Concrete curbing provides an impenetrable barrier against roots that works well to keep invasive plants contained in a flower bed and prevent grass and weed roots from entering. While this type of barrier is most effective when the concrete is set in-ground with the top even with soil grade, you can also install concrete curbing on top of the soil or set it halfway in the soil. Borders at soil grade can be passed over with a lawn mower. The concrete should be about 4 inches thick or deep and at least 5 inches wide for extra strength.
Things You'll Need
- Garden hoses
- Measuring tape
- Landscaping spray paint
- Flat shovel
- Hand tamper
- Border spade
- Carpenter's level
- 4-inch hardboard strips
- Wooden stakes
- Rubber mallet
- 1-inch wood screws
- Power drill
- Scrap 2-by-4-inch lumber
- Circular saw
- Concrete mix
- Liquid cement coloring (optional)
- Round point shovel
- 2-by-4-inch screed board
- Masonry trowel
- Concrete edging tool
- Concrete scoring tool
- Pry bar
- Plastic sheeting (optional)
Lay garden hoses beside the garden beds to lay out the design for the curbing. Set the hoses about 6 inches out from the bed's edge. Spray landscaping spray paint beside the garden hoses to mark the ground. Remove the garden hoses after transferring the design with spray paint.
Level out the soil, using a flat shovel to scrape away excess soil and a hand tamper to pack it down. If you want to set the concrete curbing in the ground, using a border spade to dig a trench 4 inches deep and at least 7 inches wide; dig the trench 2 inches deep if you want half of the curbing to stick out above soil grade. While the curbing itself only needs to measure 5 inches wide, a 7-inch trench allows 2 inches of working space. Lay a carpenter's level on the ground at various points along the border and add or remove soil as needed to make a level base.
Set 4-inch wide hardboard strips along one side of the prepared border or in the trench. Hold a level upright against the hardboard and adjust the position until the hardboard is perfectly plumb or vertical. Drive wooden stakes in the ground every 3 to 4 feet along the outside of the hardboard and screw the hardboard onto the stakes, using 1-inch wood screws and a power drill. Install one screw at the top and bottom of the hardboard at each stake.
Cut several pieces of scrap 2-by-4-inch lumber to 5-inch lengths. Set the pieces in along the hardboard every 4 feet or so to act as spacers. Place a second hardboard form along the outside of the 5-inch spacers. Drive stakes into the ground along the outside edge of the hardboard and screw the hardboard to the stakes. Remove the 5-inch spacers.
Mix concrete with water to achieve a consistency similar to thick pancake batter or thin oatmeal. Mix at a rate of about 3 quarts of water for one 80-pound bag of concrete mix; add more water slowly as needed to achieve the desired consistency. Shovels and a hoe work well for mixing concrete. If you want colored concrete curbing, you can add liquid cement coloring to the water before mixing the water with the concrete mix. Mix one 10-ounce bottle of liquid cement coloring to 1-1/2 gallons of water, which is enough water to mix two 80-pound bags of concrete mix.
Scoop the concrete mix between the form boards, using a flat or round point shovel. Fill the form boards up to the top edge of the form boards. Drag a scrap 2-by-4-inch screed board across the top from end to end while pulling it back and forth in a sawing motion to level off the top and remove excess concrete.
Sweep a masonry trowel side to side over the concrete to smooth out the top. This process draws water to the top of the curbing and forces the aggregate down so the inside of the curbing is strong, but the top is smooth.
Allow the concrete to set up for about 30 minutes and run a concrete edging tool along the sides of the curbing. This tool rounds off the sharp edges so the curbing isn't perfectly square in shape.
Measure along the curbing every 3 feet and run a scoring tool from front to back of the curbing to create small indentations in the concrete. These indentations act much the same as expansion gaps in concrete sidewalks. If cracking is to occur, it will crack around these indentations so the cracks are less noticeable.
Remove the form boards when the concrete is hard and able to hold its shape. This might take as little as a few hours, but wait a minimum of 24 hours to be safe. Fit a pry bar under the form boards and lift up to pull the stakes and boards out of place. If the curbing is set below soil grade so you can't see the bottom, insert the pry bar at the top, between the hardboard and concrete curbing and pull back slowly to pry the hardboard away from the curbing.
Spray the concrete curbing with water to keep it moist for at least one week so it cures slowly and gets as hard as possible. If the curbing is located in a sunny area that dries out fast, it helps to cover the curbing with plastic sheeting to keep it moist.
Tips & Warnings
- Mix the concrete one bag at a time so it doesn't start to harden before you get to the end of the curbing form.
- Photo Credit Jupiterimages/Polka Dot/Getty Images