Last updated: May 13, 2021

What Does Phototropism Mean?

Phototropism refers to the movement of a plant toward a light source. Light triggers the plant hormone known as auxins to move to the shaded part of the plant that is not exposed to the light.

In nature, plants change orientation to face the sun. In an indoor gardening scenario, plants grow toward the light source provided by the grower.

Essentially, phototropism is a chemical signal; when auxins are released in the plant’s system, it responds by growing cells faster on the side facing the light. If you have ever witnessed a plant grown in a pot indoors start to turn toward a nearby window with lots of natural sunlight, you’ve seen phototropism in action.


Maximum Yield Explains Phototropism

Plants require light in order to manufacture carbohydrates to support growth and life. In the natural world, the light source (the sun) moves across the sky, which changes how light reaches plants. In order to ensure better light absorption, plants have developed a means to change their orientation in relation to a light source. This is called phototropism.

In an indoor gardening situation where the light source does not change directions, plants will grow straight up. This may require modification to ensure that the maximum number of plants can be grown within a given area. For example, the training of a plant to grow laterally through a lattice or by being tied down at various points (see Screen of Green Method [SCROG]).

Phototropism is undesirable in cannabis plants because it will cause the plant to grow tall, lanky, and thin as it stretches and bends to find an adequate light source. It is imperative that growers provide ample and adequate light in their growroom or grow space so the cannabis plants do not undergo phototropism.

Cannabis plant will particularly bend and move in search of the plant’s coveted blue light. Most growers choose grow lights that offer abundant blue light such as metal halides (MH) or full-spectrum LED lights.

The opposite of phototropism is negative phototropism. Not all parts of a plant need light—the roots actually grow away from light sources. Some plants also grow away from light sources. These are usually those that thrive in shady areas or low light situations.

Other light-related plant movements include photonasty. This process is controlled by the plant, in response to light or its absence. An excellent example of this is a plant opening and closing leaves or flowers at dusk, when light levels drop, or in the morning, when light levels outdoors increase.

Other ways plants move include:

  • Gravitropism and geotropism (movement relative to a gravitational field, or toward the center of the Earth)
  • Thigmotropism (plant growth in response to physical contact)
  • Chemotropism (movement in response to a chemical in the environment)
  • Hydrotropism (growth or developmental response to water)
  • Thermotropism (response dependent upon temperature)

Share this Term

  • Facebook
  • LinkedIn
  • Twitter

Related Reading


Plant GrowthLightingPlant Science

Trending Articles

Go back to top
Maximum Yield Logo

You must be 19 years of age or older to enter this site.

Please confirm your date of birth:

This feature requires cookies to be enabled