How to Prune a Tomato

Tomatoes pruned to a single stakeHere are six good reasons to prune tomatoes:

  1. To grow more flavorful tomatoes.
  2. To grow larger tomatoes.
  3. To grow more tomatoes over the length of a season.
  4. To keep plant leaves and fruits off the ground and away from pests, insect damage, and fungal disease.
  5. To keep plants smaller and more compact.
  6. To allow tomatoes on the plant at the end of the season to ripen before the first frost.

Pruning a tomato means removing unneeded growth tips from the plant. These growing tips are sometimes called shoots or suckers. Growth tips are the new growth–the small leafy-bud growth–located in the “V” or crotch between two stems.

Pruning or pinching away new growth allows a tomato plant to concentrate its energy on the development of fruit rather than new foliage. Plant sugars used to make new growth are instead used to concentrate flavor and grow larger, healthier tomatoes.

Determinate and indeterminate tomatoes:

Tomatoes can be divided into two growth habit categories: determinate and indeterminate. Determinate tomatoes usually require no pruning. Indeterminate tomatoes perform best if pruned.

A determinate tomato grows to a genetically pre-determined size and then stops. Beefsteak and sandwich tomatoes are mostly determinate tomatoes. These tomatoes are bushy and self-topping. All of the blossoms and fruit on a determinate tomato develop at the end of growing tips at about the same time.

Indeterminate tomatoes grow unchecked. They produce vine-like stems. These tomatoes continually produce new stems, leaves, and fruit until the plant dies. Cherry and salad tomatoes are mostly indeterminate tomatoes. The growth tips of indeterminate tomato plants do not set fruit; fruit is set on side shoots as the plant continues to grow. An indeterminate tomato will have blossoms and fruits at all stages of development throughout its life. Pruning is the best way to contain an indeterminate tomato.

When to prune a tomato plant. You can prune a tomato at any time, when it is small or when it has grown large. If you know you want to contain the size of a tomato plant prune early. A tomato plant can first be pruned when it is just 12 to 18 inches tall.

Tomato pruning objectives:

  • Prune to create one to four strong stems.
  • Prune each stem to about the same length. Prune to keep the plant at a manageable size.
  • Prune to keep leaves and stems off the ground by removing the leaves and stems below the first set of fruit.
  • Prune so that leave do not shade other leaves. (Sunshine must hit leaves for photosynthesis to occur. Photosynthesis is necessary for the production of plant sugars which are required for plant and fruit growth.)
  • Avoid pruning away leaves above fruit clusters; these leaves protect fruit and stems below from sunburn.
  • Prune to allow air circulation to the center of the plant. Air circulation helps deter diseases and insects.

Tomato pruning step by step:

Begin pruning when the tomato plant is established and strong. Here’s how:

  1. After the plant is 12 to 18 inches tall, allow the first set of blossoms to grow. (Nip away any blossoms that come before.) This first set of blossoms will become the plant’s first fruit cluster.
  2. Remove all of the leaves and suckers below the first blossom cluster. They are not needed.
  3. Decide if you want one main growing stem or more. Single stem tomatoes do not require much space and can be grown close together. However, single stem tomatoes produce fewer fruits than multi-stemmed plants. (Most tomato growers allow plants to develop two or three and sometimes four growing stems.)
  4. To grow a two-stemmed plant, allow a growth tip or shoot to grow from the leaf axil or “V” above the first blossom cluster. This will become the second stem.
  5. To grow a three-stemmed plant, allow the growth tip to grow from the leaf axil directly above the second stem. Main growing stems should not be separated by more than a leaf node. This will insure that the plant grows strong from its base.
  6. When you decide to prune, do not pinch away the growth tip too soon. Allow two sets of leaves to develop on a sucker or side shoot before pinching out the growth tip. Pinch above the two sets of leaves; these leaves will protect fruit and stems below from sun damage.
  7. Re-check the plant once a week to pinch out new unwanted growing tips.
  8. When the plant reaches the desired height–usually no taller than its support, 4 or 5 feet is good–consistently pinch out all new growing tips. In a week or so time, the plant will quit trying to put out new growth at the topmost part of the plant and concentrate on new growth and fruit below. Continue to pinch out any new growth that you do not want. Keep training this way and the plant will develop a more compact shape, and it will begin to flower and set fruit more heavily throughout its height.
  9. Whenever you are in doubt, do less pruning than more. As you gain experience, pruning will grow easier and become intuitive.

To be clear, the growing tip is not the actual highest point of the plant but the new growth just below in the “V” of the leaf axil, where one shoot branches off from another. It is this new growth that you are pinching away.

Growing tips–also called terminal buds–have specialized plant cells called meristem. Meristem cells produce a hormone called auxin that inhibits cells below the topmost growing tip from dividing and creating significant new growth. By pinching out the meristem tissue at the topmost growing tip of the plant, auxin is no longer produced and the meristem tissue in the axils below will start new cell division. This directs the plant to concentrate its growing efforts and sugars on the foliage and fruit below.

Pruning tomatoes:

How to prune or pinch out new growth. Use your thumb and forefinger to pinch out the growth tip or sucker. Pinch out new growth when it is small, between 2 and 4 inches long. Simply break or pinch the new growth off after flexing it back and forth. If a sucker is thick and does not pinch away freely, use a retractable knife blade to slice it away. Prune before suckers are too large, otherwise you will leave a large pruning wound through which tomato disease may enter. Prune when the plant is dry; tomato diseases are often spread in drops of water.

(Just so you know: there are two methods of tomato pruning, “simple pruning” and “Missouri pruning.” In the simple pruning method, you pinch out any sucker or shoot sucker not destined to be a stem. Pinch it at its base. Using the Missouri method, you pinch off the growing tip after you have allowed two sets of leaves to form on the new shoot. This is the method described above. The Missouri method is used to regain control of a plant that has gone largely unpruned and become unwieldly.)

Pruning overgrown or leggy plants. You can prune or top a tomato plant that is out of control, leggy, or threatens to overwhelm its support–a stake, a trellis, or cage.

To prune an overgrown tomato, step back and take a good look at the plant. Determine which stems are the strongest stems. Prune to establish these stems as the main stems, usually two to four stems. Prune away no more than one-third of the total plant. To prune away more may send the plant into shock.

When you begin, first eliminate stems that are broken or diseased. Next, carefully cut away stems that are not part of the final vision you have for the plant. A few big cuts, will quickly open up the plant and give it form.

Once large stem cuts are completed, prune from the top systematically pinching or cutting the plant back to the desired height. As you work your way down, continue to step back and visualize the plant pruned. Eliminate unwanted foliage as you work your way down. You may have to prune away some blossoms and undeveloped fruit. Keep in mind that the plant will be stronger and more productive in the long run. Don’t worry, the plant will rebloom.

A heavily pruned tomato will need a couple of weeks to recover. Once its wounds are healed and the plant recognizes its new growing point, it will begin to produce new foliage and flowers.

Pruning at the end of the season. Indeterminate tomatoes continue to set blossoms and produce fruit until they die when the first frost comes. To get the most fruit from your plant, begin pinching away new suckers and blossom clusters four weeks before the average first frost date. The plant will direct the energy it was using for new growth to the ripening of fruit already on the plant.

Supporting tomatoes:

Support your tomatoes. Both determinate and indeterminate tomatoes will benefit from support. For indeterminate tomatoes, support is essential.

It is best to set tomato supports–stakes, trellises, or cages–in place early, before you begin to prune, about 2 to 3 weeks after transplanting. This will allow you to train the tomato to its support, to prune so that the plant takes full benefit from its support.

Stakes. Stakes are commonly used to support single stem plants. Place the stake 3 to 4 inches away from the newly transplanted tomato and train its main stem up the stake. Tie the plant to the stake with loose garden twine or a stretchy horticultural tape. A determinate tomato will need a stake 3 to 4 feet tall (early-season tomatoes that ripen in 70 days or less will not need staking or pruning), a indeterminate tomato will need a stake 5 to 6 feet tall. Use one- to two-inch square wooden stakes or metal stakes. Staked, single trunk tomato plants can be spaced as close as 12 inches apart.

Trellises. Trellises for tomato plants are supports similar to horizontal wire supports used to support berry canes. Trellises are useful when you are growing several multi-trunk tomato plants in a row. Drive a stake just to the outside of every other plant, about 4 inches from the main stem. Run heavy twine or wire between the posts. As the plants grow tall, gently move their branches to the cross wires and loosely tie the stems to the trellis. Grow the tomatoes to the top of the support and then remove or top new growth. As plants grow wide, you can string twine between the posts to contain the plants and keep them from sprawling, or you can tie stems along the cross-wires like grapes.

Cages. Cages are useful for multi-stemmed free-standing tomatoes not growing in a row. Square or triangular cages may offer more balance than round cages. Use a stake to anchor light cages and keep them from toppling. Prune the tomato to fit the confines of the cage and top the plant when it reaches the top of the cage.