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Mulch Madness

Covering your garden soil protects plants, saves water and discourages weeds. Plus, it's easy.


Be nice to your plants and yourself--mulch. Few gardening tasks are as simple and beneficial as mulching, which refers to spreading organic or inorganic material over the soil around plants.

The list of mulch benefits is long, says John Kabashima, environmental horticulture advisor for the University of California Cooperative Extension at the South Coast Research and Extension Center in Irvine.

Mulching modifies the climate for plants and prevents them from experiencing temperature fluctuations, which can be harmful.

"Plants are like humans," Kabashima says. "Drastic changes in temperature stress them. Mulch acts as an insulator, ensuring that the soil

doesn't heat and cool as quickly as outside temperatures."

Applying mulch around plants simulates what occurs in nature. In the forest, the ground is littered with fallen vegetation that insulates the trees and other plants.

Mulch, including shredded bark chips, lawn clippings, peat moss and compost, also increases water penetration and keeps soil moist longer, discourages weeds, prevents erosion, protects fallen fruit from injury, helps your garden look tidy and, if the mulch is organic, improves the soil.

Mulching saves a lot of water. Experts say that there is a 50% to 60% reduction in water usage when mulch is used.

Organic mulches--those that break down over time such as leaves and compost--greatly improve the soil.

"The minerals and organic matter gradually released from decaying mulch enrich deficient soils, replacing nutrients taken up by roots as plants grow, and often enhancing earthworm populations, which have something to feed on," Kabashima says.

As many gardeners know, lots of earthworms mean healthy soil, he says.

He says that recent research by Dr. Jim Downer, environmental horticulture advisor with the Ventura County office of the UC Cooperative Extension system, demonstrated that the microorganisms in mulch produce enzymes and other chemicals, which stimulate the plant to develop systemic acquired resistance to some plant pathogenic diseases.

Another compelling reason to use mulch is for its weed-suppressing ability. If thick enough, mulch blocks sunlight, which many seeds require to germinate and all plants need to grow.

Keep the following mulching tips in mind:

* Choose a well-composted mulch. Don't use materials such as grass clippings and leaves when fresh. Compost should also be broken down well. To kill off potential weed seeds, the compost must heat to 140 degrees. Make sure packaged mulch says "composted" on the label.

* Water before mulching an area, which will lock in moisture and cut down on future irrigation.

* Apply mulch from 1 to 3 inches thick, on the deeper end for weed control. Avoid applying a really thick layer of mulch, because there won't be enough exchange of carbon dioxide and oxygen between the ground and the air, and the plant could be smothered.

* Keep mulch several inches away from the base of plants, as excessive moisture around the trunk can promote crown diseases and encourages pests such as sow bugs and snails.

* Mulch is better at preventing weeds from sprouting than at killing existing ones. For best results, remove all weeds before mulching.

* Mulches high in carbon and low in nitrogen--such as straw, sawdust and bark--use nitrogen in the soil as they decompose. The nitrogen is later returned to the soil as microbes die, but plants can suffer before that happens.

Symptoms of nitrogen deficiency include poor, stunted and yellowish new growth. Solve this problem by fertilizing the area with a high-nitrogen fertilizer when you apply the mulch.

* Regularly replace mulch: Organic mulches break down and are incorporated into the soil, and inorganic mulches suffer from wear and tear and may become unsightly.


Organic, Inorganic Methods


There are two main categories of mulches: plant-derived organic types and inorganic mulches. Both keep soil temperatures stable, conserve water and prevent erosion, but only organic mulch improves the soil.

Perhaps the most important thing to consider when choosing a mulch is availability. The easier it is to get, the more likely you are to use it. Here are several mulches to choose from.


* Chipped or shredded bark: Attractive and decorative. Won't blow away. Decomposes slowly. Tends to harbor pests such as earwigs, termites and sow bugs.

* Cocoa mulch (trademark name): A relatively new mulch that is a byproduct of the cocoa plant. Pleasant chocolate aroma. Lightweight and easy to spread. Adds nitrogen, phosphorus and potassium to the soil (3-1-3). Attractive. Deters slugs, snails and cats. Lightweight and may blow or wash away if not applied properly. Evenly spread with rake and lightly tamp down. Then soak with a fine spray of water, which will activate a natural gum in the mulch and bind it into a loosely knit, porous mat.

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