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Q&A – What is this slime growing on my gravel driveway?

Question:
There is some type of slime or fungus growing on my limestone driveway.  I was hoping you could tell me what it might be and what causes it.  It is dry most of the time but when it rains it swells up and turns a dark greenish color and is slimy.  It is also spreading. I don't know how to treat it because I don't know what it is

Answer:
This is Nostoc algae. It is also known as witches butter or star jelly. It like places where there is compact soils and poor drainage (like a driveway). It can dry up between rains but then rehydrates and continues to grow. It does not need to be treated because it will go away with a long spell of hot dry weather. If you do want to treat you can use a fungicide that controls algae and moss that uses potassium salts or fatty acids.

Related Videos:
Nostoc
Mixing and Applying Fungicide

Related Resources:
Nostoc: A green, jelly-like substance growing in lawns
A Continuation of Nostoc Blue - Green Algae Control Solutions In Nurseries
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  • Home
  • Watch
    • TV Schedule
    • Full Episodes Online
    • How-to and Informational
    • Questions and Answers
    • This Week in the Garden
    • Garden Notes
  • Garden Topic Collections
    • Apple Trees: How-to and Information
    • Peach Trees: How-to and Information
    • Tomatoes: How-to and Information
    • Square Foot Garden Blog
  • Resources
    • Soil Testing
    • Extension Publications
    • Gardening Resources
    • Blogs
    • Organic Gardening
    • Articles
    • Privacy
  • Guests
  • Contact Us
    • Ask a Gardening Gardening Question
  • Search