Rejuvenation of Azaleas and Rhododendrons
Of course since they should have a well-developed and extensive root system, growth should be faster than for newly planted specimens, however future flowering will be delayed for several years.
Gradual rejuvenation requires several years worth of work on the shrubs. Pruning involves a gradual removal of the oldest material over 3 years. Each year approximately 1/3 of the live foliage is removed.
In year one the deadwood along with the oldest/largest stems are cut back. Remember the objective is to remove no more than approximately1/3 of the foliage, not 1/3 of the stems. Since we will be working with the larger stems it is likely that we may remove less than 1/3 of the stems to get 1/3 of the foliage. In addition to removing the dead wood which won't count against our foliage removal, we will want to remove any stems with cankers or signs of stem disease. If these stems have live foliage we need to count these as part of the 1/3. If we suspect we have stem diseases we should attempt to identify the problem for further treatment. Keep an eye out for scales and mites that may have been over looked before. If heavy scale infestations are present, consider removing the worst infested stems. Again the residual shrub should be treated.
The azalea or rhodo should responds with some sprouting of interior growth to replace the lost stems. It will be ender and succulent and a prime target for insect pests so inspect it several times during the ensuing growing season.
In year two, we repeat the process. Remove deadwood, infected and infested stems and no more than ½ of the remaining old wood foliage. (This will be 1/3 of the original volume of foliage.) If there is additional deadwood this second year inspect it closely for signs of disease or insect problems. It is not unusual to lose some due to the sudden exposure that occurs during the first year's pruning. If it is extensive and there is no obvious cause, review the environmental conditions (site factors such as exposure, nutrition, water relations). Again the plant should respond with new sprout growth, while the previous year's sprouts elongate and branch.
In year 3, simply remove the remaining older original stems. The rejuvenation pruning is complete. The plant will be greatly reduced in size, yet will have a canopy of sorts to maintain some semblance of aesthetic presence
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