How to Build a Pit Greenhouse
A pit greenhouse uses the ground to insulate its sides in colder seasons. You can dig one into the side of a south-facing hill like a cave or into flat ground as a cellar-like structure. The general plan will depend on the terrain available, your budget and how you want to match materials to the surrounding architecture. Does this Spark an idea?
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Things You'll Need
- Earthmover/backhoe
- Cement blocks or bricks and mortar
- Outdoor door
- PVC tubing and Solexx paneling (optional)
Instructions
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Develop plans for where the greenhouse will be. A south-facing hill will get more sunlight than a cellar-like structure on flat terrain. It would also avoid flooding, allowing water to flow out the south end and down the hill.
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2
Excavate the pit. You can rent a backhoe to speed up the process. Dig at least six feet into the ground in order to benefit from the ground's insulation. You don't want to bump your head on the ceiling, but you also don't want the floor so deep that the plants are in the shade all winter. Cover the floor with gravel to allow moisture up from the soil. Support the walls of soil by laying walls of brick or cement blocks.
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3
Dig a narrower trench leading into the north side of the pit if you are digging a cellar-type structure. This will give you room for an entrance door. The roof will be higher on the north side, giving you more clearance for a full-sized door. Consider putting in concrete or brick steps leading down to the door.
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Install a regular greenhouse roof on top, slanting to face the southern sky, to let in the most sunlight possible during the winter. If you use recycled windows, install glass with several layers, to maximize insulation. A roof can be as simple as unrolling plastic paneling, like Solexx brand, onto a PVC-tube frame.
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Build up the sides and back that support the roof's slant with brick and mortar or cement with rebar. You may want to match materials throughout the greenhouse with surrounding architecture. After all, this greenhouse is designed to be permanent. Make sure the roof attaches to the sides securely enough to withstand side winds.
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Tips & Warnings
You may want to install a sump pump at the bottom of the pit, to prevent flooding.
One option for a prefabricated roof is a geodesic greenhouse kit.
Note that you may not be able to have a cellar-type pit greenhouse if your elevation is low and your water table (underground water level) is high.
As with any excavation, you should check with the cable, electric and water companies before digging.
