Much Ado about Mulching

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	Much Ado About Mulching by Carol Seminara, HCMG
Summer is officially here with its long hours of sunlight, triple-digit temperatures and threatened water rationing. If you haven't already mulched, then sooner is better than later. Julie Bonnin, writing in the May 20 edition of the Austin American Statesman said it well: "Heading into summer without tucking a protective blanket of mulch around your plants is like forgetting to install insulation in your house and then wondering why your air conditioning bills are so high."
Next to good, organic compost, mulch is just about a garden's best friend and a beneficial one, too. Mulch moderates soil temperatures in both scorching and frosty months, helps retain soil moisture, prevents soil splashing to stop erosion and protects plants from soil-borne diseases (think red-tipped photinia) and retards the growth of weeds. And, too, an attractive layer of mulch makes a flower bed just look well-groomed.
Picking the right mulch can be tricky and depends, in part, on the application and desired result. There are basically two types of mulches: inorganic and organic; each having a place in the garden.
If stopping weeds is the number one priority, then black plastic or landscape fabric is a good choice, although these add no nutrients and little aesthetic appeal. Some inorganic mulches like gravel, decomposed granite and pebble are more attractive. Trendier urban gardens are sporting layers of crushed and tumbled glass mulch and even titanium screws. There's a café in Austin that mulches their garden with old wine corks. All these share the benefit of not attracting pests but, again, they do nothing to improve the health of your soil.
Organic mulches nourish the soil as they decompose, but they don't always perform well as weed inhibitors and may attract insects, slugs and cutworms, and the birds and mice that feed on them. Because they eventually become part of the soil, organic mulches have to be replenished or replaced. Grass clippings, leaves and leaf mold, pine needles (very good for acid-loving roses), shredded hardwood mulch and pecan shells are all good examples of readily available organic mulches. One caveat: while straw makes a good choice for mulching garden paths because it decomposes quickly and improves the soil, don't use hay for mulch. Hay almost always contains too many weed seeds.
Organic mulches are usually applied in layers from 2 to 6 inches in depth. Coarser mulches can be applied more thickly than those with smaller sized particles, 4 to 6 inches. Fine textured mulches, which include many wood and bark mulches, generally should not be more than 2 to 3 inches deep. According to Malcolm Beck, too-thick layers of fine textured mulch can block air circulation and suffocate plant roots, resulting in yellowed leaves and poor growth. Grass clippings and shredded leaves, too, should be kept at a depth of about 2 inches since these materials tend to mat together and may inhibit the water and air supply to the plant's roots.
To determine how many cubic feet of mulch you need, you must calculate the surface area and the depth of coverage. For example, you know there are 27 cubic feet in one cubic yard (3X3X3). One cubic yard of mulch will cover a 324-square-foot area to a depth of one inch. To determine the square footage of your square or rectangular beds, multiple the width times the length. To determine the square footage of a circular bed, multiply the radius (distance from the center of the circle to the outside edge) by itself and then by 3.14 (pi). Then multiple the square footage of the bed's area by the depth in inches of mulch desired and divide that number by 324 (square feet area covered by one inch, see above). Recently an urban myth was making the e-mail circuit warning about using hardwood mulch from downed trees in hurricane devastated areas. These mulches, we were warned, contained ravenous tropical termites that would devour our homes in days. Truth is, we already have subterranean termites nesting in our soil and, as is their nature, termites feed on cellulose. It's always a good idea to keep mulch 6 to 12 inches away from the wall of your home to prevent termites from using it as a bridge to your tasty wooden home. As for that termite-tainted mulch from hurricane-ravaged areas, according to a missive from Michael Merchant, an urban entomologist with TAMU, wood-waste from those areas is quarantined. If you're still worried your hardwood mulch might contain termites, Merchant recommended a quick dousing of a garden insecticide labeled for control of ant mounds, or you can raise the temperature of the mulch to 120 degrees to kill off any existing insect life by placing the mulch in a black plastic garbage bag and exposing it to the hot sun for several days. Merchant added a warning that recycled railroad ties present a bigger problem than termites in your mulch.
The Garden Guides website has a fun interactive mulch guide where you click on a type of mulch and an information window pops open that rates the selected mulch by appearance, cost and effectiveness as insulation, moisture retention and weed control, as well as recommended thickness of application and decomposition speed. The gamut of mulches listed range from the uncommon: aluminum foil (who knew that one layer of foil would repel aphids?) and paper pulp, to the more usual grass clippings, cottonseed hulls and straw.
More information on selecting and using mulch is also available through Texas A&M website Aggie Horticulture.