The Growth Cycle of Azaleas
If you sheared your azaleas any time after August 15, expect very few flowers on those plants next spring. Flower bud initiation, which begins at the tips of the new growth, happens in late August into early September. Shearing the plants too near that time will not allow sufficient new growth for flower buds to develop. As daylight hours shorten, plants are shutting down to prepare for the cold winter months.
If your azaleas have a few wild shoots — stems that have grown taller than normal — simply prune them out. By selectively hand pruning, you will be allowing the vast majority of the remaining stems to flower in the spring.
Understanding the growth cycle of azaleas is important to their culture.
Spring: Flowers and New Growth
In the spring, azaleas flower. As soon as the flowers drop their petals, the branches prepare to initiate new growth from the vegetative buds beneath the old flower buds. Spring growth is controlled by the dominance of flower buds. If you have small azaleas and want them to grow tall faster, snip off the flower buds in early April. As soon as the weather warms, new growth will appear. A chemical version of this technique is used by growers to produce large plants in a short time.
If your azaleas are well established and growing too much, prune the stems back as the flowers are wilting. Stems up to three-quarters-inch in diameter will sprout new branches by the hundreds. Do not prune all of the stems at the same height. Cut some stems back 12 inches, others 18 and others 24 to give the plant a more natural appearance.
Summer: The Season for Density
To create more dense plants, shear them in late June or early July, causing the new growth to generate side branches from every new stem. This is a technique used by commercial growers to prepare plants for seasonal marketing. If the grower intends to sell the azaleas in flower the following spring, the plants will not be sheared again after July 22. This assures sufficient new growth at the ends of all branches for flower buds to develop.
To fully develop, flower buds require essential nutrients, especially nitrogen from the soil.
Autumn: Mulch with Compost; Maybe Feed
Deciduous azaleas are quite common, but most of the azaleas grown in Maryland are evergreen. Mulching them with compost in the fall will generally provide sufficient nitrogen to keep the foliage green.
If the soil contains low levels of nitrogen, however, nitrogen from the lower leaves will migrate toward the flower buds maturing during the late fall and into winter. The loss of nitrogen from the lower leaves will cause the leaves to turn yellow and drop to the ground. To assure that azaleas’ foliage remains dark green all winter, growers apply ammonium sulfate to the soil after the first frost.
If you mulch with bark or wood mulches and do not apply ammonium sulfate or blood-meal, your azaleas will most likely drop their leaves, resulting in only a small cluster of leaves surrounding the terminal flower bud come spring.