by Connie Oswald Stofko “Not everything is hardy. The definition of a perennial is something that lives three or more years– if you don’t kill it.” Stephanie Cohen, known as the “perennial diva,” gave tips on summer gardening in the sometimes irreverent and often funny keynote address of the National Garden Festival in Buffalo (now Gardens Buffalo Niagara). The event was held Saturday, June 19 in the Nichols School in Buffalo. After the talk, Cohen signed copies of her books,…