“D” is for Delightful Dahlias and for December. That should help you remember that if you are a dahlia devotee, the growing cycle of the dahlia is from December to December. What we do with our dahlias in December directly determines the direction dahlias will develop. Dare you be a person that leaves dahlias alone? Or do you dig them in December?

 In Napa we are in USDA Plant Hardiness Zone 9b. That means we have mild winters that generally do not dip below 30-25 degrees. This is significant because dahlias do not like cold.  If the temperature drops below 25 degrees, dahlias left in the ground may suffer freezing cold conditions that turn the tubers into mush. Tubers may only be 1-4” below the surface and can be easily damaged.

If you decide to leave the tubers in the ground for the winter and you hear that there are reports of temperature dropping into the 30-25 degree range, you can protect the tubers with 3-4” layer of compost or blanket covers during those days and nights.

If you live up higher in the hills where it is colder than the valley floor, digging up the tubers may be your best bet to keep the tubers from freezing.  If you do dig them up, keep as much dirt around the tubers as you can. This will keep some moisture in the tubers as well as insulting them while in storage.

Cutting  straight down with a spade about 12-16” from the stem should give you enough dirt while not cutting off  or damaging the tubers. To really protect the tubers consider using two shovels or digging forks to pry up the clump. Do not pull them up by the stem as that can damage the necks of the tubers.

The next question is, What do you do with the clumps and tubers?

 

Your choices are:

Photo 1 is of freshly dug up tubers with dirt. Pick the whole clump up and place it into a large box with wood shavings, crumpled newspaper and/or peat moss to keep the clump slightly moist. Leave them there in a cool, dark place (e.g. garage) until the spring (March). Then separate the tubers and plant them.

 

Photo 2 is of tubers slightly cleaned up by water spray that can be stored in newspapers or shavings. This will leave some moisture on the tubers and reduce the risk of drying them out while stored. If left too dry for too long, the tubers will start to shrivel–not desirable.

 

 

 

 

Another alternative to the boxes of wood shavings is Photo 3.  Separate the tubers, clean them (clip the dry roots if you wish), then stack them flat in boxes filled with dry wood shavings or peat moss or vermiculite. The main stem is pointing straight up so if the eyes start to swell, they will be aimed in the right direction. In March you can put the whole bunch into the ground or a container.  

 

 

Or as shown in Photo 4 you can clean and trim each tuber with an “Eye”(the “Eye” being where the new stem will grow.) then label the tubers with a ink marker or plastic label then roll them up in plastic wrap with some shavings and store them wrapped. The advantage is they take up less space and  you can see how they are doing as well as being able to see the name of the tuber. You will also be able to see how the “Eye” is developing.

In all of these cases, store them in a cool, dark place where they will not be exposed to freezing temperatures.

In February and March you can work on the soil in anticipation of the spring planting. But how to do that, is a story for later issue.

Master Gardeners of Napa County are available to answer garden questions by email: mastergardeners@countyofnapa.org. or phone at 707-253-4143.  Volunteers will get back to you after they research answers to your questions.

Visit our website: napamg.ucanr.edu to find answers to all of your horticultural questions.

Photo credits:  Bob Niklewicz