Keeping grass and weeds away from flowerbed edges is a major time suck. While it takes a good bit of time and some work, installing concrete edging creates division between flower beds and lawns, which frees up more time in your schedule for the fun stuff in life. The concrete edging requires a trench so the concrete rests at soil level, allowing you to mow over the curb without using a weed trimmer. The trench requires a gravel base that prevents concrete from shifting and cracking.
Lay garden hoses or rope on the ground directly against the flowerbed border, following any curves in the design. Spray landscaping spray paint along the hoses or rope to mark the ground. Measure 4 to 6 inches out from the first painted line and lay hoses on the ground that are perfectly parallel to the paint marks. Spray the ground with a second line to mark the shape and width for the trench.
Measure a spade blade from the tip up to the desired depth for the trench and add a piece of colored tape to mark the blade so you know how far to insert the blade when digging the trench. The trench should measure 9 to 11 inches deep, allowing 4 inches for a compacted gravel base layer, 1 inch for coarse sand and 4 to 6 inches for the concrete edging. A digging spade has a much longer blade than a border spade, but the length and width of digging spades varies.
Cut through the turf layer and into the soil along the painted line closest to the flowerbed edge, using a digging spade that features a long, straight blade perfect for cutting straight down in the soil. Start at one end of the flowerbed and hold the spade upright. Step on the foot peg on the blade to push the blade straight down until the bottom of the colored tape touches the ground. Reposition the spade and repeat along the entire edge.
Position the digging spade at one end of the second painted line. Push the blade straight down into the soil to the depth marked with the colored tape. Pull the handle toward you to pry up the turf and soil. The object here is to loosen the soil within the two cut lines, but if some soil comes up with the blade, set it aside to use elsewhere in your garden.
Remove all the loose soil from between the cut lines to reveal the trench. Pull up the sod -- soil attached to grass -- by hand and use the digging spade or a narrow shovel to scoop out the soil.
Scrape along the bottom of the trench to make it as close to level as possible. The trench bottom doesn't need to be perfectly level because you'll add gravel and sand to level for the concrete.
Cut along the edges of the trench, using the digging spade as needed to make the edges as straight as possible. The flat spade blade does a decent job of cutting straight edges, but you might be able to see where you made each new cut as you cut the trench. After straightening the sides, the trench is ready to add and compact gravel, spread a level layer of sand and pour in the wet concrete.