Yes, chopping and spreading the fertilizer sticks is a better alternative. But fertilizer of any kind is overrated and not necessary with you plants. I suggest you skip it altogether.
Your Boston Fern needs to stay in moderately damp soil, but depending on how you repotted, it may be easy to inadvertently keep the soil too wet for too long and deprive the roots of oxygen. Remove any soil you added to the top of the original rootball. Then, allow the surface of the rootball to get almost but not quite dry before watering.
