Misconceptions concerning the acidity in pine trees and pine needles have contributed to the misleading assumption that pine straw is awful for gardens. Pine straw, a natural mulch choice to wood mulch, is the fallen needles from the foundation of pine trees which is gathered and sold in bales. The acidity in the pine needles depends upon the age of the pine needles as well as amount of leaching.
Pine straw is frequently believed to dramatically increase soil acidity, making it awful for whatever except acid-loving plants. While it’s a fact that plants do not grow well under pine trees, the reasons are not due to soil acidity alone. Based on study by the Washington State University Extension, pine needles do not make soils more acidic when used as mulch in gardens. These assumptions result from the observation that there are usually no plants growing within a pine forest among pine needles left on the forest floor. A significant contributing factor to growth suppression is that the dense root network near the soil surface which competes with other plants for nutrients and moisture. The needles themselves produce a blanket which suppresses weed growth, but this is a desirable feature for mulches.
Pine straw might not be awful for gardens, however, pine needles do contain acidic tannins that could have some impact initially. When utilized around flower beds, freshly harvested pine needles contain more tannins than aged pine needles. Expect temporary acidic increase until the tannins have leached out after a few weeks, at which point the acidity levels out to about the average acidity of rainwater. It is correct that the soil in pine forests is slightly acidic. Consider, however, this soil is blanketed with heavy applications of pine needles over the span of decades. According to the Colorado State University Extension, “it takes decades to change soil pH and will not fall by more than 0.5 units”
If you would like to prevent any short-term shift in soil acidity, especially when utilizing the pine straw around plants which like alkaline soil, choose aged pine straw which has had the tannins leached from it. Leave relatively new pine straw in a pile and rub it with water, allow it to dry for a few days, then rub it again, repeating this procedure for a few weeks before use. Another option is to use the pine crust just around acid-loving plants or to use it about acid-loving plants at first, moving it into other plants after it ages. Acid-loving plants comprise strawberries (Fragaria spp.) , lupines (Lupinus × hybrida) and hydrangeas (Hydrangea spp.) , which grow in U.S. Department of Agriculture plant hardiness zones 3 through 10, 4 through 8, and 3 through 9, respectively. Evergreen trees and shrubs that do well in acid soil include juniper (Juniperus spp.) , which rises in USDA zones 3 through 9, and spruce (Picea spp.) , USDA zones 3 through 8.
A significant benefit of pine straw, a natural mulch, is actually the result of the organic matter since it breaks down in the soil. While pine needles do not add nutrients to soil, they do increase soil porosity so oxygen may better reach the roots. The fluffy material does not become compacted or form a crust on the surface like other organic mulches, making it easy for water to penetrate the mulch and achieve plant roots. Pine needles break down more slowly than other organic mulches, demanding just approximately 1 inch of replenished fabric annually. The needles lock together easily, which means that, when combined with water penetration advantages, the mulch stays in plays and won’t clean away even when used on slopes.