potted hibiscus plants
I have several plants that are putting out many yellow leaves and the green leaves and blossoms are very tight and knotted with what looks like white foam on them . I don't want to loose them but they are not looking good. I can't upload any pictures at this time.
Certified GKH Gardening Expert
This could be Mealybug on your plants.
Treat the plants with Neem Oil.
Here are some links with more information.