Warmer weather gets us back out into our gardens, but being overenthusiastic can lead to some gardening “don’ts”, often this applies when putting out fresh mulch. It is always useful to review the “Do’s and Don’ts” of mulch usage at the beginning of the season. The 2 major rules of thumb when it comes to applying mulch are 1) mulch should only be 2-4″ deep at the most and 2) keep mulch away from the base of plants. An additional rule to remember is to try not to cover emerging perennials with mulch.  While mulch provides many benefits to our landscape plants and woody ornamentals, incorrect usage can lead to problems.

Mulch Pros (Do’s)

  • Mulch helps regulate soil temperatures; keeps roots cool in the hot sun and can insulate in cooler temperatures.
  • It can help keep weeds at the soil surface from germinating and taking over beds.
  • As mulch decomposes it increases available organic material, providing much-needed carbon and nitrogen to microbes and then to plants.
  • Mulch can provide stability and structure to soil, additionally it can mitigate drainage issues.
  • Mulching has been known to increase activity of beneficial mycorrhizal fungi.
  • Providing an additional boundary around plants can prevent damage to sensitive zones.

Mulch Cons (Don’ts)

  • Avoid piling mulch up around the base of plants, this can lead to excessive moisture retention which makes plants susceptible to disease, rot and infestation.
  • Axillary roots may develop if mulch is too high, dense and wet, these roots may girdle the tree if left unattended.
  • Also, if too much moisture is retained within mulch, not enough may be infiltrating to the root system.
  • “Sour mulch” can develop is mulch is piled too high. Compaction and heating resulting from large piles of mulch can produce anaerobic conditions and may lower the soil pH significantly.

Weed fabrics, plastic mulches and inorganic products are all worth consideration as well. Plastics and fabrics provide effective weed control, but need to be maintained and replaced as they break down over time. These also may cause problems if applying soil amendments or systemic pest and disease control becomes necessary. Plastic and fabric products also can limit moisture acquisition and soil aeration. For advice tailored to your landscape and mulching needs contact your arborist before purchasing and applying mulch products.

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