What Is A Root Trainer? (Advantages of Root Trainers)

Sometimes, plants will suffer from root damage or transplant shock when you move them into the garden.  If you have this problem, then a root trainer might be just the thing for you.

So, what is a root trainer?  A root trainer is a special container that encourages a plant’s roots to grow straight down, towards the bottom of the trainer.  A root trainer has a hole in the bottom to allow air pruning of roots, and it has grooves on the inside to prevent the roots from circling around the container.

Of course, you can find root trainers in many different shapes, sizes, and materials depending on your needs.

In this article, we’ll explain what a root trainer is, along with the pros and cons of using one.  We’ll also get into the types of root trainers you can use and where you can find them.

Let’s get started.

What Is A Root Trainer?

According to Wikipedia, a root trainer is a special container that encourages a plant’s roots to grow in a specific pattern.

Ideally, the roots will grow straight down – without going sideways or circling around the container in a spiral pattern. This creates a plug plant that is easy to transplant later in the season.

root rot
Without training, a plant’s root system may not grow the way you want it to.

A root trainer usually has grooves on the inside of the container.  These grooves further encourage the roots to grow downward, and they prevent the plant from becoming root bound in the container.

A root trainer is tall, which allows plenty of space for plant roots to grow downward into the soil before transplant.  The container is also wider at the top gets more narrow at the bottom, to “funnel” the roots towards the bottom.

A root trainer also has a hole at the bottom.  This hole allows excess water to drain out of the container easily.  More importantly, this hole causes air pruning of the roots that reach the bottom of the root trainer.

Air pruning occurs once a plant’s roots stop growing after they encounter air.  This is nature’s way of telling plant roots that they have grown too high – that is, there is no more soil above them to grow up into!

Air pruning encourages the plant to create new root growth elsewhere, which leads to a thicker root system.  This helps the plant to absorb more water and nutrients from the soil, leading to a better chance of survival and good growth after transplant.

A root trainer needs a support or rack to hold it above a solid surface.  If the bottom of the root trainer is placed against a solid surface, air pruning will not occur.

Now we know what a root trainer is – but why should we use one?

Advantages of Root Trainers

There are several advantages of using root trainers instead of ordinary pots when growing plants from seed, including:

  • Encourage deeper, straighter roots
  • Cause air pruning of roots
  • Reduces transplant shock and root damage

Encourages Deeper, Straighter Roots

A root trainer, by design, encourages roots to grow straight down, deep into the soil.  Whenever the roots encounter resistance (the edge of the container), they change direction and are “funneled” towards the bottom.  But why is this desirable?

For one thing, when a plant’s roots grow straight down, they are able to access more nutrients found deep in the soil.  When growing root crops (such as carrots), a straight central root (taproot) is desirable and prevents a deformed appearance.

cracked carrot
A carrot is the taproot of the plant, and we like to see them nice and straight, which is helped along by a root trainer.

When a plant’s roots are trained to grow straight down, they are less likely to get tangled up with the roots of nearby plants.  This avoids the problem of competition between plants for water and nutrients from the soil.

Causes Air Pruning of Roots

When a plant’s roots grow straight down towards the bottom of a root trainer, they eventually reach the hole in the bottom of the container.  At this point, the ends of the roots will stop growing, since there is no more soil for them to draw water and nutrients from.

Essentially, the roots exposed to the air dehydrate due to lack of water.  After this air pruning occurs, the plant will start to grow other roots elsewhere.

This new growth results in a stronger, thicker root system for the plant.  A stronger root system makes the plant better able to survive transplant into a garden.

Note: grow bags are another way to encourage air pruning in your plants.  You can learn more about grow bags in my article here.

Reduces Transplant Shock and Root Damage

As mentioned above, a root trainer gives plants stronger, straighter roots.  This avoids the problem of circling roots that grow in a spiral pattern (over time, this causes plants to become “root bound” in a pot).

A stronger, straighter root system gives plants a better chance of survival after transplant.  Damage to roots during the transplant process is a big factor in whether a transplant survives.

A strong, straight root system also means that you can avoid cutting the roots to remove the plant from its container.  Cutting the roots of a plant increases the risk of infection by bacteria or viruses (especially if you fail to clean your knife properly between cuts on different plants!)

Plant Roots
A strong and straight root system means you will not have to cut the roots to transplant into the garden.

Finally, a stronger, deeper root system means that a plant will be able to absorb more water and nutrients from the soil.  This increases the chance that the plant will survive and thrive in its new home after transplant.

Disadvantages of Root Trainers

No system is perfect, and root trainers are no exception.  There are a couple of disadvantages when using root trainers, including:

  • Needs more frequent watering
  • Requires a mount or rack

Needs More Frequent Watering

Water drains out of a root trainer fast, due to the shape of the container and the hole at the bottom.  This helps to avoid over watering, but it also means that you have to pay careful attention to watering.

If the soil dries out for too long, the seedling and its root system will be damaged.  Keeping the soil moist is important during the germination phase, before a seed sprouts.

Seedlings sprouted in root trainers will need more frequent watering.

If you have a setup with a large number of root trainers, you might want to automate the watering with an electronic system.  If this isn’t possible, then find a consistent schedule to water the plants.

Requires a Mount or Rack

A root trainer also requires a mount or rack to work properly.  For one thing, the shape of many root trainers means that they cannot stand on their own without support.

In addition, the hole at the bottom of the root trainer needs to be held above a solid surface (such as a floor or tabletop).  Otherwise, air pruning of the roots will not occur.

How Do You Use a Root Trainer?

First, decide on the size, shape, and material for your root trainer.  This will depend on the plants you want to grow, and when you want to transplant them.  You can make your own root trainers, or you can buy a set of them, along with accessories such as a tray, mount, or rack (more on this later). 

Next, choose your growing medium.  This will depend on what you are trying to grow, so there is no one-size-fits-all answer.

For example, carrots prefer sandy soil that drains well and is free of obstructions.  Other plants that need more moisture might do better with a thicker potting mix that retains moisture.

Carrots like sandy soil, while other plants may prefer a loam or silt mix.

Once you have filled the root trainer with growing medium (such as soil or potting mix), you will need to plant your seeds.  Pay attention to ideal germination temperature, and keep them warm enough (but not too warm!) until they begin to sprout.

After germination, you will need to provide the seedlings with light (use a grow light, or put them in a windowsill to get natural light).  They will also need regular watering to keep them alive.

Finally, you will need to remove the seedlings from the root trainer when you want to transplant them into the garden (or into larger pots).

What Can I Grow in a Root Trainer?

A root trainer is often used to grow trees.  However, you can use a root trainer to grow many fruits and vegetables from seed until they are ready for transplant into the garden.

Types of Root Trainers

Root trainers are often shaped like cones, but the key feature is that they are wider at the top and narrow at the bottom, where the hole is located.  You can find (or make) root trainers out of plastic or cardboard.

You can build a custom root trainer to any size you like.  One common size is 1.5 inches wide (square) by 5 inches deep, such as these 4-cell root trainers from Gardener’s Supply Company.

Plastic root trainers are reusable, as long as you don’t damage them when removing the seedlings from the containers.  Some root trainers are also stackable, making them easier to store in the off-season.

Seed trays may also be useful for storing and moving your root trainers, and for holding excess water that drains out of the containers.  You can learn more about seed trays in my article here.


Now you know what a root trainer is and how to use one.  You also know what types of plants can benefit from them.

You can learn more about how to promote healthy root growth in plants in my article here.

You can also learn about the best fertilizers for root growth in this article.

I hope you found this article helpful.  If so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!


Jon M

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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