Keeping your plants warm during the winter can sometimes feel like an impossible task. There are many greenhouse heating options, but one method stands above the others for those looking for a natural solution to their frosty greenhouse plants.
You can heat a greenhouse using only compost. This practice has been around since the 1940s, initially done with straw to heat greenhouses, and has evolved in recent years. Compost heating can effectively keep your space at about 80 °F (27 °C) or more if maintained.
In our world’s current energy crisis, it’s imperative to seek green solutions that don’t tax our overburdened planet, and compost heating is a great option. Read on to discover the mechanics of compost heating, the benefits, and how to heat your greenhouse only using compost.
Compost Heating: An Overview
When you hear that you can heat your greenhouse only using compost, you might assume the process is more complex than it is or that you are simply using the compost to fuel some unique heater, but that is not the case.
Compost heating is just like it sounds. Compost naturally heats whatever space you place it in.
So how exactly does it work?
Compost can create heat due to the microbial activity that begins to happen within the pile as these organisms break down the organic matter. As the microorganisms eat the compost materials, their exothermic reactions create heat.
How warm your pile gets is dependent on a few factors, such as:
These factors work together to produce heat, and compost can significantly heat the space in an enclosed space, such as a greenhouse. However, you must use a wide variety of green and brown plant matter to get the best results.
Whether you own a glass or plastic greenhouse, this heating method is a great option to keep all the frost at bay.
Heat Production Capabilities
A well-maintained compost pile can reach internal temperatures of 130-140 °F (55-63 °C), translating to a greenhouse temperature of about 80 °F (27 °C). The generated heat varies based on the pile’s size, nutrient content, and maintenance.
Compost heating has become increasingly popular next to propane heating, offering low maintenance costs and effectiveness.
It’s important to note that the effectiveness of a compost heater also depends on the size of the pile in relation to the greenhouse. Ideally, you should set up one cubic meter (1.3 cubic yard) of compost for every 2 square meters (21 sq ft) of greenhouse space.
Benefits of Heating a Greenhouse With Compost
Now that you know a little about how composting can be a heat source, let’s talk about a few of the benefits of this heating method.
Compost heating benefits include:
Using compost in a greenhouse enriches the compost. Not only will your compost be rich in nutrients for your plants, but it will also generally be free of weed seeds since it’s kept in a weed-free indoor space.
An Increase in CO2
Compost as a greenhouse heating source creates more carbon dioxide (CO2) for your plants. Plants quickly use their CO2 supply in their enclosed greenhouse, and having a constant source of new CO2 can help your plants thrive.
A Warm Greenhouse
Compost keeps your greenhouse warm. Hot composting leaves you with fantastic soil, but it will also help keep your plants warm and healthy despite the freezing winter.
A Boost in Humidity
Compost heating helps increase humidity. A good compost heater can help create more humidity in your greenhouse so long as the compost is sufficiently moist.
Compost is cost-effective. Apart from the material required to construct your compost heater, this heating process is entirely free and has relatively low maintenance.
An Eco-Friendly Choice
Compost heating is a renewable and eco-friendly option. As a natural heating source, compost spares the world’s overburdened resources.
As you can see, there are a few fantastic benefits to this type of heating, and who doesn’t love a free heat source that also turns into a great soil amendment?
The Lifespan of Compost Heaters
It’s truly amazing how warm a pile of organic matter can get with little to no effort on your part. So now that you understand just how much heat these organic heaters can produce, it’s time to talk about how long they can last.
A compost heater will last about 12 months, depending on how quickly the organic materials are fully decomposed. Around the 12-month mark, the heat will begin to dwindle, and it will be time to replace it with new nutrient-dense compost.
You can use the finished compost for gardening as mulch or soil amendment. On the other hand, the new can be used to keep your plants warm in the winter.
How to Extend the Compost Heater’s Lifespan
Over time, the compost pile will shrink as the organic materials become decomposed. Turning your pile regularly will send the fine particles to the bottom. As the amount of fresh organic matter decreases, the microbial activities will also decline, lowering the pile’s overall temperature.
To extend the heating capacity of your compost pile, you can remove the finished compost that accumulates at the bottom of the pile regularly. Replenish the pile with fresh yard waste to keep the compost going all year round.
In addition, here are some compost pile care tips to maintain optimum heating temperatures:
- Check the pile’s temperature every 3-4 days. If it falls below 104 °F (40 °C), it’s time to turn your pile. Otherwise, keep checking until the temperatures become low enough to avoid disrupting microbial activities too soon.
- Keep the compost moist. Every time you check the pile’s temperature, make it a habit to also check the moisture content. Moisture is necessary for the microbial decomposers to remain active. Ideally, the pile should be as moist as a wrung-out sponge. If it feels dry, water it from the top. Doing this once or twice a week should suffice.
How to Make a Compost Heater for Your Greenhouse
Last but not least, it’s time to discuss how you can set up your compost heater for your greenhouse. The process is simple and will generally yield results within a week of construction.
You will need:
- Wood planks
- Staple gun
- Mesh wire
- Compostable materials like fruit, veggies, animal waste, and other plant matter
Your materials don’t need to be brand new. In fact, old wood from a free pallet you have lying around will work just fine. How much wood you need and the exact sizing will be dependent on how large or small you want your compost pile to be.
Keep in mind the following dimensions when deciding the size of your compost pile: 1 cubic meter (1.3 cubic yards) of compost per 2 square meters (21 sq ft) of greenhouse space. Adjust the size accordingly depending on how large your greenhouse is.
Here’s how to make a compost heater:
Create a Square-Shaped Structure
The composter should somewhat resemble a box with no lid, using the wood planks as the framework and walls. Keep a 1-inch (2.5 cm) space between the planks to allow your compost to breathe.
Alternatively, you can recycle old 2×2 wood as the framework and staple a thick and sturdy chicken wire on two sides of the framework. This will provide a balance between heat generation and aeration.
How large you make your compost heater is entirely up to you, how much heat you need, and the available space.
Pro-tip: Make sure the bottom is elevated by about 6 inches (15 cm) off the ground, especially if your greenhouse has a concrete floor or if you intend to harvest compost regularly.
Secure Sturdy Wire Mesh Layers at the Bottom
The bottom of the pile should be made of at least three layers of sturdy and stainless wire mesh. It may be costly at first but will become cost-effective later on.
Since the bottom is elevated, the wire mesh layers will serve as a sifter so you can collect the finished compost conveniently. You can just place a shallow tray or plastic tarp at the bottom to catch the finished compost as it falls.
Add Your Compost
Add in the compost mix. Your compost should consist of compostable food scraps, animal feces, and plenty of green and brown plant matter. For an effective compost heater, the pile should contain 30 units of brown or carbon-rich matter for every 1 unit of green or nitrogen-rich matter.
You can refer to the following materials below:
- Wood chips
- Dried leaves
- Shredded paper or cardboard
- Grass clippings
- Fruit or vegetable peels
- Fresh manure
- Fresh leaves or herbaceous plant stems
- Coffee grounds
Build a “Plant Lid”
You’ll want to create a lid out of plants. Dry leaves or old lawn clipping make an excellent cap to lock all the moisture into your compost to achieve optimal heat.
Water the Compost Pile
For your compost to do its job, it needs to remain moist. This added moisture will also help to increase the humidity inside your greenhouse.
Wait About a Week
It can take about a week for all the microorganisms to get to work and for you to notice a significant temperature change. So be patient while waiting for your organic heater to mature.
As you can see, the compost creation process is relatively simple, and you can do it with materials you have lying around. Plus, it’s a pretty cost-effective way to heat your greenhouse during those cold winter months.
If you are a visual learner and want to see what an excellent functional compost heater looks like, check out Greg Pryor Homestead’s video passive heating with compost. He does a great job explaining how his composter has helped heat his greenhouse.
You certainly can heat a greenhouse using only compost, and it’s one of the most cost-effective and low-maintenance options out there. This type of heater is an excellent heat source, but it will also provide you with nutrient-rich compost for your plants all year.