Maintain with mulch: Bark or rock helps retain moisture, keep plants cool

By Loretto J. Hulse, Herald staff writer August 8, 2009 

RICHLAND -- Are the plants in your landscaping or kitchen garden looking stressed? Leaves yellowing and limp, colors faded, blooms nearly nonexistent?

"It's very hard to keep plants sustained -- waterwise -- in this heat," said Bev Marcum-McMullen, owner of C & M Landscaping-Garden-Gifts and Nursery in Richland.

Mulching is one way to help the soil retain moisture, keep roots cool and generally "keep them from going South as much as possible," she said.

Covering the open areas around plants and trees with a 2- to 3-inch layer of mulch has an added bonus too. It helps prevent weeds from sprouting by blocking sunlight from the soil.

In the Northwest, most gardeners choose bark or rock mulch. Yet even within those two there's several choices: shredded bark or chunks; lava rock or gravel; Natural hues or dyed.

Shredded bark is the least expensive. Nuggets of various sizes are priced according to size.

"Do note, any bark mulch that's been screened to give it a consistent size will cost more than mulch that has random sizes," Marcum-McMullen said.

Rock comes in all sizes, colors and textures. Marcum-McMullen recommends using rock smaller than three-quarter inch in flower beds.

"Otherwise you can't get a shovel through it," she said.

Compost is another option, as are chopped leaves. Not only are they good for your plants -- both add organic matter and nutrients to the soil -- but if your make them yourself they're free.

Instructions for making your own compost are available at all Washington State University Extension offices (look under county offices in the phone book) or online at http://gardening.wsu.edu/text/libr.htm.

If you use lawn clippings be sure they haven't been treated with an herbicide to control broadleaf weeds. Most of the plants found in the garden also are broadleaf plants and those also will affect compost.

"Compost, as it breaks down, also improves the soil. It loosens clay soils, making it more porous, and gives sandy soils more consistency by adding organic matter," Marcum-McMullen said.

To use leaves as mulch, either chop them up by running over them a few times with your mower or run them through a chipper/shredder before spreading them around plants, shrubs and trees.

With all these options how's a gardener to choose?

"Often it comes down to what look you like, then cost," Marcum-McMullen said.

Once you've decided what type of mulch you want, how much do you need?

A typical three-cubic foot bag of bark will cover an area roughly 3 feet by 3 feet and 1 inch deep.

Rock and bulk bark is sold by the cubic yard. Multiply the length and width of the area you want to cover. That gives you square feet. Take that number with you as you shop mulches and the sales staff will be able to calculate the amount and cost.

Whatever mulch you choose spread it evenly -- two to three inches deep -- around and between plants and shrubs.

Trees can be mulched too but don't mound it up against the trunk like a volcano. Instead, begin tapering it off about a foot away from the base of the tree to the point where the last few inches are bare dirt. Piling mulch against the trunk promotes decay and provides insects a path straight to and into the tree. Keep mulch away from your home's siding for the same reason.

* Loretto J. Hulse: 509-582-1513; lhulse@tricityherald.com.

See more of the Herald's Home & Garden stories at www.tricityhomeandgarden.com.

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