Mow a flat area of your lawn large enough for your proposed raised garden bed.
Remove any weeds from the garden bed area.
Lay out your 4-by-6-inch landscaping timbers on top of one another to form a square or rectangle the size you would like your garden bed to be.
Mark a point every 4 feet along each of the top timbers starting at each of the corners. Mark parallel points along the lower timbers that will match up with the points on the top timbers.
Drill a hole through each mark on each timber the same diameter as a construction rebar. The Senior Gardening website recommends using a 3/8-inch drill bit to drill the holes and using rebars 3/8 inch in diameter; the rebars should be the same length as the height of the raised bed.
Dig four narrow trenches, in rectangular formation, each 3 inches deep to securely place each of the bottom pieces of timber in.
Re-stack the rest of the timbers onto the bottom formation and drive a rebar through each of the matching holes using a hammer. Make sure the timbers are securely connected to one another and the ground.
Lay a full piece of carpet on the bottom of the garden bed. If you have scraps of carpet, cover the whole bottom surface with the scraps.
Pour potting soil into the bed when you are about to start planting. The soil should fill up the bed so it reaches a height 2 inches below the top of the wooden barrier.
Mix compost into the top 4-inch layer of soil.