Learn to care for and grow dogtongue buckwheat (Eriogonum tomentosum). Eriogonum tomentosum (also known as Wild Buckwheat, Sandhill Buckwheat and Dog-Tongue Buckwheat) is a plant in the family Polygonaceae. It is hardy in zones 7a-10b. It requires a medium amount of water. It is perennial. The sun requirement is full sun. The soil PH needed is 6.6-7.8.