When you say you applied neem oil a few times, how often was that?

Neem oil (or any other oil) can burn leaves, especially if it's applied on a sunny day. As the oily coating is exposed to sunlight, it will cook the delicate tissues below.

Thanks Jojo. I wonder if that’s it! I think the last time I applied it it was sunnier than I wanted. We went for a few weeks with rain almost every afternoon, so I sprayed around 3pm. There shouldn’t have been direct unfiltered sun anymore, but maybe it was enough sun to cook the leaves?

I would also explore the condition of the soil in that area. Oakleaf hydrangeas are notorious for developing root rot quickly when the soil remains too wet so it may be necessary to turn off the sprinkler or drip if it is raining a lot in clay soil. If you insert a finger into the soil and the soil feels wet, maybe try temporarily removing the mulch to help dry the top 4" of the soil a little; that is where most of the hydrangea roots are found. The leaves also have some leaf spots but I could not confirm if the problem was bacterial leaf spots or cercospora leaf spots. They are minor at this point though so to avoid more leaf spots, try to water only the soil, as best as you can, and not the leaves. If you use a sprinkler, try to water these plants around 6-8am so the leaves do not spend the night wet, something that can promote fungal diseases.

"I treated for Cercospora with an anti fungal, with almost no results. Then I thought it could be insects and I applied neem oil a few times, always following label instructions."

I would only urge you to always identify any problem to a certainty before applying anything. All too often I see knee jerk reactions "I sprayed this, then this, then..." and the treatments caused more damage than the original problem.

Between your local cooperative extension agent (always your best source of information since they are local) and sites like this getting a problem identified should be easy. That is always the first step.

You need to know exactly what you are dealing with before picking up a bottle of anything. Besides harming the plant it makes identifying the problem even more difficult because we don't know what issues occurred naturally and which are side effects of treatments.

Find your local cooperative extension agent and always check with them when anything odd is going on. You can call or email and you can send photos as well. You are paying for their services with your tax dollars so you may as well use them!

Compost amended clay soil sounds a bit like a recipe for disaster, specially if the compost was localized to the planting hole. Oakleaf hydrangeas need well drained soil and unless the amending was carried out over a very wide area, it will typically serve to impede or slow drainage rather than improve it. Like Luis, I'd suspect root rot.

The damage shown is not attributable to any insects nor any common foliar disease so no spraying of anything is/was going to help. cearbhaill's comments are very on point - you never want to treat a plant with sprays or pesticides until you know exactly what you are treating for. In any case, this is an issue with improper growing conditions, not a bug or disease.

btw, it was Salvador Dali that did the melted clocks, not Van Gogh :-)

Thank you all! First of all how embarrassing that I messed up the artists. Of course it's Dali! Thanks gardengal, I fixed my stupid mistake. I'm losing my mind, y'all!

Good points regarding my "treatment obsession". I'm starting to realize that this year it would have been cheaper to dig and toss the suffering plants, and plant new ones in the Fall, than buy all these expensive chemicals. You all are right!

Anyway, I think those saying root rot are right! Why did I not think about it? Pretty much every plant I have is yellowing or suffering one way or the other from this VERY wet summer - except for the grass and all the different hydrangeas (we have different panicle and french hydrangeas kinds and they are so gorgeous this year). But I forgot that oakleaf is a whole different thing! Surely that's it! I'll try to take the pictures and some leaves in a ziplock bag to the extension office, if I can take some time off during the week. But most likely it is wet feet.

We only have drip irrigation in our planting beds, and believe it or not we turned it on TWO times in the Spring this year and never more! Even the grass sprinklers we only used 4 times. I'm not exaggerating when I say it has been a wet summer.

It looks like I'll have to remove all my lavender, rosemary, oakleaf hydrangeas and gardenias from where they are and replace with more clay tolerant plants. Ugh, I wish the landscaper who planted them would have warned me. I guess this is an exceptionally rainy year, but still....

Any particular experience on good full sun shrubs for clay - please share! (I'll google and ask at the local nursery too, but not going to trust the landscaper alone this time).

Thank you all very much!

Don't feel bad about it. I lost an Oakleaf Hydrangea Alice several years ago due to too much rainfall during an El Nino Year. I had to get a landscape company work on the yard to prevent issues in the future..

I have lost a couple Okaleafs to root rot. One was about 20 years old & like Luis we had an El Nino year of flooding rain. I now try to find a slightly sloping area of the yard to plant them.

Before trashing the oak leaf, dig it up and inspect the roots. If they smell, then many call this root rot. If there are still some non stinky roots, wash off the clump and remove all the old dirt. Put it into a bucket of clean water and fill a container with decent potting soil. Decent - non organic and not too expensive! lol Make sure there are drainage holes in the container and fill with soil. Do not put anything in the bottom of the pot - just soil from the top to the bottom. Water to settle the soil and put in partial shade and let it recover. May seem like a lot of work, but you will learn many horticulture lessons on how to grow and maintain plants. When you put good soil in a hole in clay, the clay acts like a bowl and will keep the water from perking out of the bowl. What ever you do, don't fertilize or add any more chemicals!! Oakleaf hydrangeas are a bit fussy - but don't survive wet feet. The same goes for salvias, lavenders and other Mediterranean plants. The magic word is DRAINAGE! If you are not sure when planting, fill the hole with water and let it drain out. You should do this two times and if the water stands in the hole the second time, pick another spot. This method is as old as the hills and works every time! If you have your heart set on growing Mediterraneans, plant them on a 1 foot mound or more. Rocks and cement can be used to build the mound.