After hitting -20 last night in Redwood, I wandered outside this morning to see how Better Farm's greenhouse-chicken synergy is going.
We began the experiment in Mid-November, utilizing chickens to heat an 8'x16' hoophouse. Our goal? To get temperatures high enough to allow for hyper-early or even year-round planting of fresh produce to be donated to the Redwood Food Pantry.
The experiment is multi-layered; utilizing the greenhouse plastic as the first heat creator. As sunlight passes through the plastic, the greenhouse is passively heated with solar power. Two, the body heat of three dozen chickens adds to that increased temperature. And three, hay is continually added to the floor of the greenhouse to neutralize ammonia odors and to create a warm compost pile that adds a third heat source. The design is based on the Solviva Greenhouse, designed by one Ana Edey on Martha's Vineyard. She utilizes a more sophisticated design complete with water walls, heat inductors, fans, and separate housing compartments for chickens and plants, but the general concept is the same.
We created several venting stations: at the center top over doors at each end of the greenhouse, as well as on the chicken coop built along one wall of the structure. When we get our heat levels just right, plants will be added in protected cold frames. Those frames will add a fourth dimension of heat; and as temperatures outside rise, the cold frames can be swapped out for screened chicken protection.
Because the third aspect of heat comes from the composting manure and hay on the floor of the greenhouse, part of this process is a waiting game for the chickens to produce enough waste to raise temperatures even more than they have already. While it's obvious that greenhouses make the air warmer inside, -20 is certainly a pretty steep test.
Here are my findings.
Chicken comfort/overall well-being
The chickens were having the time of their lives despite the sub-zero temps and icy conditions (and this afternoon, yet another snowstorm). The girls and boys were clucking happily, chowing down on food scraps and chicken feed, and walking around like it was spring.
The outdoor temperature reading was -8 when I was outside this morning, but the digital thermometer gave a reading of 29 degrees. So on a sub-zero day, we're showing a 37-degree difference. Later on in the early afternoon, temperatures outside were 18 and the digital thermometer was holding at 38 degrees. Without any heaters in their water dishes, the chickens are enjoying fresh, ice-free beverages all day long. The temperature difference should increase as we continue with the deep-mulch compost on the greenhouse floor.
Overnight, the chickens are shut into a coop that sits along one shelf of the greenhouse. Because the coop's doors are closed, the body heat from the chickens is largely confined to inside the box. The water dishes do freeze overnight when it gets below 10 degrees. When the doors of the coop are opened in the morning, you can put your hand inside and feel how warm it is in there. That heat dissipates quickly to help warm the overall greenhouse during the day.
With weekly additions of hay to the floor of the greenhouse, it should be able to house plants by February or very early March. And next winter, we will already have an established composted floor to work with—which could allow for January plants or for existing plants to simply continue growing all year. We've also discovered other ways to raise the heat:
- Water walls—These are literally walls of durable black plastic bags filled with water. They absorb heat all day, and slowly release heat at night. Instead of bags, plastic 55-gallong drums could be used. You put the wall along the north side of the greenhouse, essentially the "back wall". Here's an illustration of a water wall gleaned from Ana Edey's website:
- Solar-powered heaters—a small solar kit could power a small space heater in the greenhouse. But other solar systems, such as fans powered by photovoltaic panels that can push hot air from the top of a greenhouse down into ducts and water-mass storage, are also possible. The imagination is the limit.
- Wood stove or rocket mass heater stove—A rocket mass heater would provide the simplest, safest, long-term option, as it utilizes a fraction of the wood of a wood stove and can provide consistent heat for up to 24 hours at a clip. This option will be looked into this spring.
When we started the experiment, we also started some broccoli plants, spinach, beets and carrots in the greenhouse. The first frost zapped the youngest plants, but we were able to bring some of the broccoli plants back inside and have since revived them. They're waiting out the weather under grow lights in the library.
Meanwhile, we're anxiously awaiting a heat spike to consistent 60s inside the greenhouse to allow us to grow the optimal amount of food for donation. This spring, we'll go back to the drawing board while the produce grows and we'll make some new sketches to reflect creative problem solving for this experiment and to ensure success moving forward.
If you'd like to participate in this project by volunteering in the greenhouse to make improvements, tend the produce, or would simply like a tour of the facility to learn more about four-season farming, email firstname.lastname@example.org.
Read more: Greenhouse-Chicken Synergy Part I