Rhododendron 'English Roseum'
I planted this rhododendron 14 years ago on a slope with high shade from large trees. It has grown, flowered, and done well until the past year or so. In spring 2018 it flowered very well, but I noticed fissures on the trunk that are seen in the attached photo and it had some yellowish leaves on about one third of the shrub. This year it has similar symptoms and fewer flower buds. What is causing these symptoms? Can I do anything to help this rhododendron or should I remove it? Thanks for your help.
We have had a few questions lately about yellowing rhododendron foliage. (The branches/wood look okay.) Rhododendrons are fairly shallow rooted and prefer highly organic soil. The excessive rainfall of the past two years has washed many nutrients from the soil. We'd recommend that you top dress around the shrub with an organic soil amendment/composted product, from the trunks out to the dripline at least. (Don't pile on the trunks.)
A slow-release fertilizer for acid-loving plants, such as Hollytone, can also be applied once.
Apply organic matter or just let leaf litter remain and decompose each year, to improve the level of organic matter in the soil and replace nutrients that are being used up.