I remember being alarmed at the "white stuff" I found beneath plants in the past. That was until I learned about Mycorrhizae - the magic kingdom that exists beneath the surface of the soil. The white stuff is good - very good! You can read all about it in the article below, but just know that wherever you uncover these networks of fungi, you have very healthy soil and very healthy plants. Try not to disrupt it more than necessary, because it takes years to grow and spread and new plants will 'lock in' (log in?) to the network and immediately benefit from its far-reaching filaments.
"Underground, below the mushrooms, are thread-like networks called hyphae. Some attach to plant roots, creating filaments that reach far into the soil, increasing the surface area of plant roots up to a thousand times. Fungal hyphae and plant roots working together are called mycorrhizae.
Oregon’s forest trees and many native and landscape plants depend on fungi and mycorrhizal relationships for optimal health and growth. A thimbleful of soil can contain miles of mycorrhizal filaments."