Knowledgebase
Bark mulch acidity #823618
Asked March 27, 2023, 2:43 PM EDT
Linn County Oregon
Expert Response
Hello,
Bark mulch will not have much of an effect on the soil acidity. If the goal is to acidify the soil for blueberries, another approach would give better results.
From Mulching Woody Ornamentals with Organic Materials | OSU Extension Catalog:
Do mulches alter the pH of the soil?
Many organic mulches are acidic. Some, such as bark mulch, may have a pH as low as 4, or even lower. It often is assumed that these acidic mulches will lower soil pH. However, in all but the sandiest soils, soil pH is strongly buffered (resists change), so soil pH changes very little after applying most mulches. Some change in soil pH may occur in the top 2 inches of soil, especially if mulch is applied repeatedly. In general, though, mulches do not change pH enough to be a major concern for woody ornamentals.
Regards,
Leo Sherry
OSU Extension Master Gardener Volunteer
