By Gail Ellis   STILLWATER, Okla. – When summer begins to fade, don’t hang up that gardening trowel just yet. A renewed season of fall vegetables awaits in your own backyard.  Oklahoma’s mild climate is ideal for fall gardening, and Oklahoma State University Extension provides educational opportunities for both experienced and novice gardeners to extend the growing season.  “Small farmers and producers have figured out there’s a successful cool season in the fall, and they’ve really upped their production with…