Horticulturalists typically divide tomato plants into two types: indeterminate (vine varieties) and determinate (bush varieties). Indeterminate plants require selective pruning to remove suckers--new stems growing from an existing stem--and thereby keep the vine from growing too many stems. Though a multi-stemmed tomato vine will produce more fruit, the resulting fruit will be smaller. Removing suckers helps the plant direct all its energy toward a smaller number of fruit and can add up to 2 oz. to each fruit's weight, according to Cornell University.
Allow the tomato plant to grow one or two main stems and produce its first set of flowers.
Identify any suckers below the first flower cluster. Wait for the suckers to grow to a length of 2 to 4 inches, according to South Dakota State University.
Cut off the sucker with pruning shears, snipping it as close to the plant as possible. Discard the removed foliage or throw it in your compost bin.