Gaza gardeners, with harvest.Photo: Grassroots InternationalThis is the time of year when gardeners start to reap their rewards--fruits and vegetables that make for a healthy feast. But for the people of Gaza, gardens produce a serving of self-sufficiency, too. Urban gardens usually bring to mind savvy urbanites indulging in an organic lifestyle--witness Michelle Obama and her model urban garden at the White House. Although urban gardens in the West may not be a total indulgence--Ms. Obama, for example, is trying to counteract the growing instances of diabetes and obesity--they are hardly a necessity. In the Gaza Strip, on the other …