Regional Gardening Reports :: National Gardening Association

In the Garden:
Southern California Coastal & Inland Valleys
May, 2001
Regional Report

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Organic mulch such as shredded bark conserves moisture, keeps weeds out, and provides a beautiful walkway through your garden.

Much Ado about Mulch

Mulching is the mantra of gardeners, especially in our hot summer climate. The allegiance to mulching is based on our being protective, economical, inventive, and lazy. Protective because we don't want our garden soil and plants to be stressed during the heat of summer. Mulch is economical because we'd rather not pay exorbitant water bills. It's inventive because many readily available materials can be used to mulch. Lazy because we'd just as soon not be out in the garden watering when it's hotter than 90oF.

What Is Mulch?

Organic matter is the magic that enables mulch to keep our gardens happy and productive. Inorganic mulches such as plastic sheeting and rocks can help, but they cannot provide the ultimate value: humus.

Humus is organic matter that's broken down into particles so fine that you can't tell what the original pieces were. Mulch is organic matter that's just chipped or broken into pieces, not decomposed, so you can still tell what they originally came from.

Why Mulch?

Mulching plants keeps soil moisture and temperature more constant. Plants and earthworms thrive when they must endure fewer water and temperature extremes. A 2- to 4-inch-thick layer of mulch decreases evaporation from the soil by 70 percent or more. This allows you to water less often. Keep mulch several inches away from tree trunks and plant stems, however, for good air circulation and to reduce the risk of crown or root rot.

Mulch keeps gardens weed free by excluding the light that seeds need to germinate and grow. Mulch prevents erosion by reducing soil crusting and cracking. As organic mulch decomposes into humus, it improves soil structure and fertility. Mulch in pathways softens the walking surface.

What to Use

Types of organic mulches include grass clippings, wood chips, manure, plant clippings, banana peels, coffee grounds, tree leaves (including pine needles), and shredded newspaper (avoid glossy paper with metal-based inks). These materials will decompose and enrich the soil. Keep in mind that the smaller the pieces of mulch, the shorter the time they take to decompose.

Use That Grass

Grass clippings can be used for mulch during any season of the year. However, fresh clippings contain so much moisture that they should be allowed to dry before being spread more than 1 inch thick. If piled thicker than that, great care should be taken to avoid compressing them until they're thoroughly dry or they'll form an impervious mat that begins to decompose anaerobically (without air), smell bad, and attract garden pests. The problem is easily solved by spreading out the grass clippings so they can dry and decompose properly.

Other Mulches

Coffee grounds, oak leaves, and pine needles are excellent mulches to use around acid-loving plants such as azaleas, camellias, blueberries, and rhododendrons.

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