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Subsurface compacted layers
Soil loosely spread over a compacted sub-soil creates special challenges. Roots often grow only in the loose soil and will not penetrate the compacted subsoil.
Large-maturing trees could become unstable and hazardous as they grow due to a shallow root system. Therefore, only small and medium sized trees are recommended if less than 2 feet of loose soil will be spread over a compacted subsoil.
The lowest areas in this landscape are likely to be very wet during certain times of the year. Evaluate this carefully and, if needed, choose trees tolerant of wet sites for the low areas. The best time to perform this evaluation is within a day or two after a significant rainfall. If site evaluation is conducted during a drier time of the year, you could mistakenly conclude that drainage is fine.
Example of tree growing in compacted soil. Here, the compaction is a result of heavy foot traffic around the tree.
Notice the dieback at the tips.
Notice how new roots are formed in the loose topsoil, not the compacted subsoil.
