How odd, ditas. I have not seen that reaction here on paniculatas, arborescens or macs & we have been in the heat wave with 100+ degrees temps since early June. The only reactions that I have seen are leaves browning from the edges inwards or leaves wilting.

My known causes of yellow leaves does not include anything that applies in your case: sunscorch, nitrogen deficiency, iron chlorosis, mites. Especially because the damage is limited to internal leaves only. Can you check for pests such as mites anyways? The problem with blaming mites is that they would not just affect the internal leaves only.

Can you post or send me a picture(s)?

Thank you Luis - i feel your concern! I just woke up one AM & first saw Kyushu tree full of internal yellowing leaves & got concerned due to an earlier ? about borer prob (treated in Spring) I quickly did rounds to all my 14 H ps & found similar shows of internal leaf-yellowing.

At this same time all the buds are starting to flash in different stages - I figured the simultaneous timing of events - heat wave + dry days/mighty sun + clusters opening. Perhaps the watering was not enough do you suppose?

Here is a link that might be useful: Paniculatas- yellowing leaves

Please clic on pix to view better ~ thanks!

I touched base with someone at the University of Arkansas that I know and he said that yes, it probably is heat stress. He explained that when photosynthesis of those inner/older leaves does not produce as much food as it once did (due to the stress of one type or another) then the older leaves cannot produce enough sugars/food to support themselves and the plant drops them. He said azaleas and rhododendrons do the same thing when stressed.

Unfortunately, that would mean nothing much can be done until the heat wave is over. I wonder if applying liquid seaweed, a weak fertilizer and very good foliar feed, directly on the inner/older leaves very early in the mornings would help. Most plants that like acidic soils respond to that: azaleas, gardenias, rhododendrons, roses, etc. Hydrangeas should as well but I would not make a habit of it because it can trigger fungal infections when the temps go down and rains arrive in the Fall. Continue extra waterings though.

WOW Luis - you never fail to amaze me! Thank you for the reassurance & the inquiries you took time for. The K Tree & all the H Ps look great otherwise, the reason I put my ? the way I did!

The Macs in more sun than others did scorch understandably & wilted more sadly this season but perked back up by evening. My Serratas seem to be holding well except the early bloomers (Blue Frost & MyM) they seem to have matured sooner!

It makes sense about the younger & newly planted, but QF is amazing ~ very negligible yellowing perhaps due to the fact that the matured clusters no longer needed as much energy support! I pruned LL down to 18" in Apr & behaves like the young ones.

Many thanks again, Luis!

Yellowing of interior leaves pretty much a classic symptom of water shortage which occurred within the past 7-10 days. Occurs in many plants, many more than hydrangeas, rhodies and azaleas.

Shortage may have been mild and/or very brief.

Beyond that, *never* fertilize a plant during heat stress. Effect is that of "salt burn" -- no, not sodium salt -- which results from excess fertilizer.

Don't discount that they could have too many cycles of water in combo with the heat.

I have younger and older paniculatas that yellow and drop leaves and I'm convinced its the amount of water. I've watched them closely and thats my only conclusion.

Thanks for your input whaas, & I agree! I get some yellowing leaves each year during a heat-wave spells but never this concerning because of the amount of yellowing leaves as you may have seen in the pix I posted.

Last season we had a longer & uninterrupted heat-wave but preceded by a long spell of uninterrupted rain that got the soil somewhat boggy even. The problem then was steam-cooking others but not the Hs. This year it is scorching ~ for the others (my petiolaris & Macs) as the amount of rain was less.

Last Winter's snow was also less & I neglected to water the Divas that required old cane protection ~ resulting to more dead old canes = less blooms (sigh) but all of them are making up by tremendous growth spurts! I'm looking into more challenging over-wintering chores w/ the sizes of these Divas & they are still flexing their growth-muscles!

Hopefully these heat lets up soon for all of us ~ today's extended forecast is promising for us!

Underneath my tardiva looks like yours. It's also blooming early. I have taken to giving it a little supplemental watering since we have not had much rain this season.

Hello, ditas. Just checking. How are your panics doing?

Thanks for asking Luis ~ every single one proceeded to do great after some of their hair fell off ~ still looked gorgeous as their blossoms filled up.

You know QF ~ I guess due to her early flashing time ~ long before heat wave came down on us, hardly had internal foliage-yellowing unlike the others. I guess the energy & water required at certain stages make a big difference!

Also interesting is the fact that since year 1 (2005) both my Tardivas have always bloomed in July ~ & now are both starting their color changes to pink!

My experiment on LL worked ~ pruned all canes, really hard to 18" in early April has behaved better w/ smaller bloom clusters & still grew to be a decent 5' tall & pleasing w/ the base raised w/ stakes & nylon hose to 2' hgt help prevent splaying/scorching on hot river rocks floor!

Again thanks for asking ~ a very good season for all H ps here!!!

Hi Luis ~ I spoke too soon re: Little Lamb experiment remedy ~ after a big storm LL looked no better than how he did last season. The canes simply couldn't handle the H2O filled bloom-clusters, despite smaller sizes this time ~ once again I was too crushed to take a pic of the disappointing sight!

It took a couple of days to completely dry up, for me to bundle up w/ nylon hose all the splayed canes, to a decent look! Ughhh!

Unfortunately I can't give up on him ~ will perhaps just replace all the stakes to taller ones & knowing what I now know, bring the wires around much higher as well. I'll still hard prune in early Spring!!!

I wonder what George (Ego45) decided to do w/ his LL? I'll review what Marshall (Mrgpag) did w/ the 25+ he planted around the flagpole in an OH library!