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How-To

Pruning Tomatoes

How to manage your plants for better health and better fruit

Photo/Illustration: Danielle Sherry

The intrinsic vigor and hardiness of tomatoes almost always guarantees a successful harvest. However, the rapid growth of a healthy tomato plant can also lead to problems.

A tomato is a solar-powered sugar factory. For the first month or so, all of the sugar it produces is directed towards new leaf growth. During this stage, tomato plants grow very rapidly, doubling their size every 12 to 15 days. Eventually, the plants make more sugar than the single growing tip can use, which signals the plant to make new branches and to flower. This usually happens after 10 to 13 leaves have expanded, at which time the plant is 12 to 18 inches tall. In the next few weeks, the entire character of the tomato plant changes. If unsupported, the increasing weight of filling fruit and multiple side branches forces the plant to lie on the ground. Once the main stem is horizontal, there is an increased tendency to branch. Left to its own devices, a vigorous indeterminate tomato plant can easily cover a 4- by 4-foot area with as many as 10 stems, each 3 to 5 feet long. By season’s end, it will be an unsightly, impenetrable, disease-wracked tangle.

 

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Prune for plant structure and health

Suckers form in the axils between the leaves and the main stem. Encourage a strong main stem by removing all suckers below the first flower cluster.

With tomatoes, we want to maximize the efficiency of photosynthesis and minimize the risk of disease. This is best accomplished by ensuring that each leaf has plenty of room and is supported up off the ground. When a tomato plant lies on the ground, or when its growth is extremely dense, many of its leaves are forced into permanent shade, greatly reducing the amount of sugar they produce. If a leaf uses more sugar than it makes, eventually it will yellow and drop off. A pruned and staked plant will produce larger fruit two to three weeks earlier than a prostrate one.

A properly pruned and supported single-stem tomato plant presents all of its leaves to the sun. Most of the sugar produced is directed to the developing fruit, since the only competition is a single growing tip. The result is large fruits that are steadily produced until frost. If more stems are allowed to develop, some of the precious sugar production is diverted from fruit to multiple growing tips. Fruit production, although slowed, never stops. The result is a nearly continuous supply of fruits throughout the season. In general, more stems means more but smaller fruits, which are produced increasingly later in the season. (This is much less applicable to determinate plants, due to their shortened growing season and better-defined fruiting period. Therefore, determinate plants require little pruning. See “Indeterminate vs. Determinate,” below.)

RULE 1: Get plants off the ground.

RULE 2: Give plants room.

RULE 3: Never prune or tie plants when the leaves are wet.

Pruning also affects plant health. The leaves of a pruned and supported plant dry off faster, so bacterial and fungal pathogens have less opportunity to spread. Soil is less liable to splash up onto staked plants. The bottom line: Upright plants have fewer problems with leaf spots and fruit rots because their leaves stay drier and free from pathogen-laden soil.

The way you choose to train and prune your tomato plants will affect how you space your plants, as well as the best method of support . There’s no one right way to do it. Instead there are a few good patterns to follow.

For more information on selecting, planting, pruning, and trellising your tomato plants (and keeping them healthy), see All About Tomatoes on Fine Gardening’s sister site, VegetableGardener.com.

Side stems affect plant vigor

As a tomato grows, side shoots, or suckers, form in the crotches, or axils, between the leaves and the main stem. If left alone, these suckers will grow just like the main stem, producing flowers and fruit.

Suckers appear sequentially, from the bottom of the plant up. The farther up on the plant a sucker develops, the weaker it is, because the sugar concentration gets lower as you move up the plant. On the other hand, side stems arising from below the first flower cluster, although stronger, compromise the strength of the main stem. For a multi-stemmed plant, your aim is to have all stems roughly the same size, although the main stem should always be stronger, because it has to feed the entire plant for the next five or six months. Here’s how I achieve this.

I keep tomatoes free of side stems below the first fruit cluster. When trained to one vine and left free-standing, tomato plants develop strong main stems. To encourage a strong stem, I trim all suckers and I don’t tie plants to their supports until the first flowers appear.

Determinate tomatoes need no pruning other than removing all suckers below the first flower cluster, because pruning won’t affect their fruit size or plant vigor. If you do any pruning at all above the first flower cluster on determinate tomatoes, you’ll only be throwing away potential fruit.

Indeterminate tomatoes can have from one to many stems, although four is the most I’d recommend. The fewer the stems, the fewer but larger the fruits, and the less room the plant needs in the garden. For a multi-stemmed plant, let a second stem grow from the first node above the first fruit. Allow a third stem to develop from the second node above the first set fruit, and so forth. Keeping the branching as close to the first fruit as possible means those side stems will be vigorous but will not overpower the main stem.

Indeterminate vs. determinate

Indeterminate tomato plants continue to grow, limited only by the length of the season. These plants produce stems, leaves, and fruit as long as they are alive.

Determinate tomato plants have a predetermined number of stems, leaves, and flowers hardwired into their genetic structure. The development of these plants follows a well-defined pattern. First, there is an initial vegetative stage during which all the stems, most of the leaves, and a few fruit are formed. This is followed by a flush of flowering and final leaf expansion. Finally, during the fruit-fill stage, there is no further vegetative growth. As the tomato fruits ripen, the leaves senesce and die. Commercial growers favor this type of tomato because all the fruit can be mechanically harvested at once. The major advantage of planting determinate plants in a home garden is early harvest.

Semi-determinate plants, as the name implies, are somewhere between these two other types. Although there aren’t many semi-determinate tomatoes, one of the most popular hybrids, ‘Celebrity’, falls into this category. I think semi-determinates are best grown to three or four stems.

Simple vs. Missouri pruning

In simple pruning, remove the entire sucker at the base. In Missouri pruning, pinch out the tip of the sucker.

There are two ways to deal with a sucker that isn’t destined to become a stem. The simplest is to pinch it off entirely; not surprisingly, this is called “simple pruning.” This should be done when the sucker is still small and succulent. Grab the base of it between your thumb and index finger and bend it back and forth. The sucker should snap off, producing a small wound that will heal quickly. Avoid cutting the sucker with a knife or scissors, because the resulting stump can become easily infected. Once a sucker becomes too tough and leathery to snap off, however, you’ll have to use a blade. I recommend a retractable razor knife.

In Missouri pruning, you pinch out just the tip of the sucker, letting one or two leaves remain. The advantage is that the plant has more leaf area for photosynthesis and to protect developing fruit from sun-scald. The disadvantage is that new suckers inevitably develop along the side stems, adding to your future pruning chores.

Missouri pruning is necessary when things have gotten out of hand. When you’re dealing with large suckers, it’s better to pinch off just the tip than to cut off the whole thing close to the main stem. For one thing, if disease hits, it’s farther away from the main stem. And for another, removing just the growing tip is less of a shock to the plant than removing a foot or so of side stem.

Suckers grow very quickly during the hot summer months. This is indeed a situation that tests one’s resolve. It helps to know that side stems started this late in the season will always be spindly and produce inferior fruit. You must be heartless and tip them all.

How to tie a tomato

There are two reasons to tie tomatoes, and there’s a different tie for each one. Train the leader to grow upright with a loose, figure-eight tie. To support burgeoning fruit, loop a long tie above a fruit cluster, and tie it to the stake 6 to 10 inches higher. Loop the tie twice around the stake and tie it tightly so the tomatoes don’t pull it down with their weight.

Once flowering commences, all tomato vines must be tied to their supports. Although vigorous, the plants are also easily damaged, so take care in how you tie them and what you use. Cloth strips work well as long as they’re not too old and threadbare. Pieces of panty hose cause the least damage to plants, but they’re not biodegradable. Twine should be at least 1/8 inch thick, or else it can cut into the tomato stems.

There are two types of ties. Training ties direct plant growth upwards, and supporting ties keep it there. The top foot of a tomato stem, or leader, is very succulent and easily snapped; it needs to be directed upwards, gently. I wrap a short piece of twine around the middle of the leader, cross it over on itself, and loosely tie it to the support. The resulting figure-eight tie reduces the chance the tender stem will rub against the support and get bruised.

Fruit will form along this stem. If left to the devices of the loose training ties, the weight of the fruit will pull the ties down the stake. Eventually, the stem will bend over and crease. Luckily, as the stem matures, it toughens; by the time fruit develops, the stem can tolerate a tighter tie. To support a fruit cluster as it fills and gains weight, I loop a longer piece of twine, 12 to 18 inches, around the stem just above the fruit cluster, creating a sling. Then I gently pull it up to take the weight off the stem. I wrap the twine twice around the stake, and firmly tie it to the stake 6 to 10 inches higher than the point of attachment to the vine. To keep the tie from slipping, I knot it underneath the point where the sling meets the stake.

A final pruning pays off

About 30 days before the first frost, there is one last pruning chore: The plants must be topped. The fruit that has set must be given every opportunity to mature. Removing all the growing tips directs all sugar produced by the plant to the fruit. This can be hard to do, as every gardener is reluctant to admit the season is coming to an end. However, this final pruning can make all the difference between hard, green fruits, hurriedly picked before frost, which later rot in a paper bag, and ripe, home-grown tomatoes in your Thanksgiving salad. Be tough, fight your nurturing instincts, and top those plants.

Staking and spacing options

Which method of support you use and how far apart you set tomato plants depends on the number of stems you allow to grow.

Cages work for plants with three to five stems. I use them almost exclusively for determinate tomatoes. Ready-made tomato cages are too little for all but the smallest determinate cultivars. My ideal tomato cage is made from 5-foot-tall galvanized fencing with openings at least 4 inches square, so I can reach in and pick the fruit. A 4-foot section makes a cylinder about 15 inches in diameter. Secure it with baling wire, and stabilize it with two stakes, one of which is at least 6 feet long. Drive the stakes in within a week of planting, but wait to set cages over the plants until the first fruits form, to simplify weeding and pruning. Space caged plants about two-thirds of their final height in all directions.

Use the same type of fencing to make a tomato fence, which works best for plants with one or two stems. To get a good, solid fence, you need a helper. Secure the fencing with 6-foot stakes every 4 feet. Here’s how I keep the fence taut. Loop each non-end stake through the bottom rung of the fence, then start to drive it into the ground so its bottom is angled away from the previous stake. Once it’s about 4 inches into the ground, bring the stake upright and drive it in the rest of the way. Set single-stemmed plants 18 inches apart, and double-stemmed plants 24 inches apart. If you stagger the planting (successive plants on opposite sides of the fence), you can knock 6 inches off these distances. Erect the fence before you plant your tomatoes.

Stakes work well for plants of one to four stems. I use 1 inch x 1 inch x 6-foot lengths of untreated oak or cedar, sharpened on one end. Drive the stakes 8 to 12 inches into the ground, depending on your soil (deeper for loose, sandy ground). To avoid damaging roots, drive your stakes in within a week of planting. Space staked plants at 18 inches for a single stem, 24 inches for two stems, and 36 inches for three or four stems.

From Kitchen Gardener Issue #27

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Comments

  1. debbieheilemann 06/03/2014

    My tomato plants are already over 6 ft tall? (Over my supports) Can I cut them back to a managable height or continue to let them grow

    1. user-7006958 06/04/2014

      I am not an expert but at 6ft tall I pinch the top or the main stalk . At this point there will be no more growing high but you will get more laterals. To keep diseases under control in my part shade garden, I do not let a lot of laterals grow either; if I have six to eight layers of flowers which will become the tomato clusters I start cutting the new laterals to force the plant into growing my fruit.

  2. user-7006983 06/05/2014

    my tomatoes are tall but no blooms, what's wrong?

    1. GardenGrl1 06/10/2014

      Call your local Extension office to find out for certain. They are a free resource! Lots of reasons why you don't have blooms yet, possibly your local weather conditions, where you have your plant in your yard. Usually this is due to having too much nitrogen in your soil. It may be time to add some phosphorus for blooms! Good luck, I hope you have lots of tomatoes this year!

  3. user-7007274 10/23/2014

    So good! Thank you very much. One question: how far from the plant would you place your stakes?

    1. andrewdahl 04/14/2015

      Directly alongside the plant, so that you can tie it to the stake. Don't worry about damaging roots with the stake.

  4. carole_mason 01/02/2015

    I have a small greenhouse my heirloom tomato plants get tall they produce flowers but no fruit and I noticed tiny white flies on the backs of the leaves I think it is the high humidity in the greenhouse nothing works to rid the plants of the flies...thoughts?

    1. user-7007404 02/27/2015

      Flowers must be pollinated to fruit.

      Outdoors, bees and wind cause pollination.

      In your greenhouse, you may try manual pollination.... Either by gently shaking them or with a small brush.

      M

      1. tony_ee 06/25/2015

        Use a battery powered toothbrush.

        Every flower that does not pollinate is a sign that I have failed.

        I hate failure.

        I had some indeterminate plants that lasted almost three years... they just gave their last fruit this February/March. I'm in coastal SoCal but even so it takes work

    2. user-7007634 06/04/2015

      The white flies on the back of the leaves are likely an insect pest called White Fly. They suck the chlorophyll in the leaves and can weaken the plant. You can try "sticky traps" (usually yellow plastic strips coated with a sticky substance on both sides) to help keep the population under control.

    3. user-7008183 07/18/2016

      Regarding your pest problem, I use neem oil sprays every two to three weeks during the evening to prevent pests and fungal disease. Neem oil does not harm beneficial insects that do not chew on foliage, like bees, butterflies, spiders, ladybugs, etc. Haven't seen whiteflies in years, and only the occasional tiny hornworm, which I get rid of, but won't survive anyways. But, I always see bees, spiders, ladybugs, and butterflies in all of my gardens, so pollination isn't a problem for my outdoor garden.

  5. uttaraghodke 06/23/2015

    http://www.garden365.com/container-gardening/growing-tomatoes-in-pots/

  6. michelewedewer 08/05/2015

    I hope you can help me. My plants are now those unsightly huge masses you were talking about. I have them on cages but they still are out of control. Can I still cut them back? I can't even walk it between my plants.

  7. user-7007784 08/24/2015

    It's the end of August here in southern Missouri any my patio tomatoes are a beautiful mass of leaves but still no tomatoes. There are flowers, but no fruit. I fertilized them repeatedly in the last couple of months. I didn't know about pruning, can I do it now?

    1. longtermconservative 06/13/2016

      I realize I found your question 10 months too late. Here in central MO, the clay soil has plenty of nitrogen, but is lacking phosphorous.. Cultivate the soil and add either phosphate/bone meal (0-10-0) or super phosphate (0-18-0). The phosphate will aid your tomatoes with more blooms and stronger stems to hold the fruit. I apply 2-3 tablespoons per plant when planting then the same amount every 3 weeks or so. It works for me -after I've done the local soil sampling so I know what I have to work with in the first place. Happy gardening in 2016!

  8. leonardo_giacalone 12/02/2015

    I have read that you should be cutting sucker branches from tomato plants. I found out that after cutting them off, I was able to root them in water. It only took three days to see a root form. Now I have that many more plants. Could any one tell the pros and cons of doing this?

  9. thomashenthorne 04/10/2016

    I am usually pretty good about pruning them for the first 8-9 weeks then slack off as fruit appears... it looks like we should prune them all the way through fall, according to this article?

  10. jitendraknigam 08/05/2016

    Nice blog......... what about semi determinate plants??? is they need suckering ?? when it start to do?? myemailid jitendraknigam@gmail.com

  11. stephencoote 10/06/2016

    This is one of the best articles I've read on training tomatoes. Thanks for posting it. Down here in NZ, the time to plant tomato seed has finally arrived. Best wishes... Stephen Coote.

  12. user-7008844 08/20/2017

    From my point of view we should let the plant grow wild
    We should not interrupt the self constructive idea of the plant
    The suckers help the plant to resist against wind and rain drops and even helps to increase the photosynthesis process of the plant

  13. carolhuotari 10/10/2017

    I have a very tall potted cherry tomato plant that has been producing for two summers. I brought in last fall, and put it in the front hall that gets some sun by afternoon. It is time to bring it in again if I want to keep it, but of course it's quite bushy as well as tall. Is there anything I can do to trim it down without harming the plant. It still has green tomatoes and is still blossoming. After being such a wonder plant, I hate to loose it. Any suggestions? I live in Maine, and wintering a tomato plant is unheard of.

  14. user-7009012 12/05/2017

    What is the difference between determinates and indeterminates?

    1. user-7009012 12/06/2017

      ???

  15. arswaim 07/15/2018

    I've definitely had healthier plants and a better tomato crop since I started pruning my tomato plants regularly a few years ago, so I would highly recommend following the advice in this article.

    Regarding supports for tomatoes, I've been using the stake and weave method. Rutgers University has a good description of the process at .

    1. arswaim 07/15/2018

      It seems URLs aren't permitted in comments. The Rutgers University document I referenced above is titled "The Stake and Weave Training System for Tomatoes in the Home Garden". Searching for the title in Google returns the document as the first result.

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