Root pruning as a tool to improve establishment of shrubs and trees

RHS project team

Dr Tijana Blanusa, RHS

Partners

Dr Ross Cameron, (formerly) University of Reading

Start date

31/01/2004 00:00:00

End date

31/01/2008 14:05:36

Keywords

Root pruning, shrubs, trees, establishment, transplanting, root growth.

The problem

Plants can fail to establish for various reasons, but poor root growth is an important contributor to the problem. Encouraging the rapid growth of roots upon transplanting is, therefore, usually linked to good plant performance and extended lifespan.

Root pruning has long been used in nursery tree production and to control vigour and cropping in fruit trees. Despite the anecdotal evidence that pruning can encourage root growth and can be particularly useful in remediating the consequences of root circling, gardeners are often reluctant to cut and prune roots.

We want to test if root pruning at planting is linked to more vigorous rood growth compared to actions such as teasing or no root manipulation.

Approach

Glasshouse and field experiments have been set up to test the impact that root pruning has on plant establishment and root and shoot growth of two shrub species (Buddleja davidii, Cistus) and one tree species (Fagus sylvatica).

For the shrubs, in three separate experiments, young plants were exposed to root manipulation and were then transplanted into larger 2-litre pots comprising a medium of 1:1:1 fine bark, sand and loam. Root manipulation treatments included:

• Control: no manipulation, plants transplanted directly into a 2-litre pot.

• Teased: roots are gently teased by hand and spread out of the confines of the original pot. There was usually some damage and loss of fine roots, particularly at the base of the rootball, but < 10% of the total.

• Light pruning: severing with a sharp knife 10mm of (exclusively fine, < 2mm in diameter) roots in the medium from all sides of the rootball, approx. 15% of the total.

• Horizontal heavy pruning: horizontally cutting and removing 30mm of roots in the medium (both fine and coarse roots and approx. 33% of total) from the base of the rootball.

• Vertical heavy pruning: vertically cutting through the medium (both fine and coarse roots and approx. 50% of total), from one side of the rootball.

• Untransplanted: plants were left in their original 0.5-litre pot and not transplanted to a larger pot size.

In our experiments, light pruning was more effective at inducing new roots than any other treatment.

In the experiment with beech trees we used three-year-old bare-rooted seedlings to which the following treatments were applied at planting:

• Control - no manipulation, plants transplanted directly the soil;

• Teasing - roots gently teased by hand and spread out into the planting hole, to mimic standard amateur and professional practice at planting;

• Light pruning - horizontal cutting and removal of 50mm of roots (with sharp secateurs removing both fine and coarse roots to achieve approximately 15% reduction in total root weight);

• Heavy pruning – removing one or two coarse roots with all attached fine roots to achieve approximately 50% decrease in root weight

• Trees were grown from March 2005 to November 2008 and their growth was monitored during this period.

Aims

To assess the impact of root teasing and various degrees of root pruning on new root growth and plant establishment.

Benefits to gardeners

The project aimed to provide the information about the benefits of root manipulation and root pruning for aiding the establishment of several shrub species and beech seedlings.

Summary of results

Our results show that there may be more effective practices than root teasing to encourage new growth and aid plant establishment. Light pruning (i.e. removal of a small proportion of fine roots) was the most effestive treatment to encourage new root growth and aid the establishment in the two species we tested.

There was a short-term decrease of plants’ CO2 uptake (i.e. photosynthesis)  after root-pruning, following by their recovery to control levels. However, photosynthesis was not increased by pruning, so the mechanism whereby new growth is sustained may be from existing carbohydrate reserves, re-distribution of assimilates or by direct effect of pruning on lateral root growth. 

The requirement for exogenous auxin to encourage new root growth is dependent on the age and developmental stage of the plants as well as the time of the year. 

Advisory information

Moving established trees and shrubs

References

Blanusa T and Cameron R (2008). Roots – to leave, tease or cut?, The Plantsman, 7 (3), 182-185.

Blanusa T, Tanner R and Cameron R W F (2008). Improving the establishment of bare-rooted beech (Fagus sylvatica) trees: use of root pruning and auxin, SEESOIL Journal, 17, 1-7.

Blanusa T, Papadogiannakis E, Tanner R and Cameron R W F (2007) Root pruning as a means to encourage root growth in two ornamental shrubs, Buddleja davidii ‘Summer Beauty’ and Cistus ‘Snow Fire', Journal of Horticultural Science and Biotechnology, 82 (4), 521-528.