University of Illinois Extension
Mulching - Bed Preparation and General Maintenance - Stepping Stones to Perennial Garden Design - University of Illinois Extension

Mulching

To reduce weeds and increase soil moisture retention, a 2- to 3-inch mulch layer is recommended. Apply the mulch after planting over the tilled soil, between plants. Taper the mulch depth gradually as it nears plants. Don't mound a heavy layer over the base of the plants. Organic mulches such as bark chips, shredded bark, leaf mold or compost are fine. Organic mulches decompose over time adding beneficial organic matter back to the soil. Because of this, you will have to replace it as necessary. Many people ask which is the best. There is no definite answer, only guidelines. Choose an organic mulch that is aesthetically pleasing, readily available and affordable. Inorganic stone mulches are not recommended for perennial gardens. Stone mulches will sink, if they don't have landscape fabric placed underneath them. Perennials increase in size over the years and the holes you cut in your landscape fabric will eventually become too small and choke the plants.

"What a man needs in gardening is a cast-iron back with a hinge on it."
-- Charles Dudley Warner (1829-1900)