My hibiscus tree has a lot of yellow leaves.
Certified GKH Gardening Expert
There are several reasons this can happen. This article explains many of them and will help you decide which is likely for your plant: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm
The Hibicus bush is a tropical plant and does not like the cold. When the temps warm to a low of 60 to 65 at night cut back the top to approx. 24 in high and use a good all perpose fertilizeer. also a little ironite at least once a year will be helpful.