I'm having my third year of hardy perenniels dying off one by one when planted at the feet of my 40 feet of daylilies. Is there something in daylilies, like in walnut trees and some other plants, that 'protects' their turf to the detriment of other plants close to them? Don't wish to cast aspersions on daylilies, as I love them, but am beginning to wonder. This is my first daylily bed, so I have a lot to learn. I see my zone didn't show up with my ID - I'm in SW Iowa in (now!) Zone 5.
I would not say that is true mainly because I have perennials growing amongst my daylilies. I have many huechera, columbines, monarda and flax planted in with my daylilies and also black eyed susans and they are all doing wonderful.
I have been growing daylilies in a mixed perennial bed for years (Zone5B). I have never felt that they were killing any of my plants. That said certain ones (especially "roadside daylilies") will crowd everything that gets in their way. I also find that the plants are very hardy. My neighbor does nothing to her garden: weeding, fertilizing, amending, etc and the daylilies have survived.
Please bare with me, since you may have already considered these factors. These are just some things that I had to learn from the hard way. I think that I would check the soil ph, drainage, etc if I was you. Are the sun patterns different? If a house or tree, etc is casting a shadow, it will definitely affect the growth of plants. The same things can also affect the moisture level. Lastly I have had problems with Thumper, Bambi, Squirrels (digging and burying acorns, etc) and Moles or Voles.
Good luck. I do know that I struggled with the beginning of the year: record warmth which caused plants and shrubs to start growing. This was followed by extreme cold. My lilac never bloomed and seems to be struggling. I don't know if you have had the same battles. The weather didn't affect the daylilies (or weeds!).
Thank you all for your comments. I guess I was hoping it was that easy, but nothing in the garden is, is it? The drainage is better at the top end of the slanted bed (along the driveway) and so is the sun. Those plants seem to die off first, so maybe it is a lack of sufficient moisture at that end. We do have buroughing critters, including wood chucks, who make a mess of our lawn and get into all the beds. I've seen no evidence in the daylilies, however. I will be vigilant with water during these hot months (all these perennials are well mulched) and fill in with perhaps natives next season if these plants don't make it. I'd like that bed to be ONE bed that requires almost no work! PLEASE! Just ONE??
If its not critters in your garden, I would suggest you think about adding some bulbs. They need moisture, but require good drainage. Try the alliums and lilies. There are some hardy plants that I also find less of a "princess" in needs: daisies, purple coneflowers, rudbeckias, perennial sunflowers and some of the hardy salvias. Good luck!