Garden Myth Busters! Pine Needle Mulch

Compiled by Marsha Mercer, Extension Master Gardener

The Myth? Using pine needles as mulch will cause your soil to become significantly more acidic.

Reality: False.

Many gardeners believe this persistent myth, perhaps because people often find it difficult to grow grass under their pine trees and assume the pine needles are to blame. But Cooperative Extension educators have been trying to bust this myth for years.

We’ll take a look at the consensus—among horticultural extension agents, master gardeners, and soil scientists around the country—that using pine needles as mulch can be beneficial in several ways and will not significantly increase your soil acidity.

As always, it’s a good idea to get your soil tested to understand your soil.

So, here’s the existential dilemma: Do pine needles fall to the ground and acidify the soil or do pine trees thrive in acidic soil in the first place?

“The question is ‘which came first?’ In most, if not all cases the acid soil was there to begin with,” writes Andrew Ristvey, extension specialist for commercial horticulture at the University of Maryland. ^[1]

“While it’s true that the soil near pines is often quite acidic, the soil pH was not determined by the tree,” according to the University of New Hampshire Extension. “Pines grow where they do because the soil and the climate are suitable, and they are not creating acid conditions themselves. When nothing grows beneath a white pine tree, it is probably because the tree has numerous shallow roots and is casting too much shade.” ^[2]

Going a bit deeper into the science, Amy Joy Detweiler, an Oregon State University Extension horticulturalist, writes: “It is true that pine needles have a pH of 3.2 to 3.8 (neutral is 7.0) when they drop from a tree. If you were to take the freshly fallen needles (before the needles decompose) and turn them into the soil right away, you might see a slight drop in the soil pH, but the change would not be damaging to the plants.” ^[3]

As needles decompose, they lose their acidity and they have little effect on the soil.

If you don’t have your own pine trees, pine needles are available in garden centers, and according to the Virginia Tech Extension, “They make excellent mulch around shrubs, trees, and in other areas where a long-lasting mulch is desired.” And they are “readily available.” ^[4]

You may also see pine straw bales for sale. Those are just fresh, undecomposed pine needles harvested from the forest floor, “a valuable woodland resource in the southern pine region of the United States,” according to the U.S. Department of Agriculture.  “Pine straw has been a popular mulch throughout the South since the 1980s.” ^[5]  

Among its advantages are it’s long lasting, light weight, high in nitrogen, fine textured, uniform in color, and pest free, and it stays in place. It does not attract termites.

Be sure to keep pine needles or pine straw well away from homes, grills, and fire pits as these pine products are highly flammable, experts say. And enjoy your pine mulch.

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[1] Ristvey, Andrew. 2025. The “Pine-needle Myth: Truth or Bust?” University of Maryland Extension TPM/IPM Weekly Report (March 28, 2025)
https://extension.umd.edu/sites/extension.umd.edu/files/2025-03/25Mar28L.pdf

[2] The Ask UNH Extension Infoline. 2019. Do pine trees and pine needles make soil more acidic? University of New Hampshire Extension.
https://extension.unh.edu/blog/2019/10/do-pine-trees-pine-needles-make-soil-more-acidic

[3] Pokorny, Kim. 2023. Myth vs. reality: What’s the truth behind some common gardening practices? Oregon State University Extension.
Myth vs. reality: What’s the truth behind some common gardening practices? | OSU Extension Service

[4] Relf, Diane and Alan McDaniel. 2020. Mulches for the Home Vegetable Garden. Virginia Cooperative Extension.
https://www.pubs.ext.vt.edu/426/426-326/426-326.html

Freeborn, John. 2014. Springtime Mulching. Virginia Cooperative Extension.
https://ext.vt.edu/lawn-garden/turfandgardentips/tips/Springtime_mulch.html

[5] Wallace, Douglas and Thomas Ward. 2011. Pine straw — a profitable agroforestry enterprise. Agroforestry Notes. USDA.
https://www.fs.usda.gov/nac/assets/documents/agroforestrynotes/an37ff06.pdf