Answer: Hay can have weed (grass) seeds in it, so it can cause problems. Straw, on the other hand, is usually free of seeds. In my garden, I lay down several (about 10) layers of newspapers in the paths, then top them with "flakes" of hay. You can often separate bales of hay into layers that fit nicely into a garden path. This method helps control weeds, and keeps any seeds from the hay from reaching the soil. The downside of mulching is that it can keep the soil from warming up in the spring. So wait until the soil is nice and warm -- a few weeks after your last frost date -- before applying the mulch. Mulch can also harbor slugs and other critters.
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