Pine trees and their falling needles are usually a sign of acidic soil, but then I guess there are all different types of pine, but day Lilies dont really like acidic soil and they may struggle there, also the pines will take all the moisture from the soil so maybe you could make a stone edging around this bed and fill with soil so the day lilies are set into half decent soil to get them going for the first few years, they do like a lot of sun to flower well, without this, you get more foliage than flowers, good luck, hope this helps you a bit. WeeNel.
I have daylilies in a raised bed under a pine tree. We cleaned out the area, put down newspapers, top soil, composted manure, and composted top soil. They daylilies had been in pots. I tried to loosen the dirt around their roots and planted them in the soil.
I have ditch lilies under one very huge pine tree. I've even tested the soil ph, it's 4.5, but they don't seem to mind. They don't even get sun except for a few hours when it's low enough to get at them from the side. They are, aside from ostrich ferns, the only thing that will grow there.