The usual way to multiply a dahlia is to divide the tuberous roots after winter storage. But dahlia cuttings are also very easy to root, almost as easy as sweet potatoes. If the supplier will ship tubers at least two months before your planting date, you can do it. It's a great way to get five or six plants from a single tuber-immediately, before the season even starts.
There are other advantages, too. Dahlias from cuttings (with no tuber to rely on) grow bigger root systems quickly. By bloom time, there is no difference between plants from cuttings versus those from tubers. Cutting grown plants later produce tubers with thicker skins that are better for storage.
Here's how to proceed. Eight weeks before you plant dahlias outdoors, fill a 2- to 3-inch-deep container with a light potting mix. Set the tuber near the surface, covered lightly with the mix. The "eye" on the narrow end of the tuber should protrude from the soil. Put in a bright, warm spot, where temperatures won't go below 50oF. The tuber will sprout in two to three weeks.
When sprouts are 3 inches high, cut them with a sharp knife of scissors just above the connection to the tuber. Plant cuttings in small containers of mix, up to the bottoms of the lowest leaves. Keep soil moist and cuttings will root in about two weeks. Transplant them to 3- to 4-inch pots and grow on until planting time, after frost. One tuber can produce up to six sprouts, and still have enough strength to be planted outdoors itself.
For more information about growing dahlias, see All About Dahlias.
Diane Bilderback lives in Missoula, Montana.
Photography by Suzanne DeJohn/National Gardening Association.
Article published on June 23, 2008.