Large-scale commercial greenhouses, particularly those that employ alternative agricultural methods, or that grow container crops, sometimes have concrete floors with integral drain systems to facilitate plant irrigation, mechanical harvesting and cleanup of the area. However, just as the frame material and covering should be based on the design and purpose of the greenhouse, the choice of flooring is also mostly a matter of choice. If a greenhouse is constructed without a solid foundation, the best solution can be a mixture of pea gravel, topped by a layer of flexible mat flooring. The pea gravel will help with drainage, while the flooring will help deter the growth of weeds. Such matting makes the surface more level, adds comfort and makes the surface easier to keep clean.
Backyard gardeners or hobbyists who consider lean-to structures or free-standing greenhouse kits might place them on a solid foundation like poured concrete for aesthetic reasons and for clean-up ease, but a good choice can also be wood-slat flooring over some sort of vapor barrier placed directly on the ground. There are numerous options available.
