Mulch basics
What mulch does, which kind to use and how deep to spread it
What mulch does
A layer of mulch over bare soil holds moisture in, evens out soil temperature, smothers weeds and protects the soil from pounding rain and erosion. It also stops soil from packing down and helps water soak in. In shrub and perennial beds, wood chips can cut watering by up to half.
Organic mulches also feed the soil as they break down. Gravel and other inorganic mulches don't.
Pick the right kind
Match the mulch to the bed.
- Wood chips and shredded bark: for trees, shrubs and perennials, not annual or vegetable beds.
- Straw: great for vegetable gardens and strawberry beds. Choose straw free of weed seeds.
- Shredded leaves and pine needles: free, light and good for most beds.
- Grass clippings: dry them first or add thin layers; thick fresh layers mat and smell.
- Compost: a thin layer feeds the soil as it covers it.
- Gravel: for dry gardens and paths. Avoid limestone gravel, which can change the soil.
How deep
Spread most mulches about 2–4 inches (5–10 cm) deep. Use the deeper end for coarse materials like wood chips, and the shallower end for fine ones like grass clippings. More isn't better: thick layers can starve roots of air and keep the soil too wet.
Keep it off the trunks
Keep mulch 3–6 inches (7.5–15 cm) away from tree trunks and plant stems. Mulch piled against bark, the dreaded mulch volcano, invites rot, disease, insects and rodents. Think doughnut, not volcano.
Timing and tips
In spring, wait until the soil warms and perennials come up. For winter protection, add mulch in late fall after plants go dormant.
Wood chips only tie up nitrogen where they touch the soil, so leave them on top and never dig them in. Skip plastic sheeting and woven fabric under mulch in garden beds.
Keep mulch a few inches away from your house's foundation, too. And skip cocoa bean hull mulch if you have a dog: it's toxic to them.
Related plant problems
Sources
- Iowa State University Extension: Using Mulch in the Garden
- Colorado State University Extension: Mulching
- University of Maryland Extension: Mulching Trees and Shrubs
- Washington State University: Wood chip mulch: landscape boon or bane?
General guidance, not a diagnosis. Written by PlantWiz in our own words from the sources above.