My Stems Are Purple!
This is a quick tutorial on what to do — or not do — if you experience purple stems when transitioning from vegetative growth to flowering in a hydroponic grow room.
Many new and experienced hydroponic growers have shifted to full spectrum LED grow lights because of the exceptional plant growth, flower quality, and now, impressive hydroponic yields.
The move from HPS grow lights to LED grow lighting is a far more energy-efficient and cost-effective way to produce equal or greater flower weight. However, some growers have noticed unexpected nutrient responses during the flowering stage, particularly relating to hydroponic nutrient uptake and plant pigmentation.
Purple Stems Under LED Grow Lights
For growers using LED grow lights containing UV spectrum diodes, purple stems and purple petioles are completely normal.
This is typically a natural pigmentation response and is often seen in plants that develop purple and red colouring during late flowering and maturity.
In this situation, purple stems are generally not a nutrient issue.
When Purple Stems Indicate a Nutrient Deficiency
If your LED grow light does not contain UV LEDs, purple stems may indicate a hydroponic nutrient deficiency.
Common Deficiency Symptoms
-
Petioles changing from green to deep purple
→ Usually indicates insufficient Magnesium (Mg) -
Main stem showing pink or purple striping
→ Usually indicates insufficient Potassium (K)
How To Correct Purple Stems in Hydroponics
In most hydroponic systems, these deficiencies can be corrected by slightly increasing the strength of your base nutrient feed.
Increasing your A/B hydroponic nutrients will often resolve the issue by supplying additional Magnesium and Potassium required during the transition into flowering.
Important Feeding Tips
- Increase nutrient strength gradually
- Avoid overfeeding and nutrient burn
- Monitor plant response closely
- Maintain stable EC and pH levels
Be Careful With Nutrient Additives
Sometimes growers attempt to fix deficiencies by adding single-element supplements. However, hydroponic nutrients work through nutrient synergism and antagonism.
Adding too much of one element can make other nutrients unavailable to the plant, even if they are present in the reservoir.
Before adding supplements or boosters:
- Check what is already included in your base nutrients
- Understand nutrient interactions
- Speak with your local hydroponic specialist if unsure
Never add a product simply because the label claims it will fix the issue.
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