Why Mulch?
Mulch's purpose is pretty basic: It acts as a barrier, keeping sunlight and some air away from the soil surface. Sounds simple enough, but mulch's smothering effect brings with it both good news and bad. Consider these positive and negative effects of tucking in your soil beneath a blanket of mulch:

Without the summer sun's rays striking it, soil stays cooler and plant roots don't stress from the heat. The bad news is that slugs, earwigs, cutworms, and other eat-and-run types love cool, moist, dark places. To minimize bugs, use only a thin layer of mulch, keeping it several inches away from plant bases.

Raindrops don't hit the soil surface, so soil is less likely to wash away or splash onto plants. This keeps plants cleaner and free of some soil-dwelling diseases.

Water in the soil doesn't thaw on sunny winter days, then refreeze at night. That's good news. The melting-and-freezing cycle makes water shrink and expand, possibly popping shallow-rooted plants right out of the ground -- a phenomenon called heaving. Heaving spells the end for plants.

Which Mulch?
Mulches aren't one-size-fits-all. To match the mulch to your garden, consider the following:

Appearance. In a showy flower garden, you want a mulch that looks good without stealing the limelight: Try bark chips, shredded bark, or cocoa hulls. For a woodland garden, leaves or pine needles are right at home. For a large or no-frills cutting garden, grass clippings or layers of newspaper are budget-smart. You can always top them with something prettier and pricier.