Prune indeterminate tomato plants for bigger and tastier fruits and overall healthier plants. Determinate plants can also benefit from pruning, but here, you need to take a different approach, as determinate varieties stop growing when they reach a specific size.
This guide will cover the why, when, and how to prune determinate and indeterminate tomato plants.
Let’s get started.
Why you should prune tomatoes (is pruning necessary?)
You do not have to prune any of your tomato plants. But especially your indeterminate tomato varieties will thank you if you do.
It all comes back to how the plant uses energy while staying healthy and productive.
Let me explain.
Tomato plants and their use of energy
When you move your tomato plants outdoors, they grow vigorously. The plant develops new leaves and branches seemingly overnight. These new leaves photosynthesize the sunlight into sugars and energy, triggering more growth.
But at some point, we want this energy to be used for producing flowers and fruits.
Pruning allows the plant to use the energy to produce larger and tastier fruits. And as a bonus, you will also be able to harvest earlier.
Helping plants stay healthy
Leaving tomato plants to grow unchecked creates dense-growing plants prone to attract fungal diseases due to lack of sunlight and poor airflow.
The flowers and fruits may not get the sunlight they need as an ever-increasing amount of foliage shades them.
Pruning the plant allows the sun to reach all parts of the plant while ensuring sufficient airflow and circulation for the plant to stay healthy.
This will, in turn, result in larger and more tasty fruits and an earlier harvest.
To summarize: Pruning benefits the tomato plant in several ways, including producing larger, tastier, healthier fruits, earlier production, better airflow, and disease prevention.
Determinate vs. indeterminate tomatoes
Not all tomato plants and varieties are the same. And one important distinction is whether the tomato plant is determinate or indeterminate.
- Determinate tomato plants grow to a specific size and tend to deliver most of their fruit at the same time, and then they are done.
- Indeterminate plants continue to grow and can produce fruits all season long.
This is why you must have a different approach when pruning different types of plants.
Pruning determinate tomato varieties
Determinate tomato varieties should be pruned with great care, if at all.
I prune the lower branches of my determinate tomato plants to tidy up the plants and ensure that no leaves touch the soil.
Added benefits include improved airflow, but I only prune branches below the first set of fruit clusters.
Pruning indeterminate tomato plants
Indeterminate plants continue to grow and produce fruits all season long. Here I prune my tomato plants in a couple of different ways.
I remove suckers and side stems to encourage fruit production, disease resistance, and airflow.
I also top prune indeterminate plants towards the end of the season when it is unlikely that any new fruit will have time to ripen. I prefer the plant to use its energy to ripen existing fruits on the vine.
Top pruning is also helpful when a plant grows too tall to be handled or threatens to outgrow its space.
When to prune tomato plants
Prune your tomato plants early morning and make sure the plant is dry. Use clean fingers or tools and ideally wash your hands or disinfect the tools when moving between plants.
I write, ideally, wash your hand and disinfect cutting tools between plants as it is a best practice I learned from a botany course. In real gardening, it is, however, not that practical. Use your common sense.
Check back on your plants regularly, and be prepared to prune your indeterminate plants weekly. I find pinching suckers with my fingers easier when they are about 3 cm / 1 inch. Trying to pinch tiny suckers may bruise the plant’s main stem.
Side stems and larger-sized missed suckers are cut using clean garden scissors.
Understanding tomato pruning methods
I use four different pruning methods for my tomato plants. Each technique serves a different purpose, and not all methods are used for all types of plants.
1. Pinching suckers
Pinching suckers with my fingers is the most common method I use for my indeterminate tomato plants.
Suckers grow in the “V” created between the main and side stems.
Suckers will grow large if left on the plant and are best removed when they reach about 3 cm / 1 inch in size.
I only pinch suckers on indeterminate tomato varieties.
2. Pruning side stems
As your tomato plant develops, it produces leaves to fuel its growth. And soon, the plant grows new branches to hold even more leaves off the lover parts of the main stem.
I grow 50+ tomato plants every season, and prune side stems that develop on the lower parts of the plant.
Never prune side stems growing above the first cluster of fruits on indeterminate plants.
I say the lower part of the plant as it is crucial to keep enough foliage to act as solar panels and feed the plant energy. I strive to keep the bottom 30 cm/12 inches of the plant free from side stems to make watering easier while improving airflow and minimizing leaf-to-soil contact.
One main stem makes it easier to stake and support the plants, improves airflow, and helps keep the plant healthy.
I prune some side stems below the first fruit cluster on my indeterminate tomato plants. I only prune the bottom side stems on mature determinate tomato plants if the leaves are yellow or risk touching the soil and are growing below the first fruit cluster.
3. Root pruning
Root pruning is far less common and is mainly used towards the end of the growing season to hurry up the ripening process of fruits on the vine.
What I have learned from my studies is that root pruning:
- Cuts off parts of the plant’s root system
- The damaged root system sends the plant into shock
- Believing the end is near, the plant speeds up the fruit-ripening process
Use a spade for plants growing in the ground and a sharp knife with a long blade for plants growing in pots and containers.
I have used root pruning for my indeterminate beefsteak tomatoes as the season ends to help speed up the ripening of the green unripe fruits on the vine. Still, I ended up with green tomatoes, but maybe fewer than I would have otherwise.
4. Top pruning
Top pruning helps manage the growth of indeterminate tomato plants and encourages the plant to focus its energy on ripening fruits as the season ends.
Top pruning is practical when indeterminate plants outgrow their allocated space or grow out of reach.
Pruning the top at the end of the season will stop the plant from growing and increase your chances of fruit ripening on the vine for one final harvest.
I top prune all my indeterminate plants at the end of the growing season or if they should outgrow their support structure or stakes.
How to prune tomato plants
Pruning tomato plants is relatively easy. Here are easy-to-follow instructions for each method.
1. Pinch off suckers or “Pruning-101”
By far the most common method of pruning tomatoes. Suckers are best pinched off with your fingers, but you can also use clean garden scissors.
Simply pinch the suckers without touching the main stem. Suckers are usually tender and come off easily.
Largers-sized suckers, or when stems grow tougher, are best cut using garden scissors or cutters.
Ensure your hands are clean, and always disinfect tools between plants to prevent spreading diseases between plants.
2. Top pruning suckers (or “Missouri pruning”)
I recently learned that this method was commonly known as “Missouri pruning.” [1]
Here you only pinch the top of the sucker leaving some leaves to photosynthesize and create energy for the plant.
If you live in a hotter climate or have fruits directly exposed to sunlight, leaving parts of the sucker can help shield the fruits from sunscald.
I use this method on plants directly exposed to sunlight during the hottest times of day.
3. Cutting tougher stems and branches
Older and more rigid stems and branches are best cut using clean garden cutters or scissors.
As a rule, I avoid trying to pinch suckers thicker than a pencil using my fingers. Here a proper garden cutter will help ensure a cleaner cut.
Ensure you disinfect tools as you move between plants to prevent the spreading of diseases.
4. Root pruning
Use a knife or a spade to cut 25-40 cm / 10-15 inches deep into the soil around half the plant.
I use root pruning to encourage indeterminate plants to speed up the ripening process as the growing season ends.
As root pruning is invasive and does shock the tomato plant, I would never use this method when the plant is still developing.
Common pruning mistakes
Like transplanting seedlings or moving plants outdoors, pruning plants often worry home gardeners.
We are afraid we will hurt the plant.
This guide should reassure you and show how simple it is to help your tomato plants stay healthy and produce an earlier harvest of larger and tastier fruits.
But if you are still unsure, here are the most common pruning mistakes I have encountered.
1. Over-pruning in hot climates
Removing too many leaves will expose the fruits to direct sun without any protection, and you risk sunscald.
And it is important to remember that suckers can help generate leaves for synthesizing energy and protect fruits from overexposure to sunlight.
Never prune more than ⅓ of the leaves in one go, and always step back to see which leaves and branches offer shade to your fruit and flower clusters.
2. Confusing determinate and indeterminate varieties
When you buy your seeds or plants, it should clearly say if the plant variety is determinate or indeterminate.
Do not simply trust the name of a type of plant. Did you, for example, know that while Tiny Tim Cherry Tomato is a determinate variety, most cherry tomato plants are indeterminate?
3. Pruning too much in one go
Take your time, and do not feel rushed to do all your pruning in one go. Pruning gradually over several days will allow you to step back and inspect the plant to prevent over-pruning.
Pruning too much at once can unnecessarily shock your plant and adversely affect the plant.
4. Not monitoring plants for subsequent sucker growth
Indeterminate plants grow suckers throughout the growing season. Monitor your plants and make it a rule to pinch suckers as needed every week.
Monitoring your plants will help develop healthy and high-yielding plants.
5. Pruning too late
Suckers grow large if left alone and can easily be mistaken for side stems.
These suckers will prevent sunlight from reaching the center of the plant, restrict airflow, and use up energy that could be better used for producing larger fruits.
Make pruning a weekly task like you probably already have a watering schedule.
6. Pruning when the plant is wet
You should prune your plants in the morning and always ensure the plant is dry.
Pruning a wet plant promotes the risk of diseases and the spread of bacterial and fungal pathogens.
7. Pruning with dirty or blunt tools
Pruning your plants will dull or dirty tools, increase the risk of bruising or damaging the plants, and creates uneven cuts that take longer to heal.
Dirty, uneven cuts expose the plant to diseases, and bacterial and fungal pathogens can more easily spread between plants.
Helpful sources:
[1] https://www.finegardening.com/project-guides/fruits-and-vegetables/pruning-tomatoes
