Keeping Azaleas and Rhododendrons Happy
Question. I planted several azaleasabout eight years ago; they are large but kind of scraggly, havinggrown tall instead of becoming round and full. A lady in our communitycuts hers back to small stubs every year and the next season they arelarge, full, beautiful bushes. After reading a great deal on thissubject I'm confused as to whether it's a good idea or not. Some say'do', some say 'don't'. Right now the plants are covered in blooms so Iknow not to do anything. But when is the best time? And what should Ido? Thanks,
---Jennifer inMcComb, Mississippi
I'm glad you asked, Jennifer—improper pruning is one of the biggestmistakes people make with azaleas and other rhododendrons (all azaleasare in the rhododendron family, and both types of plants require thesame basic care).
It's never wrong to prune them right after the flowers fade. A monthlater is still technically okay, but sooner is always better—especiallydown South, where your heat can come on fast and stress recently prunedplants. No matter where you are, never prune after June or you riskremoving the following year's flower buds.
(Note: This advice applies only to the typical early-Spring bloomingtypes, which comprise over 90% of the rhododendron family plants grownin American landscapes. Some rare and beautiful varieties grown byenthusiasts and botanic gardens can bloom very late in the season.Consult an expert if you have a non-typical azalea or rhododendron.(Heck—if you have one, you probably ARE an expert…)
Now, your neighbor sounds like one of those 'green thumbs' who can dopretty much do anything and the plants still thrive. It is generallynot wise for normal people to imitate such behavior. And your gentlewinters—much more to these plants' liking than my brutal Pennsylvaniaones—may make her technique a bit safer. But I'd still stick with thealways-safe advice of removing no more than a quarter of the plant inany one season. In your case, just take it off the top (if disease werean issue, I'd suggest removing some inner branches for better airflowinstead); if your plants are eight feet tall, remove no more than thetop two feet of growth. Six feet tall, a foot and a half, etc…
Such a pruning will begin to improve their look dramatically withoutthe possibility of you entering the fall with the delightful sight ofbare, dead sticks outside your house. Repeat this every season, and ina few years the shape of your plants should be exactly what you'relooking for. Remember—you've been letting them get leggy for eightyears; give yourself at least a few seasons to correct that condition.
After pruning, feed and mulch as I describe below and keep them wellwatered; these thirsty plants should be the first ones in ourlandscapes to see the hose during dry times.
Question. Over the past years I've hada problem with my azaleas and rhododendrons that the extension serviceat Penn State has diagnosed as Botryosphaeria.I have a lot of clay in my soil and thought making a raised bed wouldhelp. A friend who owns a small nursery has offered me a mix that is50% three-year-old, ground-up decayed leaves and 50% soil from thebottom of a lake. What do you think?
---Allen inNorth Wales, PA
Answer. Botryosphaeria is a canker causedby growing conditions so bad it should kill the plants, but they hangon long enough to die of an unpronounceable disease instead. As withmost of these kinds of problems, the answer is to simply give theplants what they want and go home early.
And what these plants want is a naturally rich, acidic soil; they LOVEgrowing in a mix of half milled peat moss (available in those bigbricks at garden centers) and half compost. If they're available alone,those three-year-old leaves should BE compost by now (unless they stilllook like leaves, then find realcompost). The lake bottom stuff might be good topsoil or it mightbe really polluted; either way, you don't need it here.
I love raised beds for annual flowers and veggies, but prefer in-groundplanting for these kinds of perennials in the North; their legendarilyshallow roots could freeze if that bed kept them above ground during areally severe winter. Dig a VERY wide hole—don't just plop them into alittle island of good soil or their roots won't travel outside ofit—throw away all the nasty clay you encounter and break up the stuffat the bottom with a garden fork for good drainage. Although they arethirsty, these plants can't stand wet feet, which unimproved clay soilvirtually assures.
Fill the hole with a well-mixed batch of half compost, half peat mossand plant the bushes at least as high above the soil line as they werewhen you got them. After planting, spread two inches of peat mossaround their base, then cover that with an inch of compost. You cansubstitute a couple inches of shredded oak leaves, pine straw, pineneedles or other naturally acidic mulch for this peat/compost mix, butDO NOT use sawdust, wood chips, 'triple-premium shredded bark' or anyother kind of wood mulch.
Mulch you must! And re-mulch every year. Spread an inch or two of peatmoss around the base of the plants, and then cover that with an inch ofcompost in the North; two inches in the South. This will feed theplants, keep moisture in the soil and create a visual reminder to keepyour big feet away from those very sensitive roots. If you want to useone of those naturally acidic mulches instead, go right ahead—justremember: No wood mulch of any kind. Or rubber. I hope you knew THATalready...
And finally, some basic rules:
- Don't plant azaleas or rhododendrons in full sun or deepshade—understory plants in the wild, they thrive beneath the canopy ofdeciduous trees or thin evergreens (or a location that gives themmorning sun and afternoon shade).
- Keep them far away from concrete, lime and other alkalinematerials.
- Prune them at least a little bit every year to remove the fadedflower heads.
- Water during dry spells. And keep their soil moist for a goodweek or three after planting or transplanting (which is best done rightafter the blooms are gone.)
- Do not overfeed. Stay away from chemical fertilizers; theseplants just despise the concentrated chemical salts in products likeMiracle-Gro and Osmocote.
Do all these easy things, my Spring-blooming friends, and you willnever have to worry about pests or disease again.
Special thanks for reviewing this article to the folks at TylerArboretum in Media, Pa—home to a world-class collection of azaleas andrhododendrons so diverse that something is in bloom from late winterthrough August! Details: http://www.tylerarboretum.org/wistercollections.htm
You Bet Your Garden Question of the Week ©2006Mike McGrath