Purple Stems: Genetics, Cold, or Deficiency?
By The Budometry TeamPublished Updated
Purple or magenta coloring in petioles and stems triggers a lot of unnecessary panic. In most plants it means nothing at all.
Part of our pillar guide: Plant Training, Pests and Troubleshooting
Usually genetics
Many cultivars express anthocyanins in stems regardless of conditions. If the plant is growing vigorously with healthy green leaves, purple stems are cosmetic.
Cold temperatures
Low lights-off temperatures, especially below 65°F, bring out purple coloring. If it is accompanied by slowed growth, warm the space.
Phosphorus deficiency
Real phosphorus deficiency comes with dark, dull, sometimes bluish leaves, purple petioles, slowed growth, and eventually bronze necrotic patches. The stem color alone is not enough to diagnose it.
The rule
Purple stems plus healthy vigorous growth means do nothing. Purple stems plus any other symptom means investigate temperature and pH first.
Frequently asked questions
- Do purple stems affect potency?
- No.
The full guide on this topic
Plant Training, Pests and Troubleshooting
Topping, LST and SCROG explained, plus how to identify and stop spider mites, fungus gnats and powdery mildew, and how to read leaf symptoms correctly.