From the Director's Desk - Mulch: The Good, the Bad, and the Ugly

By Fred Breglia

Plant health care does not begin and end with choosing the correct plant for a site. Several other factors can benefit or harm trees and other plants, factors including nutrient and water availability, soil pH, and proper pruning and mulching techniques.

“Mulch” refers to material placed over the soil’s surface to maintain moisture and control temperature. Over the long term, mulching also improves soil conditions. It is important, however, to use the proper mulching material and apply mulch correctly to garner the benefits. Otherwise, mulch may have little or even a negative effect.

Organic mulches are commonly used for mulching a landscape or garden. These materials will eventually break down and provide nutrients, add organic matter, and improve soil structure. Examples of organic mulch include wood chips, shredded bark, pine needles, leaves, cocoa hulls, and compost mixes. Depending on climate and microorganisms present in the soil, organic mulches decompose at different rates. The decomposition process improves soil quality and fertility.

Organic mulches reduce the loss of soil moisture through evaporation and insulate plant roots during times of temperature fluctuation. Mulching helps to suppress weed growth and stop the germination of windblown weed seeds. It inhibits certain plant diseases. Aesthetically, mulch provides a uniform look for garden beds and helps prevent damage from weed whackers and lawn mowers.

Though beneficial, mulch must be applied properly to offer its full spectrum of benefits to plants. Too much can actually be harmful. The correct amount of mulch applied should be between 2 -4” deep but not touch the base of a tree trunk or a plant stem. Deep mulch is often applied as a means to control weeds and reduce maintenance, but it might actually create additional problems such as root rot, nutrient deficiencies, and toxicity. Deep mulch can also create a habitat for rodents that chew bark and eventually girdle trees.

So how do you apply mulch correctly in your landscape or garden? To begin, consider factors such as drainage. If drainage is poor, applying a thin layer of wood chip mulch can help absorb excess water, improving soil aeration as it breaks down. If drainage is adequate, apply a 2-4” layer of mulch out as far as the tree’s drip line or beyond if possible. Make sure the mulch is not touching the tree trunk but instead is at least 2” from it. Reapply mulch as often as needed, usually once a year.

Mulching can be a plant’s best friend when applied correctly -- or its worst enemy when not. Following these guidelines will ensure healthier plants and fewer problems for your growing investment.


Summer 2015

Volume 33 , Number 3

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