How Can I Stop Physiological Leaf Blight of Phlox?

“I have phlox growing in a big container. The bottom leaves are looking mottled/veiny. I have fed them and also added iron, but it doesn’t seem to be improving. Is there something else it needs?” Shawn from Kenosha, Wisconsin

Answer: Tall phlox (Phlox paniculata) varieties are prone to a series of diseases and foliage disorders, but yours sounds like it is physiological leaf blight of Phlox. It is a physical disorder caused by a water imbalance in the plant that can occur in some tall phlox varieties. Water circulation goes haywire–causing water to bypass the older leaves and only supply water to the new shoots. Here are the symptoms and solutions for this disorder:

Physiological Leaf Blight of Phlox Symptoms

  1. Mature clumps are most often affected.
  2. Lower leaves become mottled with prominent green veins before they eventually shrivel and die.
  3. New growth is not impacted.

Physiological Leaf Blight of Phlox Solutions

  1. Cut plants back at the end of the growing season, yearly.
  2. Mulch plants to conserve water.
  3. Water a little bit extra–though this only works in mild cases. Sometimes the circulatory disorder simply disables older leaves from accessing water.
  4. Choose a resistant variety, such as the white Phlox ‘Minnie Pearl’ or the shorter “tall” phlox varieties like Phlox paniculata FLAME Coral or Phlox paniculata ‘Pixie Twinkle’

I hope that these tips help!

Happy gardening,

Jessie Keith

Black Gold Horticulturist


Plants are the lens Jessie views the world through because they’re all-sustaining. (“They feed, clothe, house and heal us. They produce the air we breathe and even make us smell pretty.”) She’s a garden writer and photographer with degrees in both horticulture and plant biology from Purdue and Michigan State Universities. Her degrees were bolstered by internships at Longwood Gardens and the American Horticultural Society. She has since worked for many horticultural institutions and companies and now manages communications for Sun Gro Horticulture, the parent company of Black Gold. Her joy is sharing all things green and lovely with her two daughters.

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