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How, When, and Why To Prune Rhododendrons 0

ShrubBucket Pruning Rhododendrons

Why Rhododendrons Curl and Droop in Winter 0

Now that the cold temperatures have begun to set in, ineveitably we get customers who are concerned about the drooping and curling of the foliage of Rhododendrons which they purchased in the past year.

I thought I would take a moment and explain that this is nothing to be concerned about, but a normal practice of many broadleaf evergreens. Thermotropism is a technique plants use to protect themselves from cold winter winds which may cause drying out of the leaves. Much like a human may wrap their arms around themselves when chilled or when animals huddle together, this technique helps protect the inner most part of the leaf where most of the moisture loss occurs. The colder it is the more they droop and roll. At the onset of warmer temperatures they will begin to unfurl and regain their shape. 

 

An example of curled and drooping Rhododendron foliage during cold temperatures.


Moisture loss is the number one cause of winter injury in plants. It can occur in one of two ways. The first, as mentioned above, happens when a plant is subjected to cold drying winter winds. Ideally plants should not be planted in an exposed Northern position where they would take the full brunt of harsh winter winds. If they are, shrubs can be protected by wrapping them in burlap for the winter as an extra protection layer.  The second, which is less well known, happens frequently when broadleaf evergreens are planted in a sunny Southern exposure. In this situation, on sunny winter days the foliage may get exposed to constant sunshine and warm to such a degree that the moisture contained in the leaf transpires. However, the trouble comes when the plant cannot bring moisture up from the roots due to frozen ground. The result is a plant consisting of dead, dried out leaves. For both of these situations an anti-transpirant, such as the well known brand "Wilt-Pruf" is recommended. This is a simple water based polymer spray which is applied in the fall before the onset of cold which helps the plants retain moisture in the leaves by covering it with a thin translucent film which does not let the moisture escape. It wears off over the course of several months. I always suggest that all evergreens have an anti-transpirant applied their first winter. Since most plants will not have their roots established fully into the surrounding soil, this spray is a huge help in establishing the plant through this crucial time. If your evergreens are planted in either of the above situations, it should be used every year as protection.

An example of Rhododendron foliage during moderate winter weather.

However, be aware if your broadleaf evergreens droop, curl, or turn yellow in the warmer months of the growing season. In most cases this is indicative of poor drainage and exposure to excessive amounts of water around the roots. Plants in this case should be moved or provided a significantly well drained soil.

An example of healthy Rhododendron foliage during the warmer months.

Evergreens are the foundation of our garden plantings and can be the highlight of the garden in winter. By taking a few simple steps in their initial placement and ongoing care, they will provide you with years of enjoyment not only in the colder months, but in every season of the year.
 

Related Blog Post:

How and When to Prune Rhododendrons