There are many creative ways to heating a greenhouse. Here are several methods you can use to trap, maintain and raise the heat inside of your greenhouse without using electricity! First, let's talk about some greenhouse basics.
Greenhouses are wonderful tools for
prolonging the growing season and creating a micro-habitat for plants
that desire more heat in cooler climates. Greenhouses work by trapping
the heat radiated by sunlight using a layer of clear greenhouse grade
plastic or glass. The heat they trap positively alters and extends
growing conditions through increased heat and humidity.
Greenhouses often must also be well-ventilated in summer, so as not to desiccate the plants growing within them. Typical orientation for greenhouses in the northern hemisphere is towards the South, but this might not necessarily always be the best orientation given the local conditions found on a given site.
Using large barrels of water, you can help trap radiation for heating a greenhouse. Water is slow to heat up and slow to cool down, and therefore, can help both raise and maintain heat inside of a greenhouse. Large barrels of water that are painted a dark color, such as dark brown or black will heat up more quickly by absorbing more ultra-violet radiation from the sun.
Water can also be used to reflect sunlight into a greenhouse by placing it at such an angle so that sunlight reflects off of it and into the structure. This can be in the form of a pond or multiple small ponds, a water holding trench or swale, or other similar structure. This additional reflected light potentially adds even more warmth to the greenhouse.
Another method for trapping additional heat in a greenhouse is to have a rock or brick wall inside your greenhouse (often referred to as "thermal mass"). This is typically best placed on or as part of the wall opposite the direction where the sunlight enters. Both natural and man-made stone (such as brick) captures and holds heat. Rock walls are also used with great success to grow more warmth-loving plants outside. An excellent example of this is Sep Holzer's use of rock walls and nooks to grow certain citrus variety in the cold mountains of Austria. Learn more about Sep Holzer's method's on his website here:
As it breaks down, manure produces a considerable amount of heat. If horse manure is put into large crates and placed strategically in a medium to large green house , it can produce sufficient heat to raise the temperature inside an additional several degrees. Palates of starts or seedlings can be placed on screens directly on top of these crates to provide them with more focused warmth. Of course, having crates of manure can also be a boost once that manure has aged and can be added to enrich soil.
Another creative method for heating a greenhouse is to build it against a building with which it can share and exchange heat. One example of this is building a greenhouse against a large chicken coop. The heat produced by the chickens in the coop will warm the greenhouse, and the greenhouse will also warm the chickens. The trick is to make sure to encourage warmth exchange during colder times of the year, but limiting heat exchange through exclusion or ventilation during the summer or prolonged warm periods.
Insulation is not a way of heating a greenhouse, but it is an excellent means to maintain heat and slow down its escape. This can take the form of many different things, including: hay or dirt piled up on the less sunny sides of the greenhouse. Even snow can be piled up around a greenhouse in winter to help insulate it!
Another way to insulate a greenhouse is by raising it off of the ground, by building it on bricks or other heat-absorbing or heat-trapping materials. Greenhouses can also be built partially sunken into the ground and lined with hay bales for insulation. The temperature underground is more stable than that at the surface, and if constructed properly, such greenhouses can even be used in areas with incredibly cold winters.
The best methods for heating a greenhouse are those that are appropriate to the given location and situation. Also, rather than just using a single method, combining several of the techniques suggested here is likely to give you the most productive results. Make careful observations on the land where you want to set up a greenhouse and carefully consider how you can make additions or adjustments.
Experiment and see what works best for you!
For more information on working with greenhouses, homesteading and sustainable living skills check out our Permaculture Courses.
About the Author: Filip Tkaczyk is a periodic guest teacher at Alderleaf. He also wrote the field guide Tracks & Sign of Reptiles & Amphibians. Learn more about Filip Tkaczyk.