Tomato plants grow as a vine, even though many may appear bush-like if caged or staked. Some varieties grow on small plants that never need trimming. Others will grow so large and so far they will invade neighboring plants in the row. Keeping the spreading vines in control becomes a necessity and the best method is trimming them. A common misconception is that all tomato plants need to be trimmed. Trimming is required only to keep the vines from overgrowing.
Prune vines that threaten to overrun a row before they go too far. Follow the vine back to the stem and cut it off with a sharp hand pruner.
Cut away vines entangled in the plant or other plants. Pulling the vines out will damage the plant in which it is entwined.
Remove a branch or side stem that threatens to overgrow the plant before it gets too long. Trim the branch or stem off with a sharp hand pruner and remove it. Don't leave dead plant parts on or around the plant.
Watch for signs of blight and other diseases. Remove the dead leaves from the bottom of the plant as they appear to help the plant productive throughout the growing season. Pluck off dead leaves by hand, but remove branches with with the hand pruner.