How to Rejuvenate Azaleas and Rhododendrons

Recently a reader wrote to ask for some guidance in pruning some overgrown azaleas. She described them as “some very neglected azaleas”. A challenging task to be sure- not only the pruning but telling her how also, especially with no real clue on what they look like. So why not write a little primer on the subject.

Like any shrub or tree, the pruning method you follow will depend upon the condition of the plant and your objectives. It doesn’t hurt to do a quick but careful appraisal of your situation:

Plant appraisal:

1. Size of bushes? Are they too large? Are they about the right size for the site? Are they misshapen? Have they become “scraggly”( a term often used with large overgrown shrubs)?
2. Is there any evidence of insect infestation or disease incidence? Dead wood?
3. Are they healthy with an appropriate color of green foliage? Is the bloom becoming sparse?
4. How long have plants been in this location?

Site Appraisal:

1. Are the plants growing in an appropriate environment? Enough Shade? Exposed to afternoon sun or drying winds?
2. Appropriate soil? Soil nutrition? Past fertilization activity? Soil moisture adequate? Irrigation when needed?

Owner appraisal- Objectives:

1. What type of pruning do you intend to do? (maintenance or rejuvenation)
2. Do plants need to be rejuvenated?
3. Do you wish to reduce the size of plants?
4. Do you wish to simply maintain the health and vigor of plants regardless of size?

These are all important questions to consider as the answers can give you guidance on how to proceed. For instance plants with sickly yellow foliage and a lot of dead stems may well have other problems that pruning won’t solve. Pruning may be beneficial but probably won’t solve the problem.

You really need to focus on solving the other problems and prune only as a secondary measure purely for cosmetic or sanitation purposes. If we answered the above questions we should have some feel for problems or potential problems beyond pruning needs.

Objectives are important. As in my opening paragraph, the client gave me enough information to let me know that rejuvenation was the goal. The bushes are overgrown and straggly. They are too large and no longer attractive. She wishes to reduce the size and improve appearance.

Rejuvenation– this can be a tall order for long-neglected azaleas, but certainly achievable. Basically it comes down to a choice of two basic methods- gradual or drastic reduction. Both methods require patience- azaleas and rhododendrons are not known for setting the world on fire in growth rates. Badly overgrown plants took some time getting there and will take some time to get back into shape.

The first thing we want to do is make sure that the plants are basically healthy and can be renovated. Undoubtedly there will be a fair amount of deadwood. Look also at the live branches. Are there goodly amounts of deep green foliage? Is the foliage lacey looking? Shake the foliage over a piece of white paper and look to see if there are tiny dots that move by themselves (mites). Look at the stems. Is there any sign of cankers (swollen, sunken or dead areas of bark that indicate disease)? Look closely, are there any scale insects attached to the bark? Is the bark splitting (possibly exposure to drying elements like sun or wind)?

If anything above raises a red flag, be aware you will also have to deal with these problems as a part of the overall rejuvenation process. Insect infestations must be controlled, and we will prune out stem diseases. Environmental situations such as nutrient deficiency, inappropriate pH, too much or too little water will also have to be addressed.

So let’s move onto the pruning processes. Drastic reduction can be the simplest method, because it merely involves cutting the entire shrub back nearly to the ground. That’s right, whack away. Prune it to a neat rounded group of stubs no longer than 6″. Azaleas and rhodos have dormant buds beneath the bark along the entire stem that will emerge with new branch growth once the existing dominant stems are removed.

If we are working with a basically healthy plant a cluster of new stems should emerge. There will probably be more stems than are desirable and sometime in late summer or early the following spring, the new sprouts should be thinned. One should be aware that there is a risk that some plants may not recover from this procedure.

The advantage to this method is that the work is quick, decision making is minimal, and the “new” shrub that will emerge should be uniform in growth habit or can easily be corrected.

Also, most insects and disease stems are removed. Disadvantages include the complete loss of the shrub for a spell. Here’s where the patience for this method comes in. It may be unsightly for a while till new growth covers the stubs you left. The plants will look like newly planted specimens. They may look out of place among other mature neighboring plantings.

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 overlooked 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 respond 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 throughout the process.

This method requires us to make some seemingly agonizing decisions. Do we take this stem or not? It is easy to fall prey to should I shouldn’t I syndrome. With a little practice, we soon learn that the goal is to remove 1/3 of the foliage while attempting to maintain a vestige of decent appearance (and sanity). If the shrub is scraggly to begin with it will look worse after one or two years of pruning. There will be a temporary degrade of appearance.

A word on timing. Like most spring-blooming shrubs, this year’s bloom buds were formed last summer. They over winter on the shrub. If maintaining some bloom during this process, the pruning should be done just after blooming is complete. This will also allow adequate time for the shrub to respond with new sprout growth and allow it to harden off appropriately for winter.

During this process, it helps to maintain good vigor. Late winter or early spring fertilization with an acid fertilizer is desirable. Be sure pH is below 6.0 and that iron in the soil is adequate. Good drainage is key to good azalea and rhodo health. If the pruning process results in sudden exposure of stems to the sun and winds, desiccation of residual stems could be a problem. Creating some sort of shading mechanism for the stems may be desirable.

Sanitation is also an important aspect of rejuvenation. Good sanitation procedures include the timely removal and disposal of material removed from the shrub. If stem cankers are present it is also wise to sterilize our pruning tools between each cut.

Rejuvenation pruning requires faith. Faith, that nature will do her job. That nature will forgive us for our transgressions. Somewhere down the road we will be rewarded with a less unruly plant. With a rhododendron or azalea that lives up to their reputations as the king and queen of broadleaf evergreen shrubs.

It takes some guts, but in the process we can learn so much about these heaths. We must study them intently in the process. Perhaps the ultimate payoff is that we can say we truly understand how they grow, and live and survive.