What would cause dark green surface ground mold when it rains?

Answer 1

I'm not sure it's mold you're looking at. You said "ground mold," and you also said it's green. Those two characterizations don't jibe with mold. Are you sure it's not ground moss or algae? Moss grows in shady, damp areas of your lawn or garden, right on top of the soil. It usually requires soil that is slightly acidic. In fact, some people give up trying to grow turf-type grasses in heavily treed, damp areas and foster moss growth instead by applying weak acids to the sol. It can be, surprisingly, very attractive. Japanese moss gardens are the pinnacle of the art form. Algae, on the other hand, usually grows on concrete and wood patios and decks wherever standing water is allowed to exist and wherever poor ventilation and slow evaporation leave surfaces damp. You could use a power washer to clean the algae, or you could dilute some bleach in water and apply it with a scrub brush. It might take a day or two to see results, however. *I live in Tennessee and dark green mold is common here. Mold must have a dark or shady and damp environment to grow. Bleach will kill it. Or just scrape it off with a knife. A dehumidifier will help keep it from coming back, but I dont know if you would need one in Arizona, or if they even sell them in Arizona. You might get a better answer if you ask this question in the Biology section.