Rhododendrons are attractive bushes that produce round flower clusters in a variety of colours, including white, purple, pink and red. They are a favourite in many gardens, but their lack of tolerance for heat and cold limit their availability in some areas. Rhododendrons are pruned primarily for appearance and can therefore be pruned as often or as little as you like.
Know which type of rhododendron you intend to prune. Some types of rhododendrons, such as fastigiatum, do not require much pruning, while other types, such as rigidum, may need to be pruned within the first two years. If you purchase a rhododendron at a store or nursery, ask the salesperson about the growth habits and care guidelines for your particular type of plant. Whenever possible, have a look at a mature plant to get an indication of the size and shape after a few years of growth.
Time the pruning carefully. The ideal time to prune a rhododendron plant is within a couple of weeks after flowering has ended. Soon after flowering has ended, new growth will begin to emerge and if you wait too long to prune, you will interrupt the budding process and reduce next year's blossoms. Prune the plant as early in spring as possible. This will allow the cuts time to heal.
Use only very sharp, clean tools in order to make smooth cuts when pruning. Cut the rhododendron back to a growing point, and make cuts at a slight angle in order to allow moisture to run off. For branches larger than an inch, you may want to paint the cut ends with pruning seal.
Prune the entire plant, not just the top. Removing stems from the middle of the rhododendron plant will allow better airflow and more light into the centre of the plant. It is a good idea to remove lower branches on larger plants, as this helps to train the rhododendron and makes future mulching easier. For plants that need a lot of pruning, spread the cuts over two or three years to prevent the plant from going into shock.
Remove any withered flowers once the blooming season has ended. This process, called deadheading, reduces the risk of fungus and prevents a heavy set of seed. Deadheading also makes the bush more attractive and may increase the number of flowers the following season.
Maintain the plant by removing dead and diseased wood. This type of pruning should be done frequently, regardless of the season.