While we were on our trip, I did not ask anyone to spray the Hardy Hibiscus, and it stopped flowering due to thrips. I started spraying again when we got home, then noticed something new all over the hibiscus: tiny white flying things.

These seemed to not care about my spray, and were all over. I submitted a photo to iNaturalist and received an answer: white flies. Hm. The description of the white flies says they live on the underside of the leaves, so I looked on my hibiscus, and sure enough, full of flies and eggs.

Internet knowledge said the white flies can be rinsed off with water. So I gave my plant a good rinse, let it dry, then in the morning gave it a good spray with Neem oil, peppermint oil, and castor soap solution. It flowers despite the white flies, so that is something.