Dont use straw for mulch. Use grass clippings or alfalfa hay or peat moss. These three mulches do not draw heavily on the nutrients in the soil as they decompose. Prairie hay is also acceptable, except it is usually cut and baled after seeding so you'll be seeding your garden with numerous weeds. Straw is not good because it draws too much nitrogen from the soil as it decomposes.
Offered by Roger.
Peat moss isn't nearly as effective a mulch as are common leaves. The whole reason for adding peat moss to soil is to add organic matter and especially to hold moisture and "lighten" the soil. Where I'm now located, the soil is a rich loam and doesn't really need anything added. In Oklahoma where the soil was dry and hard, peat moss added in large quantities worked wonders. In Mississippi, the soil had a very high clay content, which when dry is almost as hard as concrete. In West Texas, the soil was very sandy and peat moss worked well for holding the moisture. Besides, peat moss just laying on the ground makes a great growing medium for weeds!
Offered by Ron.
Peat moss does do wonders for rock-hard clay (which we also have here in Missouri) and is highly recommended as a soil amendment. But the biggest problem with using peat moss as a mulch on top of the soil is that when dry, peat moss is very light and will blow away with the first strong wind! The best things to use for mulch are either fresh high-nitrogen vegetation such as grass clippings (watch out for pesticides!) or long lasting, slow to decay mulches such as bark nuggets or cocoa hulls. Fall leaves do work as mulch but often contain weed seeds and are prone to anaerobic decomposition when they just sit in soggy layers (i.e., they can stink!). I personally prefer to shred and compost leaves, using the compost in planting holes for transplants.
Offered by George.