Rust colored leaves on hydrangeas

Asked September 30, 2017, 2:16 PM EDT

I have 2 hydrangea plants that get rust colored leaves. What can I do to stop it?

Marion County Oregon hydrangea rust

3 Responses

Thank you for your question about your rust-colored hydrangea. Could you please take a photo of the leaves with this problem, and attach it to a reply? Or, compare it to the photo I've attached, below, with rust on the underside of the leaves. If this is what it is, this is the explanation from a USDA article about hydrangea:

"Smooth hydrangea is susceptible to rust, which will appear on the back side of leaves as small, orange spots (see image at right). Rubbing the back of the leaves will release an orange dust which contains spores of the fungus. The disease is usually seen near the end of the growing season and rarely kills plants."

Rust is the common name for one of many types of fungus, whose spores are carried through the air. Here's a link to an OSU article about hydrangeas that offers some preventative methods. If the spots you see are not on the underside of the leaves, a close-up picture of the leaf on your plants will be necessary. Thanks!

Thanks I didn't have a picture before so I'm sending one now. There is nothing on the underside of the leaves.

Thanks for your photo. Do you know what cultivar your hydrangea is? Some hydrangeas naturally turn purple/brownish in the fall. Your hydrangea appears to be a Hydrangea macrophylla, or bigleaf hydrangea, one of 23 species listed here. (The leaves are not those of an oakleaf hydrangea, whose leaves regularly turn this color.) This source notes:

"Hydrangea leaves turning red usually happens when plants are growing in full sun and have experienced a dry spell. Cool weather — on either end of the growing season — can also trigger a red-purple color in leaves. The other issue could be a phosphorus shortage in soil, especially if leaves turn more purple than red. If you’re trying to shift flower color, you could be inadvertently tying up the phosphorus in the soil. Do a soil test to check soil pH and follow the recommendations of the test results to adjust soil pH. You may be advised to apply phosphorus to soil."

Although I see a hole in one, and some white spots on the other, either of which could be a sign of an insect infestation, I can't see either clearly enough to analyze that.

So, I'd suggest checking your soil pH (you can get an inexpensive kit to test for pH and soil nutrients (nitrogen, phosphorus and potassium) at your garden center.

Hope this is helpful. Good luck!