I don't think I'd interplant although I'd consider doing borders of, say, miniature daffs, to give a splash of colour before the daylilies return to production.

For me, there would be issues with waiting for leaves to brown off, ongoing cultivation and management to ensure the bulb clumps weren't overcrowding and losing their impact, keeping the daylily clumps at peak - and digging when the bulbs might just be settling to grow roots.

It may be different in your zone. Just a thought.

Are you familar with daffs? Most multiply rapidly in my zone. So I would plant 3 at most between daylily clumps.

Are your daylilies dormant types? Mine are evergreen so I locate other plants/bulbs a decent distance for replacement/division.

Okay, I have done this. I set my daylilies two feet apart on centers. I plant my daffodils in exactly the center between the clumps of daylilies, using 5 bulbs per square foot (planting just that center square foot). I use five different varieties of daffodils, early bloomers through late bloomers. I plant the early bloomers at the back and work forward through mid and lates. This works extremely well. I have daffodils blooming in that bed continually from the first week of February (this is zone 7b) almost up to the time the daylilies begin to bloom. The daffodil foliage is very inobtrusive since the daylily foliage comes up and covers it as the bulbs are ripening.

Here's the important part. I divide the daylilies every third year in the fall, and when I do this, I first dig up the daffodil bulbs and divide them too. I replant the largest bulbs and move the smaller ones to other areas in my yard. Because I am so careful to plant the bulbs in exactly the same spot, and because the soil is so loose, I can almost get the bulbs up with my hands, I almost never cut a bulb.

The one drawback is you want to be careful not to overwater the daylilies in the summer, because the bulbs really prefer somewhat of a good summer bake. Other than that, it's a nearly foolproof system.

Oh yes, when I divide everything, I always apply a top dressing of an inch of compost or Black Kow to the soil in that bed. I feed the daylilies with an organic fertilizer in February, May and October, giving a sprinkle of the same fertilizer to the bulbs. They like it.

I also have a large raised bed of mostly daylilies and narcissus and find it works really well, as donnabaskets describes. I just don't divide my plants/bulbs as frequently as I probably should. I have some really old Whiteflower Farm catalogues with beautiful pictures of a large border bed of daylilies and daffs. That's where I got the idea of combining these plants.