Pound two T-posts into the ground behind the row of tomato plants, spaced up to 5 feet apart, with a rubber mallet. If your tomatoes take up more room than that, use an additional T-post every 5 feet.
Measure the height from the ground to the lowest hole in the first T-post. Ensure that all other T-posts are at the same height.
Cut a piece of clothesline a foot longer than the space between T-posts.
String the rope through a hole 12 inches above the ground in the first T-post and tie it off.
Thread the rope through the same hole in the other T-posts.
Pull the rope tight and tie it to the last T-post.
Measure up 12 inches and add another rope. Continue this for the entire height of the T-posts.
Loosely tie the tomato plants into place with pieces of twine as they grow tall enough to reach the first rope. Continue doing this for each rope as the plants continue to grow.