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Adding soil under the canopy

When soil is added to a site, the good topsoil is usually removed and sold before fill is added. Since many roots can be growing in this topsoil, the result is that adding soil really amounts to removing a portion of the surface roots, then adding soil. Removing surface roots on established and mature trees can cause severe stress. Adding soil under the canopy causes more stress and can result in declining and dead trees.

Soil addition does not always result in declining and dead trees. Here are some reasons why: The root system could be deep with few surface roots, young trees can tolerate root removal and soil addition better than mature trees, well drained soil encourages a deeper root system, some species tolerate grade changes better than others. Trees growing on clay soils or on a poorly drained site are very sensitive to any changes in soil level. Consult a qualified consultant or certified arborist before proceeding. Most roots in these soils are just under the soil surface and very prone to injury.

The soil added should be of a coarser texture than the existing site soil. This will allow roots to grow because air and water can easily penetrate to the existing soil. When soil of a finer texture is added, water and air penetrate with difficulty and tree health can decline. Operating soil spreading equipment over the roots will compact the soil and can damage roots. Spread soil by hand to eliminate compaction and root damage under the canopy.

Practitioners and product manufacturers claim some success with aeration devices but the two or three research projects published to date have not shown any benefit to this technique. These systems are often comprised of pipes laid horizontally on existing site soil with vertical vent pipes up to the surface of the added soil. The idea is to provide oxygen to buried roots. It might be effective under certain circumstances.

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