Timber sleepers define garden bed boundaries to keep out unwanted traffic, however, use them carefully around edible crops to prevent potential contamination from wood preservation chemicals. Sleepers are perhaps more popularly known as railroad ties or landscape timbers, although the term is better suited to larger landscape timbers similar in dimension to the rail ties.
Edible Plant Beds
Reclaimed rail ties are generally covered in sticky black creosote to preserve the wood. Creosote, a byproduct of coke and natural gas production, can be considered a likely carcinogen by the Environmental Protection Agency and is unsafe to use close garden beds that contain plants that are edible. The creosote can leach into the ground with rainwater and be drawn up into plant roots. Pressure-treated lumber is chemically treated to prevent decay, and is usually considered safe for use in edible garden beds — with the exception of sleepers treated with chromated copper arsenate, or CCA. New timber bought for use around the home is not treated with CCA, but you might need to avoid using reclaimed lumber that might happen to be treated before 2002, when the EPA began restricting its usage.
Long sleepers laid horizontally are only practical for garden beds using straight edges. The sleepers can be placed directly on top of the ground, but they look more appealing and help avoid weed roots from sweeping to the flowerbed in case you put the timbers to the ground. Assess the width and height of the timber sleepers. Dig a trench facing the garden bed that measures at least 1 inch wider than the sleeper width. Dig to a depth equivalent to the sleeper height if you would like the top of the timbers flush with the ground level, or dig to half the height if you would like to leave a visible curb. Set the sleepers to the trench, and backfill the soil around them. Drill holes through the ends of each sleeper before placing them in position, and drive 12-inch landscaping spikes throughout the holes to anchor the sleepers into the ground, if desired.
Sleepers are laid horizontally to get straight beds, but you can stand short sleeper pieces upright if you would like a curved bed using the substantial look of timber sleeper edging. Limit the bed design to slow curves to prevent awkward gaps between sleeper pieces. Choose the height you need for the garden bed edging; add 8 inches to compensate for anchoring the sleepers in the ground, and cut several sleepers to this span. Cut sleepers to several lengths within six inches of this measurement if you prefer staggered-height edging. Dig an 8-inch-deep trench marginally wider than the sleeper width as well as the backyard bed border. Stand with the short timber pieces upright in the trench, alternating heights if required, with the pieces butted shut together. Fill in the trench around the timbers, and pack the soil tight to hold them in position.
Raised Garden Beds
Raised garden beds drain better and stay warmer than beds level with the ground. Assemble a simple raised garden bed by piling wood sleepers in a square or rectangle till a height of 18 inches. The raised bed may be any length but should be no wider than 4 feet, so you can readily access the lawn. The stacked sleepers are not as likely to fall out of position if you stagger them so the joints don’t line up in the retina ends. Anchor the first path of sleepers in the ground using 12-inch landscaping spikes. Secure the upper courses of sleepers into the lower courses with landscaping timber screws spaced about 12 inches apart. Use screws equal to 1 1/2 times the sleeper height.