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 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.

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.

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

  1. I live about 200 miles north of Toronto, Canada, and I’ve been dealing with this for about 5 years. We live in a forested area near a lake, with a long gravel driveway. It first started as a small patch that I thought was goose droppings, and has since spread quite a lot around the property despite my best efforts to get rid of it. I have been finally having great success with liquid pool chlorine. It’s the same as household bleach but much greater concentration. I do think it works better when it’s dried out because it absorbs the chlorine better. The only problem is that if you miss a spot, it just continues to spread, so you have to keep on it until it’s completely gone. And unfortunately, it even survives our harsh winters up here! 😐

  2. There is only one product that I know of which is scientifically proven to kill Nostoc with as little as one application. That is the herbicide called
    Scythe. Unfortunately, Scythe only comes in 2.5 gallon containers and costs about $180 US dollars plus shipping. (Roundup will NOT kill it at all. Don’t waste your time.)

    I have also read that burning the Nostoc with propane torches (aka “weed torches”) can work as well. Harbor Freight sells them for $20-$30
    and then you just need a propane tank.

    Best of luck with this nasty stuff.

    • OK guys, here are some things about this stuff. Some of you are blaming its appearance on Roundup. However, what is happening is that you have removed the competition cover which now allows it more access to sunlight. We have never used Roundup. It spreads very readily from place to place by way of shoe sole treads, tire treads, soil working equipment, dozers / shovels, even pets ( as our dogs run through the lush blooms, it catches up between the pads and tracks everywhere ) . Remember – # 1 – its a bacterium, so it only takes a minute amount to start a new infestation and Remember #2, it is a great hitchhiker. The stuff is getting to be very prevalent in commercial / industrial yards, and nobody pays attention to where they step anymore – then it tracks home. Improve your biosecurity to minimize new infestations.

  3. Noxall (granules). Purchased at Home Depot. Applied to my driveway just as another weedkiller, but this spring surprisingly found the driveway clean of that slimy algae. I mean – none! After 4-5 years of growing infestation.

  4. I have had good results with quick lime. It will take years to get rid of it though. I use a sifter and cover it while it is wet after a rain. I have killed it in one area but I have it in another now. I have been using the quick lime for about 3 years.

    • There is a product on the market called Preen which is a pre-emergence that will control some weeds in mondo and liriope. While I have not used it many folks here say it is effective

    • Agricultural lime pellets spread like fertilizer, on driveway. Can treat 1000 sq ft. for under $4.00 at tractor supply. Works amazing

      • Has anyone taken a rake to an area of that stuff? Well, I did a small area today to see if I could spray the gravel off. I couldn’t believe how hard that stuff had become and is binding the gravel together like glue! There’s a good 3-4 ” of gravel underneath that I had to get real wet with the hose then use my plastic rake to chip away to unbind the gravel. What small area I did now looks like I had fresh gravel put down.

  5. i use straight out bleach, not diluted, seems to be working, have had many rain storms, not growing back.

  6. Definitely going to try this. I do use Roundup on my gravel driveway, but I have a small lake within 150 yards and I have quite a few Canadian geese that like to wander my yard and driveway and blessing me with lots of land mines. I suspect their droppings are seeding everything with the Nostoc. I have read that Roundup kills beneficial bacteria in the soil (and in my gut if I eat produce containing Roundup residue.) Perhaps the absence of those bacteria would explain why the Nostoc never took hold before I began using the Roundup out of frustration with the weeds. I am wondering if throwing a little quicklime – danger: caustic to skin – on the driveway might help kill the Nostoc, I’m almost scared to try that, but I’m getting tired of nearly slipping down on the Nostoc!

    • try straight bleach, in sprayer, do not dilute, it’s killing mine, we’ve had straight rain for weeks, places i sprayed are not coming back so far.

    • Baking soda works. Buy commercial for cost-effectiveness. Non-poisonous to environment. I would avoid Roundup on such large areas. Baking soda works because it’s alkaline. So does lime for the same reason. Plus wood ashes (wood ashes are used in making lye soap, so very alkaline) work. I have used baking soda and wood ashes underneath acid-loving cedar trees and it does not hurt them.

  7. Found this on a few websites and tried it myself and …….. it worked after a couple of applications a couple of weeks apart!!
    “I have read your article as I have been troubled with this Nostoc Commune on my limestone driveway but I believe I have found a cheap and safe cure.
    I mixed 1 kg Dri-Pak soda crystals [washing soda, sodium carbonate] with hot water in 10 ltr watering can and when dissolved filled can with cold water, then using a fine rose I sprayed approximately 7 sq yds per can. I repeated this about 2 weeks later.
    My driveway is completely clear and has been for 5 months.
    I have found that most people that have been troubled with it have used Roundup, I don’t know if this is a coincidence.
    I posted this on Gardeners World and 3 people so far have thanked me as it worked for them.”

    • I too along with my father and some friends didn’t have this green goo growing in our driveways for many years until we all got diesel pickups and we thought that it was a byproduct from the diesel exhaust because algae will grow in diesel fuel. But we all started using Roundup at about the same time to kill the weeds and grass that came up every spring. After about 7 years +/- the diesel pickup moved on but the green goober was back every spring up until it would turn black and dry out from the summer heat, and we continue on using Roundup every spring and mid-summer to kill the weeds and grass. I often thought that maybe the Nostoc was a byproduct of the weed killer but just wasn’t for sure, but now after reading about it from someone else having the same problem and using the same weed killer has me thinking that it’s more than likely so.

    • Similar worked for us! Gravel driveway in southern Vermont over a pretty large area (nostoc scattered heavily, area about the size of 2 car garage? and creeping into the lawn). In September of 2018 we used Alkalinity Up from a pool supply store and dissolved it in hot water, added some cold and poured over nostoc. Manual labor with a watering can but it seems to have worked (did 3 applications over a 6 week period), none evident on driveway and it is one year later. White chunks left on driveway but didn’t care–they disappeared over the winter. Will apply it one time this month as a preventative but I think problem solved. We didn’t mind spending the money as it was worth it to get rid of this invasive beast!!

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

    • I’ve read that it’s toxic to dogs – that’s why I came to this thread. I need something to kill it quickly before they discover it. I don’t care if it kills what little grass I have or not – my backyard is full of gravel. Suggestions?

    • I sure hope not Trish. My yorkies run around in the driveway and yard and lately they have started licking their pads when they come in!

  9. 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.

  10. 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.

  11. 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

  12. 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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