Pine needles are good for use as a mulch. Pine needles are especially recommended as an organic mulch for use around freshly planted annual flowers, such as marigolds, zinnias and snapdragons.
There is little evidence to support the myth that pine-needle-based mulches acidify the soil. However, gardeners have long recommended pine-needle mulch for use around acid-loving plants, such as azaleas, blueberries and rhododendrons. While the pine needles do not cause the soil to become more acidic, they form an effective mulch that is lightweight and slow to decompose. The pine-needle mulch blocks weed growth and keeps the soil cool in the summer and warmer in the winter.