Mulch Application

There are several steps to undertake when laying mulch, some of them more strenuous than others, especially in large gardens. In expansive areas, it helps to approach this task in increments, rather than accepting a challenge of completing it in only one go-around. By dividing garden space into small areas and completing each one in turn, rewards of labor can be won several times and are easier to come by.

Mulching Techniques

• For the most effective results, before applying any mulch for the first time, cover the ground with cardboard or thick layers of newspaper to snuff out vegetation and block all light. Overlap materials by at least 6 in., leaving no bare ground or vegetation exposed. 
• With a drip irrigation system, lay newspaper or cardboard under the tubing, leaving it easily accessible. Paper and cardboard decompose in a short time after repeated rains or irrigations.
• When working in any windy conditions, as soon as paper/cardboard is put down, water it immediately to prevent it from blowing away before covering with mulch.
• Coarse textured mulches can be applied 4-6 in. deep; fine-textured mulches only need a 2-3 in. depth since they pack more closely.
• When adding plants to a mulched area, push aside mulch, expose the paper or cardboard, and cut an "X" large enough to accommodate your plant, taking care not to puncture tube irrigation lines. Fold back the flaps, dig a hole, and add the plant. When complete, lay the flaps back in place and re-cover the area with mulch.
• Pay close attention when mulching plants with woody stems, especially trees. Leave 3-6 in. of bare earth around trunks. Too much moisture at the base of woody stems causes rot.

Mulch Maintenance

• Mulch must be replenished periodically as it decomposes over time. Once an initial layer is established, there is no need to lay newspaper or cardboard again.
• Many seeds and seedlings require warmer soil temperatures than occur naturally in early spring. It helps to move mulch away from garden rows where temperature-sensitive young plants grow.
• Check mulch thickness in established beds in spring as winter rains taper off. By adding supplemental mulch then, it is possible to delay watering for several weeks as weather warms.
• Renewing mulch by early summer maximizes its effectiveness. During summer months, mulch slowly decomposes and thickness is reduced, just in time to take advantage of late-season rains.
• Allow mulch to continue to decompose as winter rains increase. Plants need good drainage during these months.
• Deep layers of mulch with woody material that cling tightly together may not need to be renewed for a few years. Thin layers of any mulch my need renewing every 1-2 years.

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