Heat and Feed Greenhouse Plants with Compost

A compost pile used in conjunction with a greenhouse creates a highly productive process far greater than the sum of its parts.

A composting greenhouse works so well because the byproducts of compost are exactly what plants need to thrive enormously. I’ll be outlining three of these byproducts that will create robust and healthy greenhouse-grown plants.

Composting Keeps Plants Warm

The bacteria that break down compost are thermophilic – meaning they produce heat as the break down organic matter. A properly built hot compost pile will heat up to 160 F. This is very hot! In fact’ 160 F is above the recommended temperature for a household water boiler.

Don’t worry, this won’t boil the air in your greenhouse, because most of this heat stays in the pile and is only released slowly. A few heat-producing piles in a greenhouse over winter will ensure that your plants are kept warm AND you will not have to pay anything to heat your greenhouse.  Some people are even using a single hot compost pile to heat their shower water for an entire season.

The greatest danger to using compost to heat a greenhouse is that it can actually get too warm. This is why any well designed composting greenhouse should have ventilation options to vent heat into the atmosphere. In mild climates, I’ve seen rudimentary systems as simple as just a bit of shade cloth work great. It harsher or highly variable climates where you want a better seal, greenhouse farmers use window panels that can be opened and closed – sometimes automatically based on a digital thermometer.

I’ve also seen small composting greenhouses where the compost bins are located outside along a wall, sharing only one surface with the inside of the greenhouse. When you’re setting up a small greenhouse in conjunction with a large compost operation, this works best. In these cases, compost left inside the greenhouse would heat the air too much.

How you design your greenhouse should be considered based on your relative sizes, outside and indoor temperatures, and the size of your compost piles. Hop along to our composting how-to site for more considerations on building your compost system and piles.


CO2 For Plants to Breathe

A little known fact about the growing environment in a greenhouse is that carbon dioxide is actually a limiting factor in plant growth. CO2 only makes up a small percentage of the air around us, and once the plants use that up in an enclosed space like a greenhouse, they start breathing slower.

Plants use the carbon inside carbon dioxide to generate new plant matter. In a very real sense, they eat carbon dioxide. Imagine what would happen if you didn’t have enough food. Your growth would be stunted, wounds would take longer to heal, and you would become sluggish. Same goes for the plants. You want to make sure they are metabolizing quickly if you want robust growth.

Fortunately for the farmer using a composting greenhouse, a compost pile produces a healthy supply of CO2, released by composting microorganisms when they break down organic matter.

Rich Soil for Rich Food

And finally, what do you get after you’ve finished up the composting process? Well, compost of course!

Most plants need highly fertile soil to grow well and for the food they provide to supply the most nutrition possible. Compost provides plants with many of what are called “micro-nutrients,” something that gets ignored by mainstream NPK fertilizers.

That’s why adding compost is the all-time best way to improve soil.

Compost and a Greenhouse – The Perfect Symbiosis

It’s hard to think of a process more symbiotic as a greenhouse coupled with a compost bin or two. All the waste products from the compost process feed the growing process then all the waste of the harvest goes right back into the compost. And it just gets better every year.