The Height of Mulch

Mulching Trees

• Trees benefit from a mulch depth between 2 and 2 ½ inches. The thick mulch layer suppresses weed and plant growth under the tree while retaining moisture in the soil. Thicker mulch layers may retain too much moisture and cause surface roots to suffer rot, while a thinner layer supplies few benefits. Applying the mulch at the right depth is only part of proper application. The mulch must also cover the ground over the root system and beneath the tree canopy. Leave a 2-inch space between the mulch layer and the tree trunk. Moisture in the mulch can cause the trunk to rot.

Mulching Garden Plants

• Vegetable and flower gardens also benefit from a mulch application for both moisture retention and weed suppression. The mulch also helps insulate the soil so it does not freeze quickly or become too hot and damage the plant roots in the bed. Garden plants require a mulch depth near 2 inches. Apply the mulch after the plants are 6 inches tall. Applying the mulch layer too soon may prevent the desirable plants from penetrating the mulch layer.

Winter Mulch

• A deep mulch depth may harm plants in summer, but a thicker layer of mulch protects the plants in winter. Increasing the depth around dormant perennial beds to 3 inches provides insulation against winter cold. Straw provides an excellent winter mulch as it doesn't compact or retain too much moisture while supplying good insulation. Apply straw to a 6-inch depth around the plants in fall before the soil begins to freeze. Remove straw in spring as soon as new growth begins and replace it with a thinner layer of summer mulch.

Combination Mulching

• Combining multiple mulch materials may minimize the depth of mulch required in the garden. Landscape fabric, newspaper and plastic sheeting prevent weed growth and retain moisture. Only a thin single or double layer of these materials is necessary to mulch the bed. A 1-inch layer of a more attractive mulch camouflages the mulching materials and adds further protection to the bed. Use bark, wood chips or gravel mulches for the top layer of mulch when combining the mulch with fabric or plastic.