Restore compacted soils

Bigstock, Earth worm 1662502

Native earthworm in healthy garden soil. Image Credit: Bigstock, Earth worm 1662502

Healthy soil typically is more than 40 percent pore space, with large pores that promote drainage and small pores which help store water. This combination enables air and water to penetrate, promotes good drainage, and allows soil organisms to breathe and plant roots to grow. Machinery, foot traffic and pounding rain compact the soil and make life in the soil difficult. Compacted soils can flood and also be droughty, since water runs off rather than infiltrating. You can repair compacted soil by rebuilding its spongy structure.

Strategies for restoring overly compacted soils:

Compost from garden being applied to landscape. Image credit: Wikimedia commons

  •   Top-dressing planting beds with several inches of compost will improve lightly compacted soils. Earthworms and other soil fauna will gradually pull it down into the soil, loosening it and improving water-holding capacity.  A 2- or 3-inch layer of shredded leaf mulch or wood chips will provide similar benefits.
  •   Cultivating the soil lightly, avoiding large plant roots.  Incorporating compost into the soil can speed the healing process.
  •   More extreme physical aeration may be necessary to repair highly compacted soils. Caution should be taken when working under and around existing vegetation to avoid damaging the root system.  Tree experts can provide guidance on the most appropriate methods which may include air-excavating tools, vertical mulching or radial trenching.
  •   Protect the soil from re-compacting.  Create pathways and use garden walls, fences or mulch to keep foot traffic off the soil.

Strategies for protecting garden soils from compaction

Lower sun trials, July 11 NC. Image Credit: Kenneth Silveira

  • Avoid working garden soils when wet.
  • Avoid bare soils.  Cover soils with either vegetation or mulch.
  • Create pathways and designated areas for walking and driving.
  • Use walls, fences and mulch to protect garden from foot and vehicular traffic.

Special considerations for landscapes that are being newly developed or redeveloped

Muddy landscape. Image credit: Wikimedia commons

    • Before development, conduct a site analysis and map areas of healthy soils and minimal, moderate and severe compaction.  To the greatest extent possible, avoid grading, vegetation removal or otherwise disturbing healthy soils.  Locate site features that require soil disturbance such as driveways, building foundations and patios in places where the soil is already degraded.
    • Work with the building and landscape professionals to develop a soil preservation plan which clearly outlines the areas that are not to be disturbed.  These areas  should be fenced off, and construction workers should be made aware they should not be disturbed.
    • During construction, restrict the areas where soil is disturbed to defined perimeters around buildings and hardscape.  The Sustainable Sites InitiativeTM (2009),recommends that disturbance be limited to 40 feet (12m) beyond the building perimeter, 10 feet (3m) beyond surface walkways, patios, parking and utilities that are less than 12 inches (30cm) in diameter; 15 feet (6m) beyond primary roadway curbs and main utility branch trenches, and 25 feet (8m) beyond constructed areas with permeable surfaces such as stormwater detention facilities and recreation fields.

Image credit: Wikimedia commons

  • Work with the building and landscape professionals to designate areas for parking, equipment and material storage, preferably using areas where soil is already degraded or will be used for a patio, driveway or building.  If possible,  use existing roads or parking areas for access and storage.
  • In areas where compaction cannot be avoided, carefully harvest and store the topsoil for reuse.
  • During construction, spread thick layers of mulch over areas that may receive occasional traffic.  Sheets of plywood on top of the mulch will help spread the weight in heavy use areas.
  • Use the lightest equipment possible to complete the job.