Lots of things are happening in the garden including mushroom growth! Fungi are a great indicator of living soil that includes beneficial bacteria and microorganisms. A healthy soil will allow increased disease resistance and quicker cycling of nutrients leading to a rich soil.
Mushrooms are decomposers that help break down organic material including plant litter while making nutrients available to growing plants. There are many studies being done about the prevalence of mushrooms helping plants fight disease and other soil borne pathogens. I'm happy to see these great signs in the garden!