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Soil replacement

Recently, a small group of arborists began experimenting with replacing soil from beneath existing trees with fresh topsoil. Moistened, existing soil is removed with a strong stream of water and a vacuum. The technique leaves most roots intact. The theory is that with time, existing soil in sites where roots are confined to a small space becomes less able to support adequate root growth.

Fresh soil is carefully replaced around existing roots and brought up to grade. The tree reportedly responds by regenerating additional roots in the fresh soil, especially if existing soil was compacted or chemically contaminated. This new technique needs much more evaluation before it becomes common practice.

mulched treesA modification of this is to remove all soil from vertical trenches dug around the tree and replace it with the loosened soil that came from the trench. If the tree is established and growing in an open lawn area, a similar increase in root growth could be achieved by killing the grass and simply adding several inches of mulch. This certainly would be less costly than replacing soil.

The same techniques can be used at new planting sites. If soil is considered too compacted, contaminated or poor to support root growth, consider replacing it or digging long trenches backfilled with good soil.