How to Promote Root Growth in Plants (6 Methods)


A strong root system is one of the key factors in growing a healthy plant.  However, a strong root system does not happen automatically.

So, how do you promote root growth in plants?  To promote strong, healthy root growth in plants, try the following 6 methods:

  • Use a root trainer (at the germination and seedling stage)
  • Repot as Needed (if the plant outgrows its container and becomes root bound)
  • Loosen and Aerate Soil (compacted or waterlogged soil slows down root growth)
  • Practice Deep, Infrequent watering (this promotes a more extensive root system)
  • Provide Proper Nutrition (get the pH and nutrient levels right)
  • Add Rooting Hormone (usually for cuttings when propagating plants)

In this article, we’ll get into more detail about each of these methods.  Then you’ll know exactly what to do to promote a stronger root system in your plants.

Let’s get started.

How to Promote Root Growth in Plants

If you want to promote root growth in your plants, the best place to start is at the beginning: at the germination and seedling stage.  Using a root trainer will help to get your plants off to a good start in their development.

Use a Root Trainer

A root trainer is a container that encourages a plant’s roots to grow downward, instead of sideways.  This results in a deeper root system, which can then branch out sideways after the plant is moved into the garden.

A root trainer has grooves on the inside that prevent a plant’s roots from circling around the container.  Instead, the roots are “funneled” down towards a hole at the bottom of the root trainer.

Once the roots reach the hole at the bottom of the container, they are exposed to the air.  At this point, air pruning occurs – that is, the roots stop growing once they encounter air.

Plant Roots
Plant roots stop growing when they are exposed to air, which is called air pruning. A root trainer will encourage air pruning and a more extensive root system for plants.

This air pruning encourages the plant to starting grow more roots in other locations.  This results in a stronger and more extensive root system that will grow deep into the soil after transplant.

A root trainer also allows you to grow seedlings in separate cells.  This will prevent their roots from getting tangled together, making it easier to transplant seedlings and reducing the risk of damage when they go into the garden.

Root trainers are often used at the seedling stage to help plants grow a stronger root system, but you can also use larger root trainers for young trees.  You can learn more about root trainers in my article here.

Repot as Needed

If your plants get large enough, you may need to repot them at least once before transplanting them into the garden.  The reason is that plants will eventually become root bound in a pot that is too small.

A plant becomes root bound when its roots start to circle around the inside of its container when they have nowhere else to go.  As the roots continue to circle around in search of nutrients, they make their way all the way around the inside of the pot.

At that point, there is no new soil left for the roots to grow into.  Eventually, the plant will stop growing, although it can maintain its size if it gets enough water, light, and fertilizer.

After transplanting into a larger pot, the plant’s roots will have more room to grow.  You can sometimes tell that a plant needs repotting if you can see roots when you look at the drainage holes at the bottom of the pot.

To repot, first find a container that is slightly larger than the current one.  Next, add some soil to the bottom of the new container.

clay pots
When repotting a plant, choose a container that is slightly larger than the old one.

Then, gently take the plant out of its old container to avoid damaging the roots.  Put the plant in the new container, on top of the layer of soil that you already put down.

Finally, add more soil until the new container is filled to where you want it (just don’t cover up too much of the plant’s stem!).

You can learn more about repotting plants (including what type of container and growing medium to use) in this article from the University of Maryland Extension.

Loosen and Aerate Soil

If you loosen up the soil for your plants, it will help to keep the roots healthy and allow more oxygen into the soil.  Loose, aerated soil will make for a stronger, more vigorous plant.

According to the Colorado State University Extension, compacted soil restricts root growth.  This makes sense – it is easier for roots to grow into a softer medium rather than a hard one.

So, before you transplant seedlings into the garden, it is a good idea to loosen the soil a bit.  You don’t have to rototill (unless it’s a new garden) – a shovel will probably suffice to break up any clumps or compacted soil.

shovel
Use a shovel to loosen and aerate the soil before transplanting into the garden. This will allow the roots to grow more freely.

In addition to providing looser soil, digging will aerate the soil.  This is a good thing, since plant roots need oxygen for respiration (in a sense, they need to breathe like we do).

If your soil is compacted or too wet, there will be less room for oxygen.  This will decrease the health of the plant, possibly even causing root rot.

Heavy clay soil is more likely to become compacted.  To counter this, add some compost to provide organic material and make the soil a little looser.

Finally, avoid walking on your soil to prevent compaction.

Practice Deep, Infrequent Watering

After a plant is established in its new location in the garden, proper watering is important.  As mentioned earlier, soil that is too wet will not have space for oxygen, and can cause root rot.

You can learn more about the signs of over watering in my article here.

Watering too often will lead to a shallow, weak root system in your plants, since they won’t need to work hard to get water.  Instead, provide deep waterings less often to encourage a stronger, more extensive root system.

water
Provide lots of water at infrequent intervals to encourage a plant’s root system to grown and spread out in search of moisture.

When plant roots cannot readily find water, they will branch out sideways or grow deeper in search of more water.  Allowing the soil to dry out between waterings will encourage this root growth.

Provide Proper Nutrition

In addition to water and air, plant roots will need nutrients in order to grow and to support the plant.

A good first step is to do a soil test to find out the pH and nutrient levels in your soil.  You can learn more about how to do a soil test in my article here.

The ideal pH will vary by plant, but most plants will be fine in soil with a pH between 6.0 and 7.0 (slightly acidic to neutral).  Some plants, such as blueberries and azaleas, prefer soil that is a bit more acidic (4.5 to 5.5).

If your soil is too acidic (low pH), you can add lime (calcium carbonate) to raise the pH.  If your soil is too basic (high pH), you can add elemental sulfur to lower the pH.

If your soil test shows a deficiency of any nutrients, you can add some fertilizer to provide NPK (nitrogen, phosphorus, and potassium).  Remember that it is possible to over fertilize, so follow the instructions on the package, and remember that not all fertilizers have the same strength!

Also, remember that the strength of the fertilizer is not the only important factor.  You also need to consider how fast the fertilizer releases its nutrients.

For example, according to the University of New Hampshire Extension, fast release fertilizers may inhibit root growth in plants.

Your best bet is to replace nutrients in the soil by adding compost or aged manure, both of which contain organic material and release nutrients slowly.

compost
Compost or aged manure are both good ways to add nutrients and organic material to the soil.

What Fertilizer Helps Root Growth?

When choosing a fertilizer to help root growth, pay attention to the NPK ratio on the label.

For example, 10-10-10 means that the fertilizer is 10% nitrogen, 10% phosphorus, and 10% potassium by weight.

On the other hand, 10-20-10 is 10% nitrogen, 20% phosphorus, and 10% potassium by weight.

Phosphorus is a necessary nutrient for proper root growth.  According to the North Carolina State University Extension, a phosphorus deficiency will limit root growth.

Phosphorus deficiency is common in commercial farmland, but rare in home gardens (and more likely in cold soil).

Phosphorus deficiency is also more likely in an area where plants have been grown for a long time with no replacement of nutrients (no addition of fertilizer, compost, manure, etc.)

Remember that too much phosphorus will interfere with a plant’s ability to absorb nitrogen and micronutrients.

Potassium is also important for a plant to develop properly.  A lack of potassium can cause poor root development, but too much potassium causes nitrogen deficiency.

Calcium is necessary for the growth of root tips.  A lack of calcium can cause black, rotten roots.

Does Nitrogen Promote Root Growth?

Nitrogen is a necessary nutrient for plant growth, but it is possible to have too much of a good thing. Too much nitrogen in “hot” (fresh) manure or in strong fertilizer can burn plant roots.

Also, according to the University of Missouri Extension, fertilizing newly planted trees with lots of nitrogen can cause lots of green growth (leaves) at the expense of roots.

When choosing a fertilizer, use a balanced fertilizer that is not too heavy on nitrogen.  When requesting a soil test from your local agricultural extension, let them know what you are growing.  That way, they can give you recommendations for the type and amount of fertilizer to use.

Add Rooting Hormone

Rooting hormone is often used when propagating plants by cuttings.  Rooting hormone can come as a powder, gel, or liquid.

According to the Michigan State University Extension, rooting hormone increases the chances that a plant cutting will take root.  Rooting hormone also causes faster rooting, and increases the number of roots that appear.

tree roots
Rooting hormone causes faster rooting and makes more roots appear.

There are many different types of rooting hormone available, including this one from Home Depot that contains Indole-3-butyric acid.  Remember that liquid formulas are usually more effective than powder formulas.

To use rooting hormone, all you need to do is dip the base end of the cutting into the mixture.  Then, plant the cutting normally in a container with the growing medium you want to use.

Be sure to use gloves to protect your hands when using rooting hormone, and follow the instructions on the package label.

Conclusion

Now you know how to promote root growth in your plants, and when to use each method.  You also know what to avoid (for example, over watering and over fertilizing) to keep plant roots healthy and growing.

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!

~Jonathon

jonathon.david.madore

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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