Pine trees (Pinus spp.) range from dwarf trees to giants of the species. Hardy in U.S. Department of Agriculture plant hardiness zones 2 through 9, depending on species and cultivar, one of the more than 120 species will suit your gardening needs and climate. While you may want a green expanse of lawn that covers the entire yard, it may look thin and scraggly around and under your existing pine tree. For the lush lawn of your dreams, choose a sturdy, shade-tolerant grass species when you plant grass under pine trees.
About Pine Trees
Most pine tree species prefer a neutral to acidic soil with a pH level between 4.0 and 7.0, depending on the species. Although there is a common belief that the pine needles that drop from the tree make the soil acidic, that is not true. The soil on which the pine tree grows is acidic because that's what the tree prefers. The dead needles lose their acidity as they decompose.
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While most pine species thrive on well-draining, sandy soils, the shore pine (Pinus contorta) tolerates both dry and wet soils, salt spray and windy conditions, making its 40- to 50-foot-tall, sprawling, irregular form a good choice for problematic garden sites in USDA zones 4 to 8.
Pine trees have a shallow, sprawling root system with a multitude of tiny feeder roots filling in the spaces between the larger roots. Competition for moisture and nutrients is fierce and make it difficult to grow and maintain a lawn or ground cover under the tree. In addition, depending on the species, the branches and needles block the rain and shade the soil. To successfully plant grass under the pine tree, you should choose a grass that tolerates partial sun and shade.
Choose a shade-tolerant grass species to plant under pine and other shade trees. In general, select a grass or blend of grasses that thrive in the same environmental conditions and USDA zone as your pine tree.
In USDA zones 3 through 7, the fescues (Festuca spp.) thrive in shade and acidic soils. These cool-season grasses tolerate dry soils and don't require a lot of fertilizer. Rough-stalked bluegrass (Poa trivialis) is a good choice for acidic, poorly draining and shady locations in USDA zones 3 through 7. It is less tolerant of foot traffic and doesn't grow well in hot and dry conditions.
Warm-season grasses that thrive in full sun and partial shade include centipedegrass (Eremochloa ophiuroides, zones 7-9), Bahiagrass (Paspalum notatum, zones 7-11) and St. Augustinegrass (Stenotaphrum secundatum, zones 8-10). Of the three, St. Augustinegrass has the finest texture, with a thick blue-green turf. Centipedegrass and Bahiagrass seeds are available, while St. Augustinegrass is installed as plugs or sod.
Plant Grass Under Pine Trees
Normally, when planting a lawn, you'd remove debris, cultivate and amend the entire area and then sow seeds or install sod. To plant grass under your pine tree, take time to carefully remove weeds and debris but don't cultivate deeply, as it will damage the tree's roots. If the ground is very hard, cultivate shallowly or rake to loosen the soil.
Rake 1 to 2 inches of compost over the entire area and wet it thoroughly. Spread the grass seed over the moist soil and rake gently to barely cover the seed. Compact with a lawn roller to ensure solid contact between the moist compost and grass seeds. Keep it moist until the seeds germinate in seven to 10 days. Continue watering regularly; the grass and tree roots will compete for moisture and nutrients.
Begin mowing when the grass is at least 3 1/2 inches tall. If you used sod instead of seeds, mow in two weeks after the sod has become established under the tree. Consider maintaining the grass 1/2 to 1 inch taller than the recommended height so more of the grass blades are exposed to the limited sunlight under the pine tree. Rake and remove the pine needles regularly. Recycle them as mulch in other parts of the landscape or put them on the compost pile. Fertilize lightly in fall and water thoroughly after fertilizing.