Greenhouses, such as hoop houses and plastic structures, which are used to cover plants growing directly in the ground can be anchored directly to the ground with stakes or rebar. For a sturdier temporary foundation, dig a small trench the size of the greenhouse's perimeter. Place landscaping timber or other wood in the depression. Backfill and secure the greenhouse to the foundation via anchor bolts drilled into the wood. Take care to research the chemicals used to treat the wood, as certain pressure-treated woods can leach contaminants into the soil.
Other methods used to create foundations include stacking and sealing hay bales. Greenhouse owners also fill containers with sand and either dig the containers into the ground level with the surface or directly place the containers on the ground's surface. The pipe frames are then sunk into the containers.
Most greenhouse kits supply anchoring materials, but there are many creative ways to anchor a greenhouse using scavenged materials such as heavy tires full of sand, adobe bricks or landscaping blocks.
Glass, fiberglass and rigid plastic greenhouses require permanent foundations, as do greenhouses built in cold climates. Permanent greenhouses are anchored to concrete foundations or to concrete slabs. The frost line in most cold regions is three feet below ground. The ground should be excavated to a depth below the frost line for insulation installation prior to pouring concrete.
Concrete pilings are created by digging post-sized holes at the four corners of the greenhouse. More pilings are needed if the greenhouse is more than eight feet long. Dig the post holes approximately eighteen inches deep. Pour the footing (the base of the piling). Place a fiber form tube in the hole. The tube should extend slightly above the hole's surface. While the cement is wet, insert an anchor bolt into the top of the column created by the tube. Affix the greenhouse to the anchor bolts.
Concrete slabs are poured at the same time the foundations and footers are poured. Pouring a concrete slab for the foundation of a greenhouse is much the same as pouring the foundation for a home or other permanent structure. Make certain you follow local building codes and hire a professional if necessary.