Our gardeners are currently enlarging the tree circles on the park lawns. Tree circles are of great benefit to trees for a number of reasons. Firstly, removing any grass growing directly up to the trunk eliminates potential lawn mower damage. In addition, by taking away the grass, you are also removing the tree’s biggest competitor for soil moisture.
Once the grass is removed the bare soil is then mulched with wood chip or well-rotted leaf mould and compost. The mulch should be about 8cm (3 inches) thick to retain the soil moisture for the tree roots and prevents weed seed germination on the bare soil, and it also has the added benefit of looking neat and tidy.
The most important benefit of enlarging the tree rings is to reduce soil compaction of the root area. By introducing a good layer of organic matter, it should invite worms and other soil organisms which move the soil about, aerating the soil as they go, providing good drainage and air to the tree roots.
A tree with aerated roots is much stronger and healthier so it’s also much better able to resist disease and pests.
After the 1987 storms at Royal Botanic Gardens, Kew, they noticed a dramatic improvement in the growth of the Turner Oak ‘Quercus x turneri’ after experiencing accidental soil de-compaction. This tree was raised nearly out of the soil by the strength of the winds, but did not fall over. It simply lifted and then came down again to root itself in the same position, but having had a great deal of soil disturbance. The storm had essentially de-compacted the soil, and the tree roots could now breath and grow well.