As it becomes more widely available, cedar mulch is often seen around trees and along footpaths. Cedar offers many of the same benefits as other wood mulches in addition to high durability, but it is also widely rumored to have negative effects, including acidifying soil.
Acidity or Alkalinity Levels
Soil's acidity or alkalinity is measured by its pH. Neutral soil has a pH of about 7.0; anything higher is alkaline and anything lower is acidic. And though cedar mulch is sometimes thought to lower pH, making soil acidic, this is not the case.
Cedar's reputation for acidifying soil may stem from the fact that cedar trees often grow in acidic soil. But whatever the cause, Chris Starbuck of the University of Missouri at Columbia, who has extensively tested cedar mulch, reports that any long-term lowering of pH by cedar mulch is unlikely.
Cedar mulch helps trees, shrubs and perennials by helping to keep soil cool and aerated while retaining moisture and promoting soil microorganisms and earthworms. Cedar mulch is not recommended in annual gardens and flower beds that need replanting every year, because it can be detrimental to germination.