solid7 said:
As long as you are comfortable with not knowing what's been sprayed, dumped, or sprinkled on whatever it was before it went in, then yes, use it. (as top dress or compost, whatever) I was just pointing out that it's a valid consideration. The 2 years was the recommendation that was given by some of the local gardening pros who I learned from, to allow any undesirable stuff to break down, or peter out.
These days it is an absolutely valid consideration to be careful about what and 'where from' anything you put in your garden. This concern of herbicide carry-over is why I stopped using horse manure in my garden a few years ago from a local stable. Even aged some of these chemicals don't break down. And there was simply no way to know about the hay/straw they were feeding the animals.
There are sprays that when applied to growing hay can go through the intestines of the grazing animal... and seriously contaminate a garden on which the manure is applied. Unfortunately some of the hardest hit plants that can be affected are those in the nightshade family - peppers, tomatoes, eggplant, potatoes...
There are the same contamination concerns with 'unused', 'new' hay/straw for mulch too. Not only from broad-leaf weed killers, but the application of round-up to kill and dry grain fields for better harvesting. If you are going to use hay or straw, know where it comes from. Make sure the grower is either organic or does not use the herbicides in question.
If you can, use for mulch things from your own yard (or horse), assuming you don't spray. Grass clippings, even small branches can be cut up. And of course leaves as others have mentioned. Great stuff.
My own choice has been the municipal green waste as perhaps safest. And I've never had an issue in years. My area of California is very dry and we were in a severe drought for years. There just arent as many lawns around any more where people use herbicides. Much of what goes into the green waste here are branches and weeds. I know there can be risk, but I need so much mulch to cut down on water use, I elected to use the free stuff. To be honest think it's as safe as purchased hay/straw/mulch. If not safer. And did I mention that it's free?
In my area local farms/orchards have the stuff delivered in double-rig trucks. If they thought secondary pesticides were a concern, I doubt they'd use it.