White Cottony Growth on Threadleaf Sundews: Mineral Deposits, Not Mold

Bill noticed a white, cottony substance on the crowns of his temperate Drosera filiformis (dewthreads) growing outdoors in full-sun tray systems. Concerned it might be a fungal issue, he asked for diagnosis and treatment advice.

The Real Culprit: Mineral Buildup

Jeff Dallas explains this is a common late-summer occurrence, not a pathogen. Two factors combine to create these deposits:

• Natural pubescence: The crown of D. filiformis naturally develops a hairy texture that becomes more pronounced as summer progresses.
• Evaporative concentration: In hot weather, plants transpire heavily. With tray watering, water evaporates upward, leaving behind dissolved minerals from the water or soil. These accumulate as visible white patches on the crown.

Simple Solution

Switch to top-watering temporarily. Letting water flush downward through the soil reverses the mineral concentration. Once rains return and temperatures moderate, the issue typically resolves on its own.

Good Growing!
Jeff Dallas
Sarracenia Northwest
www.growcarnivorousplants.com