Q: I have this stuff that looks like dark green seaweed growing on my gravel driveway. I looked online and found posts on garden forums from other people who have it and no one can seem to get rid of it. They call it “nostoc commune”.

A: It’s a common damp lawn inhabitant called nostoc. The ancients theorized that was planetary snot 🙂 but it’s only a quickly rehydrating mass of bacteria.

It likes damp spots so your best bet is to redirect water that flows over or collects in the gravel. Chemical control will be short-lived unless you eliminate the water.

This nostoc link is fascinating!