March 15, 2017

As the weather warms and homeowners and landscapers become active, many questions begin to arise when it comes to mulching landscape beds.  Information contained herein provided by Michigan State University (MSU) Extension.

Why mulch?
Mulch can provide a range of benefits for landscape beds. Here are just a few:

  • Conserve soil moisture. Mulch reduces evaporation from the soil surface and helps to ensure that water reaches plant roots instead of going back into the atmosphere.
  • Reduce soil temperatures. In a research trial in southwest Michigan, we found that 3 inches of wood chip mulch reduced midday soil temperature by 18 degrees Fahrenheit.
  • Add organic matter. As mulch breaks down it adds organic matter to the soil, which aids in the soil’s ability to retain important plant nutrients such as potassium, magnesium, calcium and iron.
  • Weed control. Mulch can help to control weeds, reducing the need for herbicides or hand-weeding.
  • Neatly applied mulch can improve contrast between beds and lawn, providing a cleaner-looking edge.
  • Avoid lawn mower blight and string trimmer trauma. Providing a buffer between mowers and weed wackers reduces the likelihood of trunk damage to trees.

How much mulch should I apply?

Deeper is not always better: 2 to 3 inches of mulch is adequate to get the maximum mulch benefit in most cases. If a site already has mulch from last year, a thin, 1-inch top-dressing is more than adequate. When mulching perennials in the landscape, take care not to spread mulch over the crown of the plants.

What’s the best material to use for mulch?

To a large extent, the “best” mulch material is in the eye of the beholder. Most organic materials such as ground bark, ground wood chips or shredded leaves can provide the key benefits of moisture conservation, weed control, thermal insulation and organic matter addition. Therefore, cost, aesthetic appearance and availability are often the deciding factors. Inorganic mulches such as rock or shredded tires do not need to be replaced, but do not add organic matter to the soil.

What about lawn clippings as mulch?

Lawn clipping are a poor choice for mulch since they tend to mat together and impede water penetration if they dry out. In addition, they are unsightly and can produce an unpleasant odor as they decompose. Michigan State University Extension says a better alternative is to compost your lawn clippings and then use the compost in your garden or as a top-dressed amendment before you apply mulch. Or use a mulching mower that returns the clippings back into your yard.

Is it true that mulch can “tie-up” soil nutrients?

In theory, organic mulches that are low in nitrogen, such as wood chips, can reduce soil nitrogen availability during the process of microbial decomposition. In reality, we see little evidence of this in trees and shrubs. We monitored plant nitrogen in landscape shrubs and found no difference between plants without mulch and those that were mulched with pine, hardwood bark and wood chips. In fact, in a couple of instances, the mulched plants had increased plant nitrogen. The one case where nutrient tie-up could be a concern is with annual bedding plants since they have limited root systems.


SOURCE:  Michigan State University Extension, Departments of Horticulture and Forestry by Bert Cregg,