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.

controlling nostoc

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

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.

Alabama Extension

The Alabama Cooperative Extension System operates as the primary outreach organization for the land-grant functions of Alabama A&M and Auburn Universities and answers home-gardeners' questions each week on Birmingham Gardening Today.

37 thoughts on “Controlling Nostoc (That Slimy Stuff Growing in Gravel Driveways and Paths)

  1. Really interested to read all of this. I’m confused as to whether it is toxic to animals or not. Can anyone confirm?

  2. I used round up early this year in my gravel driveway to rid weeds. I never had a nostoc issue until this year and after using round up. coincidence? During a dry spell when the nostoc was going dormant I treated entire areas with baking soda, sodium bicarbonate, 50 lb bags from agway.
    It turmed the areas white and remained that way for many days of dry weather. there appeared to be no nostoc in the treated areas, however after yesterdays rain ALL the nostoc is back in same areas where it was before and even after treatment with the baking soda in those same areas. so the baking soda obviously did not kill it.

    • Everywhere I sprayed round up I now have this awful stuff, they should have to pay for removal of it. Never using round up again.

  3. Thanks for your infomation. We noticed it on our gravel drive last year. Not noing what it was we raked it. Big mistake. This year we have 3 times more. Great to no about the baking soda though. Here in New Zealand we have Binn Inn so will go buy in bulk and wait for the sun to come out.

  4. My pond is full of it and i have tryed everything i even killed my fish but we drained it now we had started over and it was fine until it rained now it is back again what can i use that wont kill my fish i replaced

  5. I am desperate, have a long driveway, tried picking it up after it dried, but too much.
    At least I learned not to rake it, did that also. Any new info would be greatly appreciated.

    • I looked it up as I know nothing about this issue. Call Sally Lee at the Hanna Center at The Birmingham Botanical Garden. She has recently written on the subject. The Botanical Gardens main number is 205-414-3950.

    • Gisela,
      we also have a long gravel drive. ( Something not mentioned is of concern, I feel…could we have transferred this stuff to 2 other locations.)
      We have a steep drive and on really wet days, it is very slippery and dangerous. Walking on it, requires safety measurements too.
      I was at my wits end, until I found hope from a post last month on this site.
      I waited for a 2 day forecast of no rain, ended up being 3. I had a large bag of baking soda so I spread it on a 10 x 10 test area. It works great!!!
      Currently, the forecast is for almost a week of dry weather. I’m going tomorrow to buy several large bags of baking soda. I’m concentrating on the tire wheel paths in my first round of application, then the rest.

      • Did the baking soda work?

        Back in March I slipped on this stuff in Kentucky and broke my leg. Now that I am able to walk again my goal is to kill it before it gets me. 😏

        We had a little bit of it last year now it is everywhere on our gravel driveway. It’s like a plague.

        • MB,
          Yes, my test area of the 10×10 treated with dry Baking Soda is still Nostoc free.
          I tried the solution suggested by someone that used Baking soda diluted in water and the results are not visual to me yet.
          I wondered how burning it would work so I tried a small area and burned my burnable non-toxic trash on it…results seem positive so far.
          New area is growing in front of my garage, right where I park.
          During the sunny days, I covered it with a tarp to block the sun….no major results yet..will be using Baking Soda when it dries out.
          We’ve had a lot of rain recently, so the Nostoc is at its slimy best.
          Taking advantage of the soaked ground, I worked in the rain pulling ditches, moving the water source away from the large Nostoc area.
          …..for now, I wait for a dry spell and will use Baking Soda.

      • Where do you get bags of baking soda and what size are they? I’ve only seen it packaged in one pound boxes in the grocery store.

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