Rhododendrons and azaleas tend to be rather sensitive to their growing conditions. In their native habitats, most of them come from areas with long, cool summers and soils that are both well drained but moisture retentive. They also do best in an acid soil between pH 4.5 to 5.5.

In many parts of the United States it is very difficult or impossible to please all types of rhododendrons and azaleas. Either the summer sun is too hot or the soil is alkaline or the winter winds are too cold or the soil has a high clay content and is poorly drained.

In the southeastern states like North and South Carolina and in the Pacific Northwest, rhododendrons do fantastically well. Some species are actually native to these regions and were "discovered" by European plant explorers a couple of centuries ago. In England, Ireland or western France, you can see huge rhododendrons covered with massive blooms in the spring  and early summer. Those locales have the ideal climate and soil conditions for these plants.

In the American Midwest and other regions, it is quite a different story. Occasionally individual home gardeners will luck out and have just the right protected site with the proper soils. Sometimes, a gardener will mix the correct portions of acidic soil amendments to create the ideal site. However, more often, a newly planted rhododendron will look great the first year and then begin to die back with each succeeding winter.

Site Requirements for Rhododendrons and Azaleas

These are wonderful plants for the home landscape but you need to be aware of their specific requirements. Often, these are hard to find or create in regions other than where these plants are native.

  1. Well Drained but Moisture Retentive Soil - Some experts feel that this may be the most important factor in success of rhododendrons and azaleas. The plants are shallow rooted with delicate root hairs. If there is too much moisture, they will be attacked by various fungal root rots. If there is not enough moisture when they need it, the root system will die back.
     

  2. Acid Soil - To grow properly, they need a more acid soil than exists in many gardens. They would prefer something in the range of pH 4.5 to 5.5 but will survive in a somewhat more alkaline soil. If the pH is  too high, the plants will have light green foliage and show signs of iron deficiency. This will lead to a loss of vigor and open the plant up to damage from other factors.

    Often, garden sulfur is used to lower the pH. Aluminum sulfate is another product that is often used for this purpose but it should NOT be used for rhododendrons and azaleas. They are subject to aluminum toxicity if it is over-used.
     

  3. Winter Protection - In the winter in exposed locations, they will be subjected to winter winds and suffer from dehydration (dessication) injury. So, they need that just right location where they  get enough protection from winter winds or you must provide wind blocks or other protective measures each fall.
     

  4. Nitrogen Source - Most plants like to take up their nitrogen in the form of nitrate (NO3). Rhododendrons and azaleas prefer the ammonia (NH4) form of nitrogen fertilizers found in such products as Urea and Ammonium sulfate.
     

  5. Sun Exposure -  In order to flower, rhododendrons and azaleas must get at least partial sun each day of the growing season. Unfortunately, in many locations, this exposes them to searing sunlight in July and August when the temperatures get very hot.

In summary, if you don't live in the U.K., the Pacific Northwest, the Carolinas or other areas favorable to this genus, they can be a challenge. So for a higher chance of success with rhododendrons and azaleas:

  1. Plant hardy cultivars

  2. Give them shelter from winter winds

  3. Give them enough sunlight to set flower buds

  4. Keep them watered

  5. Provide excellent drainage,

  6. Keep the soil acidity in the proper range

  7. Use the ammonium form of fertilizer

It sounds like a lot of work but the rewards can be great. Good luck!

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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