, I’d advise you to skip this approach: the buy-in cost will be substantial.

Keep Chickens Inside the Greenhouse

Chickens, like all birds, have extremely high metabolisms. This means they are basically little walking heaters. A small flock of birds, kept inside your greenhouse, will keep it toasty warm even during the most bitter conditions.

The trick to making this work without the whole thing turning into a giant disaster is proper management. Letting your chickens simply roam inside your greenhouse is a recipe for a giant mess; your chickens will poop all over the place, attack your plants, and cause problems.

A better approach is to put their tractor, if they are using one, inside the greenhouse. This will keep them contained, minimize cleanup, and still provide just as much heat.

Another workable option is to build or attach the greenhouse to the side of their coop, and then either vent that side to the greenhouse, allowing lots of heat into it, or build the whole unit as a kind of duplex with a mesh wall. This will keep the chickens away from the plants but let lots of heat in.

Even if you keep them contained away from the plants, the one big shortcoming with this method is that the chickens will only warm the greenhouse when they’re actually inside or in their attached coop. If you let them out to free range, they won’t provide any warmth at all!