Roots normally grow underground as heterotrophic organs (parts that do not produce their food), depending on the shoot and leaves for getting the nutrition and food.
Roots will turn green when they are exposed to light which can cause the build-up of algae on the surface of the root. The algae give the roots a green hue due to the chlorophyll within and are common in Aquaponics, Hydroponics, and plants grown in water. Green roots can be prevented by reducing the root’s exposure to light.
There are some exceptions where plants have developed modified adventitious roots. These are known as aerial roots where they grow above ground and help provide food for the plant through photosynthesis and are common in air plants, orchids, and monsteras.
In this article, we discuss what causes a plant’s roots to turn green and if this is a normal phenomenon among all plants? Which plants have green roots?
What Causes Plant Roots To Be Green?
The green color in plants is generally associated with photosynthesis. Usually, most of the photosynthetic work is done by leaves and shoots: absorbing sunlight, converting water, carbon dioxide, and light into energy and oxygen.
Plants’ leaves have chloroplast (small organelles within plant cells) that can store the energy of sunlight. Chlorophyll in the chloroplast is responsible for giving plant leaves their lush green color.
However, the roots of some air plants (epiphyte) turn green and actively take a little part in or perform the whole process of photosynthesis.
Down below, we have compiled a list of reasons that can cause your plant roots to turn green:
The prime reason behind plants’ roots greening is exposure to sunlight. Sunlight can significantly affect roots’ normal functioning and growth.
In 1975, a pair of Botanists, D. T. Clarkson, J. G. Torrey shed light on green roots in their book, “The Development and Function of Roots”. According to both authors, the roots of some plants turn green when exposed to sunlight or when they develop as adventitious organs as in leafless orchids. Aerial roots of orchids contain chloroplasts and can perform active photosynthesis by trapping the energy of sunlight.
Later in 1977, Gill and Tomlinson also observed green roots and the photosynthetic ability of Red Mangrove’s roots in their research.
Botanists believe that hairy roots are responsive to light stimuli and changes in the physical environment. Hairy roots of Asteraceae, Solanaceae, and Cucurbitaceaeare are capable of becoming green when grown in the sunlight.
“Roots of all plant species in Asteraceaegenera genera exhibited greening and photosynthetic ability when exposed to the sunlight”, stated Dr. Hector E. Flore from The Pennsylvania State University.
Therefore, if you don’t want your roots to turn green, keep them away from the sunlight. See our detailed post on what happens when plant roots show and how to fix it as well as is light bad for plant roots.
I use this Miracle-gro potting mix from amazon when correcting my soil-related problems including topping up when roots begin to show. You can find it by clicking here.
Shrub and Tree Roots Above Ground:
Sometimes you will also notice roots of shrubs and trees greening when they are grown above ground.
The roots respond to the sunlight stimuli by activating chloroplast in them and absorbing sunlight energy for photosynthesis.
Most species of orchids have green hairy roots that actively participate in photosynthesis. Interestingly, the green roots of leafless orchids (Praecoxanthus aphyllus) contain chloroplast and are completely responsible for the plant’s photosynthesis to produce sugars.
How Does Light Affect Roots?
Sunlight can remarkably alter the growth, development, behavior of plants’ roots. Although most plants’ roots have an underground lifestyle, it’s a myth that roots grow in complete darkness. Sunlight can pass into a couple of millimeters under the soil surface.
Sunlight can significantly alter the development of root architecture, growth rate, and direction of roots.
Over the years, plants have evolved to be more complex and extremely sensitive to sunlight stimuli. Plants have several photoreceptors (cells that respond to light).
Some of these photoreceptors are also present in the roots as well, making roots capable of sensing light and reacting accordingly.
Light can, directly or/and indirectly, affect:
- Root growth
- Root architecture
- Root hair formation
- Lateral root initiation
- Root gravitropic (gravitational) and phototropic (light) bending
Propagation Methods That Can Result in Green Roots:
Light can easily affect your plants’ roots and turn them green if you are propagating them using the following ways:
Plants grown under an aquaponic system can have green roots. There are two main reasons for that.
- One, your plants’ might be getting exposed to sunlight.
- Two, algae are growing on the roots’ surface or in water.
Algae will grow wherever the moisture is present, especially in aquaponic systems where water is present in abundance.
The greening of roots is a common phenomenon among plants grown under hydroponic conditions.
Usually, the plants’ roots turn green when growers use transparent or glass containers that can transmit light. As we mentioned earlier, green roots occur when roots get exposed to direct or/and indirect light.
The light stimulates chloroplast/chlorophyll formation, resulting in the greening of roots.
For instance, the roots of the Peace lily become green when grown under hydroponic conditions.
However, the greening of the roots depends on the plant species capability to produce chloroplast in the roots. Without the presence of chloroplast, your roots won’t turn green even if you place them under direct light.
Planting in Glass Planters or Clear Plastic Containers:
If you are growing your plants in glass or clear plastic planters, the light can easily transmit through them and stimulate the production of chloroplast/chlorophyll.
Eventually, your roots will start reacting to light by awakening their photosynthetic ability and turning green.
Propagating Plants in Glass Jars:
The same is the case with glass jars. The light can easily pass through glass jars and reach your plant’s roots. If your plant species have the ability to stimulate chloroplast production in the roots, it will turn green in no time.
Why Aren’t Roots Green Like Leaves?
The main reason why roots are not green like leaves is the absence of chloroplast and sunlight.
Leaves are green thanks to the chloroplast present in their cells. The layer or membrane of chloroplast contains chlorophyll (the photosynthetic pigments).
The main job of Chlorophyll pigment is to absorb different spectrums of sunlight. It can easily absorb deep-blue and red light spectrums. However, the rest of the spectrum gets reflected, making the leaves look green.
Not all plants’ roots have chloroplast present in their roots. Even if some have, the ratio is very low due to the absence of sunlight.
Only aerial parts (stems, leaves, and petioles) of the plant that are exposed to sunlight possess chloroplast and green color.
As most of the plants’ roots are buried underground, a very little amount of sunlight reaches them.
The roots don’t get the chance to absorb different sunlight spectrums, resulting in no reflection and green color.
Roots containing chlorophyll become green as soon as they get exposed to the sunlight, especially aerial roots They may get exposed to direct sunlight due to heavy rain, wind, sudden temperature changes, earthquakes, and so on.
Why Do Algae Grow on Roots and How To Remove It?
Your roots may appear green when they get little surface algae. Algae can easily grow anywhere where water, sunlight, and nutrients are present.
Algae, the plant-like organism, are aquatic organisms – meaning if there is no water, there will be no algae. They also need a good amount of sunlight to grow. Algae grow faster in warm water and bright sunlight.
Propagation systems, especially hydroponic and aquaponic systems with recirculating nutrients solutions and sunlight, are an ideal environment for algae growth.
In both these propagation systems, roots are mainly flooded with water. The algae grown in water gets stuck on the root’s surface.
How To Fix Green Roots?
Remove the Algae:
To prevent algae, the first key step is sanitation. Improve the sanitation of your hydroponic or aquaponic system and stick to it. Change the water regularly and disinfect the tools and equipment before you use them.
You can also use algaecide such as hydrogen dioxide and peroxyacetic acid products to kill/clean algae growth.
In case the algae have already grown on your roots, you can remove them simply by washing the roots with clean water. Follow these steps:
- Wear gloves, now you don’t want to contaminate your roots any way possible.
- Gently take your plant’s roots out of the water.
- Be extra careful when choosing the water temperature for washing the roots. The water shouldn’t be too hot or too cold or else your plant may get shocked and die.
- Wash the roots meticulously and gently.
- Once the green is off and roots appear white or colorless, put them back in the freshwater.
Cover the Roots-
Hydroponics and Aquaponics
In the case of hydroponics or aquaponics, green roots can be prevented by ensuring that they are not exposed to light.
In water culture, they are normally grown in net cups which have holes allowing some degree of light into the pipes or rails.
As long as the holes which support the net cups are of the correct size, the light will not enter the cavity containing the plant. As a result, the roots do not get light as mold will not grow.
In other cases such as in potted plants and grounded plants, exposed roots can be subjected to an abnormal amount of light which will cause algae to build on the surface of the roots.
Potted plants can be repotted or the soil can be topped up to cover the roots. Potted plants can have the tendency for the soil to sink and in some cases, it exposes the roots to the surface and light.
See our detailed post on what causes soil in potted plants to sink.
A simple solution here is to cover the roots with potting soil.