Mulching – A Must

By Lee Oliphant, Master Gardener

Have you ever wondered why weeds grow freely on your garden’s bare earth while the floor of a lush and healthy forest is weed-free and moist?  Such natural conditions are partially the result of leaves, evergreen needles and other plant materials covering the ground.  The organic cast-off smothers weed seeds, retards moisture loss from the soil, protects shallow roots from weather extremes and erosion, and eventually breaks down to supply nourishment for vegetation.

Mulching is the most natural method of protecting your garden from the harshness of seasonal conditions and improving the health of plants and soil.  Mulching reduces many time-consuming chores such as weeding and cultivating.  Mulching helps keep plants cool when summer heat sets in.  Mulch encourages earthworms and other microscopic organisms that increase and improve nutrients in the soil.

Your choice of mulching materials will depend on where you live, what is available, what you have planted in your garden, and how much you want to spend.  There are many aesthetically pleasing organic types of mulch that will contribute to soil improvement over time.  Coniferous trees provide attractive bark that comes in a variety of sizes.  Other commonly used mulches include oak leaves, peat moss, pine needles, hay, sawdust, seaweed, rotted manure, compost (either home-made or commercial), grass clipping, and wood chips.  Buckwheat and rice hulls provide a solid background for ornamental plants such as roses.

Mulching should begin in the fall after you’ve done a general garden cleanup.  Before mulching, weed and water your garden.  Lightly cultivate the top one or two inches of soil.  Spread a layer of mulch evenly over the soil under plants.  For flower beds, mulch can be applied up to 3 inches deep, pulling it back slightly from plant stems.  Bark chips do not compress readily so they can be applied more thickly than grass clippings.  Mulch layers must not be so heavy as to prevent air circulation and obstruct moisture and the sun’s warmth.

In the spring, rake back what is left of the mulch and plant young seedlings.  Fertilizer should be worked into the soil, as it will decompose more quickly under a layer of mulch.  Work the partially broken-down mulch into the soil around the new and old plantings.  When the midsummer heat arrives and the soil has warmed, add a fresh layer of mulch to last through fall.

Particular plants thrive in particular kinds of mulch due to their environmental needs.  Azaleas, Rhododendron, Camellias, and Gardenias, thrive in an acid environment.  For these acid loving plants pine needles, oak leaves, and peat moss are appropriate mulches.  Mulch is not a replacement for fertilizer so continue your fertilizer regime.  Avoid working in large amounts of under decomposed materials into the soil.  Straw, wood chips, and grass clippings can deplete nitrogen in the soil as it breaks down, so additional fertilizer is essential if using these materials as mulch.

This year, mimic "Mother Nature" by providing your garden with a blanket of mulch.  You will improve the look and the health of your plants and the texture and structure of your garden soil.

University of California Cooperative Extension Master Gardener Volunteers can provide additional gardening information upon request .Call the San Luis Obispo office at 781-5939 on Mondays and Thursdays from 1 to 5 PM.  You may also call the Paso Robles office at 237-3100 on Wednesdays from 9 AM to 12 PM.  The San Luis Obispo Master Gardeners website is at  Questions can be e-mailed to: