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Success with Rhododendrons and Azaleas
Rhododendrons and azaleas cannot tolerate strong winds and on windy sites would benefit greatly from a good windbreak. This is because reduced wind speed reduces both moisture loss from leaves and leaf damage. Preventing moisture loss is important in the summer and perhaps even more important in below-freezing temperatures. Since most rhododendron species have broad leaves, moisture loss is high, and if moisture is lost through the leaves faster than the roots can absorb it, plant leaves wilt and burn on the margins and may eventually die if the situtation is not corrected. Deciduous azaleas are able to survive windy winter locations better because they lose their leaves in winter and thus do not have moisture needs as great as their evergreen relatives.
Whenever possible I think living windbreaks, such as hedges, shrubs, or trees, should be used since their beauty can add to the overall landscape effect. Evergreen trees or evergreen shrubs tall enough to break the wind are ideal. Even deciduous trees in large numbers will reduce wind velocity considerably. Use deep-rooted trees for windbreaks as they do not compete so vigorously with plantings for nutrients and moisture; definitely do not use maples. If possible plant Rhododendron far enough away from windbreaks to eliminate root competition.
Structural windbreaks such as picket fences are also excellent. One advantage is that plantings may be made close to them with no concern about root competition.
The corners of buildings are especially windy spots as wind velocity increases as the wind whips around a corner. Planting a needled evergreen such as pine or an upright yew provides an excellent windbreak at such corners and will greatly benefit plants on the lee side. Small microclimate alterations such as creating a windbreak often make the difference between a successful or failed planting and can be created quite easily.
A windbreak is generally considered to affect an area to a horizontal distance of about seven times its height.
Air drainage refers to the downward movement of heavier cold air and the rising of lighter warm air. It is not the same thing as wind movement but rather is the slow, steady movement of cold air into low-lying areas or into physical barriers which dam air movement. The accumulation of cold air reduces the temperature in these areas and is usually observed on still nights with little or no wind to mix the cold and warm air. Such cold air pockets should be avoided in planting rhododendrons for two reasons. First, temperatures fall below freezing earlier in the fall, damaging plants that have not yet hardened off. Second, frost occurs later in the spring, resulting in damage to early flowering plants.
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