When and How to Prune Azalea

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When and How to Prune Azalea

What’s the most common mistake folks make when pruning azaleas? Pruning in fall. 

You might think it would be safe, because these shrubs bloom in late spring, but they set their new buds right about now, and if you lop them off, you’ll get nothing next spring. Most horticulturalists will tell you the cutoff date is July 31; in warm climates you can push it a bit, but absolutely not into September. 

That said, sometimes any plant needs an emergency trim. You should never hesitate to prune your azalea or rhododendron — or anything else, come to it — if you see dead or infected wood. Cut well below the damaged part and get the branch out of the garden pronto. If you keep a stack of garden debris for burning, all the better. Just don’t put it on the compost heap, or the disease might spread to your new soil. 

Now, many an azalea and rhodie have gone their whole lives without ever being pruned, and this is just fine. They don’t need it to stimulate bud production, and most are pretty nicely shaped just as they are. But sometimes they outgrow their spot and you don’t want to move them. Other times you have to move them, in which case you should do a root prune if you possibly can. More about that in a sec.

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Here are some general guidelines for pruning azalea shrubs: 

  • The best time is late winter/early spring. Yes, you will definitely lose some buds that formed last fall. But it is the healthiest time of year for the shrub to get cut, especially if you have to do a drastic pruning. You might think right after blooming would be the best time, but that’s the height of the growth season, and it can stress the shrub. 
  • Azaleas respond much better to pruning than other rhododendrons, because they set buds all along their stems, so you have much more room for error. 
  • Rhododendrons should be healthy before you prune. If you’re in doubt, don’t cut the entire shrub back. Figure out how many branches you need to cut, and just do 1/3 of them. Next year, do another third, and so on. This is a good rule of thumb for any shrub or tree that needs a severe pruning. It’s also a lot easier mentally, strange as that may sound. It takes some courage to go out and raze a beloved shrub, believe me! 
  • Now, many times folks prune an old, neglected rhodie to get it going again. This is a good idea, and usually works. But before you do so, look carefully at the base of the plant. Do you see any new shoots coming up? If there are, you can be pretty fearless and cut back all the nonproducing old branches to the base — above the new shoots. What the new growth is telling you is that this shrub is still healthy and growing. But if you don’t see any new shoots, use the 1/3-a-year rule and check the shrub carefully to see if any new growth is happening each season. If you don’t see any, your shrub might not bounce back. 

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If you have an azalea or rhodie that has outgrown its spot in the garden, you may need to do either a top or side trim every few years. If your foundation rhododendron is now blocking the front window or completely shutting out whatever you planted behind it, trim the upper branches to just above a joint, the way you would a Rose or other shrub. Do them all at once, in late winter/early spring. If the plant takes off like a bullet and regrows too tall that first season, you might have to move it after all. But if it just puts on a few inches, you can probably get away with leaving it where it is and cutting it back every 4 or 5 years. You’ll still get plenty of blossoms on the sides and front even the first spring after you trim it. 

Side trims are even easier. If your azalea or rhodie is too wide for its spot, just get in there and cut back the side branches to a good joint, leaving a few inches between the plant and its neighbors to allow for a couple seasons of growth. You won’t even miss the blooms you may lose the first spring when you do this, because chances are the plant was so squished into its spot, it wasn’t getting enough light and air to bloom well anyway! And you’ll still have a full crop of buds on the top, front, and rear of the shrub. 

If worse comes to worst and you’ve got to move your azalea or rhododendron, the best course is to give it a root prune in early spring the year before you move the shrub. Of course this isn’t always possible, but it’s the best option, and I’m mentioning it here because if you have any shrubs you think might eventually need to be transplanted, think about doing the root prune this late winter/early spring. 

Here are some general guidelines for transplanting azalea shrubs: 

  • Take your shovel and sink it straight into the ground right up to the haft, cleanly (no waggling or loosening the surrounding soil). Repeat all around the base of the shrub, in a circle. But make the circle no bigger than you imagine a good-sized rootball would be. I mean to say, if you’ve got a 6-foot-wide Azalea, of course you aren’t going to cut a 6-foot-circle. Try to make it big enough to get enough roots, but not so huge that you can’t possibly transplant the thing. For most azaleas and rhodies, I think about an 18-inch to 2-foot rootball is reasonable. 
  • What this cut does is start new roots growing like crazy for that year before you have to move the shrub. Then when it’s time to dig it up, you make your circle about half a foot larger than the first circle. That extra half-foot will be full of new and old roots, and it will make the transplant process much easier. 
  • Remember, azaleas and rhododendrons never like their roots disturbed, so when you do transplant, be sure to plant very shallowly, mulch around the plant very well, and don’t cultivate the immediate area, especially not the first few years. These shrubs really need their space.