Dave ...
I can only address the roses as I have never grown hibiscus. If your roses are young plants and the temps are HOT, it is possible to have enough moisture in the root zone for the rose, but the plant is unable to bring enough moisture up to the top growth to keep it from "weeping". That is because the transpiration rate ... the moisture loss through the leaves ... is greater than the amount of moisture the plant can bring up to that part of the plant.
The rose is a fantastic survivor. Instead of trying to get moisture up there, it will abandon parts of the plant that it can't save and will send moisture to the parts it can save, or needs to save, for survival. Older and more mature roses have a larger root mass and can provide moisture to more of the plant's top growth. However, if the plant is stressed for any reason, even an older plant will go into survival mode. Some roses will even go into summer dormancy in extreme heat.
There are a lot of other variables that could also cause what you are seeing, so this is a very general answer to your question.
I don't know your climate and don't know what conditions you are growing your roses in this year. It can vary from year to year.
