When to Trim a Rhododendron

Rhododendrons are shrubs with large, evergreen leaves and flowers that bloom in colorful clusters. Closely related to azaleas, their lovely spring flowers and dark green foliage make them popular in many garden settings. These easy-to-grow beauties don't need a lot of pruning, but they will benefit from a well-timed trimming to help control their size and shape.

Rhododendrons thrive in mild, humid climates. Place them areas that are protected from the wind and that receive either filtered sunlight or morning sun and afternoon shade. They require a well-drained soil that is not too heavy or rocky and is rich in organic matter. Soil pH should be between 4.5 and 6, which is fairly acidic. Rhododendrons need about 1 inch of water each week, but it is important that the soil drains well and the roots don't become waterlogged.

Rhododendrons need very little pruning. If they are growing too large for their space or just need to be shaped, prune them as soon as they have stopped flowering. If you wait to prune until late summer, fall or winter, you might prevent them from flowering the next spring, because they bloom on the previous year's wood. However, you can remove dead or damaged wood at any time throughout the year.

When pruning large leaved rhododendrons, look for the growth joints, which are the visible part of the branches where the plant starts to grow each year. Prune large-leaved rhododendrons right above these growth joints, because they contain the dormant growth buds. You can prune smaller-leaved rhododendrons anywhere along the stem, because they have dormant growth buds all over.

Deadheading is an important type of pruning for rhododendrons. Remove the spent flowers from the stems to prevent seeds from developing. The development of seeds will reduce the next year's flowering. Remove only the dead buds and not the dormant buds at the base.