Many brown spots on rhododendron leaves - Ask Extension
What might be causing the brown spots on the leaves of this rhododendron? Seems to be mostly along the edges and mostly on older leaves. This Rhodie g...
Knowledgebase
Many brown spots on rhododendron leaves #628333
Asked April 28, 2020, 6:43 AM EDT
What might be causing the brown spots on the leaves of this rhododendron? Seems to be mostly along the edges and mostly on older leaves. This Rhodie gets more sun than it used to due to the removal of a large maple tree nearby three years ago.
Clackamas County Oregon
Expert Response
Thank you for the images. They reveal that the rhododendron ran short of water. since the tree was removed. Considering that it was previously shaded, but now it's in full sun, its condition is quite good.
In general, rhododendrons need supplemental water during our dry months. Once every 3 to 4 weeks generally works well.The rootzone should be moist to at least 8-inches deep. Use a trowel to determine if that is so.
If you haven't watered the shrub yet this year, it's more than likely the soil is quite dry. If so, it's wise to thoroughly moisten the entire rootzone so that the shrub will thrive though the warmer days which are certain to arrive any day now.
An organic mulch on the soil surface would also be helpful in slowing evaporation of irrigation water. Start the mulch 6 inches away from the trunk, then extend it to a foot or so beyond the dripline. Useful are a 2-inch deep layer of wood chips or 3 inches of bark dust.
And, if this season turns out to be a sizzler, consider rigging temporary shade for the shrub.
