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Too Mulch of a Good Thing

Michele MacKinnon

“Enough shovels of earth - a mountain.  Enough pails of water - a river.”
-  Chinese proverb


When we mulch our home gardens we mimic Mother Nature—if we practice moderation. Unfortunately, this annual rite of spring is overdone.


The Problem of Overuse

During a recent pruning marathon in a client’s garden, I planned to remove the oldest woody stems from several shrubs. Considerable labor was avoided when I discovered these stems had rotted at ground level. Mulch had been piled high over the crowns and performed as expected. It held moisture and blocked air flow, a formula for rot when misused. Whole new shrubs were born when branch tips close to the ground were buried in material, then rooted in place. Statewide, trees resemble telephone poles as mulch is piled higher against their trunks each year, leading to the outer bark rotting and the tree’s ultimate death. A tree’s primary roots should be visible, radiating out from the trunk like a lady’s shoulders visible in an off-the-shoulder evening gown. 

Use the Right Amount 

Follow these depth guidelines to mitigate mulch madness: 

  • 2–3 inches — perennials, keeping the mulch away from their crowns.

  • 4 x 4 inches — a 4 inch layer around woody plants, such as shrubs, leaving a minimum 4-inch space around trunks.

  • 8 inches — in areas where invasive plants or aggressive weeds have been removed and efforts to prevent their regrowth are underway.

  • Annual mulching should maintain but not exceed the recommended thickness. If old mulch has pancaked, forming an impenetrable mat, remove it before refreshing with new material.

Types of mulch material

The closest to natural material is best. Compost, partially decayed leaves, or partially decayed wood chips are attractive choices and will nourish the soil as they decompose. Small amounts of sawdust are acceptable for acid-loving plants only, such as blueberries, rhododendrons and azaleas. Cover crops, including rye, hairy vetch, field peas, or oats, act as a living mulch in vegetable gardens. Speak to a local agriculture supply store about cover crop options.


What to AvoidNever use recycled tire mulch, which contains products dangerous to children and has been known to catch fire. Inexpensive products are often made from chipped wood pallets that were chemically treated. Dyes are another common additive, which explains the black,

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brown and red choices on display each spring. These dyes and chemical treatments may pose health risks to people and are harmful to soil life. Skip landscape fabric / barrier products since weeds root in it with a tenacious hold and attempts to remove them pulls up the fabric and mulch, adding more work to an already tedious chore. 


Next Steps

Take a close look at mulched areas. Check depths and remove excessive material. Pull it off plant crowns and away from trunks and stems. Research mulch products sold in your area and resolve to use those that offer dual benefits - they beautify the landscape as they improve garden soils. Anyone can be a Master Mulcher with these simple practices.




Michele MacKinnon is a Sierra Club member, UCONN-Certified Advanced Master Gardener, garden educator and speaker. Contact Michele MacKinnon for information or questions.

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