"And, what might be too low of a pH for daylilies?"
The level at which they start to look sick! That seems like a facetious answer but actually there is no published research on the pH range for daylilies. In an article about daylilies:
http://pss.uvm.edu/ppp/pubs/oh... Sinclair Adam Jr. (who did the daylily nitrogen study published in the Daylily Journal and the link I posted earlier) suggests a range of 5.5 to 6.5. I'm thinking that's probably about right, even as low as 5 may be OK, acid-loving plants like rhododendrons and azaleas can go even lower than that. Most of the problems I've heard of came from a pH that was too high suggesting at least some cultivars prefer a more acidic soil. Also, if growing in soilless media, the pH can safely be lower than in mineral soil.
Re the rust study, yes as far as I know rust infected leaves are still required but don't send them to me. Contact me (or Becky) privately and we'll give you the instructions and address where to send, direct to the university.
