Mulching Garden Beds

Q:  I know I should be using mulch on my garden beds, but I’m confused by the many types available at the home center. What should I use?

Mulching is a key gardening technique. The benefits of mulch include moisture retention, weed suppression, moderation of soil temperatures, inhibiting disease spread by reducing soil splash, and, in the case of organic mulches, soil enrichment as they decay.

Organic mulches include shredded tree bark, wood chips (either fresh or partially decayed), composted leaves and other plant material, straw, and grass clippings. Among the inorganic mulches are plastic films, landscape fabric, stone, and rubber from shredded tires.

Organic mulches are generally the first choice for home landscapes. Bark or undecayed wood chips work well around trees and shrubs and can also be useful for pathways. Partially decayed wood chips or shredded bark are effective mulches for perennial beds. Leaf mulch is excellent for annual beds or vegetable gardens. Weed-free straw or grass clippings are also fine mulches for vegetables. Only use grass clippings from pesticide- and herbicide-free lawns and avoid thick layers that mat when wet.

Inorganic mulches such as plastic films and landscape fabric are used primarily for weed-suppression and decay quickly if not protected from sunlight. Colored plastic films can be used in vegetable beds to enhance reflection of beneficial light wavelengths. Unless they are specially perforated, plastic films are not water-permeable.

Stones do not retain moisture and can cause heat stress and root burning. They are best used away from plants for decoration. Shredded rubber mulch is problematic due to potential chemical contamination and indefinite persistence in the soil, and is not recommended for home landscapes.

Apply no more than 2 to 3 inches of mulch to planting beds and around the root zone of trees, keeping it away from the trunks. Add mulch in midspring after soil has warmed. Apply mulch only in succeeding years as needed, and do not over-mulch. If you live in a designated wildfire hazard area, be certain to observe local regulations when using mulch in your landscape.   

 

Please email plantinfo@chicagobotanic.org with additional questions.