By Trisha Gedon STILLWATER, Okla. – Gardeners know the challenges of selecting plants that will thrive in Oklahoma’s extreme growing conditions. Fortunately, the Oklahoma Proven plant program can assist with selection. “Oklahoma Proven is a plant promotion program to help guide gardeners toward appropriate garden selections that have been proven to grow well in Oklahoma’s diverse climate and soil types,” said David Hillock, Oklahoma State University Extension consumer horticulturist. “Each year, a tree, shrub, perennial and annual are selected.…