They turn yellow and fall off - am I over watering or underwatering?
Why Are the Leaves on My Hibiscus Tree Turning Yellow?
Certified GKH Gardening Expert
This article should help pinpoint the reason for your yellowing leaves: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/answers-to-what-causes-hibiscus-leaves-turning-yellow.htm
Is most certainly over watering. I have just bought a lovely apricot colour one and was told by the nursery that they don't like too much water as they are from New Zealand and that the leaves would turn yellow and droop if too much water. Hope this helps