In a recent Healthy Garden article, Paula Gross mentions research indicating that mulches of oak leaves and pine needles do not acidify the soil. In view of the tendencies of woodlands in my area to have a pH of 5 to 6, whereas lawns and fields (admittedly many of which have been limed) tend to be around 6.8, I would be interested in the specifics of the research.

—Will Ferrell, Kernersville, North Carolina

Paula Gross responds: In digging deeper for this article, I was reminded that soil pH is very stable and that it takes a lot to change it. When we want to change soil pH in either direction, we turn to inorganic materials—limestone to increase pH, and sulfur to lower it—because organic materials simply won’t have a strong enough effect in our lifetimes.

I think it is much more likely that the pH difference Mr. Ferrell observes is due to the liming of turf, as he suspects. North Carolina’s Piedmont soils tend to run acidic, but of course it all depends on the exact soil he is testing. Pockets of more and less acidic soils certainly exist.

The effect of oak leaves on soil pH has been studied extensively. A paper published by Nikolai, Rieke, and McVay of Michigan State University documented no change in soil pH after six years of mulching oak leaves into established turf grass. Abigail A. Maynard’s research at the Connecticut Agricultural Experiment Station also documented no difference in soil pH when uncomposted leaves were added to vegetable plots. (Editor’s note: You can find summaries of these studies online by searching for the authors’ names along with the keywords “leaves” and “soil pH.”)

Hard research on pine needles and soil pH is lacking, yet all university extension services I researched dispute the claim that pine needles acidify soil.

If Mr. Ferrell wants to try an experiment of his own over five to 10 years with pine needles, I can tell you he’d have an interested audience online!

Fine Gardening Recommended Products

A.M. Leonard Deluxe Soil Knife & Leather Sheath Combo

Fine Gardening receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

MULTITASKING DUAL EDGES: a deep serrated edge and a tapered slicing edge ideal for tough or delicate cuts. DURABLE 6-inch stainless steel blade withstands 300 lbs of pressure. TWINE CUTTING NOTCH, DEPTH GAUGE MARKINGS & spear point - no need to switch tools when using this garden knife. LEATHER SHEATH: heavy duty, protective, clip on sheath to keep your knife convenient and secure. LIFETIME WARRANTY.

Buy at Amazon

Sun Joe Cordless Telescoping Pole Chain Saw

Fine Gardening receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

BAR + CHAIN: 8 in. auto-lubricating bar + chain with 2.7 fl oz oil tank capacity and oil level window. TELESCOPIC: Telescoping pole extends from 3.7 ft to 7.2 ft, providing up to 14 ft of overhead reach. ADJUSTABLE HEAD: Multi-angle head adjusts from 0º to 30º 24-VOLT SYSTEM: 24V 2.0 Ah IONMAX lithium-ion battery allows for up to 32 cuts of 4" x 4" pine on a single charge.

Buy at Amazon

DeWalt Variable-Speed Cordless Reciprocating Saw

Fine Gardening receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

You can fit a variety of blades to this saw to cut fallen branches or prune larger limbs from trees in a pinch. It’s fast, tough, easy to use, and extremely versatile.
- 18.31 x 6.13 x 4 inches
- 1-1/8-inch stroke length
- Variable speed trigger with 0-3000 spm

Buy at Amazon