Why are my Rhododendron leaves yellow? - Ask Extension
The leaves on my Rhododendrons have been turning yellow.
What might be causing this?
They get morning shade and some afternoon sun.
I live across t...
Knowledgebase
Why are my Rhododendron leaves yellow? #784784
Asked March 22, 2022, 12:55 PM EDT
The leaves on my Rhododendrons have been turning yellow.
What might be causing this?
They get morning shade and some afternoon sun.
I live across the bay from Assateague seashore.
Thanks for your help!
Diane
Worcester County Maryland
Expert Response
We viewed your photos. Overall the plants do not look that bad. Other than the color, we see buds which are a good sign.
The yellow color may be due to an improper pH, and/or some possible root damage. Rhododendrons are woodland plants. They like cool, moist, well drained acidic soils and grow best in morning sun and afternoon shade. This does not look like a good location for a woodland plant.
Rhododendrons require acidic soil to thrive; a pH range of 4.5 to 6.0 is considered ideal for them. If the soil acidity (pH) is not in the range preferred by that plant species, the roots will not be able to access all of the nutrients they need, even if plentiful in the soil. The masonry surrounding the plant and the rock mulch if a type of marble, may be leaching limestone in the soil and raising the pH. The pH can be adjusted to a certain extent with soil supplements, though gradually. A nutrient deficiency does not correct itself quickly, nor do all added nutrients replenish what was lost out of existing foliage; sometimes, only new growth shows improvement due to how nutrients are moved through the plant's tissues. It can take months for a pH change.
Second, if the plant's roots are in poor health, they will not function properly to be able to absorb needed nutrients. Root decline in rhododendron is often tied to overwatering or poor drainage. In that case, even ideal soil pH and nutrient levels will not improve leaf symptoms of deficiency until healthy roots can regrow. If your plant has been growing and blooming normally, with no excessive leaf shedding or branch dieback, then the root system is probably in good shape. Check the drainage in the area and make sure there are no downspouts dumping water in the root zones.
At this point, a soil test is the only way to determine the pH and nutrient deficiencies. It will let you know if the pH is too high. Lab tests are more accurate and thorough than at-home kits. This page discusses the testing process, lists area labs, and discusses pH changes. Results will give you pH and nutrient deficiencies. https://extension.umd.edu/resource/soil-testing-and-soil-testing-labs
Here is more on growing rhododendrons. Scroll down to leaf chlorosis and yellowing leaves. https://extension.umd.edu/resource/azaleas-and-rhododendrons-identify-and-manage-problems
In the future you may want to consider planting a native shrub or ornamental grass that matches the site conditions and planning for mature height and width.
Marian
The yellow color may be due to an improper pH, and/or some possible root damage. Rhododendrons are woodland plants. They like cool, moist, well drained acidic soils and grow best in morning sun and afternoon shade. This does not look like a good location for a woodland plant.
Rhododendrons require acidic soil to thrive; a pH range of 4.5 to 6.0 is considered ideal for them. If the soil acidity (pH) is not in the range preferred by that plant species, the roots will not be able to access all of the nutrients they need, even if plentiful in the soil. The masonry surrounding the plant and the rock mulch if a type of marble, may be leaching limestone in the soil and raising the pH. The pH can be adjusted to a certain extent with soil supplements, though gradually. A nutrient deficiency does not correct itself quickly, nor do all added nutrients replenish what was lost out of existing foliage; sometimes, only new growth shows improvement due to how nutrients are moved through the plant's tissues. It can take months for a pH change.
Second, if the plant's roots are in poor health, they will not function properly to be able to absorb needed nutrients. Root decline in rhododendron is often tied to overwatering or poor drainage. In that case, even ideal soil pH and nutrient levels will not improve leaf symptoms of deficiency until healthy roots can regrow. If your plant has been growing and blooming normally, with no excessive leaf shedding or branch dieback, then the root system is probably in good shape. Check the drainage in the area and make sure there are no downspouts dumping water in the root zones.
At this point, a soil test is the only way to determine the pH and nutrient deficiencies. It will let you know if the pH is too high. Lab tests are more accurate and thorough than at-home kits. This page discusses the testing process, lists area labs, and discusses pH changes. Results will give you pH and nutrient deficiencies. https://extension.umd.edu/resource/soil-testing-and-soil-testing-labs
Here is more on growing rhododendrons. Scroll down to leaf chlorosis and yellowing leaves. https://extension.umd.edu/resource/azaleas-and-rhododendrons-identify-and-manage-problems
In the future you may want to consider planting a native shrub or ornamental grass that matches the site conditions and planning for mature height and width.
Marian
