Hay, and straw, have benn used in the past to insulate homes, cold frames, etc. Given that the ability of these grasses to retard heat loss, or heat buildup would probably make that a not good idea.

I found that old hay that had been out for a year or two doesn't grow so much some of the seeds expired some sprout in the bale and die
Plus its almost always free that way

g'day dan,

the way i see it mulch needs to be around 6"s thick to do the job and at that much of any seed won't germinate, but what does never perpetuates as a weed as such much of it never gets to maturity and all i do on the occassions i get any sprouting is pull it and tuck it under the mulch for extra nutrients.

len

Here is a link that might be useful: lens garden page

Earlier this year I mistakenly put hay on a few beds instead of straw. The beds with the straw worked out great. The beds with the hay started sprouting grass like crazy. And this isn't just your normal grass. This is agricultural grade grass to be grown for hay. It grows very rapidly, very tough root structure, and almost impossible to remove without pulling by hand. That's fine if you have one or two small beds, but these beds are 4'x50', so hand weeding is not really a great option.

As for solarizing it, I don't think you could get the inside of the bale hot enough. Perhaps if you broke it apart, spread thinly, covered and solarized, maybe. But that seems like alot of work when straw is a good option.

By all means, try it. put a compost thermometer down into the center of the bale and watch to see what happens. Clear plastic would be my first try for max heating and to encourage any seeds to sprout. If you don't get any sweating inside the bag, add some water, doubt you'll need to but watch anyway.

Another way to solarize would be to lay it out on the ground spread out and cover with clear plastic that is sealed to the ground all the way around the edges. The mulch depth will effect the temperature at the bottom of the mulch. I've never tried this method but will probably get around to it one of these years; with summer temps. here reaching 100 deg., no doubt it would cook!

I totally agree that this is worth an experiment, seeing as how you can save $6 per bale. Instead of fussing with trying to get bales in a plastic bag, I would line the bales up, maybe with a few inches in between for heat penetration. If it doesn't rain, water the bales well. Water enhances the heating.

Then as Michael357 says, use a sheet of clear plastic (gets hotter than black) and cover the bales, sealing all around the edges with boards or whatever. Do this in full sun in the hottest part of the summer. Doing it on pavement would probably enchance the effect.

When successful, solarizing is supposed to kill weed seeds in the soil, I would imagine it could handle the density of a hay bale? Laying the hay out in leaves would probably make the process go faster.

The lazy way is often the best, I find. Just keep the bales soaked with water, and seeds will sprout and rot (this is in warm weather). If some sprout on the surface, I'd cover with an opaque tarp - I've seen plants happily grow under clear plastic. I'm about to spread bales of hay that have been soaking in the weather since August - no sprouts. I feel confident they won't cause trouble.
Straw sprouts too - with oats, wheat etc. Not a problem but a bonus - I flip it over to rot.

I recall a television program about building structures made with bales. They were demonstrating the fire retarding aspects of the bales by placing them next to an intense fire. Like a fire door, it repelled the flames for hours without burning into the bale. I'm thinking solarizing wouldn't work any better.

I have tried to think myself out of this "problem" before. Good answers folks!

Thanks for the input.Food for thought this winter.

Straw bales are effecient insulatores due to the structure of the bale itself. It's not an inherent quality in straw per se. Even more true with respect to fire resistance. Don't ever try the fire experiment at home - that stuff is definately combustible! Wife had a relative who lost his farm because the straw laid up for stock composted and ignited. Also straw bale building books all mention that fire on a building site is a huge danger.

As for the OP - I side with the folks who say to water the bale (maybe split it out some) cover and let the sun do your heavy work.

Why not try wood chips I get mine free. Never had any carbon problems but I do add blood meal for sprouting rows or new plants. My srawberries jumped out of their row and moved into foot deep wood chip walk ways.