Mulch your garden for summer survival. Here’s how to choose the right materials

A rose by any other name may still be a rose, but mulches need defining.

There are 17 different materials considered on the University of California’s Statewide Integrated Pest Management website, and some are marginal at best. Becoming a connoisseur of mulch is a good idea if you are looking for long-term benefits in your garden.

As the UC-IPM websites above states: “A mulch is any material placed on the soil to cover and protect it. Many types of landscape mulches are available. The most common are bark and other wood products and black plastic or landscape fabric materials. Other products include paper (e.g., in rolls, or sheet mulch), yard compost, hulls from nuts (almonds) or cereals (rice), municipal composts, and stones.”

With current organic waste laws, especially AB1383, communities will soon be required to haul back their composted garden cart waste. Gardeners can take advantage of this new “waste stream,” and mulch their gardens to reap the benefits.

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Be wary – mulch varies in benefits and drawbacks:

Chipped, ground or shredded bark

Attractive, often called “walk on bark” at landscape supply yards, relatively expensive, but slowly improves soil as it degrades, medium textured mulch is heavy and not subject to blowing or “floating off” with irrigation or heavy rains. Light weight mulch is subject to weed germination. Can be placed over plastic or landscape fabric. Minimum 3-4 inches is best.

Chipped, ground or shredded wood

“Medium to coarse textured products are long-lasting and resistant to wind movement. Sometimes inexpensive or free. May not stay in place on slopes.” Definitely stay away from any dyed or treated woods as they may have dyes or preservatives that are harmful to local waterways.

Black plastic (solid polyethylene)

“Very effective, widely available, relatively inexpensive but has many drawbacks: Restricts air and water movement. Drip irrigation under the plastic usually must be used since overhead irrigation cannot penetrate it. Breaks down in a few months and is unattractive unless a top mulch is applied. Tends to tear and break readily, allowing weeds to grow through holes. Not the best choice for long-term weed control.”

Clear plastic

Not recommended because it will encourage weed growth.

Geotextiles, or landscape fabrics (spun or woven polypropylene and polyester)

“Very effective, relatively long-lasting if covered with bark or other suitable mulch. Allow air and water penetration. Expensive, may be unattractive without a top mulch. Brands differ in effectiveness and resistance to ultraviolet (UV) light.”

Grass clippings and leaves

Readily available, but should be composted for best results. May mat and cause problems with water penetration over time.

Gravel and crushed stone

Not recommended because of the problems which arise as the stone or gravel mixes with soil and becomes difficult to separate. Use landscape fabric under it if you do decide to use, since gravel mixed with soil will favor weed growth.


“Uncomposted yard and tree trimmings. A variable mixture including bark, grass, ground wood, and leaves. Relatively inexpensive. May contain weed or pathogen propagules if not well composted. Can increase problems from small vertebrate pests (e.g., voles).”

Paper, or sheet mulch

Easy application. Can be purchased, typically in rolls. May be useful to decrease weed pressure until newly planted groundcover fills in open spaces. Tends to break or tear after transplanting or if walked on. Hinders air and water movement, so rain and overhead irrigation tend to run off, which can favor weed growth at the paper’s edge. May create a hydrophobic (water-repellant) barrier.”

So, why use mulch, especially in summer months?

Benefits of mulch

  • Weed control: By limiting light to any weed seeds in the soil, a good layer of mulch will help prevent their germination.

  • Conserves soil moisture: “In addition to good weed control, mulch conserves soil moisture by reducing evaporation and reducing water use by weeds. Mulch moderates the soil wetting and drying cycle between irrigations and moderates soil temperatures around roots, improving plant growth. Mulch also reduces compaction and erosion from irrigation, rainfall, and foot traffic.”

  • Mulch moderates soil temperatures: “Mulch moderates the soil wetting and drying cycle between irrigations and moderates soil temperatures around roots, improving plant growth. Mulch also reduces compaction and erosion from irrigation, rainfall, and foot traffic.”

Do you have a gardening-related question? Contact the San Joaquin UC Master Gardeners at 209-953-6112. More information can also be found on our website

This article originally appeared on The Record: Mulching: Do’s and don’ts of using mulch, compost in gardens

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