Dahlias: A Little Work, a Lot of Show

“There's just something about the riot of colors,” said Debbie Spiller of Rochester, a home gardener who loves her dahlias. “They're the fireworks of flowers.”

As the last dahlia blooms fade this fall, the eternal question looms for gardeners: to dig or not to dig? That is the question, but there is not really one straightforward answer, said Wayne Lobaugh, owner of Lobaugh's Dahlias in rural Chehalis, a grower and hybridizer of dahlias. Lobaugh, who digs and divides his tubers each fall, said the biggest enemies to dahlia tubers left in the ground to winter are hard freezes and excessive moisture.

“If they freeze it shatters the cell wall,” Lobaugh explained. “So if you dig them down six inches and put down good winter mulch to keep them from freezing, you can be OK. Of course if you have heavy, wet soil, you'll lose them.”

Spiller moved to Rochester from Woodinville four years ago. She said in Woodinville, her yard was very sunny and warm and she could leave her dahlia tubers in the ground over the winter - provided she put about six inches of a good insulating mulch over them. But she said the rocky soil and colder weather in Rochester does not allow that.

“You can leave them in if your soil will be dry,” said Spiller, who raises her three dozen dahlia plants in raised beds. “It's  not the cold that's the problem for them, it's the wet.”

Somewhere between mid October and mid November is the optimum time for digging dahlia tubers. But the timing is different every year based on the weather. You want to wait until after the plants have died back after the first frost but before any hard freezes hit.

“Pick a time when your spouse is watching football and you can't stand to listen to it anymore,” Spiller joked.

Once dahlia tubers are dug, they must be thoroughly dried before storing, because any kind of moisture can cause problems. Spiller puts her washed tubers next to a wood stove or heating element to dry for a few days since she believes the wet Northwest fall weather won't thoroughly dry them. Then she stores her dry tubers in individually labeled paper grocery sacks.

Dina Wild, Chehalis, owner of Wild Side Dahlias, said she prefers to keep her tubers in plastic shoe boxes filled with vermiculite, a common technique used by many dahlia growers. Wild, who raised about 175 dahlia plants of about 80 varieties this year, said she learned the technique from Lobaugh. Lobaugh uses the vermiculite technique but said sawdust is another good medium for storage. Wild said she has even heard of gardeners who simply store their tubers on tarps in their garage. 

“Ask 100 people and you'll get 100 answers,” Wild said of the right way to dig and store dahlias. “If you hear of a trick, try it. You've got nothing to lose but a few tubers.”

Labeling is another important aspect to storing dahlias. With 2,400 plants, each bearing about 4 splits, labeling is a necessity for Lobaugh. But he said even amateurs who care about the location of their plants in the spring would do well to find a way to label their tubers when they dig them up.

“Trust me, you're not going to remember which one is which,” he said.

For most growers, fall dahlia digging also includes splitting. Like many tubers, dahlias produce nodes that can be split from the main root to make new plants. Like potatoes, dahlias produce eyes where new growth can occur. Spiller said she actually likes splitting her dahlias in the spring because she feels it is easier to spot where the eyes are because they have actually started to sprout. Wild said she prefers to split in the fall, both because she sells her tubers over the winter, but also because the tubers are softer and easier to split in the fall. But no matter when you decide to split, Spiller's one piece of advice is to pay attention to what you are doing. Dalias have three parts: leaves; stalk; and root. When you divide a dahlia tuber, each split must contain both a piece of the root and a piece of the stalk to be successful.

“If you just break off a dahlia bulb and hand it to somebody it probably won't grow,” Spiller said.