Purple Stems: Genetics, Cold, or Deficiency?
Purple or magenta coloring in petioles and stems triggers a lot of unnecessary panic. In most plants it means nothing at all.
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.