Really the only benefit from any type of fertilization is if the plant is somehow nutrient deficient. If they look good, healthy color, proper new growth, budded as normal, etc. then no fertilizer is required.

For the perenials that bloom just once a year, around this time,it is not going to make a difference in floweing this year, However, fertilizers, if needed, is always good for general health of plants, especially when they have active root system.