Ask a Question forum→Hydrangeas yellowing, dark young leaves with curl

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Connecticut
Ukgoffee
May 31, 2020 10:09 AM CST
We have grown hydrangeas around our patio for 20 years. The end bushes are original. The smaller in between are 3 years old. We live in CT. Leaves are yellowing on all hydrangeas around the patio and across the yard. Some new leaves are dark green and have leaf curl. No pests are evident. We mulch with sweet peet and two seasons ago the flowers were pink from the mulch. We added aluminum sulfate and the PH is currently 5.5. We had some black spot fungus last year but other than that, the only challenge has been some cold winters. We added hollytone this weekend as we would any Spring. Any ideas?

Name: Luis
Hurst, TX, U.S.A. (Zone 8a)
Dog Lover Region: Texas Salvias Roses Hibiscus Plumerias
luis_pr
May 31, 2020 12:22 PM CST
Welcome to NGA, Ukgofee. They may be starting to have some heat stress. Hydrangeas normally start getting heat stressed when temperatures are close to 85F and-or conditions are very windy (which dries out the area in the top 4", where the roots typically reside). The leaf edges may curl at first. Some foliage may yellow out. Paniculatas are famous for "showing their feet" under heat stress. It is also possible that some leaf damage from late frost in May 9, 10, 14 may also now appear. It crops up earlier for me down in Texas and looks like a nice stem whose tip suddenly browns out a little (several inches only). Be ready to ramp up waterings to Summer Levels if temps stay warm or if conditions remain windy. Maintain 2-4" of mulch. Watch out for signs of leaves browning from the edges inwards, which can mean they need more water.

Also be on the lookout for pests arriving soon in the northeast. Leaftier (leaf curling may be due to this pest too), scale and mealy bugs show up at the end of May and in June.

ust one application of fertilizer should be enough for the whole year although it would be ok to add some "minor" fertilizers like coffee grounds if you want. But do stop all fertilizing when it is terribly hot or three months before your average date of first frost minus two weeks (maybe around Oct 1st for you, more or less). I try not to always add fertilizers and aluminum sulfate at the same time. That is because some fertilizers for ericaceous plants and the aluminum sulfate, both, contain sulfur and too much can bother the roots. So, I either apply them two weeks apart or I use an organic fertilizer like cottonseed meal, organic compost or composted manure.

Do you have any pictures you can share? What city are you located in?
[Last edited by luis_pr - May 31, 2020 12:28 PM (+)]
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Connecticut
Ukgoffee
May 31, 2020 2:37 PM CST
I uploaded about 8 pics. Not sure why they aren't here. We just reached 82 for the first time this year.
I'm in Westport CT.
We are less than a mile from the Sound and our Spring has been quite cool. Our peonies just bloomed for the first time today.
Thanks for the help -

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[Last edited by Ukgoffee - May 31, 2020 2:49 PM (+)]
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Name: Luis
Hurst, TX, U.S.A. (Zone 8a)
Dog Lover Region: Texas Salvias Roses Hibiscus Plumerias
luis_pr
May 31, 2020 3:52 PM CST
Nothing bad in Pictures 1 and 2. I think you had a little damage from a late frost in Picture 3. The leaf damage sometimes resembles what you see in the bottom center of Picture 3 immediately above. The browning is part of it but sometimes you see this lighter damage that resembles as if something slightly scrapped small pieces of the leaves. See the topmost leaf in that bunch.

At first, the leaf damage may have odd colors like shades of purples, red, oranges. Then it progresses to brown. Sometimes an opportunistic fungal infection can set in on the leaf and add a twist to it all. There are other times when the damage is different and the leaf turns an ugly, almost blackish, dark green color.

Those open flower buds are a good indication of how the plant "feels". If it were being bothered by something, the flower buds would be the first thing to go. Since the flower buds have not been prematurely aborted, there are no "red alerts" to worry about.

While temps have been cool, winds may have been active as you are near the coast. I did not see temps going into the 85F range. The closest was 81F. I do not see any temps >= 85F in the near term either. I did see a freezing low (32F) on May 9th and maybe some frost on May 10, 13 and 14 with lows of 34F. Any of those would have caused some leaf damage. Luckily, it was a brief drip and then temps went much above freezing during the day.
Connecticut
Ukgoffee
Jun 2, 2020 10:41 AM CST
Thanks Luis - I appreciate your help. The yellow is more pronounced this morning. This is normal? I just don't want to be too late if something needs to be done to help.
Best
Eric

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Name: Luis
Hurst, TX, U.S.A. (Zone 8a)
Dog Lover Region: Texas Salvias Roses Hibiscus Plumerias
luis_pr
Jun 2, 2020 1:33 PM CST
Is your soil sandy?
Connecticut
Ukgoffee
Jun 2, 2020 9:45 PM CST
Thanks Luis - I appreciate your help. The yellow is more pronounced this morning. This is normal? I just don't want to be too late if something needs to be done to help.
Best
Eric

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Connecticut
Ukgoffee
Jun 2, 2020 9:58 PM CST
Loamy dark soil - but there's a fair number of small stones in the soil. We are at the top of an old granite quarry. I haven't turned on the sprinklers yet so I thought they might be dry, but I raked the mulch back when I used the hollytone and the soil was moist, not damp.
Name: Luis
Hurst, TX, U.S.A. (Zone 8a)
Dog Lover Region: Texas Salvias Roses Hibiscus Plumerias
luis_pr
Jun 3, 2020 12:04 AM CST
Rocky soil disturbs the tiny fibrous roots that typically grow in the top 4" of the soil. Makes it hard to "grow". Are the rocks "sharing space" with the hydrangea roots or were they somehow removed when you planted the shrubs? I have not planted near a quarry before. what kind of quarry was it or is it(curiosity)? Limestone? Have you ever done a formal soil test? Is your soil loam or sandy loam? Have you checked the soil pH level either with a formal soil test or with one of those soil pH kits sold at plant nurseries?
[Last edited by luis_pr - Jun 3, 2020 12:35 AM (+)]
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Connecticut
Ukgoffee
Jun 4, 2020 7:28 AM CST
Thanks Luis - it was a granite quarry. This bed has been planted and mulched for 20 years. I could plant a 3 gallon container with a hand trowel pretty easily. The smaller rocks start about 12" down. We prefer blue hyndrangeas. When they turned pink in 2018, I tested the soil with a recently calibrated Precision PH meter that I use on my aquariums and it was 6.4/6.5 (I am also a monster fish keeper and my tanks are pretty hi-tech). I added aluminum sulfate in 2018. The colors were pink, purple and some blue in 2019 so I added aluminum sulfate again. There are two hydrangeas in another part of the garden that I did not add aluminum sulfate to and they also appear to be yellowing. Our gardeners applied a horticultural oil to our shrubs in March and an insecticide in May. I am trying to find out from them what it was specifically.
Name: Luis
Hurst, TX, U.S.A. (Zone 8a)
Dog Lover Region: Texas Salvias Roses Hibiscus Plumerias
luis_pr
Jun 4, 2020 10:23 AM CST
There are some hydrangeas that produce mixed color blooms (blues, purples, pinks) naturally. One of the most advertised ones is Bloomstruck from the Endless Summer Collection. I am not sure if acidifying one of those guys will produce all blues at some point or not. You may need to get the soil pH into the mid to upper 5's. Just a comment. Let me know if continued acidification down to the 5's helps should you ever try that. I am just curious because I asked the Endless Summer folks about Bloomstruck and they replied that in higly alkaline or highly acidic soils, it may not have as many mixed colors. When I pressed for more details, I got silence so maybe they do not want to "spill the beans".

I do not have one like Bloomstruck; mine are usually just one color (white or pink). My 7.6 acidic soil is typically amended in Spring to prevent signs of chlorosis. Hydrangeas in good composted soils tolerate the alkalinity with this but, should they 'email me' about having chlorosis ;o)) in early Fall, I will take a look and amend the soil again.

There is only one unnamed lacecap rebloomer that gets lots of amendments (aluminum sulfate) though. It is a colored hydrangea that is part of "an experiment".... meaning, I am trying to produce purple flowers. Purples are hard to produce because they require a narrow soil pH range and I try to get the soil pH from slightly acidic to neutral. And of course, I usually get purples by amending the soil. Some years, I get a weird purple that looks great in the late afternoon hours. But eh, this is nothing I could replicate well, mind you. This is as experimental as the recipes that I use when I cook. A pinch of this, and so forth. Hee, hee, hee.

What types of hydrangeas are the ones that are yellowing and how much? Do you have pictures of those? Take one of the shrub so I can get a feel of how widespread is the yellowing, then close ups of some yellow leaves. Summer is here almost so this could be sort-of ok.

Were you having pests that needed taking care of in May and again in May? Or was this done as a preventative due to insect problems on prior years around those dates?
Connecticut
Ukgoffee
Jun 7, 2020 6:09 PM CST
Loamy dark soil - but there's a fair number of small stones in the soil. We are at the top of an old granite quarry. I haven't turned on the sprinklers yet so I thought they might be dry, but I raked the mulch back when I used the hollytone and the soil was moist, not damp.

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