A new room addition is scheduled for next March. How would I go about relocating and dividing my Dahlias that are in the way?
Dahlias are commonly dug up, divided, and replanted. They can be moved now through March without any concerns. It's an annual event for some gardeners, but for most, it's done periodically.
Typically, you wait until the foliage turns yellow before starting; however, they may not go dormant with our mild climate. If the foliage is still green, cut the plants off two to four inches above the ground and then strip the foliage back to the trunk or stub.
Next, you sever the lateral roots with a round nose shovel or spading fork by encircling the clump(s) eighteen inches from the trunk/stub and down twelve inches. Once the circle is completed, gently pry back on the shovel or fork to loosen the soil. Dahlia clump(s) are then gently removed from the hole by lifting upward.
You can use the stub as a handle. It would be best if you were gentle as many of the clumps have small tubers that can break or crack easily. The long skinny part of the tuber is referred to as the neck. Dahlias with broken or cracked necks will not survive so remove them from the clumps and discard them.
You now have several options available to you.
Option one is to store the clump(s) as is until next year.
Option two, wash all the soil off the clump(s) with a stream of water, exposing all the tubers. The darkest color tuber is last year's plant. It is also referred to as the mother tuber. Once the clump(s) has air dried, you can store the clump(s) or divide them. Option three, store the parts. The choice is yours.
The new tubers are separated from the clump with a sharp knife, a pair of scissors, or hand shears. They must be sharp as the wounds are less likely to become infected from a nice clean cut. Dahlias sprout from the eyes. A tuber will not sprout unless it has at least one' eye.' The eyes are typically found at the top of a tuber. Also, at the end of the neck on the ridge where the tuber joins the clump. When a tuber is removed from the clump, the ridge containing the eyes must be attached to the tuber. In some cases, this will require taking a piece of the mother clump as well. Also, trim off any excess roots. Individual tubers or clumps are stored in paper bags or in open boxes in a cool location, usually a garage.
NOTE: You'll find an excellent step be a step, pictorial, 'How to' site for dividing and planting Dahlias at http://www.dahlias.net/dahwebpg/TuberStor/TuberStor1.htm .
It identifies the Mother Tubers, where the eyes are located, etc. Some of the information doesn't apply to the Bay Area but the step-by-step pictures are great.