Master Gardeners: Why mulch?

<p>Miniature daffodils emerge in mulch and white pine needles.  |  Julie Moore/Submitted</p>

Miniature daffodils emerge in mulch and white pine needles.  |  Julie Moore/Submitted

Spring is the prime time to be out in the yard spreading mulch in garden beds and around trees. If you are considering this for your home for the first time or even if you have spread mulch in the past, it’s helpful to have an understanding of what mulching accomplishes.

Organic mulches, those made of plant materials, perform a double duty in the garden. First, they improve the growing conditions of plants and trees by helping soil retain moisture and greatly reduce the amount of watering needed. Mulches ease soil temperature fluctuations, keeping them cooler in the summer and warmer in the winter and thereby lessen plant stress. Additionally, weed seeds have little chance of sprouting under mulch, limiting weed plants.

A second overall benefit of organic mulch application is that it slowly decomposes into rich compost, which improves the soil structure. It helps a powdery soil gain substance and a clay soil becomes less compacted while adding nutrients and improving the soil fertility.

The University of Illinois Extension experts suggest that newly mulched areas need 2 to 4” placed on well drained soils. In areas with poor drainage use less, since mulch shouldn’t stay wet as it may cause root rot in the plants below. Think of mulching as a project to be done “as needed.” If a mulched area has an adequate amount, break up the layers to improve air circulation with a pronged hoe and enjoy the mulch for another season. If weeds are growing in the mulch – time to reapply.

Composted hardwood mulch is known for its rich brown color and earthy scent. It is partially composted and provides all the benefits we look for in mulch. Newly chipped trees or bark chunks are typically less expensive, light colored and more appropriately used around trees and shrubs instead of perennial beds. As they are not pre-weathered, they can draw nitrogen from the soil. Compensate by adding nitrogen fertilizer to plants in the area, according to package directions. Cocoa hull mulch, appropriate for flower beds, has a chocolate smell, a nice dark color and provides good drainage to plants. The aroma is often attractive to pets and can be toxic if ingested, so use cautiously.

Next week: Tips for proper mulching to save trees and shrubs.

Email your home garden and lawn questions to or phone the Master Gardener Helpline at 630/955-1123. Visit our website at

Julie Moore has been a Master Gardener volunteer with the University of Illinois Extension in DuPage County for 10 years and has a degree in Ornamental Horticulture from the University of Illinois.