Marin Master Gardeners
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Give your garden TLC with mulch

November 28, 2014
Martha Proctor

Mulch, mulch, mulch, compost, compost, compost. That's the mantra of Master Gardeners everywhere.

Mulching receives high praise because it enriches and protects the soil, which greatly improves the growing environment. Compost is valued because it improves soil structure and provides an excellent source of plant nutrients. Mulching and composting are two of the simplest gardening practices and two of the most beneficial.

Mulch is the addition of a protective layer composed either of an organic or inorganic material spread on top of the soil. Organic mulches improve the soil by continually providing nutrients as they slowly decompose. Organic material improves root growth, helps the soil stay loose and, most critically with our drought, increases the infiltration of water and improves the water-holding capacity of the soil. Organic matter provides an ideal environment for earthworms and other beneficial soil organisms.

Inorganic mulches lack the soil-improving characteristics of organic mulch, but are suitable in certain landscapes. Examples of organic mulches include grass clippings, straw, newspaper and bark chips while stones, brick chips, and gravel are examples of inorganic mulches.

The list of benefits provided by applying mulch is extensive. Of particular importance, while California finds itself in the midst of an extreme drought, is mulch's ability to conserve moisture thus reducing the need for frequent watering. In summer, 2 inches of mulch cuts water loss by 20 percent and lowers temperature in the top 4 inches of soil by 10 degrees. Mulch also protects the soil from erosion, reduces weed growth, especially annual weeds, by as much as 90 percent, and provides a more finished look to the garden.

If and when we do receive heavy rains, it reduces the compaction that results from the impact of such rains.

Mulches applied in late fall help insulate plant roots without compacting the soil. In mid- to late spring, apply mulch after the soil has warmed. This helps prevent cool, wet soil that tends to slow seed germination and increase the decay of seeds and seedlings.

Decide which mulch would work best for your site and conditions, and purchase or accumulate what you need. Often the materials are already available on your property, such as leaves, grass clippings or newspaper.

• Leaves: Collect leaves in the fall, chop them with a lawn mower/shredder, compost the leaves during winter and spread them over the soil in spring.

• Grass clippings: Spread clippings over the soil immediately after mowing to minimize the chance of the leaves heating up and rotting.

• Newspapers: save old newspapers, but discard pages with colored dyes as these are thought to be harmful to soil microflora and fauna. Use 3 or 4 sheets together, anchored to prevent the sheets from being blown away.

Mulch can be purchased in bags (typically in 2- or 3-cubic-foot bags) or in bulk from garden centers. If your garden is on a hill, using bagged mulch affords easier handling, especially for small projects. Purchasing in bulk is cheaper if you need large amounts and have a way to transport it.

The basic guideline for using mulch is to apply a layer that settles 2 to 4 inches deep. Coarse mulch, which only needs to be applied annually, is best for weed control. Do not apply mulch right up to the base of shrubs or trees. Place mulch so you can see the root flare or 6 to 12 inches away from the trunk to reduce the risk of damage from disease, insects and rodents.

Now you know why the Master Gardener mantra includes mulch, mulch, mulch.

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