Often gardeners are encouraged to mulch with straw, especially for food crops like, um, strawberries. Too often, the gardener, severed from his or her agricultural roots, mulches with hay instead. In Missed stacks and mistakes: distinguishing between hay and straw and other heaps, Alan Ritch explains the difference:
Hay, of course, is fodder for the animals; and straw is the inedible waste-product remaining after the grains have been beaten from it.
These days, hay comes from tractor-mown fields which may have originally been sown to timothy or alfalfa, but may have degenerated to something closer to a mown meadow; there are usually oodles of weed seeds in hay. Straw is the stems remaining after grain has been harvested. While no grain field is completely weed-free, it is in the grower’s interest to keep the weeds out as much as possible, and what weed seeds there are presumably would be included with the grain and not the stems. Hence, straw is what you want for your garden.
Hay in Art documents Ritch’s obsession with the agricultural commodity, and is worth a visit even if your interest is purely theoretical. History, art, literature, religion–it’s all here, and it’s all about hay.