But there's another reason to point those plants north.
"Vertical is way cool," says Bruce Butterfield, research director for the National Gardening Association.
"Way cool" comes in many forms: arbors, trellises, lattice frames, stakes, tepees, and tuteurs or obelisks, along with some unorthodox methods and materials that resonate with the frugal, the artistic, and the diehard do-it-yourselfers.
In her research, Sweet, a landscape designer from Los Altos, Calif., saw flowers and vegetables planted in rain gutters suspended from arbors or mounted on walls; tomatoes growing out of the bottom of industrial buckets dangling from fences; and vines clambering up vintage headboards or weathered wooden ladders.
"You can get really creative," Sweet says. "It's fun."
Vertical plants and props also earn their keep as architectural statements and problem-solvers.
They offer what designers call "exclamation points" in otherwise flat landscapes. They add lushness and depth, and save space. They enliven gnarly stumps and dead trees, and hide unsightly sheds, air-conditioning units, utility poles, and fences.
They also can provide privacy.
Last year, Megan Jann, a lifelong South Philadelphian, moved from one rowhouse in Pennsport to another just blocks away. She plans to re-create the old house's privacy screen this summer at the new place, which shouldn't be hard. Jann's system is pretty simple.
To the top of her 41/2-foot-tall cinder-block walls in the backyard, she bolted generic wooden trellises measuring 2 feet by 6 feet, next to the barred sides of her son's outgrown crib. She placed them horizontally, rather than vertically, so the wall became 2 feet higher and each "trellis" covered a 6-foot-wide swath.
