This little rhodo (PJM?) started this year with really yellow leaves. I’ve had it in the yard for over 10 years. I live in Mimico, base of Etobicoke, Toronto, near the lake so it always a little more temperate in the winter. I gave it a dose of nitrogen in the spring but nothing changed. I have almost 40 other types of rhodos and azaleas and no other plant has this issue. Any idea what is going on and what I could do about it? Could it be winter damage? It was surrounded by burlap (on stakes surrounding it, not on the plant itself) so it was protected from winter sun and wind. Love to know your thoughts.
Thank you for contacting the Toronto Master Gardeners.
The fact that you have over 40 other Rhododendrons and none of them exhibit yellowing leaves indicates that your plant is not happy with its site. In general Rhododendrons prefer to grow in a moist, acidic (pH 6 and below) organic-rich soil. They will tolerate a higher soil pH, but well-drained soil is a must.
As mentioned above Rhododendrons are picky when it comes to soil as well as the amount of water they receive. It has been an extremely dry summer. Have you been watering your Rhodendron on a regular basis? Yellowing leaves could be an indication of either too much or not enough water. Rhododendrons do not like “wet feet. Does your soil drain well? Watering less often but deeply is the key to happy, healthy plants.
It could be that your soil is too alkaline. You can purchase a soil test kit at your local garden center. If the soil is too alkaline the plant will not uptake enough iron causing a nutrient deficiency causing the leaves between the veins to turn yellow. I cannot determine from your photo if the entire leaf is yellow or if it is just exhibited between the veins. . Trying to change the soil acidity is easier said than done unless you’re prepared to add a soil acidifier forever, because the soil tries to revert back to what it was before.
These plants grow best when planted in part shade to full shade in a protected site out of winter winds. Rhododendrons are shallow-rooted and will benefit from the addition of a layer of organic mulch to conserve moisture and moderate soil temperature fluctuations.
Lastely, on our site you will notice that the Toronto Master Gardeners are happy to answer your gardening questions if you live in the City of Toronto. If you live outside of Toronto, please check the Master Gardeners of Ontario website to find your local Master Gardener group in the province.
For your area please contact the Etobicoke Master Gardeners here.