Pine needles are preferred by many gardeners because they are a natural, readily available and inexpensive way to mulch garden plants. Mulching plants contains soil erosion, retains moisture in the soil and provides a steady supply of nutrients to plants as the needles decompose. Pine-needle mulch, or pine straw, has a rich, earthy color that many gardeners employ as contrast against the bright blooms of annuals, perennials and green-leafed plants. Acidic-loving plants respond particularly well to pine-needle mulch. When saving pine needles to use for mulch, it's a good idea to water the mound of needles periodically. Piles of dry pine needles can create a fire hazard, especially if kept too near the house.
Blueberries prefer acid soils with a pH level of about 4.5 (soils with a pH of 7 or less is considered acidic). Pine straw spread around the base of blueberry plants helps them maintain a proper pH value as the mulch gradually decomposes.
Broad-leafed hostas---also acid-loving plants---do well with a thick layer of pine needles spread around the base of each plant. Not only will the mulch keep the soil moist, but it will also provide a pleasing contrast to the lush blue-greens, greens or yellow-golds of different hosta varieties.
Because annuals mature and bloom relatively quickly during the growing season, pH levels in soil aren't as critical to them. Pansies, zinnias, snapdragons, dahlias and marigolds respond well when mulched with pine needles, especially since pine straw is light enough for young annual plants or bulbs to push through as they grow toward the sun.
Azaleas, Rhododendrons and Camellias
The vivid pinks, reds, whites and oranges of azalea and rhododendron shrubs add a dramatic beauty to any garden. These largely evergreen shrubs thrive in damp, acid soils. Mulching with pine needles ensures proper pH soil levels for azaleas and rhododendrons throughout the growing season. Camellia growers in the Gulf states of the U.S. spread pine needle mulch around their prize-winning camellia shrubs not only for soil nutrition and temperature maintenance, but also for aesthetic reasons.
Flowering perennials such as daylilies, Shasta daisies, coreopsis and canna lilies grow well when mulched with pine needles. Pine straw also prevents mud from spattering on plants after a heavy rainfall.