When planting a tree its primary need, until it grows out new roots, is available water. This is because during its time in the nursery, it has had a constant water supply to maximize above ground growth, while at the same time its roots have been pruned or ‘formed’ into pot shapes to limit transplant shock and for ease of transport.
Therefore, when planted into its final home, a tree recognizes that it must immediately extend new roots, however it can only do this in an aerated soil and so the soil must therefore be free draining. When trees are planted in city scenarios using traditional pit planting, water drainage is frequently an issue. At the same time, the ability of the soil to aerate is limited by compaction and small soil surface area.
However, when we plant a tree into raised soil above the existing grade both problems are solved. Water can freely drain, enabling aeration throughout the mound and around the young tree roots. At the same time, the surface area of the soil is greatly increased so gases can easily enter and exit the soil mass, especially if a mulch is applied over the entire berm surface, providing added cooling and aesthetic benefits.
When our planting priorities are focused on providing maximum aeration to the available soil, then a young root system establishes quickly and less watering is needed. Aeration is thus a significant health benefit to the tree. Most importantly, tree replacement costs are dramatically lowered, much longer tree lifespans are achieved and city populations are far less frustrated!