The River Oaks Plant House — also known as the greenery purveyor that regularly festoons the corner of Westheimer and Buffalo Speedway with dancing bears and other fake topiary — will be closing up shop at the end December. Headmaster Mark Desjardins writes in an email that St. John’s School notified the owners of the more-than-30-year-old store in September that its lease would be terminated by December 31. The prep school had purchased the property from the Henry J. N. Taub family, along with the land under Blanco’s Bar & Grill, in a 13-acre deal completed exactly a year earlier.