abc logo Growing In Less Than Ideal Conditions
Rhododendron ABC's #18

We have now mainly covered general and basic points that one should consider in order to grow and propagate these extremely variable, but always interesting, plants. Now I should like to take a specific subject -- that of growing Rhododendrons and Azaleas in arid and drought situations. As I write this, we in the Western Oregon and Southwest Washington region, which we have always claimed to have a salubrious Rhododendron climate, have just experienced two months of unprecedentedly warm (hot!) and dry (virtually no precipitation) weather. Needless to say, our favorite plants have not been happy. The Summer of 1994 should probably be called the "Summer of Scalded Rhododendrons"!

So, just what has happened to our favorite evergreen (some deciduous) plants during this almost record-breaking dry spell? As one considers the places in the world where rhododendrons have developed, it soon becomes obvious that these places are almost always well-watered. Consequently, the plants have not developed deep roots. necessary to locate deep ground water, nor have they developed succulent leaves and stems suitable for water storage. These two traits mean that long periods of no rainfall can be disastrous, the plants being unable to reach deeply for ground water and unable to rely on stored water.

In these respects, rhododendrons are among the most drought susceptible woody plants. The only recourse they have is for their leaves to shrink and curl so as to minimize their area and help conserve life-giving moisture in their tissues. All rhododendrons respond in this manner, some more rapidly than others. In fact, I have noted several speciesthat can almost be used as indicators of the state of ground moisture. These are Rh Williamsianum, Rh oreodoxa and Rh calophytum. When their leaves begin to shrink and curl, the message is "get the irrigation equipment ready." Other, less susceptible plants will show the signs in a few more days if water is not forthcoming. The problem is somewhat tricky. One should be careful not to over water. Remember that the arid conditions happen near the end of the growing season and the plants are starting to become dormant in preparation for winter's low temperatures. If they are inundated with a lot of water, they become more susceptible to fungal attack and are less liable to resist the parasitic organisms, whereas, warm temperatures and lots of moisture are ideal for fungal growth. So, one must be judicious in the use of irrigation -- keep the plants alive, but don't overdo it!

So we come to the realization that our salubrious rhododendron climatecan let us down. This makes the siting of plants even more important. During 100° F days (we had three or four such days consecutively in July), almost all Rhododendron leaves will show some ill effects if exposed to full sun light. Some will only yellow, others will turn brown and, in the most susceptible, leaves will die and fall from the stems. When this happens, plants are in real trouble and are in danger of succumbing.

The damage to the leaves by sun-scald will always appear at first in the center of the leaves and then radiate outward. The best solution is to make sure that the plants have shade, especially during the hot afternoon sun. Showering with water helps, but the danger of over-watering means that this is not the best solution. The best thing is to remember that rhododendrons should be planted where there is plenty of light and can sense the sky over their heads, but where they are not exposed to a hot afternoon sun.

Commercial growers take steps such as temporary screening or watering with fine mists to protect their plants. Such solutions may or may not be available to hobbyists. So, let's learn from the Summer of 1994. Plant siting is very important. Most plants will not be lost if irrigation is used, but scalded leaves and denuded stems will be apparent long after welcome autumn and winter rains replace continuous days of sunshine -- weather, that we humans think is wonderful, but that our plants find most inhospitable.

I, for one, almost have a guilty conscience to find myself enjoying the dry, sunny while my plants respond by shriveling and curling.

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Dave Goheen