My yard contains a good amount of Missouri clay and I would like to plant some day lilies; will they survive/thrive in thick soil like this? Also, do they do well in direct sun or shade and what type of irrigation do they prefer?
Here in NY, I have heard daylilies alternatively referred to as 'ditch lilies'. So called because they often grow on the upper edge of road ditches. While daylilies would prefer well-drained soil, they are liable to grow reasonably well in unimproved heavier clays as well. If you like you can improve drainage by adding some coarser soil or compost to the mix when you plant. They won't tolerate prolonged standing water, but they also don't want to dry out completely. Daylilies prefer to be watered deeply, getting the soil wet 8 inches or more down, then allowing the top layer to dry out before watering again. In your clay, this might not have to be done very often as it is liable to hold water quite well.
Daylilies prefer full sun, a minimum of 6 hours a day.