Pruning Determinate (Bush) Tomatoes – Don’t Skip This

Pruning determinate tomatoes takes less work than pruning vining varieties, but it’s still far from simple. While there is less to do through the growing season, it’s important to prune bush tomatoes at the right time, and in the right way.

As we’ll explore, bush tomatoes are usually happiest in warm, well-ventilated spaces, but for those without greenhouses or conservatories, pruning can help to create a similar growing environment and encourage faster, healthier yields.

So let’s dive in with our secateurs as we learn everything there is to know about pruning determinate tomatoes.

What are determinate tomatoes?

Determinate tomatoes, also called bush tomatoes, grow to a pre-determined height (3-4ft), develop multiple suckers, and produce fruit at the end of each stem. Determinate tomatoes can produce beefsteak, salad, or cherry tomatoes, so care can vary slightly depending on the crop.

How to identify determinate tomato plants

It can be tricky to determine (pun intended) what type of tomato a plant is at the seedling stage. However, there are some clues you can follow if you don’t know the exact variety, or you are growing from saved (possibly cross-pollinated) seeds.

Determinate tomatoes usually have more tightly packed leaves, and seedlings produce more side shoots. By the time a determinate tomato seedling has reached 1ft tall it will often have two or even three main stems.

As flowers appear, it’s simple to differentiate between determinate and indeterminate tomatoes. Determinate varieties only flower at the end of a stem. Indeterminate tomatoes develop flowers evenly along shoots.

Should you prune determinate tomatoes?

Determinate tomatoes need less pruning than vining tomatoes but should be pruned to reduce disease and pests, speed up ripening, and encourage either earlier or larger yields. Below, we’ll explain how and why pruning determinate tomatoes works.

Disease prevention is a clear benefit of pruning determinate tomatoes. Pruning tomatoes regularly to remove dead, damaged or diseased growth is essential regardless of the variety you grow, but as we’ll see later, you can also help to prevent disease with considered early pruning.

Pruning determinate tomatoes at the right time speeds up ripening. Ripening is the process where cell walls begin to break down, producing sugars, and releasing the flavourful chemical compounds that define taste. By removing foliage as fruits form, you allow the sun to warm the skins and speed up the process.

Yield can be improved by early pruning of determinate tomatoes, but there are a few schools of thought on exactly how this should be done. We’ll look at how to achieve better yields through proper pruning later.

How to prune determinate tomatoes

So, we know why to prune determinate tomatoes, but understanding and practicing how to prune them is a whole new skill. Pruning indeterminate, or vining, tomatoes is pretty simple: limit their height; remove side shoots; leave one or two main stems; done. 

There are three basic rules for pruning determinate tomatoes:

• Remove low foliage
• Remove diseased growth
• Keep suckers

The first two rules are really quite simple and aimed at disease prevention, the third is more nuanced:

1. Remove low foliage to prevent southern blight, and stem rot. We know that watering tomato foliage leads to blight, mildew, and pests. That means only ever watering at the base of the plant. However, when you water at the base of a plant, soil splashes up onto the stem. After dry weather, this can lead to soil-borne pathogens entering the stem and causing bacterial and fungal problems.

This is much more likely if there are leaves around the base. Remove the bottom 4” of foliage from bush tomatoes to prevent soil splashing onto the leaves. Keep on top of this right through the growing season.

2. Remove diseased growth to stop the spread of disease. Any leaves with brown spots, yellow lesions, or orange specks dotted over their surface should be removed and burned. There are fungal sprays that can be used to treat most tomato ailments, but they are expensive, and tomatoes grow new foliage quickly. 

Cut back any diseased or damaged growth whenever you see it and continue to care for your tomato plants as normal.

3. Keep suckers on determinate tomatoes. I know that most common knowledge says to remove everything above the first flower cluster and leave two or three suckers below it, but that’s not always the best way. 

To identify a sucker, look for the secondary stem that develops between a leaf and the main stem. A sucker will usually grow at a diagonal angle, and it’s easiest to tell the difference when it’s small:

Suckers are the branches that develop fruit. On vining tomatoes, suckers need to develop trusses, which then host foliage and fruit on separate vines. On determinate tomatoes, those suckers directly hold the fruit. So this really is the most important pruning tip when it comes to yield, and quality.

In simple terms; more suckers means more, but smaller, fruit; fewer suckers means less, but bigger fruit. But, if you water regularly, and feed weekly, tomato plants are capable of hosting far more fruit than we give them credit for.

This year, we’ve experimented with pruning bush tomatoes. We’ve followed two methods, which we’ll explain below (spoiler: both work).

There are two ways to prune your determinate tomato plants:

Method 1 (pruning suckers):

1. When you plant seedlings into their final position, leave them to develop naturally until they are around 1ft tall.
2. Remove any lower foliage within 4” of the soil, and continue to do this right through the growing year.
3. When the first flowers open at the top of the plant, cut off any suckers above that point.
4. Remove all but three suckers below the first flowers.
5. Continue pinching out suckers to create an open structure.
6. When the first fruit starts to show, keep removing suckers, and cut back any diseased or damaged foliage.
7. As fruit ripens, remove leaves to let in light.

Method 2 (leaving suckers):

1. When you plant seedlings into their final position, leave them to develop naturally.
2. Remove any lower foliage within 4” of the soil, and continue to do this right through the growing year.
3. When the first flowers open at the top of the plant, increase watering so that the soil is evenly moist, and does not dry out.
4. Continue watering regularly, providing plenty of light, and feed at least once a week to support the additional growth.
5. Prune out any dead, damaged or diseased foliage and stems whenever you see them.
6. When tomatoes are ready to harvest, remove around 50% of the foliage to focus the plant’s energy on fruit.

Comparing pruning methods:

So, we know that how you prune determinate tomatoes doesn’t necessarily change your yield, but does that mean it’s okay to take the lazy route? Well, no. On our tomatoes left to develop naturally without intervention, they all showed signs of late blight. 

The larger fruiting types, like the heirloom Beefsteak (Determinate), and the classic determinate plum, Roma, produced significantly smaller fruits on the unpruned plants. They also ripened slower. However, the cherry and salad determinate varieties, Maskotka especially, produced significantly more fruit on the unpruned plants.

To make matters more confusing, Banana Legs, a small-fruited plum tomato produced tons of fruit on the unpruned plants, and limited fruit on the determinate tomato with pruned suckers. But, the texture of the ripe Banana Legs was much nicer on the pruned plant.

What did we learn?

1. Limiting suckers is definitely better for disease prevention, thanks to improved aeration.
2. Beefsteak and plum bush tomatoes should have suckers limited.
3. You can keep the suckers on cherry tomatoes and salad tomatoes.

The best tools for pruning determinate tomatoes

It might seem obvious, but using the proper pruning tools with tomatoes is incredibly important. They are soft-stemmed plants, so incredibly susceptible to bruising, which creates a gateway for disease.

Rule one is hygiene. Before pruning any tomatoes, clean your tools. To be extra safe, dip your tools in a bucket of water, mixed with a sprinkle of baking soda and detergent (horticultural soap is ideal, but any antibacterial soap will work), between each plant.

The only tools you will ever need to prune tomatoes are pruning scissors (for safer pinching) and bypass secateurs (for clean cuts). Avoid anvil secateurs at all costs!

Conclusion

Determinate tomatoes are perfect for smaller gardens, and generally hold up to diseases better than vining tomatoes thanks to bred-in disease resistance. However, pruning is still important, and knowing how, and when to prune determinate tomatoes gives you the opportunity to develop your own strategies.

The accepted wisdom of the gardening world is often outdated, so we need to experiment a little to find the best way to manage our crops. We’ve done just that at TGH for this article, and I hope our experiments in how to prune determinate tomatoes give you confidence with your own crop this year.