How Do Pine Needles and Leaves Change the PH of Soil?

Pine needles are often sold as mulch.

Soil pH is measured as the balance between the alkalinity and the acidity of the soil. Most garden plants do better in slightly acidic soil, but others prefer it slightly alkaline. Adding various materials to the soil -- including pine needles -- can change the balance.

A Myth

Homeowners can use pine needles as mulch around plants without fear of affecting the pH balance. The University of Wisconsin Cooperative Extension considers it a myth that adding pine needles to the top of the soil will make the soil more acidic. This is a widely held belief, even among landscape and agricultural professionals.

Temporary Effect

Adding pine needles directly into the soil may make the soil temporarily more acidic, but this effect disappears as microbes convert the needles to humus. The University of California at Davis states that nature works over thousands of years of continuous application of pine needles to permanently modify and acidify the soil.

Compost

Pine needles added to compost will not affect the compost's akaline/acid balance either. The same microbes in the soil do the work in the compost and will eventually balance the pile to neutral.

References

• Landscape And Garden: Inorganic Soil Amendments
• University Of California at Davis: Changing pH in Soil
• University of Wisconsin Cooperative Extension: Pine Needles Cause Acid Soil -- Fact or Fiction