Need-to-Know Dahlia Basics
Growing them is relatively easy, if you know a few basics. Natives of Mexico, they thrive in rich, well-drained soil and require lots of sun. Because they're cold-hardy only in Zones 9 to 11, gardeners in frigid regions often treat dahlias as annuals, though they can be dug up and overwintered. Tubers should be placed directly in the ground in late spring, after the soil warms up, about the same time you'd set out tomatoes. You can also give them a head start indoors, potting them up four to six weeks before the last expected frost. Don't water until after the first leafy shoots emerge, however, since soggy soil causes tubers to rot. Dahlias taller than 3 feet need staking, so set up bamboo poles when you plant to avoid disturbing their roots later on.
Shown: An heirloom with dainty collarette blooms, 'Clair de Lune' grows roughly 3 feet tall, making it perfect for patio pots.