Q: I have green Jello-like stuff growing in my yard. It started a few years back as a small patch about the size of your hand in shaded area that has now grown and spread 20 yards in all directions. In dry weather, it dries up into a black, flat, paper-thin patches on the ground.
A: It’s a cyanobacteria called nostoc. Most of us just call it “algae”. It doesn’t harm grass but it DOES indicate that conditions aren’t particularly good for grass. In particular it tells me that the soil is mostly clay or silt and is pretty compacted. Possibly it’s in an area where the soil stays moist or where it’s shady.
All of those conditions inhibit grass growth…..but Nature always has ideas about what CAN grow on a spot. The nostoc found a good environment and so you see it regularly, depending on soil moisture and warmth.
I’m sure a thorough aeration would help, followed by consideration if grass will really ever thrive in this area. If not, plant ferns or hosta or azaleas. If you don’t fix the current environment, nostoc will pop up again and again.
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