Which Mulch is Best?

Adding a three to four inch layer of mulch now beneath shrubs and trees, out to the drip line, can help stop weeds, keeps the ground more moist and feeds the plant as well. But which mulch is best?

Each type of mulch has its Pros and Cons:

Bark lasts a long time, looks nice, feeds the soil slowly, suppresses weeds. Beware of finely shredded redwood bark: the hairs can easily ignite if someone tosses in a cigarette butt.

Cocoa shells look nice, last a long time, but may be toxic to dogs.

Chipped/Shredded tree trimmings: inexpensive, feeds the soil, supresses weeds, but needs to be replaced yearly.

Pine needles: best spread at least three inches deep around acid loving plants.

Compost: Inexpensive, provides soil nutrients and improves soil structure. But weed seeds can germinate in it.

Grass Clippings: inexpensive, but should be applied when thoroughly dried. Also, clippings from weed-like grasses, such as bermudagrass, may get established in other areas. And, don't use grass clippings from a lawn that has been treated with weed killers; in particular, postemergent selective herbicides. This could harm the roots of desirable plants.

Straw: Not to be confused with alfalfa, which can germinate if used as a mulch. Keeps weeds down, retains soil moisture, adds nutrients as it breaks down. Can be bulky to transport in bales (get bale hooks!). A good mulch for walkways, too. Ruth Stout wrote entire books on the subject of using straw mulch in the garden. They're collector's items now.


Leaves: Why do you think God named them "leaves"? "Leave" 'em be, where they fall. Better yet, shred the leaves with a bagging lawn mower to create a quicker nutrient source for your flower beds and borders. They break down quickly, so leaves must be constantly added to an area.


Weed Cloth: inorganic, suppresses weeds while allowing air and water to pass through. Needs a layer of bark on top to keep it from disintegrating from sunlight. May keep soil too moist. May lead to surface rooting of plants. Pulling up weeds that are growing in weed cloth may pull up portions of the cloth as well.


Newspapers: inexpensive, suppresses weeds. Must be replaced often, needs to be secured in place.

Plastic: Suppresses weeds, but does not allow air or water to pass through. In the summer, it may raise soil temperatures too high. Hold in place with bark.

Rock: Looks good, but provides no nutrients, may raise soil temperatures too high for the plant.

Benefits of organic mulch:
• retains moisture
• keeps soil temperature constant, reducing plant stress
• suppresses weeds
• gradually increases soil organic matter
• attracts beneficial organisms that improve soil fertility and porosity.
• Mulch encourages healthier plants, reducing the needs for pesticides and fertilizers.
• protects roots and plants from mechanical injury.
• On hillsides and around homes, it suppresses the spread of brush fires.

Some cautionary notes: 
• Don't pile up organic mulch around the trunks of trees and shrubs. • Keep mulch a few inches away from trunks to lessen the chances of rots and other diseases.
• Don't import someone else's problems. Avoid using as mulch any diseased plant material, including suffering tree limbs, diseased leaves, herbicide-treated lawn.

To cover an area with three inches of mulch: apply about 1 cubic yard for every 100 square feet of area.

One of the downsides of mulch: native bees will be dissuaded from nesting in mulched areas. To attract ground-dwelling native bees, keep a portion of your yard unmulched.
 

For a great publication about mulch, download this pdf, "The Landscapers' Guide to Mulch" from the California Integrated Waste Management Board.

And, the video!