Hydrangea is an easy-to grow bush that blooms with round, pom-pom type flowers. The colors are soft and muted shades of pink, blue and lavender. Like all plants, the hydrangea has certain requirements that need to be met in order for it to thrive. Depending upon the variety, the hydrangea is hardy to USDA Zone 4 to 9.
Some hydrangea species bloom on old growth and some on new, so it's important to know the habits of your particular hydrangea plant. In general, mophead hydrangeas never need to be pruned, just remove old flowers and any dead branches. Big leaf hydrangea, the most commonly purchased variety, bloom on old wood only, so when pruning, keep this in mind. If the plant dies back completely in the winter, it will take another season to begin new blooms.
Powdery mildew, a fungal disease, can be identified by a powdery substance on the leaves of the plant. If caught early it can be controlled with a strong spray of water from the hose. Rust, also caused by a fungus, will appear on the underside of leaves, as small orange spots. Use commercial fungicides, according to package directions, to control infections.
Hydrangea, especially bigleaf hydrangea, is susceptible to chlorosis, an iron deficiency. If the plant is being grown in a soil with a high pH level, it will be more likely to suffer from iron chlorosis. A good solution to this problem is to apply aluminum sulfate, according to package directions, to the soil around the base of the hydrangea. Pine bark mulch around the base of the plant will also work. Remember, if you are growing a hydrangea cultivar that changes flower color, aluminum sulfate will cause blue flowers.