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Mulch Myths

Public Domain - Wikimedia Commons
Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Gfp-wood-chips.jpg
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Mulching is a time-honored technique in the garden. Using plant-based materials like wood chips, bark, leaves, grass clippings and compost are all ways to add “organic” amendments to your soil. (I am using the term organic to mean nutrients derived from plant materials rather than plastic or rubber mulches.)

Plants need soil, water and sunlight to grow. The soil substrate, other than your watering regime in lieu of rainfall, is the place where you as the gardener have the most control. Consider a soil test, which is relatively easy to perform and cost effective, when you are ready to start a new planting. Micronutrients and pH are two important data points to have, especially if you’d like hydrangeas pink versus blue, or to have a successful blueberry planting. Your local cooperative extension office can help with soil test kits and interpreting results.

So, back to mulching. Is there a best mulch to use? YES! If you can get clean, disease-free wood chip mulch from the local arborist or tree removal service, that is your No. 1 choice. In study after study, wood chips are the winner. When you start a planting, using wood chips as the heavy mulch around your new plants gives higher survival rates and better growth (read the fact sheet here, “Wood Chip Mulch Improves Plant Establishment and Survival).

Using wood chips is preferable to recycled cardboard too! Why? Cardboard can have many other chemicals embedded in it, and cardboard prevents gas diffusion from the air to the soil to the roots (link here for more information). And wood chips are free! Many municipalities will let you come get wood chips from their site — and many arborist companies will drop chips at your site. There is an app for wood chip drops!

BC_Garden_Mulch.jpg
Robyn Puffenbarger
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Wood chips in the garden at Bridgewater College to make the paths. We had chips delivered from arborists and college grounds crew.

What texture should the mulch be? To quote our expert guide, “coarse and chunky,” since this lets both gases and water infiltrate the soil and roots.

How deep should you mulch? At least 3 inches to prevent sunlight from reaching soil so you prevent weeds from sprouting, deep layers as you establish a new bed of 4-6 inches near new plantings is recommended.

Another question is about whether adding mulch changes the nitrogen levels in soils, and the research says no, mulches do not change soil nitrogen levels. For more on mulch myths, see this link and for more in-depth reading on horticultural myths, one more link!

Happy gardening,

Robyn

VHG Co-Host, Professor at Bridgewater College, and a Central Shenandoah Valley Master Gardener
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