Straw is a very inexpensive and useful material for composting, mulching and animal bedding (we use it for all of these purposes). If you use it for mulch you’ll probably get some seeds that will germinate, but I’ve never found it to be a big problem in a small vegetable garden. I get my straw from the feed store, but you can often get it for free from yuppies on Craigslist who have bought it to give their parties the Hee Haw ambiance we enjoy 24/7 at the Homgrown Evolution compound. If you buy it from the feed store remember to ask for straw, not hay. Hay is green and a lot more expensive. You feed hay to your horses.
But one warning from my friend, permaculturalist David Kahn. It’s tempting to pick up bales that stores have used after Halloween, but make sure they weren’t treated with fire retardant. Fire retardant has some nasty chemicals in it you don’t want in your garden. When in doubt, just go to the feed store–straw it ain’t expensive!
Addendum 10/27/09: Reader Polyparadigm raised another potential issue with using straw in your garden or compost pile: halogenated pesticide/herbacide residues. Clopyralid is an example–while banned for use in lawns in many places it’s still allowed on hay and grain crops . All the more reason to grow your own mulch and carbon materials if you can–don’t throw out those fall leaves! Here’s what Polyparadigm says:
“I’m glad I read through to the end! I was thinking this would be a warning about clopyralid and its close cousins. Which bears some mention: Halogenated pesticides aren’t broken down by any but a few soil organisms.
Clopyralid and aminopyralid mimic the hormones in broad-leaf plants, causing them to grow un-evenly and die from wrong-facing, crinkled leaves and other symptoms. Grasses are un-affected, so fields of grain and lawns have been sprayed with this sort of chemical, as a cheap way of keeping broad-leaf competitors at bay for a few years.
These chemicals have a half-life of 11 months in hot compost, and are often applied at such high rates that certain plants won’t grow in garden soil dressed with finished compost from a mix of sources, if one of those sources is a treated lawn or field.
A quick bioassay will test for this in straw: peas sprouting from soil mixed with that straw will look deformed if the field that grew the straw was treated. Browns of a similar texture from a source you know to be clean should probably be used for a control group.”