Hi Scott, you may want to post this on the daylily forum as you might get more suggestions there, This forum is for true lilies. That said, here goes. If they are a reblooming variety of daylily they need more frequent division to keep the clumps healthy and blooming well. Every 3 or 4 years may be appropriate. Where are you located? It's always a good idea to include this info in your post as the advice may vary depending on what area of the country you are in.
It's always a good idea to get a soil test done, but when I fertilize I use a balanced fertilizer (10-10-10) in the spring when they are emerging. I use a fair amount of compost worked into the soil whenever I divide or transplant so I go light on the fertilizer. Good lluck with your daylilies.

Here is a link that might be useful: daylily culture

If they are Stella d'Oro they may need dividing every other year.....