JARS v64n1 - Tips for Beginners: Tipping Point

Tips for Beginners: Tipping Point
Kath Collier
Boring, Oregon
Reprinted from the Portland Chapter Newsletter, August 2009

Last winter, several large rhododendrons tipped over. In July, another large R. 'Loderi Venus' tipped over at Crystal Springs Rhododendron Garden (CSRG). Why does this happen and what can you do about it?

A plant can be tipped over by strong winds, ice storms, fallen branches from other trees, and even from people (kids and adults) climbing or hanging on them. Tipping accidents can happen even though a plant has been able to happily survive in the same spot for years. Some plants are just more prone to tipping, and sometimes our pruning practices will increase the potential for a plant to tip. When you examine the downed plant, take note of the shape. Has it been pruned in a "tree shape"? I would guess that plants that have a greater canopy to root ratio are more apt to tip over. Why?

You have probably noticed that most rhododendrons and azaleas create shallow root mats that include a tangle of both old and new roots. The bulk of the root mat typically extends out to the plant's drip line. The bulk of the roots will also be found in the top foot of soil.

Root pruning may be needed not only to help save a tipped over plant (dried out roots are "gonners") but also when moving large plants. The process for moving large plants ideally starts a year before the actual move date. Reiley (1992) recommended cutting a circle around a plant approximately 15 cm (six inches) smaller than the root ball diameter a year in advance of the move. The depth of the cut should be about the length of a spade blade. If the circle is small enough, the area will be saturated with old and new roots that will help hold the root ball together when moving the plant the following year.

Recovering a plant that has tipped may include major pruning of some limbs and roots, working up the soil and tucking the roots back in, staking the plant in an upright position, and extra watering of both the leaves and roots during the warm months (because there are less roots, there will be less transpiration and plants can dry out).

Reference
Reiley, H.E. 1992. Success with Rhododendrons and Azalea . Timber Press, Portland, OR

Kath Collier, a member of the Portland Chapter, is ARS Secretary.