Garden edging is underrated. Though the term can refer to physical pieces of edging -- wood, plastic, metal, concrete, brick or stone borders that delineate the perimeter of a planting area -- as a verb, "edging" refers to the act of making the border by hand in the soil, such as by digging a trench. This natural approach to edging saves money and does not use unsustainable resources.
Purpose of Edging
Edging is one of the secrets to a well-kept garden. It's purpose is to make distinct transitions between areas of the landscape, such as the border between a lawn and a flower bed. You may not notice edging if you're not looking for it, but it's hard not to appreciate the crisp, clean feel that it provides. On a practical note, edging prevents creeping lawns grasses and other aggressive plants from taking over nearby plantings.
The Necessary Tools
At a minimum you will need a shovel -- the sharper the blade, the better for edging around a thick mat of sod. As you may have guessed, there are special tools called edging shovels that make the work easier. The blade comes presharpened and is completely flat, unlike a "flat shovel" which actually has a slight angle. You'll also want a wheelbarrow or garden cart ready to haul away the chunks of sod and a pair of gloves to protect your hands from any soil-borne pathogens that may be present.
A Straightforward Technique
Slice vertically into the soil with your shovel of choice along the line where you want to define the edge. If edging a lawn, stand in the lawn facing the adjacent bed and pry up on the sod with each slice. The goal is to form a trench 4 to 6 inches deep between the two planting areas. An edging shovel isn't good for scooping up the chunks of soil and sod, so have a regular shovel handy, as well. After you make one pass, go back and clean it up to make a smooth, crisp line. A trenching shovel is useful for scooping the dirt out of the trench after you've loosened it.
The point of edging is to prevent plants from growing beyond it. A few weeks after you cut a nice, clean edge in a lawn, you'll notice the grass is starting to grow into the trench. Before long, it will invade the neighboring soil and you'll have to repeat the process. For some slow-growing grasses, two or three edgings a year is generally sufficient, while others may need it monthly during the growing season. You may want to place a few rocks along the edge of the trench or mark it some other way, such as with solar lights so that unsuspecting visitors or busy children don't hurt themselves.