Using pine needles as mulch is commonly done, but some things should be understood beforehand. Pine needles are extremely acidic and will lower the PH of the soil very quickly. Sometimes that is a desired result, and some plants, such as azalias, rhododendrons, camellias and gardenias are acid-loving and will thrive in acidic soils. Blueberries and Loganberries also love acidic soils. If the soil becomes too acidic, the PH can be raised by the addition of oyster shells or lime. Soil testing kits can be found at most garden supply centers, and will help determine the PH of the soil.