Troubleshooting
Garden Phlox problems — and how to fix them
Garden Phlox (Phlox paniculata) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Powdery mildew
The most notorious problem: white powdery coating on leaves from midsummer onward. Prevent by spacing plants well, watering at the base, and selecting resistant cultivars ('David', 'Laura', 'Robert Poore'). Treat with potassium bicarbonate or neem oil at first sign.
Spider mites
In hot, dry conditions, fine webbing and stippled, bronzed foliage indicate spider mite infestation. Mist the undersides of leaves with water regularly and apply insecticidal soap or neem oil. Ensure adequate soil moisture to reduce plant stress.
Stem and crown rot
Caused by Phytophthora or Fusarium fungi in waterlogged or poorly-drained soils. Infected stems turn brown and collapse at the base. Improve drainage, remove affected tissue promptly, and avoid wetting crowns when watering.
Prevent garden phlox problems before they start
Most garden phlox issues are care-mismatch, not bad luck. Dial in the basics:
Looking for garden phlox in general rather than its problems? Read the full garden phlox care guide — light, water, soil and feeding.
Garden Phlox problems — FAQ
Why is my garden phlox powdery mildew?
The most notorious problem: white powdery coating on leaves from midsummer onward. Prevent by spacing plants well, watering at the base, and selecting resistant cultivars ('David', 'Laura', 'Robert Poore'). Treat with potassium bicarbonate or neem oil at first sign.
Why is my garden phlox spider mites?
In hot, dry conditions, fine webbing and stippled, bronzed foliage indicate spider mite infestation. Mist the undersides of leaves with water regularly and apply insecticidal soap or neem oil. Ensure adequate soil moisture to reduce plant stress.
Why is my garden phlox stem and crown rot?
Caused by Phytophthora or Fusarium fungi in waterlogged or poorly-drained soils. Infected stems turn brown and collapse at the base. Improve drainage, remove affected tissue promptly, and avoid wetting crowns when watering.