If your fence is draughty, make a false back from exterior grade plywood

If your wall has drainpipes, has a protruding window cill or is uneven, simply make a timber framework around the obstacle

If you have no suitable wall or fence, fit an exterior grade plywood back and drive in two fence posts to support the lean-to

The Lean-to greenhouse can stand on concrete, slabs or gravel. If you wish to grow in the soil place a row of slabs under the front rail to form a firm base and provide a path