Rose of Sharon Leaves Hardening
I have a rose of sharon planted for 2 years, started from a seed. I noticed a week ago the leaves are starting to harden and slightly curl on one side of the plant. The plant is very healthy looking, vibrant green and has not flowered. It is planted in an area that has at least 6 hours of sun. Not sure of the gardening zone.
Most plants grown from seed take longer to bloom than those propagated by other methods. Give your althea at least 3 more years before getting alarmed about lack of blooms. Since your plant is getting 6 hours of sun, that should be plenty. I think your thickening of leaves is a type of virus. I suggest that you take fresh samples to your local agricultural extension office for identification and recommendations. Althea are sturdy, hardy plants and thrive in spite of some difficulties.
Did you have a hard frost last winter that injured the plant? This could be the cause of your problem. If it does not flower this year I would suggest getting a new plant or taking a few cuttings off the current one to propagate it.