By Jenny Harrington Updated November 28, 2018
Tomatoes come in two growth varieties: determinate and indeterminate. Determinate types have self limiting growth and rarely reach above 4 feet high. On the other hand, indeterminate tomatoes, which includes many of the heirloom varieties, continue growing until fall frost and can grow 6 feet or more in a single season. Pruning back or topping the plant prevents upward growth and diverts the plant's energy into producing fuller lateral stems. This leads to a more productive plant that can produce more fruit as well as fuller fruit and one that is easier to support.
Using a Cage or Stake to Help the Plant Grow
Make sure to place a tomato cage over the tomato at planting. It is also possible to drive a 6 foot stake into the ground near the main stem. Do not forget to tie the tomato stem to the stake as it grows, if applicable, using cloth plant ties to hold it in place. However, caged tomatoes don't require tying.
Removing the Suckers to Promote Growth
It is important to remove suckers that form in the joint where a lateral stem meets the main stem. Pinch off the sucker bud when it's smaller than a pea. Allowing suckers to grow results in multiple main stems that can all continue growing for the entire season. This means that more energy is used to grow stems and diverted away from growing fruit which can result in smaller or not completely ripened fruit.
Topping the Plant Before It Grows Too Tall
Top the tomato plant when it grows to the top of its cage or stake. By doing this, it allows more of the plant's energy to be directed at growing the fruit as opposed to the stems. Cut off each top vertical stem with shears, removing the stem 1/4 inch above where a side shoot diverges from the main vertical shoot. Select a side shoot to prune back to at the desired height of the plant.
Making Sure to Cut Back the Top Weekly
Do not forget to cut back the tops weekly as the plant puts on new growth. Each time you top the plant it diverts energy to the lateral stems, which slows top growth and may stop it completely.
Tip
Top tomatoes promptly when they begin to grow too tall. Allowing the plants to become badly overgrown weakens the stem, and severe pruning can stress the plant.
