Let’s take a break from the cold, the slop and the just endlessness of January to appreciate one of the quintessential plants os summer: the dahlia. To find dahlias in their native range, you would need to take a trip to the lush area around Mexico City — not a bad idea for January under any circumstances!
Dahlias (Dahlia pinnata) are the national flower of Mexico and thrive in the well-drained, rich soil of that region. Dahlias are related to northern garden staples such as asters, zinnias and sunflowers. Like their cousins, dahlias like sun and they require a fair amount of fertilization to thrive and bloom. The native plants are all singles but thanks to hybridizers, dahlias come in a wide range of sizes, colors and forms. (Apparently, there are about 50,000 dahlia varieties.) You can find tiny-bloomed dahlias and many growers pride themselves on growing “dinner-plate” dahlias, which can up to 17 inches across. The plants can grow up to 20 feet tall, though most dahlias are in the 2 to 4 foot range.
You can grow dahlias from seed or from root divisions, though root divisions seems to be most popular in Minnesota. The University of Minnesota Extension Service has a great page on dahlias with instructions on how to do either method. Because dahlias are heavy feeders, it’s recommended that you prepare the garden bed where you plan to grow them with lots of compost or manure. Choose an area that gets 6 hours of sunlight a day at a minimum. Dahlias also require a fair amount of water and some additional low-nitrogen fertilizer during the season (5-10-10 is recommended). While dahlias like water, they do not need to be heavily watered in the spring and they prefer well-drained soil.
Pests and Diseases
Slugs, sadly, love dahlias. You may want to leave out some slug bait or other control, especially as the dahlias emerge in early summer. Dahlias are also prone to powdery mildew and other fungal diseases. This website from the Pennsylvania State Extension Service offers a list of disease and control options.
The best thing about dahlias is the blooms, which can start in June and last all the way until frost. Dahlias love to be cut for floral arrangements and the more the blooms are cut, the more the plants will bloom. Many growers recommend pinching out the first center stalk to promote more branching and blooming. This website offers tips on growing, pinching and picking dahlias.
For more information on this plant, check out the Minnesota Dahlia Society, which hosts a dahlia show every year.