Sounds like transplant shock, not dying though. If the blooms browned so quickly, there may have been numerous reasons: insufficient water, too much heat stress, competition from tree roots for the water, drainage works too well due to sand, etc.

In year 1, I would not worry about the blooms if the leaves remain green; continue TLC now that summer is here. Water the plant if it appears wilted in the morning, And remember to increase the amount of water per watering per plant now. A moisture meter or the finger method can help you determine when to water regardless of the wilting. Insert a finger into the surrounding soil to a depth of 4" and water if it isis dry. If it is an extreme wilting episode, water the soil immediately from the root ball/crown/base outwards. If just wilted, water only if the soil is dry. Wind can also dry them out too quickly so evaluate if the area is windy.

I have some whose blooms opened early and now with temps in the 90s-100s, the blooms are not looking so great either. They may turn brown either from opening early or from the "hot everything", etc. ;o(

Not a happy camper. Looks like it has been getting a lot of heat and afternoon sun... no thanks to the neighbor. Transplant shock setting in as it cannot handle things this sunny and hot with a small root system. You can (short term) give it artificial shade by using outside chairs, umbrellas or something you can construct or prepare. A temporary measure, of course.

It is now getting too much afternoon sun due to your neighbor's pruning of the trees. So, concentrate on quick & fast things to alleviate the problem... short term wise. Then transplant it out of the way of all this sun/heat; later on, concentrate on looking for a new location but transplant it there in the Fall. Now is not a good time to transplant a hydrangea to a new location in our hot summer zones. It is ok to put it in a pot & then place the pot in shade though.

1. Start by keeping it well watered and by doing something that gives it shade immediately. Umbrellas, chairs, anything that blocks the sun...

Consider the blooms. When the blooms collapse like this, I try to salvage the blooms by watering but, if they do not perk up and they remain pointing downwards no matter what, well, then forget them... cut the petiole that links the bloom to the stem. Basically, I let the water that used to go to the blooms and make it go to the remaining leaves. It happens to me when the shrubs are new/small and get a bad heat spell during the summer. Bottom line, sometimes watering fixes the blooms but, sometimes it does not help; and if it does not help, I then cut the blooms off.

Next, consider transplanting to a place where there is morning sun, afternoon/evening shade (or dappled sun) in the summer months. But put the shrub in a pot/container now and replant in the Fall. It is too hot now to plant a new hydrangea or transplant one. So, put it in a pot again and keep the pot in full but bright shade until this Fall.

While waiting for Fall to arrive, observe which locations have morning sun only during the summer months. Then, move it there when it has gone completely dormant. Note: keep the pot near a place where you will see them often so you will not forget to water/fertilize the plant. Add computer/electronic reminders if you think you may forget to water the shrub while it is in the pots.

You can prune the leaves that turn all brown when they turn all brown. Leave them all there until then. You may even loose a few stems but no panic. Sometimes in the summer, I have lost all stems but, in Spring, I get new ones since the trick is not to loose the roots.

Luis

“I left for a few days and came home to this!”

Hydrangeas need even moisture, and that is difficult to create when planting under thirsty trees if you aren’t checking soil moisture daily. If it were my situation, I would set up watering on a timer when I was away.

In this case since the neighbor’s tree removal changed growing conditions and they are new plants, rig shades for them now as Luis suggested, remove all flowers, and plan to move them in the fall when the weather cools. If the new setting also has tree roots, set up drip irrigation. My preference is a leaky hose since it’s easy and has IME worked well. You can place it under the mulch and leave it there year round.

Careful if you have pests around. I got a soaker hose for my hydrangeas and on the first night, something took a bite at night and almost cut it in two. Grrr, I was so mad. I was only able to run a test during the day I bought it before something broke it. What timing! No real good idea what it could have been. I ruled out the dogs though. ;0)

Mosquito spray? Hard to tell without looking what chemical (what active ingredient) was used, how much, if they directly sprayed it on hydrangeas, what were the temperatures and humidity on the spray day and what effect the active ingredient has on hydrangeas. My city is doing spraying for mosquitoes but it has never had any impact on hydrangeas before. Of course they spray from an airplane or trucks and I suspect you used a landscape company. So most likely, they use different chemicals.

Can you ask them what did they use, where did they spray (they probably will not remember) and then look up info on the active ingredient? See if the chemical was directly applied and if there was chance it "sat" on the leaves for a long time with hot temps?

But today, I myself have one plant showing leaf signs similar to your second photo (bottom left corner) and at least in my case, it would be sunscorch because the shrub above it has had some parts that dried out so the hydrangea is getting more direct sun. It is located near the front of the house, where it would be difficult to get any insecticides. I am going to have to move mine as it now gets sun at lunch time and evening time.

Can you post pictures of the other hydrangeas (first showing the shrub and its location and then some close ups of the lesions)? When (hours) do they have direct sun? And ck with the landscape company and post their comments.