Before I lived on a farm and needed to know the difference between straw and hay, I used the terms interchangeably. I learned very quickly that in farm country this is not done. So for anyone out there who has not yet been enlightened, hay is dried greens- grass, alfalfa, clover- and it is used for feeding purposes. Straw, on the other hand, is made from the dried stalks of wheat that are cut and baled after the grain is harvested; used for bedding only. In the garden the difference is important as well. You don’t want to use hay in the garden, because it will be full of weed-seed, grass-seed, and other things that you probably don’t want growing there. Straw is great for keeping the weeds down and helping moisture to stay in the ground, rather than evaporating out of the soil in the hot sun.