Between travels and plant maintenance, October has almost slipped right by. We are still in bloom here in gardening zone 7. As the days shorten, the stems get longer and the blooms are flashing their disks to the pollinating bees.
After a dahlia plant has been in the ground for 125 days or more, the tubers are mature enough to be taken out of the ground for storage. No need to wait until frost. It is decision time. Should I dig the clumps, or leave them in the garden and hope they survive the winter?
We discuss this decision every year because many gardeners think that digging and storing is the worst part of growing dahlias. Frankly, I agree, particularly when it is cold or rainy. This decision generally separates the hobbyist from the gardener. If I only grew a few dahlias, I would probably leave them in the ground. If I am growing expensive or hard-to-find varieties, I would dig and store them.
Leaving Dahlias in the Ground
The major threats to dahlia clumps are frost and sogginess. Do not use this method if rain puddles around the plants, or if you have a deep frost in your area.
Cut the plants until the stalk is solid. Leave the plant tag on a stake. Pile some dirt around the stalk. Cover with a layer of plastic bubble wrap and pile leaves or mulch on the wrap. Secure the wrap with lawn pins or rocks.
Uncover the pile in the spring and either wait for a sprout or dig up the clump and take a look for eyes. If multiple shoots appear, retain only one or two of the most vigorous. Dahlias are vigorous feeders. Competition among numerous shoots in the same area will weaken the plants.
Digging Dividing and Storing
I dig carefully so as not to break the neck of the tuber. You need a tuber and a piece of rounded stalk tissue (also called the "crown") to get an eye (and thus a plant next season). The "neck" is the connector from the crown to the bulbous part of the tuber.
Shake or wash off the dirt and divide the clump in half down the stalk. I do not look for eyes. Then further divide each half to get "divisions" consisting of at least one tuber and a piece of stalk. You must have that crown!
Then bag the tubers in one-gallon plastic storage bags or small waste-basket bags. Make sure that half the volume of the bag is vermiculite, preferably the coarse type. Write the name on the bag and put the tag inside. I store the bags in a garage closet with a bottom heater set on low.
There are many other ways to dig, divide, and store dahlias. We have listed a few links below.
The Forget Method
Do nothing in the autumn and see if shoots come up in the spring. If not, buy a few dahlias from your local dahlia society, or elsewhere. In many cases tubers cost less than an annual plant.