To build a raised garden bed, prepare the ground, build the box, level the box, and plant flowers or vegetables. Finishing the raised garden bed with an irrigation system is optional.
Choose a location for your raised garden bed that is sunny and easily accessible. Mark a 3-by-5 foot area, and remove the top layer of sod in this area. Check to see if the ground is level, and make adjustments with a shovel. Place a piece of landscaping fabric over the prepared area. Build the frame using 2-by-4s for the sides of the box and 4-by-4s as posts in the corners of the box; do not use treated wood to make beds for edibles.
Cut the boards and posts to length, then attach the boards to the posts using screws, making sure that the boards are flush and square with the posts at the corners. Attach all four sides together, and place the box over the landscaping fabric. Make sure that the box is level when in place. Cut away any excess landscaping fabric on the sides of the box. Fill the box with at least 6 inches of soil, mixing in compost or fertilizer as desired.
Plant your flowers or vegetables in the soil. For more convenient watering, wind a soaker hose between your plants. Cover the hose with a little soil. Attach the hose to a timer for automatic watering.