Mitch said:

What's their feeding schedule?

Whatever nature gives them.

Perhaps helping them with some 5-10-15 or 6-12-12 is in order. =)
Fertilizing them twice a season, with either, helps.



I doubt it's from lack of water. Have they received any water, in the last
month?

Oh, yeah. I'm in NW Illinois. We had some major long, heavy rains.
I think someone said that 2 weeks ago we got 5" in 3 days.

The soil is very well-drained, by the way.

I wouldn't worry about them. Most varieties of day lilies are pretty tough.
The weather probably was the biggest factor, but if you haven't been
feeding them, then the nutrients per plant is probably getting pretty low.
Fertilizing now, and dividing them this fall, should bring back the
flowering, next season.

When first reading and replying, I had "true" lilies in mind. They *are*
bulbs, but most day lilies grow from fleshy roots. Still, they prefer not
to have their feet wet, IME. My apologies for using the wrong terminology.
=)

--

Eggs

Time is money, money is the root of all evil, and knowledge is power.
Therefore, procrastination is the key to world peace.