Phil Stevens wrote:Willow is a good idea. What about alder? I think that's pretty bendy and it grows in the PNW.
I used Speckled (Tag) Alder because it is prolific on my land in ~2" shoots. I tried taking straight ones and bending them into an arch but most broke. But the other aspect of the Alder is that the shrubby growth pattern produces some that grow out to the side and then turn up, so I was eventually able to find enough that grew with a natural curve and were able to form a arches without breaking.
I think willow is one of the archetypal "bend-don't-break" plants, and would be particularly appropriate for this application. I had trouble bending Red Pine, I'd expect White Pine and Fir to have similar problems, but this doesn't seem to require a huge curve in the bend.
One thing I did was to lash the poles together while they were loose, then bend them while fastening the ends in place...