I'm using straw for the first time this year in my raised beds, so I don't know how long it takes to break down. But there are a few weeds, sort of a long grass (wheat, I guess). Not many--and they are easy to pick out (and don't really spread like other weeds).

Good quality straw will not produce many or any weeds. It is the stalks of a grain crop after harvest. This of course depends on the source and how thick you mulch. Hay on the other hand is grass and weeds baled to provide feed to animals. It often has many types of grass and weeds in it, making the results of mulching risky.

I mulched a small area with straw this year just to test it out and will NEVER do it again. While the straw itself doesn't produce weeds, the ground underneath certainly does unless you have some sort of weed barrier underneath the straw. I neglected to put down a weed barrier under my straw and now have straw with giant weeds coming through which is a complete nightmare. So, you may want to put down newspaper or cardboard or something beneath the straw.

Just my experience.

My favorite author, Ruth Stout, would tell you if you have weeds--either hay or straw, your mulch isnt thick enough, and if its growing on top of the mulch, turn it over.
I've never gone wrong following her advice.

I've had weeds come in with some straw.

Straw mulch lasts about a year in my garden.

I've used both straw and hay mulch for years. As mentioned above, the secret is to lay it on thick. If you put it down 6 inches thick in spring, it will be reduced by 80% by late fall. I've never used straw that was seed-free, but it has a lot fewer seeds than hay.

The thing is, permanent mulch gardening is something that you need to stick with. If you mulch even one year with hay, you're going to get a million weeds for years thereafter if you don't continue the mulching.

I usually just peel the squares off the bale and lay them out like floor tiles. If I have a decent supply of cardboard, I may lay that down first, but again, the secret is to lay it down thick, and keep adding to it as required. I also pile on shredded leaves, pine needles, lawn clippings, whatever I can get my hands on.

Yes, if you use mulches and have weeds, you're not applying it thickly enough. I do like to use newspaper underneath my mulch, though.

For the most part what people that use straw as mulch see as "weeds" is really some of the seeds left on the straw germinating and growing. That is the only kind of growth I have seen when I use straw as a mulch, and it is not a problem. If other "weeds" do germinate that can mean the thickness of the mulch was inadequate.
How long the straw would last before being digested will depend on the Soil Food Web in your soil. Gardeners with a very active SFW will see that straw get digested in a relatively short (one year) time frame while those with no SFW could see straw last much longer.

I, personally, used about a six inch layer of straw with nothing under it, and had weeds - real, fat, green weeds, not hay/straw growing - coming up within weeks. I, too, laid down my straw in flakes like tiles and still had issues. I just don't think straw alone can keep back the hardy weeds here in New England.

I put down newspaper under mulch in one area a few weeks ago. It's so windy here that both the straw and paper blew off of one end. I added a few stones over the paper now, but really need to add more straw since some took off in the wind! Something you might want to consider if you get a lot of wind- add a few stones!

Karen