Tomato plants create excess growth called suckers. Suckers are not necessary for fruit production and "suck" energy from the plant. Where the plant's main stem and a branch form a right angle, a sucker will be a new stem with a leaf sticking out at a 45-degree angle between the two. When you remove suckers, your tomato plant can focus energy on producing larger tomatoes.
Look for suckers in the crotch between the main stem and a side branch of the plant. Early suckers will look like a green bump, or node, about the size of a pencil eraser. The suckers should form along lower portions of the plant first. But as the plant grows taller, you will see them forming on upper portions as well.
Wait two to three weeks for the suckers to grow into 3- to 4-inch long stems with a leaf on the end. Pinch the sucker off from the plant as close to the main stem as possible, using your thumb and forefinger. You can use a knife or scissors to snip the sucker off, but be careful not to cut the main stem or side branch.
Remove all suckers from indeterminate plants, such as Beefsteak slicing tomato plants. Indeterminate plants produce a continuous series of flowers and tomatoes, growing a few at a time over the course of a growing season. Removing suckers will allow these tomatoes to be larger than typical slicing tomatoes.
Carefully remove the suckers from determinate plants, such as Roma paste tomato plants. Determinate plants flower and produce ripe tomatoes all at once, making only one harvest. For determinate plants, remove suckers that grow only along the main stem below the first set of flower clusters, leaving any suckers that appear above the first cluster. If all the suckers are removed from determinate plants, the number of tomatoes in your single harvest will be fewer.