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Garden Phlox · Phlox paniculata

Why does my garden phlox have white spots on its leaves?

Those white spots are almost certainly powdery mildew, a common fungal issue for garden phlox. It happens when air circulation is poor or humidity stays high around the foliage. Check the leaves for a dusty, white coating that wipes off easily.

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spots on a plant
Photo: Scot Nelson, CC0

Check these first

  1. Look for a white, dusty coating on the leaves.
  2. Check if the plants are crowded too closely together.
  3. Feel the soil to see if it stays wet for too long.

Likely causes

  1. Powdery Mildew

    Most likely

    How to tell: You will see a white, floury substance covering the leaves and stems. It usually starts on lower leaves and spreads upward.

    What to do: Remove the most heavily infected leaves to reduce the spore count. Apply a fungicide like neem oil or a mixture of baking soda and water to the remaining foliage every 7 to 10 days.

  2. Poor Airflow

    Possible

    How to tell: The plants are crowded together, preventing wind from drying the leaves after rain or watering. This creates the perfect damp environment for fungus.

    What to do: Thin out your plants by removing some stems to increase space between them. Ensure your phlox is planted in an open area with good natural breeze.

Leaf spots on other plants

Find out what's wrong with your garden phlox

The list above covers the usual causes. Pocket Botanist looks at a photo of your actual plant and tells you the likely cause, how serious it is, and what to try first. Identification and a health check are free.

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When to worry

It is rarely fatal, but it can make the plant look unsightly and weaken it over time. Treat it early to keep the plant looking healthy through the season.

Stopping it coming back

Water at the base of the plant instead of overhead to keep the leaves dry. Space your plants at least 18 to 24 inches apart to encourage airflow.

Garden Phlox: spots? Check yours with a photo

Every plant is a little different. Take a photo of your garden phlox and Pocket Botanist tells you which cause is most likely, how serious it is, and what to try first. A few checks a day are free. Save the plant and you get care reminders timed for it.

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Questions people ask

Will the white spots kill my plant?
Usually no, but it will stress the plant and cause it to look ragged. It is best to treat it as soon as you see it.
Can I just wash the spots off?
Washing them off might remove the visible fungus, but the spores remain. You need a fungicide to stop it from coming right back.

Guides to these causes

More problems with Garden Phlox

Back to the Garden Phlox guide

This article was generated with AI on from the plant’s care profile and is general information, not horticultural advice. Read about how we build these guides.