What causes my hibiscus leaves to turn yellow?

I have 2 Florida Sunsets and this one is always complaining about the heat, and wanting more water, and is such a brat that sometimes I want to just tear it out and throw it away! The other one is almost as bad. Maybe I should move them to filtered sun. Or maybe to the backyard where they would only get morning sun and not much of it.

With temps around 100 every day (they get full pm sun) some days they wilt and I have to spray them to cool them off. It works, but every time they get stressed out for any reason they drop all their buds. So I seldom get to see a flower actually blooming.

I would consider moving them someplace a bit less sunny. It's not a great idea to move them in the heat of summer though, wait until cooler weather. If you can rig up some shade for them for the remainder of the summer that might help them be happier until fall comes around and you can move them. Mine do better when they get some shade in the PM, and we only have occasional 100+ temps not every day like you do. They do need some sun to bloom well so the area with just a little AM sun may not be enough, but definitely if there's a way you can get them some shade during the heat of the day they should spend less time being stressed and more time blooming. In a hot climate like yours they're always going to be pretty thirsty, and I've found the trick to keeping them happy is to keep the moisture level fairly consistent--alternately letting them dry out too much and then drowning them with water is a sure way to get lots of yellowing leaves, dropping buds, etc.

ecrane3--thanks so much for the advice! I'll do as you suggest and give them some shade and not so much afternoon sun as they get now. There is a place for one of them in the back yard where I have a variegated ginger that is getting too much sun and not looking good. I'm going to move that to a shadier place, and that should be just enough sun for the hibiscus.

You are right--this is not the time of year to transplant them, not for them or for me! I am yearning for cool weather; I have so many things I want to do, but it's way too hot for anything more than watering. The back yard and half of the front now have an irrigation drip system that saves me time and blistering heat. So when cool weather comes I'm going to finish that.

Thanks again for your suggestions!

Jo

I have a different opinion --it's likely the root structures are for some reason not developed adequately to move water from deep enough in your soil. Either the roots have never grown deep enough, or the deeper soil is not taking in or holding water through the hot part of your days, or a combination of these two. So the only place the plants can get their water is from the first couple inches, which dries out quickly. You may be applying enough water every day, but it's probably either running off/away from deeper roots that can draw it up, OR, the water's reaching deeper soil, but for some reason your roots aren't able to get it up from there.

I think you may be misinterpreting what the "cooling" spray is actually doing. My hunch, consistent with the theory above, is that the water you're spraying on them to "cool" them is actually dripping off the leaves (minor cooling effect, yes) down to the topmost soil where your plants have their only good drinkin' roots.

Before you erect a shade structure, I'd suggest you try this approach, as an experiment:
-beneath the drip line of one plant, mulch heavily, a good 4 inches thick.
-beneath the other, no mulch
- pour the same, generous amount of water on each plant at the same time in the morning (use a couple full watering cans, to excess, for this purpose)
- don't water any more until you see one or both plants start to wilt as you've described.
- if the mulched plant doesn't wilt, or wilts only much later than the other, I think this would prove my theory.

If my theory is not right...frankly that wouldn't be terribly surprising.

But if it is, the simple solution would then be to mulch both plants heavily, water early and heavily, more as needed.

The more permanent solution would be to dig the plants up, enlarge and deepen the holes, a lot; fill the bottom with nice, fresh, soil (ideally use one tapla's recipes, but make sure you have a good proportion of water-holding soil component at least a foot deep); remove any hard soil from the root balls, then replant them, feed a day or two later.

Hope this helps.

This message was edited Aug 15, 2009 10:06 PM

gee, I didn't think they liked to have their roots wet for any amount of time, certainly not long enough to add any moisture retaining elements to the soil mixture. I'm curious to see how the experiment turns out. Please post what you find out!

Hibs need what all plants need --the right mix of root aeration and access to moisture.

The positive response to a "cooling" spray (which, I theorize, may succeed only because the spray drips onto shallow roots) suggests access to moisture may be constrained. It may be that the roots haven't been able to grow deep enough to reach a more consistent moisture source, or that water is not consistently reaching or remaining accessible to those roots. Replanting in a deeper, larger hole with soil mix that can provide both moisture and aeration could help the plant right away, and foster better root growth to take further advantage of the new set up.

Thanks for your input--I am going to try JPlunket's suggestion, and if that doesn't prove out, then I'll try the second suggestion, and if that doesnt work I will re-plant them when cool weather comes.

As to the cooling spray: I mist them only, so there's not much dripping. Also mist drooping periwinkles and one time a large esperanza (they love the heat and never droop but that day was a blistering 110 heat index, and I should not have been outside at all!), and several other plants, and about 40 minutes later they had all perked up. This was the hottest time of the day.

Will let you know what happens. Today is a little cooler--temp 83, heat index 87. Maybe I can do it today.