bump.

GP: I was hoping someone knew the answer...that why I did not respond earlier. I have never had that happen to mine, but when I googled it last week looking for an answer, what I read sounded like maybe fungal issues. Have you seen any leaf issues? HH need moist soil and I have mine in partial.shade. This year I noticed a distinct decline in their robustness but the flowers seemed to open just fine.

Hardy hibiscus can drop flowers for lots of reasons, with very hot weather being one of them. They also are happier with weather that stays consistently the same, whether it is consistently hot and dry or cooler and wetter. It seems like mine goes into a stall when the weather abruptly changes from one pattern to another.

Thrips or gall midges would have been my first guess but you looked for thrips and didn't see any (and I always have ants on mine and that doesn't seem to impede flowering). I know y'all had a good, cooler and wetter period earlier in the summer and then the weather sort of abruptly changed and y'all got hotter and drier, so I'll guess the plant didn't like the temperature change. That's just a guess though.

I have hardy hibiscus in barely-amended clay soil that sometimes holds too much water and it doesn't seem to bother the hibiscus plants at all, though that is not the same as having them close to an air conditioner drain. However, I've grown swamp hibiscus near the air conditioner drain for years....or, at least, I did until 2011. Even the water from the air conditioner drain didn't keep them alive through that summer. The swamp hibiscus I had in the formerly swampy land and on the edge of the used-to-be pond that doesn't hold water any more also died in 2011. Drought can kill them, but wet soil never has---not even when we had 12.98" of rain in one day in April 2009 and they stayed in that extra-wet soil for a couple of months before it finally dried out.

My hardy hibiscus in the flower border around the veggie garden bloomed beautifully in July, and I think that's because of all the rain that fell in our area in May and June. It has just sat there and stalled since then, but we're in severe drought and it likely just hasn't had enough water to bloom. I've watered the garden enough to keep the perennials alive, but not enough (apparently) to keep them happy and blooming.

If yours is in sandy soil that drains very well, it may just need to be fed. Hardy hibiscus can need an occasional feeding in sandy soils where nutrients leach out of the soil during periods of lots of rain. It could be all that rain central OK had earlier this year leached out the nutrients if the plant is in sandy soil. I've never had to feed mine, but it is in clay which is a whole different situation. Our clay is mineral-rich and very fertile so I don't feed the hibiscus that grows in that clay.

I'm not sure what the exact issue is with yours, but thought I'd throw those ideas into the mix.

Dawn

Last night I pulled off an unopened flower, pretty and red that was just starting to turn dark on the tips like all the others and got a white paper towel, opened it up and all that fell out was lots of pollen. No thrips. I'd done some research and read to do that online, this was the only cause of this problem I ran across in diagnosing symptoms.

It must be too much water from that drainpipe. The leaves are very healthy, the color is good, that plant looks great, about 3' x 3' nice and bushy with lots of buds. The flowers look nice and red like they are going to open up fully but just turn black. They don't fall off, they are well connected and you have to really tug to get the blackened flower off. No leaf drop or yellowing. The soil is nice good, deep garden soil thats been amended through the years with compost and sand.

I plan to move it when its dormant. I think maybe a couple feet further from the drain will possibly solve it. I chose the spot because it stays moist but I think the plant is too close. Get this, there is a low growing Texas Opuntia macrocentra cactus and a clump of iceplant planted right in front of it that are fine. The water drains out a hole in the base of the wall but it is really wet right by the wall. Its a west side exposure so it gets full afternoon sun.

Thanks for the comments. I babied this plant from a seedling all winter and its just a bummer.

Up until about 3-yrs ago, I had a magnificent dinner plate size hardy hibiscus on the East side of my house for 9-yrs. The soil wasn't anything special, but it was slightly elevated. In all the years I had it the only time I ever watered it was in drought conditions. Even then, maybe just once or twice a week. It came back every year, even the few times I forgot to cut it back after the first frost. What did it in, I have no clue....and I sure miss that beauty!

You might try the hibiscus forum, being sure to identify your climate zn. They are fairly active but seem to be in colder or warmer zones, so for best info probably give as much info as you feel comfortable with posting. Good luck