Wondering how to keep a greenhouse warm in winter without investing in electric or fuel-supplied heating systems?
Yes, it can be done. And without adding any more costs to your household budget.
I mean, who needs another bill right? Right.
Now, you might be wondering why bother keeping your greenhouse warm during the frostier months anyway – why not just enjoy the season?
Well, this girl likes her greens.
Ok, you caught me. I DO like greens, but I’m not a superfan.
I like them…but more like sprouts on a sammich. NOT full blown salads. Unless they’re Southwestern salads. Then, bring on the arugula.
ANYWAY, I like to keep growing over the winter because, well, I like to grow vegetables. Like any normal, sane person.
The other reason to keep a greenhouse warm in winter is because if you ARE growing anything, you’ll want to provide a healthier living environment for your vegetables, prevent cold spots, and reduce the risk of fungal diseases.
I have more readers growing crops in the winter, and naturally, a common question is how to heat a greenhouse in winter for free (which mean you can grow a wider variety of vegetables, too).
Understand the Basics of How to Keep a Greenhouse Warm in Winter
Before we delve into our ideas, let’s first establish some basics.
In this season where temperatures can go unpredictably low, you can only do so much. In other words, don’t try to grow oranges in sub-zero weather. You won’t be successful, right?
So, let’s talk about some basics to help you run your greenhouse in winter.
- Choose the right crops to grow for the season. Go for low-lying greens like kale, spinach, and mustard greens that can stand below-freezing temperatures
- Invest in a good quality thermometer like this one that can read max and min temperatures throughout the day.
- Only heat the areas necessary. Grouping plants together will help you save energy and cost.
- Install proper ventilation to prevent the spread of fungal diseases and maintain a healthy growing greenhouse.
Here are 3 more effective strategies in controlling the temperature inside your structure without having to waste fuel or energy.
Store Thermal Energy Using Thermal Mass
Thermal mass heaters are the bee’s knees, and easy to incorporate into your greenhouse.
If you’re not sure what I’m talking about, thermal mass, sometimes called a heat sink, absorbs and stores solar heat energy.
This involves putting materials around your greenhouse that absorb heat from the sunlight during the day. These heat sinks are then capable of slowly releasing thermal energy at night time when the mercury drops like crazy.
Here are some effective methods to collect thermal mass:
Idea 1: Build a cobbled pathway across the floor of your greenhouse using dark gravel or small stones (you can reach out to a local nursery or a dealer that sells rocks for driveways). These rocks naturally absorb heat – and the release of this heat keeps your plants warmer during the dark, cold hours of winter.
Idea 2: Since water has higher heat capacity than land or soil, try putting water or rain barrels around the interior of your greenhouse. Place dark barrels at a Southern-facing location, where they can easily absorb sunlight in the day. Make sure they’re also near tender plants that need more warmth at night
Idea 3: Use cinder blocks or earthenware ceramic pots to further absorb solar heat. They can be used to support planters on table-tops and benches, and they can release their heat around the plants (this is also a good idea to keep your chicken flock’s water from freezing over the winter).
Note: Painting these materials dark (i.e. black) helps absorb more thermal mass and one additional tip on how to keep a greenhouse warm in winter.
Build an Indoor Compost Pile
This is a genius idea that’s also one of the most sustainable techniques to keep your greenhouse warm this winter.
(Psst…it’s also cost-effective since you can build it nearly for free AND you won’t have to use power or fuel to heat your greenhouse. This is what we call Win-Win-Win.)
As the material in your pile composts, bacteria that break down organic material generate a considerable amount of heat to the environment.
We cover compost piles in depth in Organic By Choice: The (Secret) Rebel’s Guide To Backyard Farming. Save 10% with coupon code GREENHOUSE right here.)
Insulation is another option to keep a greenhouse warm in the winter.
So what do I mean by insulate?
Well, you can insulate the entire greenhouse using plastic sheeting, OR you can add row covers (yes, row covers over crops inside your greenhouse) for added protection.
Plastic helps absorb more heat without keeping the sunlight away from your crops. Combined with the other ideas in this article, you have quite a few ways to keep a greenhouse warm in winter.
There are many other natural techniques for keeping your greenhouse thermally controlled throughout the year. In the most challenging seasons, let these suggestions guide you on how to heat a greenhouse in winter for free. You don’t have to do everything. You just need to find the right combination that will work best for your set-up.