Against a north-facing wall, beneath a deep roof overhang, under the branches of a large tree: Dry, shady spots like these are among the most challenging places for plants to grow. “It’s a double whammy,” said Julie Janoski, Plant Clinic manager at The Morton Arboretum in Lisle. “There’s not much sunlight, which plants need to make their food. But there’s also a short supply of water, because ...