Raised planter beds provide many advantages; they offer better drainage, prevent people with back problems from bending too low, contain good-quality soil where every inch is meant specifically for planting, and can be built over slopes or an area where soil quality is poor. Raised beds are enclosed by structures that contain soil and prevent it from spreading. Many people use wood, though the treated kind contains chemicals not suited for vegetables or herbs. Wood-plastic composite (WPC), also known as composite wood or man-made wood, is a combination of recycled plastic and wood waste that lasts longer than wood.
Measure and demarcate a 4-by-8 foot area over your selected site for the planting bed and spread powdered chalk over the corners. Measure a 44.5-by-92.5-inch area within the demarcated bed and mark the corners with stakes. Extend twine through all the stakes to form a rectangle that serves as the interior of the bed.
Wear gloves and clear all vegetation, rocks and stones within the stakes and twine and discard. Remove the stakes and twine as well. Dig a 2-foot deep trench within the stakes-and-twine boundary, and collect the soil in a tarp or wheelbarrow.
Level the base and pour a mixture containing equal parts compost, peat moss and sand into it. Rake it well.
Measure 8 inches from one end of a plastic composite post and drill a 1/2-inch wide centered hole over the spot. Also measure 24 inches from this drilled hole and drill another identical centered hole. Repeat the procedure of drilling two holes into each of the remaining 17 posts.
Lay the first course of posts horizontally around the rectangle. Stack rows over one another until you use all the posts. Line the drilled holes of each subsequent posts before lowering it in place.
Insert a 1/2-inch wide, 3-foot long construction rebar into a drilled hole in the composite wood. Hammer it so it penetrates the aligned holes below and into the ground. Keep its top in level with the composite wood, so it does not protrude. Drive the remaining lengths of rebar into the holes of the first course of composite wood.
Fill the bed with soil mix until 2 inches from the rim and level with a rake.