What I'm looking for is a dynamic accumulator that takes full sun and has minimal water requirements, but is perennial. I know Borage will self seed, but I'm worried it won't "win" and grow in my environment (which is basically your typical fruit orchard with grass everywhere). I'm trying to crowd out the grass around the trees and provide shade/nourishment at the same time.
The first thing that comes to my mind is comfrey, the good old-fashioned stuff that spreads by seed as well as by extending its roots. It's normally considered invasive because it competes so well, so many people buy expensive root cuttings of specific cultivars that do not set viable seed. But I love the traditional stuff -- it competes well with grasses and spreads nicely. I started with a seedling in a tire in the middle of my orchard area, and now I have volunteers coming up everywhere and trying to crowd out the grass. (It probably helps that I scattered seed pods all over last year after it flowered.)
Many people report success with borage reseeding itself, but in my climate borage is fragile and doesn't do very well outside a well-tended bed.
Hey thanks, that does help! I do also have some Comfrey planted, but I was starting to worry about it's need to have moist soil. The location is full sun, and although fairly moist for 3/4 of the year it gets quite dry in the summer here (Seattle area).
Maybe it will be okay after all though. It will at least get some partial shade from the trees and maybe from the Borage (depending on how tall it gets).
And I do have the trees on a drip line, so I could possibly loop it out to give the Comfrey a little water as well when it is really hot and dry.
Comfrey really doesn't need moist soil. It will do just fine without water in the western PNW... it'll be hard to ever get rid of, but I think the plant is delightful. It's great if you sprain something to, to have the root or leaves on hand.
Be joyful, though you have considered all the facts. ~Wendell Berry