I continue to find your site and information so useful. Thank you for your help! I’ve just taken a photo of my PJM rhodo because I’ve never seen the leaves this red. I’m wondering if it’s a nitrogen or a heat thing. The shrub has been in this raised bed at least four years, happy and facing west under a Japanese maple, but it is the first summer without what used to be a chokecherry just to the south. There is a smaller maple there now, about 10-12′. But having said that you can see the leaves on the south part of the rhodo aren’t red at all! Also, given the leaves, should we be surrounding the PJM with burlap when we wrap our oakleaf hydrangea shrub, come winter? (We are planning to leave the standard ginko, now stake-free, alone.)
We associate red leaves with fall, and seeing them in summer indicates that something has accelerated the ageing process in a plant. Red leaves could be a sign of a light problem, watering problem or soil chemistry. Perennial plants are particularly susceptible to nutrient problems; sitting in the same soil year after year, they deplete soil chemicals and will benefit from the application of yearly compost.
Plants may function well until a new plant is introduced close by. Fertilizer intended for the newcomer can leach through the soil to the roots of its new neighbours, adversely affecting the acid/alkaline soil balance that the original plants need to function.
Excessive sunlight, caused by the removal of your chokecherry may overwhelm chlorophyll production in the leaves of your shade shade-loving rhododendron, with the result that leaves appear red.
During the summer, extremes of high heat followed by cooler temperatures cause nutrient imbalances. Anything that dehydrates roots and plant tissues can lead to red leaves.
If your rhododendron is planted in a spot that receives direct winter winds, consider building a burlap wind barrier around your plant. One of our earlier posts entitled Wrapping Rhododendrons gives information on how to go about winterizing your rhododendrons.