Have you been noticing slimy green algae in your driveway, flowerbeds, or lawn? This slimy mess typically appeares after several days of warm, wet weather. As more rains fall, accompanied by high temperatures and equally high humidity, growth is encouraged... AND spreads!
This seaweed – like gooey green mass is more than likely 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.
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...I've tried it myself) to removing small infestations with a shovel. Improve drainage and forego irrigation of affected areas may help long-term, (but short-term not so much). Typically soils high in phosphorus will also see a more prevalent growth of this seaweed...
Don't rake! This 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 messy goop.