21+ Yellow Leaves On Hibiscus. We cannot tell you exactly what is wrong with the plant without knowing a lot more than you are likely to be able to tell us. Prune away any affected growth and prune back.
The hardest part is determining the cause of the stress. This does not look like typical insect fungal diseases cause yellow or dark spots, not what we see in this photo. The stress can be of any type, and figuring out what kind of stress is the challenge for the gardener.
The leaves on my hibiscus are not only turning yellow but have brown patches and the veins in the leaves are exposed.
From what we see this looks most like contact damage of some sort. However, too much or too little can cause problems with yellowing leaves. Plant binned but it's showing up on dropped leaves on other plants. Both hardy and tropical hibiscuses can suffer from yellow leaves and overall decline.