This sounds like one of two things…or possibly both. First is overwatering. Once an Althea is established, little watering is necessary. If you feel the need, set a slow running hose at the base of it for an hour or two and then don’t water again for a month. NEVER spray the leaves with water as this promotes diseases. Also check the base of the altheas to make sure that you haven’t buried the stem too deep or piled mulch up against the bark of the althea. This is a very unhealthy situation…it is like slowly strangling the althea (or any woody shrub or tree. It is a VERY common mistake. When you plant or mulch, the last step is to check the stem where it enters the soil and brush back dirt or mulch until you can see the original spot on the trunk where it enter the soil. I might also be good to feed the altheas right away with some Espoma Flower-Tone to help them along.