A lot of northern gardeners treat tender bulbs — such as calla lilies, caladiums and gladiolus — as annuals, allowing them to die at season's end. Instead, overwinter them so they'll be fit and healthy in the spring. To make it simpler, plant tender bulbs in containers. After frost kills the tops, whisk the containers into cool storage in a basement or attached garage. Water sparingly — maybe once a month — while they're dormant so the soil doesn't totally dry out, and bring the containers back out in spring.