Definitely use the old hay that's been sitting out in the weather. The fresh hay (definitely if it's 1st cutting) will likely have viable grass/weed seeds in it. The moldy old stuff won't.

Also be sure that the hay doesn't contain any broad-leaf herbicides - again, the older stuff is probably safer in that respect (though some herbicides are persistent, essentially the inside of the bales have been "cooking" and I think 2-3 yrs is safe even if the field had been sprayed). But best to take a tomato plant, if you have one to sacrifice, and muclh it with that hay now, see if it starts shriveling. You can cover your bare earth with burlap or plastic while you're waiting for the test results.

g'day bert,

in the end it won't really matter new or old, they will all break down the same and and same nutrients if they came from the same source.

dunno about any weed/grass growth from them well not that it would take over the garden? lay the stuff thick enough say 6 or 8"s, that will suppress nearly every thing, even volunteer growths.

len

Here is a link that might be useful: lens straw bale garden

Thanks! I had thought the same between both of these responses. So HMMMMM

Try to get some WHEAT STRAW. Big difference between hay and straw. The weed seeds will still be inside the hay bales even if it is old. You might be introducing weeds yet unknown into your garden(?) Wheat straw will only have random wheat seeds which are easily controlled and pulled

I have used hay for mulch for close to 56 years. The key is getting hay cut at the proper time (no weed seeds). The hay I get is old or spoiled (rained on), but only once did I get hay full of weed seeds. I didn't use it.

First cutting hay will definitely have seeds. But if it's been sitting outside for 2 years it shouldn't be a problem.