Azaleas require specific types of care in order to generate the blooms everyone loves. Without the proper soil type and conditions, the correct lighting, pruning, watering, protection from pests and the careful application of fertilizers when needed, azaleas will produce less than satisfactory blooms and may even quit blooming altogether.
Pruning at the wrong time of year can cause azaleas not to bloom. Azaleas form the buds for next spring's flowers right after the blooms from this year have fallen off. They need enough time to ensure the bud is fully developed. Pruning after June means you may be removing many or all of next year's blooms. Winter pruning gives the plant no time to generate new buds. The best time to prune azaleas is right after they have bloomed. If the plant is the size you want, simply snip away the dead flowers. If the bush has gotten too big, now is the time to trim it back, down to half its full size. This leaves plenty of growing time for the plant to set new buds before frost arrives.
Azaleas are fairly particular about soil conditions. Clay soil does not allow good drainage, and azaleas don't like their roots to be saturated. Clay soil should be modified with additives to help loosen and break it up--half compost and half peat moss.
The shrubs also prefer acidic soils and may fail to bloom in alkaline soil. Concrete in sidewalks and building foundations can cause the surrounding soil to become alkaline. Acid-forming fertilizers with 12-4-8 or 15-5-15 combinations can be used to boost the acid levels of the soil. Some gardening sources recommend avoiding chemical fertilizers altogether. Instead they suggest adding a layer of peat moss followed by a layer of compost around azaleas.
Azaleas need a delicate balance of sunlight and shade. Too much sun is damaging, but deep shade also prevents them from getting enough light to bloom and grow. Ideally, azaleas should be planted under trees with a high canopy and receive dappled sunlight. Under thin evergreens is another good location for filtered light. If trees are not available in your landscape, look for a location that provides morning sun and afternoon shade.
Azaleas are very thirsty plants. They should be watered whenever the surface soil is dry to the touch. However, the roots may rot in standing water, so keep watering light and frequent during dry periods. Providing natural, non-wood-based mulch around the base will help maintain moisture. Too much or too little water can prevent an azalea from blooming.
If deer or rabbits have access to your azaleas, they could be the cause of your lack of blooms. The animals will nibble on the buds in the winter, robbing your plant of its spring bouquet. Azalea lace bugs suck the plant's juices from its leaves. The foliage turns a silver-gray color on the underside. Without healthy leaves, the plant cannot support flowers or grow the buds for next year's spring blooms. Lace bugs can be controlled with a thorough coating of insecticidal soap.