UCCE Orange County Master Gardeners
University of California
UCCE Orange County Master Gardeners

Soil Management


Mulch, what is it

Mulch is any material spread over the garden soil to cover it.  Mulch can improve water penetration, regulate soil temperature, and help to prevent soil erosion.  During the warm summer months, mulch reduces water loss and keeps soil cooler for plant roots.

There is no one answer for ‘the best mulch’ to use.  Factors involved in making your choice will depend not only on what kind of garden area (vegetable garden, succulent landscape, around trees, etc.) you would like to mulch, but also your personal preference for the appearance of the mulch.

There are two classes of mulch:
• Organic mulches -- Organic mulches can conserve moisture, prevent surface crusting, improve water penetration, and cool the soil.  Organic mulches include compost, very fine wood chips, grass clippings, sawdust, leaves, clippings, chipped and shredded prunings, wood products, and hardwood or softwood bark chips or nuggets.  Gorilla Hair is a stringy redwood & cedar bark that forms a long lasting mat.  However, it is sharp enough to puncture the skin; it is also very pricey, something you may want to consider since you will probably be renewing your mulch on an annual basis.  Other organic mulches that are good are redwood and cedar mulches.  In time, organic mulches decay, providing nutrients and improving the soil texture at the same time, which is especially helpful for heavy clay soils.  Plan to replenish landscape mulches periodically because of decomposition, movement, or settling. 
 
 Inorganic mulches -- Natural inorganic mulches include sand, gravel, and pebbles. They do not provide organic matter for soil, but do conserve moisture. If using rocks as mulch, consider placing a landscape fabric underneath to create a layer between the mulch and the soil and to prevent rock pieces from sinking into the soil.  Black plastic has been used as a mulch to improve weed control, but it restricts air and water movement. Synthetic mulches, which are manufactured materials that are called geotextile or landscape fabrics, have been developed to replace black plastic in the landscape. Geotextiles are porous and allow water and air to pass through them, overcoming the major disadvantage of black plastic.

Apply mulch to a weed-free area of soil to a depth between 2 to 4 inches.  Applying mulch at depths of greater than 4 inches may injure plants by keeping the soil too wet and limiting oxygen to the plant's roots. However, lesser depths may have less weed control benefits. Disease incidence may increase when deep mulches are maintained.

Whenever you apply mulch, be careful to leave some space around the plant crown or tree base. If you pile any kind of mulch up against the crown, you may cause the stem/trunk to rot, so keep the mulch material at least 1 to 2 inches away from the stem or base of the plant.

We hope this helps you to make a decision on the mulch you would like to use.  Most importantly, you are considering the use of mulch in your garden – good for it and good for the environment!

If you can’t find the answer on the site, don’t despair! We also have the capacity to personally assist you through our hotline.  Just contact us by email or by phone (voicemail) at 949 809-9760 and we will respond to your inquiry.
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