Research

Research projects

Remediation of root circling in ornamental shrubs

A frequent problem with plans transplanted from pots into the soil is root circling. Circled roots of pot-bound plants commonly fail to distribute in the soil profile. This may restrict water and nutrient uptake, reduce shoot growth and cause establishment failure. However, little is known about the extent of the problem in ornamental shrubs and the means of remediation.

Experiments were designed to test the hypothesis that root pruning (alone or in combination with plant hormone auxin) can be used to used to encourage new root growth and aid plant establishment.

Liners of Buddleja davidii 'Summer Beauty' and Cistus 'Snowfire' with severely circled roots were used for the experiments. On transplanting into the soil mixture, three root manipulation techniques (teasing, light and heavy pruning) and two concentrations of auxin indole-butyric acid - IBA (500 and 1000 mg per litre) were applied.

Plants were grown in the glasshouse. We have measured responses of stomata and plants’ ability to assimilate carbon dioxide (i.e. to photosynthesize) at regular intervals after root manipulation. Root and shoot weights and leaf areas were measured at plant harvest, eight weeks after transplanting.

Light root pruning alone was most effective in stimulating new root growth in both species. IBA application did not consistently increase root weights in either species or in combination with any type of pruning. Short-term decrease of photosynthesis following root manipulation (up to 15 days in Buddleja and seven days in Cistus) did not adversely influence root and shoot growth. However, upon recovery of photosynthesis to control levels, it was not further increased.

Work is currently underway to understand

• The mechanism whereby root pruning stimulates new root growth.
• The longer-term effects of root pruning on root and shoot growth in the field.

Tijana Blanusa

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