Sick Rhododendron - Knowledgebase Question

O'fallon, MO
Question by scrusso
August 16, 2000
I have a Rhododendron plant and I really love her beautiful flowers. At this time she is very sick, her leaves are full of spots and she didnt bloom this year. I'm at between zone 4 and 5 , she is a north east location of the house. She used to bloom for me for many years(4). I transplanted her 2 years ago to simular location. I think I need a better fertilizer.

Answer from NGA
August 16, 2000


It sounds like a combination of things. Rhododedrons are native to forest "understory" (the dappled light cast by high-canopies trees). The symptoms you describe indicate disease, or nutrient deficiency caused by alkaline pH. Ideally, the soil pH should be no higher than 5.0. Rhododendrons also like regular moisture, and dry conditions can stress the plant. I recommend fertilizing with ammonium sulfate, which will lower the pH more rapidly than other fertilizers. Follow the label recommendations to correct acidity. Also mulch the whole area with acidic peat moss, and keep the area evenly moist. Best of luck!

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