By Julia LaughlinFor The Oklahoman, julia.laughlin@okstate.eduIt is not always easy to decide what plants to use in your garden and landscape, especially if you have limited space, but the Oklahoma State University "Oklahoma Proven" program, in its 20th year, is designed to help you do just that. Each year since 1999, a tree, shrub, perennial and annual worthy of state landscapes are chosen by horticulturists to help consumers choose plants appropriate for Oklahoma gardens.Read more on NewsOK.com