Rhododendron Pruning for a Sustainable GardenPosted on October 8, 2015
Why have an article about rhododendron pruning in October when the best time to prune a rhododendron is late winter/early spring while the plant is dormant? We just wanted to get this information out to those ready to do an October pruning, and perhaps cause you to consider waiting.
Rhododendron Pruning for a Sustainable Garden is an art form. Learn how to prune a rhododendron plant sustainably, taking out dead and dying material and submitting diseased portions for testing to determine the cause. Remember to sterilize your pruning shears. When finished, you’ve enabled the plant to focus its energy on the living material, contributing to healthy, beautiful growth and awesome blooms.
"Welcome to Green Jay Landscaping. Here we are inspecting one of our estate management projects. So, here we have some dieback on one of our rhododendrons. Now these old plants, and all the other plants seem reasonably healthy, but we see some dieback here. However, there’s also some new growth here, so what I’m going to do is prune the rhododendron to take out that dead and damaged material.
Rhododendron With Cigarette Burns
We also see some discoloration of leaves. Something that we want to look for is cigarette burns in the leaf. This may be due to over application of fertilizer. This is a classic indication. One thing we could do is send a tissue sample out to Rutger’s Plant Diagnostic Laboratory for an evaluation. We’re going to look at this and, once again, this is completely shot. I’ll take this out. Now if this was much thicker I would need loppers. This will give it a better appearance and also reduce what I'm seeing as potential damage. It looks better already. Here’s another dead stock. I’m going to remove that. And here’s some other dead stuff, but there’s a flower here.
One thing you want to do in pruning is to be sure you’re using sharp shears that have been sterilized in a 5% Clorox solution so that you’re not taking plant pathogens and disease and transporting it from one plant to the other.
Once again, here we have some dieback, but at the same time we have some green. We’re going to remove those dead parts. We want all the energy to go to the healthy tissue: Healthy flowers, healthy stem stalks, roots. We’re going to remove any dead, dying and diseased components of our plant—as much is possible. And that's a little example of proper rhododendron pruning technique. Thank you."
Rhododendron Pruning Tips
Rhododendron Pruning: Three of the basic reasons.
Supporting the health of the plant
Shaping the plant for aesthetic reasons
Trimming the plant back to prevent overcrowding
The second two occasions for pruning can largely be avoided if the plant has been placed in a location that supports its growth to full size. For example, if the location is too close to other plants, too close to the house or perhaps in front of a window, it’s best to select a smaller-leaved dwarf variety of rhododendron. Otherwise, as the plant grows you’ll find yourself needing to drastically trim it back to prevent overcrowding. This is not the healthiest, most sustainable way to maintain a rhododendron.
Rhododendron Pruning: Growth Cycle & Best Timing
You can prune large-leaved rhododendrons at any time of year without harming the plant. However, the best time to prune large-leaved rhododendrons is late winter/early spring when there are no flower buds, just before the plant’s annual growth cycle begins.
The annual growth cycle begins with a flush of growth that terminates with a rosette of leaves (a truss) that averages around 6 inches in length. Younger rhododendrons will produce 2 flushes per year, older plants produce one flush followed by a flower bud. Rhododendrons retain their leaves for 2 years.
Rhododendron Pruning: Remove Dead and Diseased Plant Material
When pruning, the first step is to remove all dead and diseased wood. Follow any dead or diseased portions of the plant to where the healthy living tissue begins and make the cut there. Remember to disinfect the sheers in a 5% Clorox solution between cuts so that you don’t transfer disease from one cut to the next.
Rhododendron Pruning: Deadheading - Remove the Old Flower Trusses
Snip the truss off about ¼ inch above the new growth (the truss is the remaining flower structure of the recent blooms after the pedals have fallen off). You might be tempted to just break the truss off, but the break could inadvertently take some of the new growth material with it. It’s safer to use pruning shears.
Some rhododendrons don’t need to be deadheaded. If the flower stalks shrivel up and disappear on their own, you don’t need to deadhead that variety of rhododendron.
Rhododendron Pruning: Shaping Your Rhododendron (best technique for smaller plants)
You’ll notice rhododendrons produce a new whorl of leaves each year. Follow the whorl clusters on a branch down to the cluster you want to keep, then prune the branch about ¼ inch above that whorl cluster.
The best time for shaping is late winter while the rhododendron is still dormant.
Rhododendron Pruning: Rejuvenation Pruning (best technique for larger, leggy, overgrown rhododendrons)
Here, you’re going to remove most of the branches of your rhododendron. Cutting at strategic points will promote a flush of new growth that you can shape over the coming years.
Each rhododendron has a few primary branches. Pruning the primary branches at different heights will create a natural looking plant as the new growth emerges. Where to make the cut? Notice that each branch has tiny, pin head sized pink dots along its surface. Each dot is a tiny bud. Make your cut ½ to ¾ inch above a healthy bud (one of the larger, firmer, fuller buds). Pruning above a cluster of multiple buds will produce new growth of multiple branches. That creates a fuller, more beautiful result.
As with shaping (above), the best time for rejuvenation pruning is late winter while the rhododendron is still dormant.
Rhododendron Pruning: Conclusion
A thoughtful, strategic pruning program is not very time consuming and will result in beautiful rhododendrons with awesome blooms!
Jay Archer, President