Mulch is anything you lay on the ground to prevent weeds, retain soil moisture and help keep your soil both warm in cool weather and cool in warm weather. While mulch is typically organic material such as compost or dried leaves, it also can be man-made. Black plastic is often used as mulch because it effectively blocks weed growth and keeps soil warm or cool. But it does not allow rainwater to penetrate the soil and benefit your garden, except around the base of plants, where you have cut holes for them. Consider using porous black shade cloth or landscape fabric instead---your soil will thank you for allowing it to breathe.
Using Black Mulch
Determine where you need mulch. Vegetable gardens are prime locations that benefit from all types of mulch, but you can use it around fruit trees, roses and other ornamentals.
Spread a layer of compost over your planting area before you lay down your black mulch. If you want to set up a drip irrigation system, do this beforehand as well, especially if you will be using black plastic.
Spread your black mulch over the planting area before you plant your plants, if possible. Cut it to fit your planting area. Then plot out where you will plant each plant. Cut "Xs" with scissors every place you plan to put a plant. Consider their adult size and be sure to leave sufficient space between the holes you cut. If you wish, you can anchor your plastic mulch with earth staples or cut pieces of wire coat hangers.
Plant your plants in the holes you have cut by folding back the corners of your "Xs."
Water your plants at their bases to ensure that the maximum amount of moisture gets through to the soil.
Control snails and slugs, which can thrive under black mulch, by spreading iron phosphate granules (sold as the commercial product "Sluggo") around your garden area. You can also make beer traps by burying small jars in strategic locations and keeping them full with beer.