Types of Mulch

Beyond the practical advantages of covering the ground—water conservation, soil health, weed control—mulch contributes to the beauty of a garden setting. Spread beneath stems and branches, it highlights colors, shapes, and textures of foliage and bark. When selecting materials, it helps to experiment with several types to find the most pleasing effects. You may want different applications in different areas of your garden. 

Straw

Commonly used in vegetable gardens, straw is one of the most effective mulches. It is extremely porous, yet it traps air and effectively moderates soil temperatures. Bales, composed of light weight, easily separated compressed flakes, will cover large areas. Some gardeners prefer it as an undercoat beneath a more attractive material because it is less costly and attracts large numbers of earthworms.

• Rice straw is usually available in late summer and early fall from Central Valley rice harvests.
• Rice straw is weed free, can be used immediately, deteriorates quickly when winter rains are heavy, and needs annual renewal.
• Wheat and oat straw last longer than rice straw due to their coarser structure, but hold large amounts of seed that are best destroyed with moisture and partial decomposition before use.
• To eliminate seeds in wheat and oat straw, place bales where you want to spread straw later.
• Soak bales with water until they are covered with 1-2 in. of sprouted grass, or leave bales exposed to rain for a month or more during the winter. Be sure that you place them where mulch is to be applied before they get wet; they're difficult to move when soaked.
• Use straw quickly as soon as sprouted grasses have died or dense bales will rot completely.

Alfalfa Hay/Pellets

Though more expensive, alfalfa offers all the advantages of straw plus the added bonus of more nutrition. Straw is a carbon source whereas alfalfa contains more nitrogen that moves into the soil.

• Alfalfa is seedless and can be used immediately without the soaking treatment described above; it has a longer life than rice straw.
• Some gardeners prefer to use spoiled alfalfa, loose piles or partially composted bales, that has become unusable as animal feed.
• Pellets are merely small chunks of compressed alfalfa. Sold in bags, they are easy to transport. 
• Whether in bale or pellet form, alfalfa and straw are available at most feed stores.

Barks and Hulls

Attractive barks and hulls can be purchased in bags or in bulk . Bagged materials are useful for small areas of only a few square feet; bulk purchases are needed in more expansive gardens.

• Reddish brown cocoa bean hulls are appealing for their rich color and initial chocolate smell; however, chemicals in the shells are toxic to dogs and cats and shells are not long-lasting.
• If applied too thickly, cocoa bean shells become gummy after a while and lose their porosity.
• Various types of barks have the advantage of being long-lasting as well as attractive. Their irregular shapes allow water to pass through easily into the soil. 
• Barks are composed of thick cellulose cells that take many months, often years, to decompose. They are attractive but less effective than other organic mulches in enriching the soil.
• Shredded redwood, like any bark, takes a long time to decompose compared to other mulches. It is functional but has a reputation of appearing to look like an artificial material. 

Yard Waste 

Recycling plant materials generated on your own property retains the nutrients these plants drew out of your soil. It’s best to shred large leaves to prevent clumping and woody materials to reduce size.

• Fallen leaves raked onto beds in the fall will decompose under winter rains, protect soil from erosion, add nutrients to beds, and insulate dormant plants during cold spells. 
• Grass clippings are better consigned to the compost pile because they tend to clump unless they are spread very sparingly or mixed thoroughly with other materials.
• Shrub clippings and flower stems and clippings can be used under more attractive materials.

Municipal Garden Waste/Chipped Trees/Recycled Wood

Large-scale recycling enterprises sell bulk materials by the yard relatively inexpensively, though transportation costs for delivery can equal the cost of materials.

• Consider the source of commercially recycled materials for use in your garden. Recycled lumber products are better used for pathways and ornamental areas than for vegetable gardens since they may be impregnated with unknown chemicals.

Compost

Compost is most valuable as a soil amendment for adding fertility and texture to soil. It is made up of fully decomposed plant materials that supports microbial life.

• Compost and mulch are not necessarily the same. Many gardeners use compost as mulch for its slow release of nutrients.
• Generally, mulching materials are not fully decomposed and only become compost over time. 
• Mulch should be used as a top-dressing only, never confused with compost and mixed raw into garden soil. Raw materials rob soil of nitrogen as they decompose and plant growth slows.

Gravel

Fine, crushed, or coarse gravel and colored rock can act as both mulch and decorative hardscape element in parts of the garden.

• All types and sizes are long-lasting and attractive, but, like some of the barks, they provide no  nutrients to the soil.
• Because gravel is so permeable, it allows weed seeds to fall through. Some gardeners lay gravel over plastic sheeting or weed cloth, but these materials exclude air, suffocate soil microbes, and do not promote a healthy environment for root growth.

Additional Information

• A layer of mulch helps with weed suppression and water conservation, but wood mulches are combustible so they should not be used in a widespread or continuous manner.
• Avoid wood mulch in the 0–5’ zone around your home. Separate mulched planted areas with noncombustible materials such as concrete, gravel, or a mown native grass strip.
• Composted materials have demonstrated the least hazardous fire behavior in mulch flammability research studies. Choose well-composted, larger-size arbor mulch and avoid shredded bark mulch, which tends to smolder.
• https://sonomamg.ucanr.edu/Firewise_Landscaping/

May 2022