Being a greenhouse keeper is part of sensible earth stewardship. You have options.
EARTH SHELTERED Use the earth herself to provide radiant heat and capture a constant temperature. These underground greenhouses are called “Walipini” (pit greenhouse) in South America. The Benson Institute’s experiment was built in Bolivia, high up in the Andes where it gets really cold. Their greenhouse costs $250-$300 in materials and is designed to provide vegetables year-round for seven people. They recommend a minimum of 94 square feet of growing space per person.
Part of Your Home! Use a big bay window, or add an extension with a door from your home into it, and a door to your outside garden. How utterly convenient!
Inflatable greenhouses and Pillowdomes
Pillowdomes can be irrigated, and fertilized, by the “exhaust” from large, transparent tanks containing fish. The aquaponic tanks also serve as an effective heat sink, allowing an indoor climate warm enough to grow bananas in February, in New England, with no fossil fuel heat source.
Passive SOLAR greenhouses design features can include –
- Low walls, only 39-47 inches, painted black. Made of adobe and straw. Alternatively, the floor could be sunk below ground level to provide better thermal mass, but this would require more labor to build.
- A domed or sloped roof of wooden poles stretched over clear polyethylene sheeting
- Small windows are constructed in adobe walls to allow for opening and closing to raise or lower temperature
- The floor can be painted black or covered with something black to increase the heat it stores.
- If thermal mass needs to be increased more, fill black plastic bags with gravel or sand; these will store heat. Two liter bottles painted black and filled with sand will do the trick! Black stones can also be used.
- Water tanks can act as a heat store. It might be worth considering aquaponics in a solar greenhouse, as a large fishtank will regulate the temperature of the room. A large rainwater catchment, painted black, will work too.
Use your space well – notice all the plants in black containers in this Bolivian greenhouse, and the ones placed vertically along the center structural support!
Additional Greenhouse Heating Tips!
- Start smart! Position your greenhouse to receive the longest average amount of direct winter sunlight. Best choice? A location with both direct sunlight and minimal wind exposure.
- Install passive solar panels – as simple as soda cans!
- Strategically place Mylar blankets to reflect light onto your solar panels and onto your greenhouse.
- Keep the heat! Install specially designed foil and plastic insulation on the north-facing wall of the greenhouse, or whichever side gets the coldest wind. Double the insulation in very cold areas.
- Seal all joins well – no air leaks allowed! And be sure your door fits snugly.
- 32 Gallon black trash can. Fill with water, plus some antifreeze (the kind that doesn’t kill pets and kids). Here is one person’s report: Yesterday it was really warm (high 70s) but at night when the air temp was down to 57 the water was still at 67. I am thinking that will make a difference tonight when it goes down to 28! Hear, hear!
- Or 55 Gallon drums! Detailed Instructions
Though these images are large scale examples, adapt the principles to the size that suits your needs.