Ditch lilies have typically very agressive roots and if you don't get all of the roots removed, they will just come back again. The root system is extensive so when digging them out, be sure you got all of the roots system. They are invasive.

Julia

And it will likely take two or three years to get all the ditch lilies out. The regular ones don't change.

kay

Just a note..... you said "Last year I dug out all the ditch lilies blooming before they seeded" Just an FYI ....... Ditch lilies do not form seeds. They are stoloniferous ( spread via root ) which is why everyone is telling you that you need to get rid of all the roots, even small pieces or over time they will regenerate and pop up new plants.

Organic kitten is correct . Regular daylilies i.e. hybrid daylilies don't revert to ditch lilies

And the sad news is--I have an area I've worked hard to get rid of every piece of root for 20 years. Still not totally successful. Keep at it!

Brad