University of Maryland Extension

Compacted Soil

compacted soil under a large tree

Compacted soil can lead to tree and shrub decline. 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. Soil compaction may be the result of foot traffic, heavy equipment, or any activity that applies pressure to the soil. Plant roots grow in the pore space between soil particles. In compacted soils overall pore space in the soil is reduced, resulting in decreased oxygen and moisture in the soil. Fine roots have difficulty penetrating the compacted soil. Poor root growth reduces the plant's ability to take up nutrients and water, results in less vigorous growth and makes the shrub less resistant to environmental stress.

compacted soil on a grassy area
Paths typically contain compacted soil

Correction of soil compaction is difficult. Cultivating the soil to incorporate organic matter is not recommended in areas with existing trees or mature shrubs. The process of vertical mulching is the best method of aerating soils adjacent to plant roots. Use an auger to drill holes 2-3 inches in diameter, 12 inches deep in the root zone area. Holes should be made at 2-3 foot intervals, starting midway between the trunk and the drip line of the plant, and extending beyond the drip line of the tree or shrub. Fill the holes with finely ground pine bark, compost, or peat moss. These products increase pore space in the soil and allow greater root growth in the area.

Prevention is the best way to avoid compacted soil. 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 also helps to prevent soil compaction.

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