A tomato trellis is a must for keeping tomato plants off the ground and improving air circulation around the stems and leaves. While there is a variety of tomato cages and trellis systems available at an even larger range of prices, you can make your own for less in an afternoon. By building a tomato box trellis you can grow tomatoes wherever you want and still give them the support they need.
Arrange two 4-foot 2-by-12 boards, and two 2-foot 2-by-12 boards to form a rectangle with each board resting on its 2-inch side. Align the boards so the ends of the 2-foot boards butt up against the sides of the 4-foot boards.
Screw three evenly spaced galvanized screws through the 4-foot boards and into the ends of the 2-foot boards to connect the box. Set your plywood over the rectangle to close the box and screw through the plywood and into the boards every 6 inches to attach. Flip the box over and set aside.
Lay the 5-foot long 2-inch boards on the ground running vertically. Space the two outermost boards 40 inches apart. Adjust the two middle boards to be evenly spaced between the outer boards about 1 foot apart.
Set the 44-inch boards horizontally over the vertical boards. Align one board along the top ends of the vertical boards. Space the three remaining boards a foot apart from the top downward. Screw these boards together with one screw at each intersection or use twine to tie the boards together.
Stand up the trellis with the unconnected ends of the vertical boards pointing down. Put the trellis inside the box you built in Steps 1 and 2.
Align the trellis along one of the 4-foot boards of the box to be the back of the tomato box. Screw three screws through the 4-foot board and into each of the four legs of the trellis.
Fill the box with potting soil up to 1 inch from the top. Plant two tomato seedlings into the box, 3 feet apart and 6 inches in front of the trellis. As the tomatoes reach each new rung of the trellis, use plant ties to attach the main stem to the support.