Root Pruning and Auxin Application Alter Root Development of Hickories

Diversification of taxa is an important goal of those who manage urban landscapes.  Some otherwise desirable species have not been promoted for use due to reports of challenges associated with their production or establishment.  A reputation for coarse root systems with dominant tap roots, and for slow shoot development among seedlings, has limited the use of hickories Carya Nuttall. We examined effects of root pruning and auxin on root and shoot development of seedlings of several species of hickory that are adapted to diverse natural habitats.  Our hypothesis was that pruning of the primary radicle shortly after seed germination and subsequent treatment with auxin would increase root branching without curtailing development of the shoot.  Carya aquatica Nuttall, Carya cordiformis K. Koch, Carya laciniosa Loudon, Carya ovata K. Koch, and Carya tomentosa Nuttall were treated by removing 7 mm of the primary radicle followed immediately by applying the auxin indole-3-butyric acid (IBA) via Hormex® rooting powder #3.  The number of lateral roots and length of the primary stem of the shoot system were among measures made 44 days after treatment.  Results confirm that the treatment we applied can change architecture of root systems without restricting shoot growth.  For example, for C. aquatica, the 15 treated seedlings showed a mean increase in lateral root count of 34% with no difference in shoot length compared to untreated seedlings.  Root pruning and application of auxin have the potential to ease the production of Carya in nurseries and may improve the success of trees planted in the landscape.