Mulch Madness

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.

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Organic, Inorganic Methods

MULCH TYPES

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.

ORGANIC

* 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.

* Hay: Attractive insulator that promotes water penetration. Not as readily available as other mulches. Flammable, so don’t apply in fire-prone areas. May contain grain or weed seeds that germinate.

* Homemade/bagged compost: Excellent soil improver. Attractive dark, crumbly material. Easy to buy or make from organic materials found in the yard and kitchen, such as grass clippings, leaves and produce scraps. Creates a friendly environment for weed seeds, and if not composted properly may contain them. May also blow away if applied dry. Best worked into soil upon application.

* Lawn clippings: Readily available. Avoid applying when fresh, because grass can mat and reduce water penetration. New clippings will also ferment, and the heat and ammonia released can injure or kill plants. Dry clippings and mix them with shredded leaves or another low-nitrogen organic material, or compost them. Never use clippings from a lawn treated with herbicides, and avoid weedy grasses, such as Bermuda and crab grass.

* Leaves: Readily available. Decompose fairly quickly, improving the soil. Will mat and interfere with water and air movement. Shred new leaves and let them age for two weeks before using. These partially decomposed leaves won’t blow around as much as dry leaves.

* Shredded newspaper: Readily available. Unattractive and tends to blow away. Attracts earwigs and sow bugs.

* Peat moss: Adds acidity to soil and contains very few weeds. Expensive when used in bulk and is difficult to re-wet if allowed to dry out. Best mixed into the top layer of soil.

* Pine needles: Attractive, free of weeds and long-lasting. May blow away in high wind.

* Sawdust: Improves soil’s organic content. Inexpensive or free. Will mat and inhibit water penetration. May rob soil of too much nitrogen. Blows away and decomposes quickly. Add nitrogen to the soil when applying. May also contain organic compounds that can harm young plants.

INORGANIC MULCHES

* Old carpet: Long-lasting and durable. Unattractive and can produce an offensive odor when wet.

* Black plastic (polyethylene): Effective and easy to handle. Warms soil somewhat. Breaks down in a few months and is not very attractive, often requiring a top mulch, such as bark. Weeds grow easily through any holes.

* Clear plastic: Similar to black plastic. Encourages weed growth. Weeds grow easily through any holes. Discourage weeds by adding a top mulch, such as bark.

* Crushed stone/gravel: Attractive. May become infested with weeds if used alone. Also expensive and may get too hot in the sun.

For further information on mulching, consult Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Division of Agriculture and Natural Resources Publication 3359, (800) 994-8849; https://Danrcs.ucdavis.edu.