Retention Time in Three Nursery Container Volumes Impacts Root Architecture.

Roots descend and circle once they meet nursery container walls, sometimes resulting in severe defects. This has been attributed to extended retention time in small containers. Four retention times in 11 and 57 L containers were tested for their impact on root architecture inside finished 170 L containers. All taxa (Acer rubrum, Magnolia grandiflora, Ulmus parvifolia) retained for four months in 11 L containers required delicate handling to shift into 57 L containers because roots had not bound substrate together, making the shortest retention time (four months) impractical. Although shifting was easier for longer retention times (seven, nine, and twelve months), root system quality measured by root deflections declined with increasing retention time in 11 and 57 L containers. A greater percentage of the five largest roots grew down container walls than either circled or grew straight into substrate of 170 L containers. Nearly all the largest roots were deflected by the 11 or 57 L container with almost none reaching the 170 L container wall. Shorter retention time in 11 and 57 L containers was associated with a smaller percentage of trunks circled, more roots reaching the 170 L periphery, and for elm and magnolia, more trunk growth. [ABSTRACT FROM AUTHOR]