Pine straw is comprised of the needles that have been naturally shed from pine trees, mainly longleaf, slash and loblolly pines, making it an ecologically friendly product. Its fine texture makes it easy to apply around small plants, and its attractive brown color complements their flowers. It is often sold by the bale and is fairly inexpensive.
When applied to a depth of two to four inches, pine needles are an effective weed suppressant. This protects your plants from competition from other plants for water and minerals. The fine texture of pine needles makes it easy to mulch close to the crown, the growing point, of annuals and perennials, reducing the potential for bare spots.
Pine straw is light and airy, and the air spaces within it give it the potential to act as a natural insulator, keeping the ground cool in summer and protecting it from frost in the spring and fall. This is especially beneficial for bulbs, reducing the cycle of freezing and thawing that can heave them out of the ground.
Under a mulch of pine straw, the ground stays more evenly moist than it would exposed to the sun and drying winds. You'll use less water during the summer, and your plants will grow roots closer to the surface with protection. This is especially useful for plants such as fuchsias, ferns and wildflowers that like a moist but well-drained soil.
Contribution to Soil Fertility
Pine needles are leaves and, like other leaves, have a balanced mineral composition that adds nutrients to the soil as they decay. Pine straw decays slowly, making it a long lasting mulch, but when it breaks down into small flakes of organic matter and a sticky substance called humus, it helps the ground hold water and nutrients, benefiting the growth of subsequent plantings.
The Question of Acidity
Pine needles are often thought to be acidic and to make the ground beneath them more acid. While green needles are acid, the dried ones are closer to neutral, making them suitable for both acid-loving plants, such as rhododendrons and blueberries, and plants that like a more neutral soil, such as spinach and corn.
Pine straw is the best mulch for erosion control since it is not washed away by rain. This keeps the soil in place around the roots of shrubs and groundcovers planted on a slope, resulting in faster growth.