How Deep Do Tomato Roots Grow? The Definitive Guide
A common mistake among amateur gardeners is that they focus on healthy stems and foliage and do not consider the root at all. A lush top is achievable if you focus on a good root system provided the soil is capable of supporting a healthy plant. There's a famous saying in the gardening niche, "feed the soil, not the plants" and this holds true for all kinds of plants, tomatoes are no exception.
How Deep Do Tomato Roots Go?
As you may have guessed, there's no answer that holds true for all varieties and in all cases. We are going to individually take a look into the various factors that come into play, such as:
- Tomato variety.
- Depth of the container.
- Soil structure.
- Soil quality.
- Planting technique.
But before we dive into the individual factors I would like to address one of the main reasons people ask this question and it's got to do with raised beds.
How Deep Should My Raised Bed Be?
If you are looking for a quick answer because you are building a raised bed or if you want to know whether your existing raised bed is deep enough for tomatoes, you would be glad to know that just 1 foot (30 cm) is sufficient. Notice that I say sufficient and not ideal. The ideal depth would be greater than 2 feet (60 cm) because in general, tomato roots can grow anywhere between 2 and 3 feet, even though around 2 feet is more common.
The Structure of Tomato Roots
Tomatoes are dicots, that is, they have two cotyledons, the embryonic leaves (the first leaves that show up from the seed). Another factor that dicots have in common is the fact that they have a taproot system as seen in the image below when compared to monocots that have a fibrous root system.
A taproot allows the plant's root system to penetrate deep into the soil while it sprouts secondary roots along the side of this main root which helps it absorb water and nutrients from the soil. Taproots are famous for going straight down provided there are no obstacles in the way.
Tomatoes, due to their taproot system, have a deep root going down up to 3 feet (90 cm) in extreme cases which happens when the plant is in search of water or nutrients in poor, but loose soil conditions.
An ideal root length would be one that supports the plant structure while at the same time provides sufficient water and nutrients. Some varieties of tomato are very weak and gardeners have to provide additional support in addition to providing a strong root system. A balance needs to be struck and you can influence root growth, so let's see how.
Factors Governing Tomato Root Depth
To help you determine how deep your tomato roots are going to grow, you would need to understand the factors that limit their growth. Let's take a look at each of them, one at a time.
Tomatoes can be differentiated into two broad groups, the determinate and indeterminate varieties. The former grows until it has reached a certain size while the latter continues to grow throughout the growing season. Many of the famous heirloom tomato varieties are indeterminate for instance.
As expected, indeterminate varieties have a further reaching root system and their taproot goes deep into the soil because they just like the foliage continue to grow throughout the growing season provided that other factors do not limit this growth.
Depth of the Container
Tomato roots are naturally limited by the depth of the pots or containers that they are planted in. At the end of the growing season when you uproot the plants it is not unusual to notice the taproot has made circles around the base of the container even if your container was 18 inches deep (45 cm). You may notice this when you are transplanting seedlings/young plants too.
If you plant in a raised bed, however, the depth of the raised bed is very often the depth of your container because the soil beneath the bed is often impenetrable hard clay or just soil that was never tilled. If the quality of your soil below the raised bed is good, the roots of your tomato would definitely grow beyond the limit of the raised bed if they need to.
This follows what was said above. Even though tomato roots and roots, in general, are resilient and can grow into even tiny crevices, there are situations where the soil is just too compact and root growth is impossible. Once your tomato has reached such a layer the root would continue to grow, but laterally, just like it would do at the bottom of a container.
When I use the term soil quality, I am referring to its nutritional value. Roots, in general, grow in search of nutrients and water. Homegrown tomato plants receive a lot of care and they do not need to spread their root system too much to seek nutrients. The roots would still grow considerably, but in a very different way than if they were planted in poor soil conditions. To learn about the different kinds of nutrients a tomato plant needs at different stages of growth read my guide on fertilizing tomatoes.
Roots in healthy soil would be very dense (as seen in the image at the start of this article) and a lot of energy would be spent on secondary roots which slows down the growth rate of the taproot, thereby lowering the overall depth of the root system by the end of the growing season. This is very similar to tomato foliage that grows dense under sufficient light, but long and stringy under low light conditions.
Most plants do not like their stem to be underground, but tomatoes are different, they can handle it, in fact, they grow better when they are deeply planted. A day before you transplant your tomatoes you should cut off the bottom leaves (up to 2/3rd of the plant) and let the would heal up. Place the now bare stem into the ground.
Since tomato plants can grow roots from their stem, this allows them to grow taller without support (much like a building with a deep foundation) in addition to allowing them to reach more nutrients (the original root system is deep into the soil). I have written a complete guide on transplanting tomatoes which you may find helpful.
How to Deep Root Tomatoes
Possible Problems With Deep Rooted Plants
There are special cases wherein you would want to try and prevent your tomato from going too deep into the Earth.
- Frost: Most people plant their tomatoes once the danger of frost has passed. Planting deep into the earth only when the top portion has defrosted is not the best idea because tomato plants love warm soil. This would not cause a problem, but growth would be lowered a little, and fruiting may be delayed by a week.
- Impermeable soil: There is no problem at all if your plant cannot grow roots through impenetrable soil, but if water cannot seep through either, the roots are going to be soaked up all the time. This can lead to problems such as root rot. The problem may not spread up the root system, nonetheless, it is something that is best avoided. Learning how to best water tomatoes is an important skill that helps prevent a lot of issues.
- Clayey soil: Clayey soil tends to hold water for longer than sandy/grainy soil. This is not a problem if your plants grow in it all the time because they would be used to it. There are instances, however, when this can be a problem. For example, if you grow tomatoes in a raised bed you definitely do not water the bed such that water seeps into the ground below. However, if you got a clayey ground below the bed and if your tomato roots have penetrated into it, a heavy shower towards the end of the season can lead to splitting of ripening tomatoes due to the sudden influx of water into the fruit.
If you are interested in knowing more and reading about some experiments conducted, you should check this out on the soil and health library. It is the most detailed experiment on tomato root growth that I have come across.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.