By Bob Nikelwicz, UC Master Gardener of Napa County.  

Last February I did a talk at the Napa County Library on dahlias and planting them in containers.  I like growing in containers as the shady areas in my backyard shift over the course of the year.  Dahlias need at least six to eight hours of direct sunlight to do well.  In my yard I can keep up with the sunlight simply by rolling the pots to different places for a couple of weeks at a time.  

For the most part, that method worked pretty well last year. Almost all my dahlias looked healthy and produced blooms in myriad colors, shapes and sizes. Bob was a happy gardener. 

Now I need to start the process all over again. When I have some dead time between football games and filling my compost pile with fallen leaves, I find that it’s a good time to “dilly dally” with my dahlias. 

To get great blooms later, these are the steps I took recently to start the cycle all over again.

I have many large pots on wheels, from 18 inches to 24 inches in diameter. I rolled them under an overhang in the yard and went to work digging the tubers up.

First, I filled a large tub with about 5 gallons of water and added 1 cup of bleach. I’m not sure if that was too little bleach or too much, but I thought it was a good idea to clean off any harmful spores or bacteria. 

Using a small garden fork and starting outside of the zone where I figured a clump was, I slowly lifted each clump. Then I hosed off the dirt and soaked each clump in the bleach water for 5 to 10 minutes to loosen deeper dirt. Then I rinsed them again with the hose and dried them. It’s your call whether to follow my guesstimation on the bleach or not use bleach at all.

The next step is tedious: dividing each clump. You don’t have to do it now. You can store whole dry clumps and wait until April to unpack them, at which time you should see the budding “eyes.” But if you divide the clumps now, they’ll take up less storage space because you can throw out any damaged or rotting tubers. At planting time, each tuber needs to have a healthy neck and at least one eye. 

After cleaning them, I laid the clumps out to dry on flattened cardboard under the overhang for a couple of days. I wanted them to cure and be totally dry before the next step. 

Once they’re dry, you can store the clumps in paper grocery bags, file boxes, used pillowcases or even plastic bags. They need air during storage so don’t seal the containers. 

To prevent sprouting, store the tubers in a cool, dark, slightly moist location. The garage seems to be the storage area of choice for dahlia enthusiasts in Napa County. You can use sawdust, shredded paper or Vermiculite as a medium to keep the tubers from drying out. Too much moisture in the medium and the tubers may rot; too little and they will shrivel up. 

In spring, I start my dahlia containers in the garage where I can control the temperature and light.  I try to keep the temperature above 50°F and I use a timer to keep the garage light on for 8 to 10 hours a day. The dahlias typically break ground in two to six weeks. 

I move my newly planted pots outside when the stems break ground, typically in April. Avoiding frost is essential so you don’t lose the tender new growth. 

If you missed some of the tubers when you were digging them up to store, don’t panic. In Napa Valley, many gardeners leave their dahlias in the ground year round and get successful blooms early. So, if you see unexpected growth emerging in the spring, consider it a prize. It’s a reminder that plants really do not need us to grow. We just think they do.  So enjoy any spring surprises as you dally with your dahlias.

Workshop: Join UC Master Gardeners of Napa County for a workshop on “Starting Your Own Vegetable Seedlings” on Saturday, January 10, from 2 pm to 4 pm, at UC Cooperative Extension, 1710 Soscol Avenue, Napa. We’ll cover all the basics, including proper moisture, temperature and light for successful seed starting, and care of seedlings until they are ready for transplant. We provide some seeds, containers and soil; bring your own seeds if you like. Reserve here.

Help Desk: The Master Gardener Help Desk is available to answer your garden questions.  Use our online Plant Problem Help Form or email us at mastergardeners@countyofnapa.org. Include your name, address, phone number and a brief description of the problem.  You can also visit us in person on Mondays and Fridays from 10 am until 1 pm at the University of California Cooperative Extension Office, 1710 Soscol Avenue, Suite 4, Napa.