Hi Margaret,

Those are the main flare roots bulging. They want to be exposed to the air. Uncover them, pull back the turf at least three feet from the trunk and let the tops of the roots be exposed. The tree should not look like a telephone pole coming out of the ground. 

https://africanvioletsocietyofamerica.org/event/african-violet-society-of-minnesota/

Please do this for all your trees. Covering their roots stresses them and makes them more vulnerable to disease and pests and over all shortens their life span.

Good luck,

Sally Granath

St. Louis County MG