Pruning your tomato plant down to two or three stems allows the plant to direct energy toward growing larger fruit. During the first month of a tomato plant's growth it uses all of its energy to develop new leaves. The new leaves aid in photosynthesis, helping the plant produce more sugar; eventually, it produces more sugar than it can use, causing the plant to branch and flower. If your tomato is an indeterminate variety, it will continue growing and become more tangled. Pruning back to two or three stems will create a stronger, healthier plant.
Allow your tomato to grow normally until its first flower clusters appear.
Pinch off all the suckers and leaves below the first flower cluster.
Remove the suckers when they're still small by grasping the base of the sucker and bending it back and forth until it breaks.
Let the plant grow a second stem from the node just above the first flower cluster and a third stem from the node just above that.
Pinch off all other suckers that form in the angles between the three main stems and the leaves.
Stake your tomato plant to support it as it grows and develops fruit.
Tie the stem loosely to the stake to encourage it to grow upright without damaging the stem.
Help the plant support the fruit clusters by looping a longer piece of string around the stem and stake just above the fruit cluster and tying it 6-10 inches above the cluster.
Remove all growing tips on the plant 30 days before the last frost in your area according to the USDA Hardiness Zone Map. This final tomato pruning forces the plant to use all of its sugar to help ripen the fruit before the first frost kills the plant.