When it's time to get your vegetable garden ready for a new growing season, many gardeners think first about their soil. For gardening in a raised bed, however, there's a little more to it because often landscaping fabric is put under the soil to act as a defense against weeds while still allowing water to flow through. You'll want to line raised vegetable beds before the garden is planted in the spring, or just after the last vegetable is pulled from the garden in the fall.
Spread out your tarp on the ground right next to your raised bed or as close to it as possible. Dig in the raised bed to loosen the soil and shovel it out of the bed and onto the tarp, removing any debris as you go.
Cut out a section of landscaping fabric as long as the width of the bed plus one foot to begin lining the bottom. Each bottom piece will be this length.
Place one strip of the landscaping fabric in the bed along a width side. The fabric should run six inches up the side walls of the bed along the length of the fabric as well as the cut ends.
Overlap the next piece of fabric by four to six inches over the previous fabric strip, again with each of the cut ends running up the sides. Continue to add strips to the bottom of the bed until you come to the opposite end, and have it extend up that width side by six inches as well.
Adjust the fabric strips to make sure there aren't any gaps along the base of the bed, especially where the fabric curves upward to cover the sides. Staple the pieces in place to the inside of the raised bed. These should secure at any overlapped portions as well as any puckering at the corners to hold them flat.
Cut one final piece of fabric to run the total length of all four sides plus six inches. Line the sides of the bed with this piece running around the inside edges of the bed, starting an inch from the top of the bed and running down over the bottom liner.
Hold the cut ends of the side liner to overlap by six inches and staple these ends to the raised bed. Continue around the sides to staple the fabric every six inches both at the top and along the bottom where it overlaps the base pieces. Add the soil from your tarp to the bed to cover the fabric.
You can choose to add garden soil or compost to the bed as you add the soil back into it. Just be sure to dig, turn, and mix the soils together well.