Most tree roots spread 2-3 times the radius of the canopy, and often reach out 5 times the radius of the tree canopy or more in dry conditions. So, for example, if a tree is 6m wide, the radius of the canopy is 3m. The root spread = 2 (to 3) x canopy radius = 2 (to 3) x 3m = 6m (to 9m).