Straw is generally a bi product of small grain production, what is left after the grain is harvested. Having spent some time in your county (inlaws live on Tacoma mountain) where is small grain (oats, wheat etc) grown in the area?

I have seen mulch hay given away free from time to time on the SW VA craigslist but it's not delivered for that price!

Mitsy --- That's a shame! I've had varying degrees of seeds in my straw mulches over the years depending on how well they threshed the grain before leaving the straw behind. You'd be able to tell if that's the problem vs. if you got hay because hay is generally much finer in texture while an individual straw is likely to be around a quarter of an inch in diameter. If what's coming up looks like a cover crop, it's probably from straw, too --- the sprouts you get from hay look like a newly seeded lawn (and are much more troublesome to yank!)

Now's a great time to go on Craigslist and find a local farmer baling up his rye who'll sell you a whole trailer-load! I'd say that the straw I've gotten from farmers has been less seedy than the stuff I've gotten from the feed store, although I could be just misremembering.