Lewis County Master Gardner, William Pittman (right), shows workshop participants a cluster of tubers at the base of a dahlia plant at a recent workshop in the Borst Park demo gardens.
When you plant a dahlia tuber in the spring, it's a single, bulbous object like any other.
But if you dig it up in the fall, it's a whole different thing: a massive, tangled mass of lumps and bumps that can be overwhelming to the uninitiated.
At least that was the case for Dave and Barb Overlin, of Winlock.
The couple grow about 30 dahlia varieties and always dutifully dig them up each fall. But they admitted they were a little confused about how exactly to proceed with portioning up the root system.
“Digging up the ground is the easy part,” Dave Overlin said. “The trouble is dividing them.”
Knowing how to divide dahlias is fairly simple, said master gardener Gaylend Wilmovsky, one of a handful of WSU Lewis County Extension Master Gardeners who recently presented a dahlias workshop at the Fort Borst Park demo garden.
Each tuber hanging off the larger root ball is a lunch box, he explained, a store of energy that can create a plant. At the end where the tube attaches to the larger ball is an eye, a small bump of new growth ,which is where the new plant will grow from if planted. The mistake many gardeners make in dividing their dahlias is they look only for the larger tuber part.
“You've gotta have that eye,” Wilmovsky said.
The showy-flowered dahlia is a tender perennial, meaning that in most places the tubers cannot survive cold winter temperatures and wet conditions in the ground. But the tubers can survive if they are dug up in the fall, stored for the winter and then replanted in the spring. Master Gardener Bill Olson said when it comes to timing for digging and dividing dahlias usually a good rule of thumb is to cut your dahlias back right after the first frost. If, as was the case this year, the first frost is later than usual and you would like to put your dahlias to bed for the winter you can cut them back any time in the fall after they have finished blooming. After cutting back, wait one week to dig them up then one more week before attempting to divide.
A freshly dug dahlia can contain dozens of tubers, all attached to the main stem. Wilmovsky said he first looks for eyes, which will resemble a small bump, then uses a brass hammer and a chisel to cut through the attachment to create a new singular tuber that contains both an eye and the larger tuber portion. If a tuber is without an eye or if you cannot identify which tuber goes with which eye, that specimen is best left to the compost pile.
The tricky part, said master gardener William Pittman, is that in the fall dahlia eyes can be very difficult to spot. With a little guidance and patience you can usually find most of them but if they're still causing you difficulty you can always just store the entire root mass in one piece until spring.
“The eyes are a lot easier to see in the spring,” Pittman said. “But they're tough as nails to cut in the spring so you have to be really careful with that.”
Like most other bulbs and seeds, dahlia tubers need to be cleaned and kept in a cool, dry area for the winter. Many gardeners loosely wrap their tubers in newspaper or peat moss to protect them. The tubers can then be replanted in the spring after the last frost. According to the Puget Sound Dahlia Association the best time to plant dahlias is somewhere between April 15 and June 1.
After attending the Master Gardener session, the Overlins said they felt like they had a better handle on how to divide their dahlias in the fall. Barb Overlin said in the past they had split the mass somewhat haphazardly and, not wanting to take too much off, had only divided the large group into just a few viable tubers when she knows now they could have gotten a lot more.
“Being too timid was our problem,” she said. “You have to be aggressive with them.”
