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By Michael D. Whalen, Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver

With increased environmental awareness among today's gardeners, many are learning new practices such as leaving grass clippings on the lawn, saving excess plant materials for making compost and taking advantage of the many benefits of organic mulch.

Mulches help reduce evaporation from the sun, thereby decreasing watering needs. They suppress weed growth naturally, diminishing the need for chemical herbicides. Mulches also prevent sudden changes in soil temperature, which helps prevent tender premature growth during winter warm spells. Such growth is killed easily in early spring by the return of cold winter temperatures.

An often-overlooked source of free mulch is the woody prunings from our yards. Rather than automatically bundling twigs and branches for trash pick-up, consider, instead, how they could be used. If you're doing extensive pruning that results in lots of leftover brush, consider renting a chipper to grind the wood into mulch.

Small amounts of disease-free woody plant material can be cut up and spread out beneath the tree or shrub from which it came. Other good spots for mulch include around ornamental shrubs and flowers, on garden walkways, along fences or next to an alley.

Keep in mind that organic mulches break down over time, and eventually will need to be replenished. While this decomposition recycles nutrients back to the soil, it temporarily depletes nitrogen levels in the process. Occasionally, you will need to supplement nitrogen if you begin to notice signs of poor plant performance, such as yellowing lower leaves or weak growth. Sprinkle a few handfuls of general purpose nitrogen fertilizer around the mulched plants, up to two pounds of actual nitrogen per thousand square feet.

It may be helpful to use a landscape barrier in conjunction with your mulch to hold down weeds. If you decide to use a barrier, avoid (the dreaded) solid black plastic. This solid plastic material interferes with air and water exchange with the soil. Instead, try a breathable fabric material with two to three inches of mulch spread on top. When you consider that plant trimmings take up approximately 25 percent of the space in our landfills, you can see how a little bit of sensible plant recycling can go a long way.

A good example of a community-wide application of this concept is the Treecycle Mulch Giveaway sponsored by Denver Recycles. This annual program allows Denver County residents to pick up as much as two cubic yards of free mulch, all made from the 19,000 Christmas trees saved from the trash by Denver Solid Waste Management. The mulch giveaway for 2006 will be on May 6th. For more information, see 2006 Tree Mulch Giveaway.

Photograph courtesy of Judy Sedbrook

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Date last revised: 01/05/2010