Mulching, The Only Way To Go
In addition to making a dandy homemade cold frame, hay and straw have other, more common uses in the garden. For instance, both make terrific raw material for the compost pile during those times when leaves and grass clippings are not readily available. Both are also ideal mulching materials in the vegetable garden.
Of the two, I actually prefer straw because, in my experience, it is easier to spread and break down. There are gardeners, however, who prefer hay. Either way, you will notice that the bales are bundled in sections roughly 16 inches square and that the three-inch thick sections are easy to separate from the bale. So if you will make your garden paths roughly the same width, you can easily mulch your paths and make them weed-free by plopping the sections in place.
To mulch a bed, just grab a section and pull it apart so that the straw that falls on the bed is fluffy rather than compacted. A 3- to 4-inch layer is ideal, although I know gardeners who use more. You can actually plant right through the mulch by pulling it back, plopping in a seed or transplant, and then putting the mulch back in place.
Even though straw and hay are great for mulching, they often share a common problem: weeds. Unless you purchase clean, weed-free straw or hay, you may unknowingly introduce all kinds of undesirable and non-native weeds in your garden. Hay often has more weeds than straw, but straw can be contaminated with whatever it is cut from, so it can be a problem. To eliminate the weeds, I would recommend buying several bales in late fall and leaving them out over the winter. The combination of cold, rain, and bright sunny days will make the bales slowly rot and most of the weed seeds will be destroyed in the process. Rotten hay or straw is actually better for the garden than the fresh versions. Another way to expunge the weeds is to break open the bale, spread the straw over the ground, and let the birds eat all the seeds they desire.
After several months the straw seems to disappear and become part of the soil