Posted on by Jason Gibson

Why are my plants stretching?

A question I’ve been asked countless times. Tutorial time.

So, why are your plants stretching?  Well, when your plants stretch for light, this is called phototropism.

This can be seen when your seedlings are left on a windowsill, the reason this is happening is because plants can detect wavelengths and light intensity at all angles. The cells on the shaded side grow quicker, tilting the stem towards the direction of the light intensity.

If the light intensity is directly above the plant then auxin will diffuse down the stem stimulating even growth.

If only one side of plant is exposed to light, auxin diffuses away from the light causing the stem to bend.


Shade Avoidance Response

Plants depend on light for photosynthesis, and they have developed a system to detect competition from their neighbors to respond accordingly. Light reflected from neighboring plants is reduced in its far-red (R/FR) ratio. The phytochrome (PHY) photoreceptors perceive low R/FR and trigger shade avoidance responses that allow plants to compete for light.

The correct response to a specific light cue depends on the environment. Plants native to sunny environments are sensitive to foliar shade and show robust shade avoidance. Such changes in shade-avoidance response are adaptive and are due to heritable genetic differences.

 Plant Stretching Cell Elongation Diagram

Harness the Laws of Light Energy

Light energy is bound by the laws of science. The inverse square law tells us that light is travelling twice as far from the source – every additional 30cm of distance away from the light source, lumens and therefore canopy penetration diminish greatly!


Moving Lights Vs Stationary

High Intensity Discharge (HID) Lights radiate temperatures that can burn, so when the light is mounted stationary they must be kept at a sufficient height to avoid any plant tissue damage. 

Employing a light mover will prevent this damage. The lamps are continually moving, so lamp, to plant distance can be decreased. Light moving equipment allows greater penetration of a higher intensity balanced spectrum light to lower areas of the plants, resulting in healthier more compact growth.

When using light movers, the user can expect approximately a 15-25% rise in yield, as long as certain parameters are maintained in regards to how far, each light travels.

Now you know why plants stretch, take some preventative action, employ a light mover, obtain healthier plant growth and increase your yields through wise management of grow room lighting.