Cannabis plants tend to stretch a lot during the flowering phase, which can lead to long, unstable shoots. This can affect light distribution and reduce yield. In this guide, we explain how to control stretching to promote compact, healthy plants.
Why do cannabis plants stretch?
Stretching is a natural reaction to a lack of light or genetic predisposition. Sativa-dominant strains in particular tend to grow very tall. However, the following factors also play a role:
- Light intensity & spectrum: Light that is too weak or the wrong wavelengths (e.g. too much blue light in the growth phase) can promote stretching.
- Temperature & humidity: High temperatures (above 28°C) and high humidity promote elongation growth.
- Genetics: Some varieties stretch more than others.
🔍 Counter-perspective: Not all stretching is bad! When growing outdoors, a little stretching can improve the light pick-up.
Effective methods for controlling stretching
1. optimize light management
- LED vs. HPS: Modern full-spectrum LEDs reduce stretching compared to sodium vapor lamps (HPS).
- Adjust the light distance: Lamps that are too far away lead to a lack of light and stretching.
- Red light in the flower: Red light (660 nm) promotes compact growth.
2. apply training techniques
- Low-stress training (LST): Growth is directed sideways by carefully tying the shoots.
- Topping: Removing the main tip promotes bushier growth.
- SCROG (Screen of Green): A net helps to keep the plants flat and evenly aligned.
🔹 Alternative method: Super cropping (controlled bending of the stems) – risky but effective.
3. control climate & nutrients
- Lower the temperature at night: 2-3°C less than during the day slows down stretching.
- Reduce nitrogen: Too much N in the flower promotes length growth.
- Use silicon: Strengthens the cell structure and reduces stretching.
❓ Open question: How much do nutrients really influence stretching compared to genetics?
When is stretching a problem?
- Buds too dense: Poor ventilation → risk of mold.
- Unstable stems: break under bud load.
- Uneven light distribution: lower buds remain small.
💡 So lution approach: Choice of variety! Indica-dominant hybrids stretch less.
Conclusion
Cannabis stretching can be effectively reduced through targeted light management, training and climate control. Experiment with different techniques to find the best method for your grow!