Mulch obliged

An article in the Nov. 9 Home & Design section incorrectly described how to make a mulch "doughnut" around a tree. Two or three inches of mulch should be put down around the base of a tree, several inches away from the trunk. The mulch should extend from there to the far edge of the tree canopy, known as the "drip line," so the tree's roots get maximum benefit.

When Margie Wolf orders a load of mulch to be delivered to her Haddon Township home, she goes for appearance. She likes it dark, preferably black, so it'll provide the most contrast with her lawn and flower beds.

"I don't know what it is," Wolf says of the mulch she and her husband use, "but I like the color." If it happens to be good for the environment, she adds, "that's good. We like to help a little bit."

Most people choose their mulch the same way the Wolfs do - by how it looks, as opposed to whatever benefits it confers on plants and soil - according to David Ablaza, manager of McNaughton's Gardens in Cherry Hill.

"They come in and say, 'My neighbor has this,' and they want their yard to look better than their neighbor's," Ablaza says.

Garden centers like McNaughton's typically sell a dozen or more kinds of mulch, most in spring but plenty in fall.

Organic choices come from things that used to be living, such as leaves and licorice root, bark or wood (cedar, cypress, pine) that's shredded or made into chips or "nuggets." Inorganic products range from tiny pebbles and lava rocks to recycled tires and a "kid-proofed" substance for playgrounds called Turf 4 Tots.

Whatever they choose, a growing number of people are buying. According to the National Gardening Association, 23.8 million American households purchased mulch in 2006, compared with 16.2 million households in 1996. That's an increase of almost 50 percent in a decade, coinciding with the rising interest in professional-looking home landscaping.

Drought, too, is a factor, says Robert C. LaGasse, executive director of the industry's Mulch and Soil Council. Mulch helps soil hold water, he says, noting, "Severe conditions in north Georgia are driving sales like crazy."

But what to choose? With the addition of all the inorganics, along with organic mulches now dyed black, brown, even yellow, blue and red, the world of mulch has never been more confusing.

That goes for the language of this world, as well. Any idea what "top dress" means? How about calculating how many cubic feet to buy? Maybe you're not even sure what mulch is: It's simply a covering that's spread on the ground around plants.

Mulches made of organic matter are the best choice in most circumstances because they eventually decompose and enrich the soil. If you need something other than a plant blanket - say, you have a pathway or steep hill to address - inorganic mulches may work better.

Organic mulch helps keep soil temperature constant in the extremes of summer and winter. It also encourages root growth and keeps soil light and fluffy at the surface, which allows rain to be absorbed more effectively. This, in turn, reduces runoff and erosion.

Most important, says Robert Berghage, associate professor of horticulture at Pennsylvania State University, mulch won't stop your large perennials or already-sprouted weeds from growing - but it will put the kibosh on weed seeds trying to poke through.

"If you mulch, you won't have this continuous resupply of weeds," Berghage says.

Finally, mulch can unify even a hodgepodge of a garden, connecting disparate beds and plantings with a single leitmotif. "It hides all kinds of problems," says Ablaza, who uses cedar mulch, McNaughton's best seller, at his home in Deptford.

But you should also know and appreciate that, as your organic mulch ages, it breaks down, making the soil more fertile.

This is critical. For though we're fixated on huge blooms and explosive color, plants that never sleep, and a landscape that outshines the neighbors', it's that boring relation, soil, that really matters.

How else to explain one of the most oft-repeated sayings in horticulture, which goes something like this: "If you have $20 to invest in your garden, spend $15 on the soil."

So consider mulch an important investment, right up there with your 401(k).

Unlike money socked away, however, more mulch is not better. Two or three inches, no more, is recommended, with a one-inch "top dressing" - mulch sprinkled around - to refresh later in the season.

Many of us ignore this advice. Homeowners wanting a soft, luxurious look - and landscapers hoping to sell it - often pile on five or six inches. Soon, the garden looks like a lumpy down comforter.

"It's way too thick. From everything I see, that's the biggest problem," says Julie A. Snell, public-landscapes project manager for Philadelphia Green, the urban gardening arm of the Pennsylvania Horticultural Society.

Too much mulch can rot roots. It can upset soil chemistry, suffocate plants, and carve out condos for mice. And at about $3 a cubic foot (or more), too much mulch can cost too much money.

There are other missteps: mulching that's done twice a year when once is enough, and "mulch volcanoes" around tree trunks.

"Those are a real no-no," says Gladis M. Zinati, assistant professor and nursery-management specialist at Rutgers University, Cook College.

Mulch should not touch the tree trunk (or plant stem), she explains. It should be ringed around it, like a doughnut. And the "hole" should extend to the far edge of the tree canopy, which is known as the "drip line." That way, the tree can breathe easy.

And you can, too - till mulching time next year.

Mulch is sold by the cubic foot or yard. Julie Snell, of the Pennsylvania Horticultural Society, offers this formula to figure out how much you'll need:

Calculate the square footage of the area to be mulched by multiplying length times width.

For a 3-inch layer of mulch, multiply your square footage by 0.25. This will give you the total in cubic feet.

If you need to know cubic yards, divide the cubic-foot total by 27. There are 27 cubic feet in one cubic yard.

Here's an example: Say your garden is 8 feet by 15 feet. To find out how many square feet that is, multiply those numbers. Answer: 120 square feet.

To convert this to cubic feet, assuming you want a 3-inch layer of mulch, multiply 120 square feet by 0.25. Answer: You'll need 30 cubic feet.

To convert your 30 cubic feet into cubic yards, divide by 27. Answer: You'll need about 1 cubic yard.

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