Advice about mulching under plants - Ask Extension
I understand that it is a good practice to have a few inches of mulch under planting to reduce weeds and slow down evaporation. But I’m a bit stuck ...
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Advice about mulching under plants #920357
Asked October 21, 2025, 10:43 AM EDT
I understand that it is a good practice to have a few inches of mulch under planting to reduce weeds and slow down evaporation. But I’m a bit stuck on how best to do this.
If I place a few inches of mulch around the base of trees or shrubs I am likely to bury the flare at the base of the plants which is not good. How do I avoid burying the flare?
I don’t want to use cedar chips as the mulch and am inclined toward a darker bark dust. Is a finer or coarser type better for this? It seems some will be more acidic which could benefit certain plants while annoying others. Is there a one type fits all or is it better to use different mulches depending on the plants?
Thanks for your thoughts.
Multnomah County Oregon
Expert Response
Organic mulch is excellent for soil health, moisture retention and can suppress weed seeds sprouting. Recommendations are to pull it back from the plant’s trunk, coarse is better, and there’s no need to change type for different plants.
Choosing the mulch source is something to research. If you choose a decorative bark mulch, don’t apply it deeply, as it can repel water rather than hold it. (The purpose of bark, after all, is to hold water in the tree trunk.) Bark “dust” can mat together like a thick dry blanket, but soil health is improved by exchanging water, air, microbes and more. It’s a porous, organic surface breaking down on the soil surface you want to aim for. Bark nuggets are better than fine dust, and arborist wood chips are better yet. My neighborhood requires I use bark dust, so I pile on arborist chips with a very thin bark layer to disguise the chips.
Research shows that the nitrogen used and acidity created on that layer where mulch touches soil won’t really affect the soil below.
Read more at this WSU page on myths, especially the section on Mulches. Specifically, one on the Myth of Pretty Mulch, and this, on bark mulches. This about wood chips is why I’ve been using them heavily for years. They incorporate into my soil, improving drainage bit by bit, no digging needed.
Choosing the mulch source is something to research. If you choose a decorative bark mulch, don’t apply it deeply, as it can repel water rather than hold it. (The purpose of bark, after all, is to hold water in the tree trunk.) Bark “dust” can mat together like a thick dry blanket, but soil health is improved by exchanging water, air, microbes and more. It’s a porous, organic surface breaking down on the soil surface you want to aim for. Bark nuggets are better than fine dust, and arborist wood chips are better yet. My neighborhood requires I use bark dust, so I pile on arborist chips with a very thin bark layer to disguise the chips.
Research shows that the nitrogen used and acidity created on that layer where mulch touches soil won’t really affect the soil below.
Read more at this WSU page on myths, especially the section on Mulches. Specifically, one on the Myth of Pretty Mulch, and this, on bark mulches. This about wood chips is why I’ve been using them heavily for years. They incorporate into my soil, improving drainage bit by bit, no digging needed.
