Curved borders bring a flowing feel to your garden that is much less harsh than a garden of perfectly straight edges. This looks best when the curves are gradual rather than tight, which is also necessary when you want to install an edging material with the border. The easiest, most affordable way to edge a curved border is with a trench border, also called the Victorian trench, that simply cuts off the grass and provides an open barrier to prevent grass and weeds from spreading into flower beds. The look, despite the name, is natural, making it work well with those flowing lines around the beds.
Cutting the Trench
Lay garden hoses on the ground in the desired pattern for the edging. If you want to edge an existing flower bed, you can create new curves in a straight flower bed or follow existing curves, if applicable. Lay the hoses at least 6 inches away from any plants in your flower bed.
Spray landscaping paint directly beside the garden hoses to transfer to design to the grass or soil. Landscaping spray paint is chalk-based and non-toxic, but you can sprinkle flour along the hoses instead. Remove the garden hoses after marking the ground.
Hold a border spade straight up, positioned on the marked outline at one end of the border. Step on the foot peg to push the blade down into the soil about 4 inches deep. Pull the blade out of the ground, reposition it on the line beside the first cut and step down to cut through the soil. Repeat this process along the marked border. An easy way to achieve the proper depth is to measure the spade blade and place a piece of tape at 4 inches; stop digging when the tape is no longer visible.
Stand inside the flower bed, facing out toward the lawn side. Hold the spade at a 45-degree angle with the ground, positioned 4 to 6 inches in from the vertical cut, and push it into the soil until it meets the vertical cut. Pull back on the handle to pry up the grass and soil. Repeat this along the entire border until the soil is removed in a 45-degree wedge strip. If you're edging along a curved walkway, cut straight down along the walkway's edge and cut the 45-degree angle downward from the grass side toward the walkway.
Go back over the vertical cut edge, using the spade to smooth any bumpy edges caused by the slight curve in the blade. The vertical trench wall should now be perfectly smooth and uniform.