Charles Koiner Conservancy for Urban Farming Executive Director Kate Medina, and Loiederman school community liaison Carol Fernandez, right, welcome teachers from nearby Weller Road Elementary to explore the Farm Hub for a potential field trip. (Photo by Rosanne Skirble/Maryland Matters)On a cool spring day recently, the 1-acre farm A. Mario Loiederman Middle School in Wheaton buzzed with activity. In the lower field educational garden, students…