Extending the growing season opens up new opportunities for home and market growers. Imagine what you could do if the ground never froze. Heating your hoop house allows you plant more and harvest longer. The only question is, how do you heat your hoop house without using unnecessary electricity?
Unheated hoop houses extend your growing season without pinching your budget. That does not stop us from wishing we could add just a little heat to our tunnels. A few more degrees opens up new winter gardening opportunities, not to mention protecting our crops from the ravages of particularly deep freezes.
It is possible to heat a hoop house without adding to your energy bill or greatly increasing your carbon footprint. The following techniques are affordable and require almost no electricity to build and use.
Passive Solar Heating
Greenhouses, cold frames, and hoop houses all rely on passive solar heating to keep the mercury up. Light from the sun enters the glass or plastic and is trapped, keeping the interior several degrees warmer than the exterior. This works great when the sun is out, but temperatures plummet at night and on cloudy days. It is possible to use passive solar heating to your advantage during this time by relying on heat sinks.
Heating with Water Barrels
Water holds four times more heat than air. Using water as a heat sink is a highly economical method of heating your greenhouse. The water acts as a battery, storing the thermal energy and releasing it slowly over time. The more water, the more heat energy is stored and released.
Fifty-five-gallon barrels make excellent heat sinks. They also function as corner posts for tables and provide additional heat to the near vicinity, so place tender crops nearby. Try spray painting your barrels black for maximum heat absorbency.
This method will not allow you to grow tropical plants in colder zones. It will keep temperature loss at night down to a minimum without costing you a fortune.
Concrete Stores Heat
Believe it or not, concrete and stone store heat better than soil. That chilly concrete floor is actually warmer than your garden bed. While concrete floors are not ideal for hoop houses, they work well in greenhouses. Stone is half as effective as water, however, so in your hoop house those water barrels are the better bet.
Heating with Wood
Wood is a renewable resource that, when harvested sustainably on your own property, is a cost-efficient solution to chilly temperatures. Wood stoves are expensive new. Craigslist, yard sales, and word-of-mouth are the best ways to find a small wood stove for your hoop house or greenhouse.
Before you install a wood stove in your growing space, seal all gaps, cracks, and holes to prevent excess heat loss. Also take the time to do a little research about wood stove heating to prevent fire and injury. If your hoop house or greenhouse uses plastic, be very careful about the exhaust pipe. The metal heats up quickly and melts plastic, so cover the area with heat resistant materials to prevent structural damage.
Small, efficient wood stoves save you time and money. Combined with thermal mass storage like water barrels, a small wood stove produces enough heat to keep your crops nice and toasty until morning.
Rocket Mass Heaters
Rocket mass heaters are the most efficient way to heat your greenhouse. Unfortunately, they require a high skill level to construct. This makes them a poor choice for many hobby gardeners. The premise behind the rocket mass stove is the same as that of those water barrels. The wood burning stove is constructed and encased with a large amount of stone, brick, or ceramic. This creates a large heat mass that releases heat over a longer period of time than simply burning fuel.
Heating with Compost
Heating with compost is an attractive option that appeals to anyone with a large amount of organic material on hand. Compost heating is effective at heating both hoop houses and greenhouses, however, as with rocket mass heaters; it takes a certain amount of skill and finesse.
Most compost heating systems rely on heat exchange. Tubes filled with water or air is buried beneath the soil and beneath the compost pile. The compost heats the water in the tubes, which is then circulated through the greenhouse to warm the soil. This process usually requires a small pump or fan, which is, of course, reliant on electricity.
Maintaining a compost pile large enough to generate the amount of heat needed is complicated. Composting is a science and is most effective as a heating solution when used on farms with large amounts of material and the equipment to move it.
The Compost Hot Bed Method
Small scale hoop houses still benefit from compost. Try placing a compost bin inside the hoop house or using a “hot bed” technique beneath raised beds. To do this, dig out an area at least two feet deep by four feet wide. Six foot wide beds are ideal as this provides plenty of room for compost action to occur.
Keep the removed soil close by. Fill the pit with compost. Animal manure mixed with bedding or straw creates a nice, hot base. Wet it down like you would a regular compost pile and let it sit for a few days with frequent turnings. Once the pile is hot, cover it with the removed soil and plant your seedlings.
Electric Fall Back Plan
Regardless of your intentions, it is not a bad idea to have an electric space heater as a fallback plan. Oil filled, radiant space heaters are efficient and generate plenty of heat. Putting your heater on a timer saves electricity and prevents the heater from running all night.
Choose the Method That Works For You
Choose the heating method that makes the most sense for your farm or garden. Creating extra work for yourself takes the joy out of gardening, and investing too much time and money in a hobby project is financially problematic. For best results, try a combination of these techniques to heat your hoop house this winter.