I don't quite understand what you mean by "they won't grow, just put on new plants". That sounds like they are growing, but perhaps you were expecting that the leaves would get huge and the plants taller? As long as they look healthy and are spreading a little, I don't thik you have a problem. However you may just have smaller-growing varieties than you had anticipated. Hostas like to be kept growing in moist soil and do not enjoy drying out, so perhaps your lack of rain has affected them. Of course the ash tree is sucking up all the available moisture when it does rain. I suggest moving them to a less dry place. Perhaps you can get someone to prepare a nice partially shaded bed for them with plenty of compost in the soil to retain what rain falls. When you dig the plants (water them the night before) take a fairly large clump and then separate the individual crowns from each other. If the plants are robust you can just take a spade and split the plants into two or more pieces before replanting. Try to do this on a cloudy day in fall while the ground is still warm from the summer.