Od Magic — Patricia A. McKillip

Brenden Vetch has a gift. With an innate sense he cannot explain to himself or describe to others, he connects to the agricultural world, nurturing gardens to flourish and instinctively knowing the healing properties each plant and herb has to offer. But Brenden's gift isolates him from people -- and from becoming part of a community.Until the day he receives a personal invitation from the wizard Od. She needs a gardener for her school in the great city of Kelior, where every potential wizard must be trained to serve the Kingdom of Numis. For decades the rulers of Numis have controlled the school, believing they can contain the power within it -- and punish any wizard who dares defy the law.But unknown to the reigning monarchy is the power possessed by the school's new gardener -- a power that even Brenden isn't fully aware of, and which is the true reason Od recruited him...