Can Roots Be Exposed to Light, or Do They Prefer Total Darkness?

Because of the many types of containers you can use when starting a hydroponic garden, a common question that beginners often ask is, “Can roots be exposed to light?” After many years of gardening with uncovered roots, I have found that plants nearly always grow better if their roots are kept in complete or near darkness. There are several things that can happen to the roots if they’re exposed to too much light, but plants are tough, does it even matter? If you’re one of those pondering over this, you’re in the right place. We’ll explore this topic in-depth, and by the end of this article, you’ll have a comprehensive understanding of the role light plays in root growth and development, particularly in hydroponics, and whether roots prefer darkness.

Roots Grown in Darkness

The Science Behind Light Exposure and Root Growth

Understanding root exposure to light starts with comprehending the basics of plant biology. Light is essential for plants, as it is the foundation of photosynthesis – a process that enables plants to manufacture food. This, however, primarily concerns the upper parts of the plant. So, what about the roots?

Light and Root Interaction

Contrary to the common belief, light does, in fact, influence root growth. This influence, however, is indirect. When the plant parts above the ground absorb light, they produce sugar and auxin, a type of plant hormone crucial for growth. These substances are then transported downwards to the roots, promoting their growth, especially in young roots. So, in a way, light does have a beneficial impact on root development.

The Dark Side of Light

Nonetheless, the story doesn’t end here. While light is indirectly beneficial for root growth, it’s also true that excessive light can cause problems. Overexposure to light can lead to increased temperatures, leading to excessive moisture loss and eventual drying of leaves. It could also instigate the growth of algae and mold. Algae, in particular, can cause the roots to turn green.

How Roots Get Exposed to Light?

Roots are generally protected from direct light exposure as they are embedded in the soil. However, several situations can lead to their exposure to light. Let’s explore them one by one.


When plants become root-bound, meaning their roots have filled up all the available space in the pot, it’s time for repotting. During this process, roots can get exposed to light and air. Although light doesn’t directly affect the roots, the exposure to air can instigate the growth of mold and algae, which can, in turn, interfere with root development.

Glass Planters

Using glass containers for growing plants is another scenario where roots can be exposed to light. These transparent containers allow light to pass through, lighting up the roots. However, since roots are designed for anchorage and exploration of soil for water, they remain embedded in the soil, and light exposure doesn’t usually harm them.

Environmental Conditions

Changes in environmental conditions such as temperature, heavy rain, and wind can lead to soil erosion, causing root exposure to light. Also, in potted plants, as the organic matter in the soil decomposes, the soil level can sink, leading to root exposure.

Root-Bound Plants and Aerial Roots

In root-bound plants, roots crowd under the soil, which can get exposed to light as light penetrates several centimeters below the soil surface. On the other hand, aerial roots, also known as air roots or breathing roots, hang from trees, naturally exposing them to light.

Protecting Roots from Light: A Guide for Hydroponic Gardeners

In hydroponic systems, where plants grow without soil, roots are often exposed to light. With no soil to act as a barrier, how can we protect these roots from light?

Use of Dark Containers

One of the most common ways to protect roots from light in hydroponics is by using dark containers. These containers prevent sunlight penetration, ensuring roots aren’t exposed to light.

Clear Container Allowed Light to Roots

Light Control in Hydroponics and Aquaponics

If you’re cultivating plants hydroponically or aquaponically, it’s imperative to manage light exposure carefully. While roots in these setups don’t necessarily require light, overexposure can lead to algae growth on the roots.

Soil Top-Up for Potted Plants

For potted plants, where sinking soil can expose roots to light, topping up the soil with a nutritious potting mix can be a simple and effective solution.

Do Roots Prefer Darkness?

While we’ve established that roots can tolerate some light, it’s also accurate to say that roots prefer darkness. Roots naturally grow downwards and away from light in a behavior known as ‘positive geotropism.’ This tendency is particularly apparent in hydroponic and aquaponic systems.

In Conclusion

The relationship between light and root growth is complex and nuanced. While roots can tolerate some light exposure, they generally prefer the darkness. As a hydroponic gardener, it’s important to manage light exposure to prevent issues like algae and mold growth. Whether through the use of dark containers or careful management of light levels, protecting your plant roots from overexposure to light is an essential part of maintaining a thriving hydroponic garden.


Located in Portland, Oregon, Tim started gardening in his 20's and after a couple of decades felt like he had some things to share.

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