I have a hill covered with orange day lilies that bloom beautifully every year. This year 1/2 of the area did not . bloom. What would cause this?

It's possible that your clumps are too thick. I don't know a lot about species daylilies, which it sounds like you may have, but hybrid daylilies tend to bloom less when their clumps are too large. In gardens, we see more blooms again if those clumps are dug and divided; that may not be something that you can do with yours, though.

Also, how has your weather been? Our heat wave and lack of rain here has also resulted in fewer blooms.

I was wondering about rainfall, too, especially on a slope. Could the soil be thinner in one area, or are there trees taking moisture from the ground in one area?