The ideal structure of topsoil (at least 10 to 12 inches deep) is granular, crumb-size groupings of soil particles and plenty of pore spaces. The ideal subsoil structure is blocky, with cubes of soil and vertical openings. Compacted soil has few air and water pore spaces and tends to be poorly drained.

Remedy for poor structure: Compacted soils in perennial beds will benefit from a yearly one-to two-inch-deep topdressing of compost. A compacted layer in annual beds can be broken up by double digging or deeply tilling the soil below the hardpan layer and mixing in generous amounts of organic matter. In some soils the thickness of the hardpan layer may require building raised beds or planting in a different location.