A properly cared for tomato plant will grow vigorously once the summer heat sets in. Left untended, many tomato varieties will grow long, vining branches that can pull the plant to the ground under their weight. Often, staking a tomato plant isn't enough to keep it healthy because the leaves start to shadow each other and prevent effective photosynthesis. A bushy tomato plant stays wet for longer from dew and watering which invites disease. If a tomato plant is putting all of its energy into leaf growth, the fruit will be sour and less abundant.
Trim off any leaves that are touching the soil. These leaves will draw insects and disease from the ground that will harm the rest of the plant.
Prune off leaves that look sickly or yellow. If sick or dying material is left on the plant, it can harbor bacteria.
Cut off any suckers that appear under the first flowering branch. Suckers are new branch growth that appears in nodes between the main stem and another branch. Suckers draw sugar and energy away from the fruiting process and weigh the plant down.
Prune tomato plants only when they are dry. If the plant is wet, it gives bacteria a greater chance to grow in the wound.
Remove unwanted tomato leaves by pinching them off with your fingers, if possible. If the stems are too thick to pinch off, use sharp, sterilized scissors or hand shears. Make the cut on the stem between leaf nodes.
Allow suckers to grow a set of leaves before trimming them off. The leaves will help the plant produce more sugars through photosynthesis, and they protect fruit from scalding in the heat of the sun.
Pinch suckers with your fingers if they are soft enough. If they have become too woody or thick, slice them off with a sterilized razor blade.