Rehab for stressed rhododendron?

Asked May 3, 2016, 5:49 PM EDT

We have a very old rhododendron on the north side of our home that we believe was stressed/damaged by the extreme summer heat in Portland last year. The plant is over 6 feet tall. Normally, it is completely covered in healthy green leaves and bursting with white blooms about this time of year. Instead, it lacks leaves on about half of it and the remaining leaves are mixed with rusty, drying clusters. Our other rhododendrons that received more shade from the harsh summer sun seem to be doing well, acting as normal. Is it possible to rehabilitate this plant with this type and extent of damage? Or, is it time to bring an expert on site? I have included pictures. A wide angle of the entire plant, and a closeup showing the comparison of the green and damaged leaves. The plant is on the North side of our home and is mostly shaded except for afternoon sun that can reach the plant coming from the West, which is the side that has the most extreme damage. Thank you very much. Daniel

Multnomah County Oregon trees and shrubs diagnosis of plant problems horticulture

1 Response

Thanks for your question and the photos. It appears your rhody needs a little attention, but its problems do not appear fatal. The new growth appears healthy.

Here's what I would do.

First, carefully cut out all of the dead and dying material with a pruners. Follow all dead stems down to where they originate and remove them. Do not remove stems that have green growth on top.

Then, reassess the plant. I'm guessing the multiple trunks will be exposed to view; they are quite lovely. You may want to make a few additional pruning cuts to re-shape the shrub a bit.

Next, treat what may be the reason for the die-back. The leaves appear to have a nutrient deficiency. See how the veins of the leaf are darker than the outer part of the leaf. Rhody's need acidic soil. An unhealthy plant is less able to stave off hot sunny summer days, cold winters, and such.

Oregon State University Extension has two one-page guides for explaining how to evaluate and care for your rhody. They list options for curing the nutrient deficiency and for routine care. You can view them at these links: http://extension.oregonstate.edu/gardening/node/775 and http://extension.oregonstate.edu/gardening/rhododendrons-and-azaleas-need-strong-acidic-soil

Good luck.