Root tips turn black

  Q: On my orchids, if the new roots do not enter the potting media when 2-3 inches long, the tip turns brown/black and stops growing. Could this be due to not misting the plant often enough?   A: Extremely low humidity (<25%) usually causes the symptoms you describe. Frequent misting with high-quality water can help (frequent misting with low-quality water can exacerbate the salt problem, by building up a layer of salt on the roots).