Here are feeding instructions from my favorite Hibiscus vendor. Theirs are completely drool worthy and they know how to grow them lol.

http://www.hiddenvalleyhibiscus.com/care/feeding.htm

Thanks, Sultry! I'll try anything at this point.

Interesting that they don't like too much phosphorous. Neither do brugs, it seems. You get a lot of blooms with high potassium fertilizers with brugs, but they'll lose all their leaves.

Yes, this article points out the need for potassium and to limit phosphorus. I have read this before. There are relatively inexpensive hibiscus fertilizers online.

I'm not seeing the potassium sulfate cheap (to me) online. $13/lb with shipping is not cheap. I'm someone who won't eat beef because it's too expensive, so imagine me paying that much for hibiscus food for one stubborn hibiscus! LOL Now, if I had 100 hibiscus, I could get 5 lbs. for $16, but at a tsp. per plant per month, for only two plants, that would last years!

I think I may just have to burn some wood for ashes or eat more bananas. LOL I read that all plant scraps have potassium, so I guess I'll have to start burying them around the hibiscus instead of in the courtyard. If my banana tree dies, I can chop that up and put pieces around the hibiscus too.

What I can't understand is why the one slap up next to it is blooming like mad all the time, and it isn't. I have to question whether potassium is the problem, unless the other bush is sucking up all the potassium and the red one is getting none, but that doesn't seem plausible.

Hibiscus are such weird plants.

FWIW, I use Maxicrop powdered seaweed extract as a foliar feed and soil drench. It's very high in potassium, and a little goes a long way. 1 tsp. makes 1 gallon of liquid.

I ordered mine from Peaceful Valley several years ago, and I've only used about 2/3 so far.

https://www.groworganic.com/maxicrop-kelp-extract-lb.html

And just like animals and people, I believe plants can vary in their vigor, even if they're the same variety. Plus you never know what's going on underground...

Carol, I can't even tell you how many people came into the garden centers I've worked at asking why a row of all the same shrubs, planted at the same time, had a couple dying and the rest doing well. The soil in FL can vary from one inch to another, and you never know what was in that spot once that left residual bacteria or insects.

They love magnesium. Try a lil epsom salt.

ericmd01 - I may as well. Both the red and the gold one next to it, which used to bloom like mad all the time, have stopped blooming entirely. Everything else in that bed is growing well, so I don't understand. It may not be getting enough sun, since the trees have grown and are now blocking a lot of the sun to that corner, but they still should be getting enough sun to bloom. I've just about given up on them. They aren't dropping buds, they aren't even making buds. They aren't mine and were here when I moved in, so I can't take them out.

How wet are you keeping the soil? I read they need more moisture for vegetative growth and less moisture for flower. Here's one I have blooming atm.

Pretty. I'll do it tomorrow right before it rains....if it rains. It's supposed to.