Some basic tools and a few pieces of wood are all you need to build a simple rack for growing seedlings and small plants. The rack is easy to build and sturdy, but you may want to screw it to the wall so it won't topple or otherwise create a risk for toddlers and climbing kids. Take the time to measure your boards accurately before you cut, to save yourself a ton of hassle down the road.
Cut the two-by-fours into smaller lengths. You need four 6-foot pieces, eight 4-foot pieces and eight 2-foot pieces.
Cut the sheet of plywood into three 27-inch-long by 4-foot-wide shelves for the unit.
Attach two 2-foot pieces flush at the ends of two 4-foot pieces to create a rectangular base. Insert one screw into the center of each joint to connect these wood pieces.
Repeat with the remaining wood pieces to make three additional rectangles. These rectangles will become the top of the unit, the base of the unit and supports for the shelves.
Attach the sides of your growing unit by taking one of your 6-foot pieces of wood and placing it at the outside edge of one joint. The 6-foot piece should stand straight up, perpendicular to the base rectangle. Screw it in place with four screws -- two into the 2-foot board and two into the 4-foot board.
Repeat with the three remaining 6-foot pieces, attaching them to each of the three remaining corners of the base rectangle.
Screw another rectangle onto the top of the 6-foot posts to add a top to the unit and give it additional stability.
Screw the last two rectangles into the unit at even intervals between the top and bottom rectangles. Use four screws per corner.
Slide the three 27-inch by 4-foot plywood boards onto each of the three bottom rectangles, and secure each with a few screws.
Attach one S-hook on the 2-foot pieces of each rectangle, and hang shop lights from the S-hooks on each level.