In Boston, there are three signs that winter has finally lost its grip: The appearance of marathon runners, the cheerful yellow daffodils that line its streets, and the fleshy, pink and white blooms of magnolia trees whose branches sway against a backdrop of stately brownstone homes in the Back Bay neighborhood. Spring has arrived. The extensive canopy of 300 or so magnolias in Boston’s Back Bay neighborhood is the result of one visionary resident, Laura Dwight, a woman who wanted to address signs of urban decay prevalent across the city in the 1960s. Today, the trees are under the stewardship of residents and the watchful eyes of members of the Garden Club of the Back Bay. Why We Wrote This April in Boston is known for daffodils, the Boston Marathon, and the Back Bay’s blooming magnolia trees. It was one woman’s vision for planting magnolias in the 1960s that transformed the neighborhood into the spring stunner it is today. “Laura Dwight lived in the Back Bay when the Back Bay was sort of a fading rose.…