Frequency of girdling roots in relation to planting depth for all maple species. The first root of trees planted at ‘at grade’ was within 2.5 cm (1 inch) of the soil surface.
| Root flare relative to grade [cm (inches)] | Number of trees | Average number of girdling roots/tree |
|---|---|---|
| + 2.5(1) | 1 | 4 |
| at grade | 21 | 5 |
| -2.5(1) | 2 | 3 |
| -5.0(2) | 13 | 5 |
| -7.5(3) | 2 | 9 |
| -10.0(4) | 7 | 5 |
| -12.5(5) | 1 | 4 |
| -15.0(6) | 4 | 5 |
| -17.5(7) | 1 | 1 |
| -20.0(8) | 2 | 2 |