The East Texas "winter" is officially a week old and we are still consistently above 80 degrees during the day. If the days weren't so short I would swear it was April. Even some of my dormant mulberry saplings are starting to leaf out. Rather than worry about what that might do to baby trees I am taking the time to do something new this winter. I'm composting with gusto.
"Necessity is the mother of invention" I am told, and I might have never considered compost as a heat source unless I was limited to 15 amps and an antique wood stove for heating my greenhouse project this winter. It is not possible for me to generate more than 5,200 btus with the power I have available and the stove requires almost constant supervision. Texas weather likes to lull us to sleep with warm days & mild evenings until one mid-January or mid-february day we wake up to -6 Fahrenheit and everything I planted dies. (Not this year, I hope.)
I have composted the lazy way for years. I would just pile junk up all year in a shady spot and then turn it over in the Spring to harvest the good stuff found near the bottom of the pile. That isn't really composting "intentionally". Internet research led me to several youtube videos of other garden addicts using piles of kitchen scraps, leaves, and grass clippings as a steady and reliable source of "free" heat INSIDE their greenhouses. The ingenious folks in these videos were taking advantage of the fact that compost generates its own heat - as microbes & critters decompose the organic material in the pile. These piles are capable of reaching core temperatures up to 160 degrees and some sources claimed that 1 cubic yard of compost can generate 1,000 btus/hour, 24 hours a day, for up to 6 months! That's a whole lot of heat that doesn't send a monthly bill!
So, I've decided to repurpose the area planned as my future worm bin and use it this winter as a compost heater for the greenhouse. The concept I settled on is a hybrid of three different solutions used successfully by other gardeners. It was such an epiphany that I had to share it here. Feel free to take this idea and improve it any way you can for your own benefit.
(That is one of the best perks of garden clubs.)
Basically, water is the material that transfers the heat at the core of the compost pile and allows it to be used to heat the air. I am using a 55 gallon drum (painted black) to store the water. A submersible pump is used to move the water from the bottom of the storage tank where it is coldest, through a plastic tube coiled inside the compost pile. This tubing makes multiple passes through the depth of the pile so that it remains inside the warm core as long as possible absorbing heat. After looping through the compost it is pumped through a small, aluminum, radiator coil (designed for cooling transmission fluids) where it pre-heats the air entering a small space heater/fan. If the incoming air is warm enough then the thermostat will not engage the heating element. If the incoming air is too cold, then the t-stat will turn the heater on. Either way, the fan runs automatically, keeping the air moving and the potential for fungus down.
The full system will not be operational until this Thursday evening when the radiator I ordered finally arrives. But I have had the compost pile prepared for a week now and it is already generating heat I can feel on the surface. The water inside the black drum is consistently 5 degrees warmer than the soil it sits on due to heat gained from the sun during the day. When the sun does not shine, the water inside the barrel will act as a heat sink for the compost pile and release the warmth slowly into the area all night long. I am excited to learn how well this system works!
One of the key ingredients I have learned must be included in your "intentional" composting effort is a proper compost thermometer. The temperature of the pile is a critical metric that you should be aware of in order to work out the timing and management of the compost. They are inexpensive and I purchased mine on Amazon. In fact, the manufacturer included a handy PDF that describes how to properly manage a compost pile. I have attached that document to this post for you to download for free, if you like.
I plan to follow up in future weeks to let you know how this experiment ultimately works out, but initially, I am very pleased. Five-six months from now the weather will be warmer, a new season of plants will be "Springing", and I will have another 1.5 cubic yards of fresh compost for the garden.
Win, Win, Win!
Thanks for reading!
~Steve