Controlling Nostoc (That Slimy Stuff Growing in Gravel Driveways and Paths)

“What IS this stuff growing in my gravel driveway? It looks like a sort of alien pond scum but growing on terra firma. In addition to looking gross, walking on it can be hazardous because it’s extremely slippery!”

“IT” first appeared after several days of warm, wet weather a couple months ago. At the time, not much attention was paid to it, and after a few dry days it went away … or so we thought.

Then more rain, accompanied by high temperatures and equally high humidity, it was b-a-c-k, and spreading. Getting rid of this gross growth so it won’t spread into the lawn (or is it too late?) is the issue.

If you’re one whose property has been skipped over by “random, scattered” storms this summer, you probably don’t have this problem, but read on because you might see it in the future.

This seaweed – like gooey green mass is possibly Nostoc, a cyanobacteria that can grow on grass, stone, or concrete. Usually it’s “happiest” in low areas that drain poorly, conditions that support a number of unwelcome growths in our lawns and landscapes. Much like mushrooms, certain conditions support its emergence, although it can remain desiccated and dormant in lawn or driveway for weeks and months.

Nostoc algae or nostoc balls (Cyanobacteria Nostoc spp.) in gravel.
Photo copyright, Ashley Kulhanek

While Nostoc isn’t harmful or toxic, it looks weird and as mentioned, is very slippery. Drier weather and low humidity cause it to retreat, but will likely pop back with the next round of rain showers.

Management options range from baking soda (it really works, according to online comments) to removing small infestations with a shovel. Improving drainage in and foregoing irrigation of those areas may help long-term, but short-term not so much.

Raking the stuff is not recommended, as that just breaks up and spreads the algae further. Moss and algae sprays are effective in some situations but even they primarily suppress, not eliminate, the material. Other treatments are being tested; meanwhile be aware of safety issues associated with the algae, and realize the weather conditions that created it’s appearance may not occur again for several years.

By Sallie Lee, Urban Regional Extension Agent, Alabama Cooperative Extension System.  Contact Sallie at leesall@aces.edu.

The Alabama Cooperative Extension System (ACES) operates as the primary outreach organization for the land-grant functions of Alabama A&M and Auburn Universities. ACES is committed to affirmative action, equal opportunity and the diversity of its workforce.  Educational programs of ACES serve all people regardless of race, color, age, sex, religion, disability, sexual orientation, or national origin.