Oh, one more thing - did this happen to mostly the outer leaves?

It happens especially with newly planted hydrangeas in the summer. The combination of heat and not being established causes it to happen. I’d water everyday the temperature is 80 or Above this season.

Like the others implied, planting a hydrangeas in the summer months is ok but can be stressful on the plant. Until now, the shrub has been coddled in the greenhouse and at the plant nursery where they can control temperatures, control sunlight, give it water & food as needed. But ouch, now it is outside and bombarded by sunlight, temperatures and winds outside of the norm that it is used to. And the worst of summer is yet to come.

So observe how the plant's leaves and bloom respond. When the edges begin to brown out and the browning moves inwards, the plant is not getting enough water. The trick with a 3 weeks old plant however is that its root system is unable to absorb water as fast as the leaves loose moisture because it is windy, because it is getting too much sun or because of heat stress.

As a result, the shrub wilts the leaves or even start to brown out if the conditions persist. Luckily, the plants should get over these wilting episodes on their own by the morning... provided that the soil is kept uniformly moist with no periods of dry, wet, dry again, etc.

So begin by ratcheting up the watering levels to summer levels. Try to water deeply such that the soil is kept moist all the way down to 8" deep. The amt of water need will vary based on what type of soil you have and such but start trying 1 o 1.5 gallons of water per hydrangea per watering. Water only the soil, early in the mornings... like 6-8am, from the root ball outwards. The roots are currently occupying the space of the pot only so this is where you need to concentrate... and then a little further beyond. Just do not forget to water the important root ball.

The consistent lack of moisture causes the leaves to brown out from the edges inwards. Once they partly brown out, they stay partly brown out. I would leave them alone. If they fully brown out, I would still leave them since all the leaves will "somewhat soon" (in the Fall) dry out as the shrub goes dormant. If they bug you though, cut the petiole string that connects a leaf to the stem.

Hydrangea mopheads will soo start developing invisible flower buds at the ends of the stems, whether that be rebloomer flower buds on new growth or non-rebloomers that bloom only once so do not cut the ends of the stems. By the end of May 2019, you can cut any dried out looking stems that have not leafed out in Spring 2019.

To minimize the chances of moisture problems, use the finger method (or your moisture meter): insert a finger to a depth of 4" and water if the soil feels dry or almost dr (or water if the moisture levels get dry or almost dry on the meter). Do this early, 6-8am, for 2-3 weeks every day. Write a note on a wall calendar on days in which you had to water. After 2-3 weeks, review the notes and see about how often you had to water. Set the drip irrigation or sprinkler to water at 6-8am or so and provide the plant with 1 to 1.5 gallons of water. If the temps change by 10-15F degrees then use the finger method again.

To control aphids, you can use a hard power wash with a hose (best and cheapest solution), an insecticidal soap or an insecticide spray. However, if it is hot, be aware that some insecticidal oils/soaps should not be used above some temperatures so use a hose and hit the leaves from underneath too. Ants, which typically like to "follow" aphids will -if present-, go away in a while. Check to see if you need to also hose other shrubs too.

Luis

Thanks so much for the quick and detailed advice---I definitely really appreciate it! @cutting edge plants yes, most of the browning is outer and concentrated the most in the areas no directly under the tree. It's started to creep in but only a little bit so far. I realize I forgot to mention location —northern nj, in case that affects any input. My initial hesitation for watering it more was trying to not overwater it but by the information here, it's clear it needs more.

Enjoy the new "baby". Its "temper tantrums", due to moisture, occur or are most pronounced when it is either windy or/and north of 85F. So on the hottest days or windy days of this summer, ck it out to see how it is doing.

Or would it be more correct to say “temperature tantrums”

Hee, hee, hee!

Tantrums indeed! It's been overcast with lower temperatures yesterday/today and it's already looking much better. I now know what to expect when temperatures go up again. This forum has been so helpful. Thank you all again!

I had the same problem with the brown, curling leaves. I live in Florida and it is SUPER HOT and SUNNY or POURING RAIN. I received a beautiful hydrangea as a gift. I left it in my front garden where it mostly gets morning sun and dappled sun later on. The flowers died (which I didn't think anything of, since flowers bloom then die). But a few days later I saw that the leaves started to brown and curl in like that. I gave it a solid drink that day and the next day without improvement. I took it out back where it's shadier and pulled off the worst of the dead leaves. I saw that the plant is still growing new leaves under all the leaves so it wasn't in too bad shape. The last two nights it has POURED FOR HOURS each night. Any advice on making sure the plant can handle the hot sun AND the crazy rains?

Rain: It probably depends on the type of soil one has and how well it drains. For example: If your soil is sandy, it drains very, very well so these heavy rains are not an issue. Several hours of rain should not be an issue but it depends on how much rain fell, soil type, etc.

Hot sun: provide shade by 10-11am for macrophyllas and shade in the afternoon and shade at night.

Consider growing in containers if the soil drains too well, not well or is too salty.

Water: insert a finger into the soil to a depth of 4" (the depth of most hydrangea roots) and water as soon as the soil feels dry or almost dry.

Wind: hydrangeas tend to wilt when they get heat stressed and that includes when times when it is windy so look for planing locations or pot locations that are not excessively windy.

Flowers: you can deadhead the spent flowers at any time.