Do cedar mulches kill other plants?
Many living, growing woody plants contain allelopathic chemicals, which can prevent seeds from germinating or kill young seedlings. Most compounds have no effect upon established plants. Cedars (Thuja spp.) have not been found to have this ability. Even Juglans nigra (black walnut), the best known allelopathic species, has not been shown to have negative effects when wood chips are used as a mulch.
For more information on wood chip mulches, see “Using Arborist Wood Chips As a Landscape Mulch” WSU Extension Fact Sheet FS160E.
Submitted by: Linda Chalker-Scott, November 2, 2015