As the summer winds down and the garden outside the greenhouse is wan and fading, up pop the dahlias. With jaunty bright flowers on tall stalks, they scoff at the coming of fall like flamboyant Auntie Mame defying middle age.
There are dahlias of many colors, mostly in pinks, reds, oranges and yellows, with blooms that range from little buttons to huge dinner plates. I do best with dwarf dahlias—a foot or 18 inches tall—because my only really sunny bed is next to a sidewalk. Flowers with tall stalks tend to flop across the walk and be broken off by passersby. Dahlias routinely grow 3 feet tall and some varieties can top 6 feet, and I’ve sworn off staking, so I’ll stick with dwarfs.
The ancestors of today’s garden dahlias grew wild in Mexico. In Chicago, dahlias are not winter-hardy, so although they are perennials at home, we grow them as annuals. At least I do. Some people lift the tubers in fall and store them over the winter, but not me. Too much work.
You can buy dahlia seedlings in spring at garden centers. And especially if you have a greenhouse for protection from spring frosts, it’s perfectly possible to grow dahlias from seed. But most people plant tubers—fat roots like little sweet potatoes. You can find mail-order sources online, such as Swan Island Dahlias, that sell tubers of a wide range of varieties.
Their Mexican ancestry is a reminder that dahlias really do need full sun. They also need superb drainage. Sticky clay soil won’t do, which is why you don’t see as many dahlias around here as you do some other places. Mixing in plenty of compost or other organic matter before planting the tubers will help.
Growing dahlias in Chicago takes good timing. They need months to grow tall, but they can’t go in the ground until the soil is warm enough in spring. I plant them about the same time as tomatoes.
The wrong weather can be a monkey wrench: You want the soil to be moist, but not soaking wet. That was a big problem this spring when we had rainstorm after rainstorm. The soil never seemed to be dry on the weekends, when I garden. I have some dahlia tubers I never did get planted this year.
Overall, dahlias are very easy-going plants. They get an undeserved reputation for being tricky from the dahlia-obsessed who grow them for competition. Pushing dahlias to produce the immense dinner-plate-sized blooms that win contests really is a complex challenge: You need to prune off all but one or two blooms so the plant puts all its resources into them, and then water and fertilize fanatically, all the while protecting your singular obsession from heavy rain and other weather. I’ve seen dahlias under parasols and tents.
But for those of us who just want cheery late-summer color, dahlias are unfussy and reliable (if you get the tubers in the ground).