Effect of far-red and blue light on rooting in medicinal cannabis cuttings and related changes in endogenous auxin and carbohydrates

Ashley Manning
Jul 16
2 min read

Authors:

Wannida Sae-Tang, Ep Heuvelink, Wouter Kohlen, Eleni Argyri, Céline Nicole, Leo Marcelis

A new peer-reviewed study has shed light literally on how to increase rooting success in medicinal cannabis cuttings by tweaking your lighting spectrum. Conducted by researchers at Wageningen University & Research, this study tested different combinations of red, blue, and far-red light during the early stages of propagation.

Key Findings

Far-red light significantly improved rooting success in one of two experiments, especially when applied during the first 7 days of propagation.
Blue light had little to no effect on rooting performance.
Short-term exposure to far-red light (just the first week) improved rooting without causing excessive stem elongation, a common concern with far-red use.
Rooting response varied with environmental conditions like substrate, temperature, and light intensity.
No clear correlation was found between rooting success and measured auxin or carbohydrate levels, suggesting light may act via other signaling pathways or transport mechanisms.

Implementation Steps for Your Grow

Whether you're a small-scale home grower or managing a commercial facility, you can apply these insights right away:

✅ DO:

Incorporate far-red light (700–800 nm) into your rooting chamber setup.
Use far-red light during the first 7 days only after cuttings are taken.
Monitor plant height if using far-red beyond the first week to prevent unwanted stretching.
Use rooting-friendly substrates like stonewool, which showed higher rooting success in the study.

❌ DON’T:

Rely on blue light to improve rooting—it had no significant benefit.
Assume far-red will always help; environmental conditions matter—start small and track your results.

💡 Bonus Tip:

If you're trying to reduce reliance on synthetic rooting hormones, far-red light may offer a cleaner, compliant alternative for improving rooting outcomes.