Answer: Failure of flower buds to open could be due to a number of reasons. The buds you seed could be foliage buds rather than flower buds. Pick one off and cut it in half; if it has color, it's a flower bud; if it's green, it's a leaf bud.
If they are flower buds, the problem could be bud blast. Plants which are not sufficiently hardened off or are exposed to unseasonal warm spells can start bloom prematurely. These blooms are seldom satisfactory and many times get frozen before opening fully. In any case, the seasonal bloom is lost. Also, disease may attack the buds before they open.
Low temperatures. The buds could be flower buds that FROZE during the winter and in your area, this could easily be the problem. Cold climates are too cold for many azaleas. Most azaleas have a low temperature at which the flower buds are damaged and will not produce flowers. It varies greatly from variety to variety. You may need a hardier variety like PJM.
Nutrients. Improper nutrients my be a problem that affects cold hardiness and flower bud set. A few things you can do are to fertilize with phosphorus (super-phosphate) per directions to increase hardiness and flower bud set. This can be done any time. Do not use nitrogen rich fertilizers as they may inhibit flower bud production and also reduce cold hardiness. Lawn fertilizers are notoriously high in nitrogen and should be kept away from flowering plants.
Acidity. Measure the pH and acidify if necessary. Since your plant looks healthy, this is probably not the problem. Azaleas like acid soil, but if the soil is too acid, the symptoms can be the same. Very acidic soil can prevent the roots from taking up nutrients.
Protection. If the plants are wrapped in burlap during the winter, they may gain a few more degrees in hardiness.
Drought. When soil moisture is too low, the buds will not open. Watering will usually resolve this condition if detected soon enough.
Hope I've covered all the bases! Best wishes with your azaleas!
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