Transplanting Rhododendrons

A couple weeks ago I attended the Western Regional Conference of the American Rhododendron Society (ARS). There were several classes to learn more about rhododendrons. I will post my notes from them soon, but for tonight I'll share what I learned about transplanting rhodies.

This weekend I put some of my new knowledge to the test and transplanted one of my inherited rhodies that was being overrun by a birdnest pine. Here is a picture of R. Macronulatum 'Crater's Edge' at the end of its bloom in early spring (this was in April.) It is a vibrant pink, especially at that time of year, but the plant is engulfed by the shrub behind it. Here is picture from later in the year.

Earlier this year I decided to move the plant to a place with more room. I started the process by pruning the plant back by 1/3rd in the spring after it had bloomed. I removed a few larger branches that were growing into or across other branches and removed all the dead wood from the plant. Pruning will make the plant grow new smaller roots that should help it overcome stress from transplanting. Then I waited until fall to transplant.

Once the temperature began to cool off and the rains returned I thought it was time.

Rhododendrons have very shallow roots, which is great if you need to move one, but that also makes them a little tricky to care for (at least for me). The roots dry out easily in hot weather and also rot if they are too wet. You can also cook the roots by watering too much during heat spells...one of my own pitfalls. To overcome root rot, the plants need really good drainage. Good drainage depends on your planting mix and how you plant the plant.

My first step in transplanting was making a good planting mix that has good drainage. The Rhododendron Species Foundation Garden uses a mix of 50% beauty bark, 25% bark nuggets 25% rubber bark, which they said was a porous lava rock from a specific quarry in the Portland area. I used what I had on hand. I used 50% hemlock bark, 25% douglas fir nougats and 25% lava rock as my mix. My lava rock is red, theirs was black, so there may be some issues with iron. I'll have to see.

The next step is to prep the area where you are moving the plant to.  I dug a hole a bit wider that what I estimated the rootball of the plant would be, and dug it about twice as deep.  This plant is about 30" tall. I dug a hole about 30" across and 12" deep. I then broke up the dirt in the bottom of hole, so it was loose for another couple inches down. Then I back-filled the hole with my planting mix, leaving about 2" below the grade of the bed. In the center of the hole, I built a slight mound that I could spread the roots over.

Now its time to move 'Crater's Edge.' Gently dig around the plant. I make a circle around the plant about the same size as the body of the plant. Keep the shovel tip going straight down into the bed all the way around. Once you've gone around the plant start working the shovel down and under the soil toward the center of the plant. Go slow and gently wiggle the blade of the shovel to loosen the rootball, while you go around the plant again. Eventually the plant will pop out.

You may cut some roots. In this case, the rhody's roots were growing into the shrub behind it and I had to cut the roots to get it out. This will stress the plant, but there were enough other healthy roots, that I'm not too worried.

The next step is moving the plant. Here, I was only moving it a few feet away so I was able to carry it in the shovel. For larger plants you may need to use a wheelbarrow, tarp or large piece of cardboard to support the plant while you move it. For smaller splants, I recommend at least putting it into a pot to keep the roots from drying out or loosing all the soil around them.

Now the plant is at its new home. Gently spread the roots out over the mound in the hole. Be sure to stuff planting mix into any gaps under the roots. This keeps air pockets from forming in the roots that can lead to disease. 

Then fill the rest of the hole in with planting mix. Keep the base of the rhody above the level of the garden bed. This also helps with drainage.  

Finally, cover with a layer of mulch around the plant (but off the base). 

Now 'Crater's Edge' has more room to grow and hopefully will look great next spring!