Georgia pine trees (Pinus palustris), also known as longleaf pines, adapt to various soil types in their native habitat in the southeastern United States. From the Atlantic Coast -- extending from Virginia through Florida -- and as far west as the state of Texas, Georgia pine trees often dominate the landscape where they grow best. Although the Georgia pine grows in boggy clay soil, it is most commonly found in dry, acidic, sandy soil. Fifteen- to 18-inch long needles, which grow in thick tufts, are acidic while green, but lose their acidity within a few weeks after shedding to the ground and exposure to the elements, making very little impact on soil pH levels.
Reaching heights up to 125 feet in U.S. Department of Agriculture plant hardiness zones 7 through 10, evergreen Georgia pine trees grow best in climates with hot summers and mild winters, surviving from near-sea level to approximately 2,000 feet above sea level. Georgia pines survive fire better than most other trees because of their long tap roots and ability to regenerate. In locations burned over by fire, Georgia pines grow best because of the limited competition from other trees and shrubs and the grassy groundcover.
Pinestraw -- or pine needles -- shed annually, mulching the ground beneath them. Freshly fallen pinestraw has a pH range of 3.2 to 3.8. Acids from pinestraw leach into the soil when exposed to rainfall and the elements. The highest levels of acidity occur after a rain on two-week old pinestraw, according to research conducted by one Texas pinestraw retailer. Initially, pinestraw leachate -- water washed through pinestraw -- had a pH level of of 4.9 to 5.1. After six or seven weeks of exposure, pinestraw leachate tested in the 6.0 range, the same pH level as fresh rainwater.
Mulch and Compost
When used as a mulch, the initial acidity of pinestraw leachate is broken down by microbes in soil, neutralizing the acids, resulting in no significant change in soil pH, notes the University of Wisconsin Extension. When added to compost, the pH of the compost becomes slightly more acid at first, but is quickly neutralized, yielding no net effect on the pH of the finished compost. Decomposed, or fully processed, organic material, whether in the form of mulch or compost, has a neutral pH range of 6.8 to 7.0.
The ability of most plants to absorb nutrients and resist disease organisms is greatest when the soil pH ranges between 5.5 and 7.0. Within this range, bacteria that break down organic matter and certain fertilizers to release nitrogen function most efficiently and nutrient leaching out of soil is reduced, according to the University of Vermont Extension. With pinestraw maintaining a stable pH level of approximately 6.0 after the first several weeks after falling, pinestraw contributes to optimal growing conditions for a wide range of plants.
While mulches, such as freshly fallen or introduced pine needles, impact soil pH slightly for up to several weeks, soil pH generally maintains at a steady level unless the soil is amended with minerals. Washington State University Extension recommends iron or aluminum sulfate or elemental sulfur to increase soil acidity, and horticultural lime to increase soil alkalinity.
- Fine Gardening: Pine Needles in the Compost
- The Longleaf Alliance: What's In a Name?
- USDA Forest Service: Longleaf Pine
- Aggie Horticulture: Longleaf Pine, Longleaf Yellow Pine, Southern Yellow Pine, Longstraw Pine, Hill Pine, Pitch Pine, Hard Pine, Heart Pine
- PineStrawInfo.com: Pine Straw Mulch Acidity: Separating Fact From Fiction Through Analytical Testing
- USDA Natural Resources Conservation Service: Longleaf Pine
- Washington State University Spokane County Extension: Soil pH
- University of Vermont Extension: pH for the Garden
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