Preventing grass and weeds from growing close to a fence saves endless weeding and creates a neat, tidy look. Solutions vary according to the garden's style and the grass type. Trim excess growth before starting work, and speak to your neighbor before spraying herbicides along boundary lines because they may have plants they wants to protect.
Maintaining an Edge
If grass and weeds are growing close to a fence, a neat and unobtrusive barrier is a shallow trench cut with an edging spade. Mark a line 5 or 6 inches from the fence and parallel to it and push an edging spade 4 inches into the soil along the line. Lever the spade upward toward the fence, lifting out a plug of grass and weeds. Continue along the fence to create a trench of bare soil. Cut the line in the same way two or three times a year during the growing season to prevent grass and weeds invading the trench. This solution is effective for lawn grasses that grow in clumps, such as tall fescue (Festuca arundinacea), which grows in U.S. Department of Agriculture plant hardiness zones 7 through 10.
Filling a Trench With Mulch
A trench filled with mulch close to a fence deters grass and weeds. Dig a trench next to the fence 4 inches deep and 8 inches wide. Spread landscape fabric along the trench and fill it with a mulch such as wood chips, bark chips or gravel. Gravel suits formal gardens. This method is effective for perennial ryegrass (Lolium perenne), which is hardy in USDA zones 3 through 6, and other clump-forming grasses. Don't create a mulch-filled trench if the fence is at the bottom of a slope because heavy rainfall will fill the trench, wash the mulch away and rot the fence wood.
Creating a Hardscape Barrier
Bricks, pavers and other hardscaping materials create an effective long-term barrier to grass and weeds growing close to a fence. Bermudagrass (Cynodon dactylon), which grows in USDA zones 7 through 10 and spreads sideways through underground shoots, struggles to invade hardscaping. Dig a trench 1 1/2 inches deeper than the bricks or pavers and 1 inch wider next to the fence. Lay landscape fabric in the trench and fill with 2 inches of sand. Lay the bricks or pavers on top of the sand and hammer them gently with a rubber mallet to slot them tightly into place and level them. Check they're level with a builder's level. The top of the bricks or pavers should be 1/2 inch higher than the surrounding ground. Fill any gaps with sand.
Preventing Growth With Herbicides
Herbicides control invasive grass and weeds growing close to a fence and prevent regrowth. Put on a long-sleeved shirt, long pants and gloves, and spray a ready-to-use 2 percent glyphosate product over the existing growth on a dry, still day when the grass and weeds are actively growing. When the growth has died, which may take up to two weeks, remove it. Glyphosate kills most plants, so don't spray it on any plants you wish to keep. Spread a pre-emergent weedkiller, such as a 1.47 percent trifluralin product, at a rate of 1 ounce per 10 square feet and irrigate to activate the grass and weed barrier. Alternatively, apply both herbicides according to the manufacturer's instructions. A 1.47 percent trifluralin product prevents grass and weed regrowth for three months, providing the soil surface isn't disturbed.