What is compacted soil and why is it a problem?
- Soil compaction occurs when soil particles are forced closer together, reducing pore space.
- Adequate pore space is important because it provides room for air and water movement around soil particles and allows plant roots to grow and provide water and nutrients to plants. Fine, feeder roots have a difficult time expanding in compacted soil.
- Compacted soil can lead to tree and shrub decline or death, of even older well-established plants. A tree or shrub that is in decline lacks vigor, has reduced growth, and shows other stress symptoms, such as wilt, scorch, early fall color, and/or dieback. These symptoms usually progress over a number of years.
Causes of soil compaction
- Heavy pedestrian traffic, cultivating and walking on wet soil in gardens, compression by construction equipment, cars and trucks parked under trees, and any activity that applies pressure to the soil damages the soil structure (the arrangement of individual soil particles).
- It is a major problem after construction projects.
- Soils high in clay content are more likely to compact than sandier soils.
- Prevention is the best way to avoid soil compaction.
- Keep foot traffic to a minimum, using defined pathways to direct traffic. Fence areas around trees and shrubs during construction projects to keep heavy equipment away. Use double, overlapping plywood sheets to protect the soil surface, if the use of heavy equipment is unavoidable. A 3-inch layer of organic mulch over tree roots also helps to prevent soil compaction.
- Correction of soil compaction is difficult. Cultivating the soil to incorporate organic matter is not recommended in areas with existing trees or mature shrubs.
- Contact an arborist for an onsite evaluation of your trees. Sometimes they will use an air spade to fracture compacted soil without removing it. Air spading is often done in small “pie slices” underneath a tree canopy and backfilling them with a mix of native soil and organic matter.