rhododendron - Knowledgebase Question

Morton, WA
Avatar for redrosebud
Question by redrosebud
April 29, 2006
I have about 20 Rhodo's. This last winter the leaves on about 4 of them have turned yellowish-green or yellow. Are they lacking something?


Answer from NGA
April 29, 2006
A fairly common ailment of rhododendrons is chlorosis. It is really an iron deficiency of the plant. The leaves turn pale green to yellow. The newest leaves may be completely yellow with only the veins and the tissue right next to the veins, remaining green.

Rhododendrons are acid-loving plants. They prefer soil with a pH between 4.5 and 6.0. The yellowing is due to a deficiency of iron in the plant. The soil is seldom deficient in iron. If the pH of the soil is 7 or higher, the iron is in an insoluble form so the plant is unable to absorb the iron from the ground. A high soil pH can come from overliming, or from lime leached from cement or brick. Plants use iron in the formation of the green pigment in the leaves. When the iron is lacking, the new leaves are yellow.

For treating chlorosis, spray the foliage with a chelated iron fertilizer and apply it to the soil around the plant to correct the iron deficiency. Correct the pH of the soil by amending it with sulfur, iron sulfate or ammonium sulfate. Work the amendment into the root area to lower the pH. To help maintain an acid pH, use fertilizer that is specially formulated for acid-loving plants.

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