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Is Light Bad for Plant Roots? What you should know

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Plant roots can become exposed to light when repotting or if they are grown in a water culture. Water propagation also is a common practice in growing new plants and root exposure to light can become a concern.

Light does not have any effect on plant roots and is required by plants to create food that will produce healthy growth for both the plant and the roots. Roots can become green as a result of algae growth on the surface as a result of overexposure to light. Algae growth can be reduced by shading the roots.

Light can promote mold growth in the soil and in hydro setups, it can promote algae growth. See our detailed article on what causes green plant roots.

In this article, we discuss how plant roots can become exposed to light, what to expect when there is too much light and what you can do about it.

Does Light Affect Plant Roots

plant roots in glass jars exposed to light

Light does affect plant roots. Light helps the root growth with sugar and auxin especially to the young roots by absorption from the upper parts of the plant. In other words, light can also affect root growth positively.

The only way light can affect root growth is if the entire plant is deprived of light. Here the lack of light will stunt the growth of the plant as well as the roots.

However, there are some plants that can tolerate low light conditions. 

A few examples of plants that can tolerate low light are:

  • Dracaena
  • Chinese evergreen 
  • Bromeliad
  • Spider plant
  • Snake plant

We have written a detailed article on how long can a plant survive without light which will give helpful insights on plants and their light needs.

Too much light will increase the plant’s temperature and can lead to the drying of leaves through excess moisture loss. The light intensity also plays a role when it comes to root development. 

As the other parts of the plant grow towards where the light is, roots grow away from it heading to the dark soil to make sure that the plant is anchored and absorbs mineral nutrients and water.

Light can only penetrate less than several millimeters due to the high absorption of soil. 

Shallow roots are not affected by the light even if they are exposed on top of the soil.

If your roots show signs of damage, you can use this high-performance, water-based rooting gel, which comes at a great price on Amazon. It has a full spectrum of mineral nutrients that promote root growth. 

HydroDynamics Clonex Rooting Gel

How can Roots become Exposed to Light?

Environmental conditions such as a change in temperatures, heavy rain, and wind can lead to light exposure of roots in the soil through erosion.

Sinking soil in potted plants will also cause roots to become exposed to light as the organic matter breaks down. 

You can see our detailed article on what causes soil to sink and what you can do to fix it while protecting the plant’s roots at the same time.

We are first going to look at how roots can be exposed to light during repotting.

During Repotting

Transplanting or repotting becomes necessary when your plants are root bound and just sit there failing to grow. 

During the transplanting process, the roots are likely to be exposed to light and air. The main problem is not light but air, as direct light does not affect the root system. 

Exposure to air is that which causes the growth of algae and mold. The algae and mold is the one that causes root development issues.

Through Glass Planters

Is light bad for plant root

Glass containers expose the plants and the plant roots to light but as roots are designed for anchorage and exploration of the soil for water, they remain embedded in the soil. 

This is the reason why in clear pots or glass pots the roots seem to be invisible to the eyes.

I have reused glass candle jars to plant succulents with success. Some roots are exposed to light as it passes through the glass and there is no adverse effect to the plant nor the roots.

Root bound plants

In cases of root-bound plants, the roots seem to be overcrowded under the soil. 

Light penetrates several centimeters below the soil surface, and since these roots crowd under the soil they are likely to be exposed to the light. 

In other cases, the root-bound plants have sensing cells in the apical region of the root apex.

Aerial roots

Aerial roots or better known as air roots or breathing roots hang from trees, thus it is inevitable that they are exposed to light. 

They engage in photosynthesis and that is why it makes sense that they grow exposed to dappled light.

How to Ensure Roots are not Exposed to Light

The commonest way to protect roots from light is by using dark pots. 

The dark spots have no penetration of sunlight and so they can be the best to use in order to prevent the roots from being exposed to the sunlight. 

Especially the vegetative cuttings, require a minimum of light exposure to provide energy for root initiation and development. 

The soil in potted plants has a tendency to sink over time. This is due to the breakdown of organic matter in the soil. As a result, some roots may become exposed at the surface.

An easy fix to this is to top up the soil with a nutritious potting mix that will cover the roots. 

I use this Miracle-Gro Potting Mix from Amazon, which ensures my plants stay healthy long after repotting. Take a look and compare it to other potting mixes.

Miracle Grow Potting Mix

Do Hydroponic and Aquaponic Roots need Darkness?

Green Plant roots in aquaponics

As we all know, roots always grow to bend to escape light. Instead, they shy away from light to find darkness. And so do hydroponic and aquaponic roots. 

The aquaponic and hydroponic roots do not require light but can be exposed to some degree of light. 

Although light may not harm the roots, overexposure can lead to algae growth on the roots which can give it a green hue from the chlorophyll.

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