A popular organic mulch, hay is commonly used to protect soil and plants from the elements, to line pathways, and to address various needs in the garden. What many people don't realize, however, is that various products are often labeled as "hay" at garden centers, but there are many different types of hay and straw that are commonly sold in bales. While they are easily confused, it's important for gardeners to become familiar with the differences.
Hay and Straw
Salt hay, or Spartina patens, is a grassy plant that grows in salt marshes and wetlands. Martha has long used salt hay in her gardens. It is useful for keeping weeds from growing in paths, preventing runoff, and keeping soil from turning into mud whenever it rains or the garden is watered. A layer of salt hay will keep soil moist and encourage worms to come to the surface, which will help to aerate the soil. It also makes an attractive path to walk on between garden rows. Salt hay is an ideal all-purpose mulch because its seeds won't grow away from salt water -- so it won't germinate in your garden.
What is commonly termed "Golden straw" is either oat straw, Avena, or wheat straw, Triticum. This straw is a by-product of the process of separating oat or wheat seeds from their stalks. Golden straw is often used as bedding in horse stalls; because there are no seeds, the horses won't eat it. This straw spreads nicely, and the lack of seeds means there is no risk of it germinating in your garden. It can be used in the same way as salt hay.
Just as its name implies, feed hay is used to feed livestock. Though inexpensive and plentiful, it is not a good choice for use in gardens because it is full of seeds. The main ingredient of feed hay is alfalfa, Medicago sativa. It also frequently contains flowers and seeds from many other plants and weeds such as clover and golden rod. These seeds are likely to germinate, resulting in a garden full of weeds rather than flowers and vegetables.