You can easily make a 2' x 3' (suitable for square foot gardening) or 2 1/2' x 2 1/2' (suitable for a zucchini) raised bed from 2 pieces of 5' cedar fence lumber. This size is a modest beginning for an urban garden or fits into an odd nook to expand an existing garden.

Step 1: Gather Your Materials

The raised bed frame requires:

2 pieces of 1x6 5' lengths of cedar fencing, with no or only smaller knots
1 2x2 cedar baluster, or a cedar tree planting stake
16 1 1/2" deck screws

Cedar is the common rot-resistant lumber in my region. Another species may be common in yours. DO NOT USE TREATED LUMBER as it will hinder plant growth and the chemicals may be transmitted to your food. Deck screws are made to not readily rust in outdoor conditions.

For a new bed:

a piece of cardboard slightly larger than the frame
enough soil to fill the frame 5" deep

The cardboard kills the grass under the bed (no digging!). Over time it and the grass will decompose and enrich the soil. If your plants are shallow rooted (such as lettuce, greens, radishes, beans, peas, green onions), you can plant right away with 5 inches of soil.

A 2`x3` bed 5 inches deep requires 2.5 cubic feet of soil.

Step 2: Tools Needed

For your construction you will need:

saw (either hand or powered)
drill with screw bit to fit deck screw head and drill slightly smaller in diameter to the deck screws
tape measure
pencil to mark cuts
knife to cut cardboard and open garden soil bags

Step 3: Measure and Cut Lumber

Measure either 2 feet (for a 2' x 3' frame) or 30 inches (for a 2 1/2 ' square frame) from the end of each fence piece and mark it. A single mark is all you need if you are using a chop saw. If you are using a hand saw, either use a square laid over the mark to then trace a line the full width of the board, or measure and make a second mark so you can use a straight edge over both marks to trace a line the full width of the board.

Measure the width of the fence board. Measure that distance from the square end of the baluster and mark it. Then make the cut. Do this three more times to get the four corner braces. A saw cut is usually wider than a pencil line, so you do not want to mark all lines at once and then make your cuts; if you do, the first piece will be your desired length, but the others will be a little short.

This frame, however, is rough carpentry, not fine furniture, so being off a sixteenth of inch here and there is not a disaster.

Step 4: Securing Long Side Boards to the Corner Braces

To make strong corner joints (so that frame will last a number of years), you will be securing the side boards to 2x2 pieces. Cedar readily splits (that's why it makes good roof shakes), so you will be drilling pilot holes for the screws.

Lay two corner pieces on a flat work surface. Place a 3' piece over them, Line up one edge of the board with the side of the corner piece. Drill your pilot holes at least an inch from the board sides and roughly 3/4" from board edge. Line up the other edge with the other corner piece and repeat. Switch to the screw bit, be sure your board edge and corner piece side are still lined up, and screw in the deck screws.

Repeat with the other 3' piece.

You now have the two long sides of your frame.

Step 5: Completing the Frame

Doing the next step is easiest on a perfectly level work surface -- or with a helper to hold the upright pieces for you.

Stand the two sides so that the corner braces face toward each other (like [ ]). Place one of the short sides on top of them with short board's edge lining up with the long side surface. Drill the pilot holes so that the screws will go into the corner brace (about 1 1/2 inch in from the short board's edge). If you don't have a helper, it will be easier to put in the deck screws now, then line up, drill, and screw the second end.

Flip the now three-sided frame over so that the finished short side is the bottom and the remaining open side is the top. Position the last board. Line up one end, drill and screw. At this point any subtle warp in any of the boards will manifest itself with the last corner not completely lining up. A helper is useful to hold that last corner in a lined-up position so you can drill and screw the board in place. I was able to handle the wow myself.