A raised gardening bed gives gardeners more control over soil composition, plant sprawl and water drainage. Lettuce is a cool-season crop, but you can extend its growing season by adding sun protection to the raised bed during the warmer parts of the year. A raised bed will also allow you to choose a specific type of soil with amendments for the particular type of lettuce you want to grow. Segment this 3x6 raised bed to grow different types of lettuce.
Plan the location for the raised bed. Choose a location that will expose your lettuce to several hours of sunlight each day. Get the best results with a spot that receives morning sun with some shade, artificial or natural, during the hottest part of the day.
Clear the site. Remove all unwanted plants and weeds from the spot. Avoid building the raised bed over an area with a lot of tree roots. The roots will draw away water and nutrients from your soil.
Cut one 6-foot-long 4x4 piece of lumber into four 16-inch posts. Stand two of these posts on their short ends 6 feet apart. Place a 6-foot-long 2x6 board on its narrow edge so that it meets with the posts. Attach the board to each post by screwing two 3 1/2-inch screws through the board into the post.
Place a 3-foot-long 2x6 board on its narrow edge. Attach the board to the post on the side adjacent to the side where you attached the first board. Screw two 3 1/2-inch screws through the board into the post. Stand one of the remaining posts on its short end and place it at the opposite end of the 3-foot-long board. Screw two 3 1/2-inch screws through the board into the post. Attach a 6-foot-long 2x6 board to the adjacent side of the post and opposite the first 6-foot-long board. Complete the rectangle with a 3-foot-long 2x6 board.
Build a second level of 2x6 boards by attaching them to the posts with 3 1/2-inch screws. Do not leave a gap between the levels. The boards will not reach the edges of the posts that are presently facing upwards.
Turn the structure over so that the part of the posts not covered by boards form legs or stakes. Dig holes deep enough for the posts so that the edges of the boards meet the ground. Add a inch of pea gravel to the holes to aid drainage. Tap the structure gently to ensure that it is in place.
Add the soil mixture of your choice to the bed. Place lettuce seeds or transplant seedlings into the raised bed.