[Kiki]

I was digging to clear ground for planting garlic and found a big dandelion root with masses of white fungus on it - reminded me of white rot though the weed itself looked healthy.
Anyone know what this is and if it's bad? 

[savbo]

if the dandelion looks healthy this could just be a mycorrhizal fungus. Shouldn't so your other plants any harm and could do them good

sav

[Trillium]

If the dandelion is healthy and the white stuff on the roots is sort of thread-like HERE then it's mycorrhizal fungus which is very beneficial to all plants.