Debunking the Myth of "Roots Grow During the Dark"

Debunking the Myth of "Roots Grow During the Dark"

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Cannabis Cultivation: Dispelling the Darkness Myth Surrounding Root Growth​

In the world of cannabis cultivation, there seems to be an endless list of do's and don'ts, often shrouded in mystery and hearsay. One such growing myth suggests that cannabis roots develop primarily in the dark, implying that the night cycle is critical for root development. Is there any scientific truth behind this belief? Let’s dig into the claim to understand where roots really get their vigor from and if darkness plays as critical a role as some might think.

The Myth About Dark and Roots Explained​

The myth in question seems to have sprouted from a fundamental misunderstanding of plant biology and the misapplication of relevant facts. The belief is that during the dark phase of the light cycle, cannabis plants focus their energy on root growth rather than foliage. This myth often leads growers to extend dark periods in hopes of stimulating root development. To debunk this myth, it's key to understand how cannabis roots grow and what really influences their growth.

How Cannabis Roots Grow​

Cannabis roots grow constantly as they search for water and nutrients to sustain the plant’s growth. Unlike the parts of the plant above soil that do indeed rely directly on light to grow through photosynthesis, roots are not dependent on light cycles. Instead, they grow due to the plant's overall energy production and health. Here's what science tells us about root growth:

Energy Allocation​

Plants continually allocate energy to root growth, sourced from the sugars produced by photosynthesis. Photosynthesis happens in daylight, and the generated sugars or energy compounds are not only used immediately but can be stored for later processes, including root development. There’s no switch that flips inside the plant to halt shoot growth and begin root growth; both processes occur simultaneously, governed by the plant's overall energy balance.

Hormonal Signals​

Plant hormones such as auxins play a significant role in root development. These hormones are constantly shuttled within the plant, signaling where to grow or slow down. Although their movement and effects are ever-present, the cycle of day and night can subtly affect hormonal distribution. It's not the dark alone but rather the entire rhythm of the plant's environment that guides its growth hormone signals.

Stress Responses​

Plants do have a sort of “day” and “night” response that helps them maximize their resources, which is sometimes confused with the myth in question. Stress factors like drought or nutrient deficiency can trigger survival responses, often resulting in enhanced root growth as the plant seeks to support itself. However, these responses are stress adaptations, not a normal function of the circadian cycle.

The Influence of Light on Cannabis Cultivation​

Understanding the interaction of light with plant life is crucial when cultivating cannabis. Cannabis plants undergo various physiological responses during light and dark periods:

Photosynthesis Versus Respiration​

During the light periods, photosynthesis is the process by which plants convert light, CO2, and water into oxygen and glucose, leading to foliage growth. When the lights go out, the plant depends on stored energy reserves and enters a phase of respiration, using up oxygen and releasing CO2. While it's true that respiration, which occurs day and night, is slightly higher during the dark period, this doesn't necessarily mean that more energy is directed to the roots.

Circadian Rhythms​

Cannabis plants, like many other organisms, follow a circadian rhythm – internal biological clocks that dictate numerous processes, including leaf movement and growth rates. While these rhythms are influenced by light cycles, they are not merely reactions to day or night. The intricate timing of circadian rhythms ensures optimal plant functions and growth over a 24-hour period.

The Truth About Cannabis Roots and Nighttime​

Root growth is an ongoing process that relies on the overall health and vigor of the plant, which is tied to light exposure since light dictates photosynthetic efficiency and energy production. While roots do continue to grow in the dark (as they do continuously), the darkness itself isn't their growth trigger. Rather, roots require adequate moisture, proper nutrition, balanced pH levels, and a suitable growing medium.

Practicing Good Root Hygiene​

For healthy root development, regardless of the light cycle, here are some best practices:

Proper Nutrition: Ensure your plants have access to essential nutrients, which are vital for root growth.

Adequate Watering: Roots seek moisture, so consistent watering within proper limits is essential.

Optimized Soil: A well-aerated soil with good drainage supports healthy root expansion.

Temperature Control: Roots prefer a slightly cooler environment than the foliage. Keep the root zone temperature in the ideal range of 18-23 degrees Celsius (65-74 degrees Fahrenheit).

pH Balance: Cannabis roots absorb nutrients efficiently in a pH range of 5.5-6.5 in hydroponic systems and 6.0-7.0 in soil. Regularly check and adjust the pH as necessary.


While it's a charming thought that cannabis roots stretch and grow in the quiet dark, the myth is just that—a myth. Roots develop due to the plant’s overall energy, which is produced during photosynthesis in the presence of light. The dark period is essential, not because it directly stimulates root growth, but because it is part of the plant's natural day-night cycle, which is critical for overall health and development.

Rather than extending darkness to foster root growth, focusing on providing your cannabis plants with the right conditions for complete health is the true secret to a robust root system. Always remember, holistic care trumps mythic shortcuts in the garden. Cultivate with knowledge, patience, and care, and your cannabis plants will reward you with the vigorous root systems that underpin luscious, bountiful canopies.
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  • thcrootz
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very interesting. Thank you for this. I love learning about the details too.
  • Imanoid2
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The whole plant is always growing. As long as you give it the needed nutes, water, etc. When one plants a tree, most folks wonder that first year. Why isn’t it growing? It is. Hopefully the roots are filling out and spreading underneath. It needs to suspend and stabilize itself, before it can start to add canopy. The fan leaves collect the light. That creates a draw on the roots bring the nutrients and water to grow the remaining canopy. Humans require sleep. The body heals itself best with REM or delta sleep after 90 -120 minutes. A plant, will continuously grow as long as its needs are met. I do 18 veg. Then 11. I believe in what the poster said!
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