Size of a Formosa Azalea

Growth Habit

• The "Formosa" azalea is an evergreen plant and a member of a group called the Southern Indica hybrids. It blooms profusely in spring, covering itself in deep magenta, single flowers that can be 3 inches in diameter. Its flowers can be so abundant that the foliage is completely hidden at the height of its blooming period. This variety is slow-growing and has a generally upright growth habit, forming a gently rounded bush that can become up to 8 feet tall at maturity when grown under ideal conditions and left unpruned.

Sun and Soil

• The "Formosa" azalea grows best in a spot that gets either full sun for a few hours each day or light, drifting shade for most of the day. Like most azaleas, its leaves and flower buds can scorch when located in full sun for the entire day, especially in areas with hot summer sun. In such a climate, the best location is one that gets a few hours of morning sun, followed by shade in the afternoon. The shrub tolerates any type of garden soil that's well-drained, although it prefers fertile loam. Adding some compost at planting can help increase your soil's fertility. If it contains clay and tends to hold water, add some fine sand to improve its drainage. Water weekly, or more often in extreme heat.

Controlling Size

• Although the "Formosa" azalea is naturally quite tall, you can control its size with regular pruning, which can restrict the plant's height to about 4 feet. Cut back its branches by about one-third during the first two or three years, and then pinch back soft new shoots each year to promote bushiness while preventing a significant increase in height. Pruning is best done immediately after flowers fade, since the plant blooms on old wood and branches that grow during summer and early fall and produce flowers the following spring.

Problems

• Like most azaleas, the "Formosa" variety is subject to several insect pests and diseases that can interfere with its growth. Fungal problems that include petal blight and root rot can develop when it's grown in damp or excessively wet conditions. The best way to avoid these diseases is to locate the plant in an area with good air circulation, clear debris from under the plant regularly and water with a soaker hose to avoid wetting the shrub's foliage. This azalea may also attract spider mites and lacebugs. These can be controlled by spraying all parts of the plant thoroughly with insecticidal soap, diluted at a rate of 5 tablespoons per gallon.