Root dimensions of landscape tree cultivars

Entire root systems of 46 trees, consisting of eight utility-compatible cultivars in four genera, were excavated and measured as to length of longest roots, depth, and dry weight of roots inside and outside standard root ball sizes. Root lengths were longer along rows than across rows, were closely related to trunk diameter, and differed among genera. Roots of Syringa cultivars were up to twice as long as those of Amelanchier. Depths were more variable, and no differences were detected among genera. The most surprising finding was that 53% to 100% of root biomass would be retained within standard root balls of trees up to 6 cm dbh, and even 29% to 83% retained for trees up to 20 cm. In contrast, previous studies using different methods concluded that only 2% to 9% of roots would be retained in standard root ball sizes.