Hibiscus: Yellowed Leaves, 1 by LadibugZ9

LadibugZ9 wrote:
I hope someone can help me with this. My leaves are turning yellow and falling off. New leaves and older leaves. I am also having to spray daily with soap for whiteflies. Is this plant diseased or do I need to fertilize? This plant has not flowered yet this season. We have had horrible weather this year. It rains nearly every afternoon. This plant is the most affected. Two other younger ones are somewhat affected and one is not affected at all and is filled with buds. They are all in the same bed!

Early in the spring I added compost and manure along with a little Osmocote. Do I need to fertilize? If so, what do you all recommend?

Here are a couple of pictures. The whole plant: