mg-logo
UC Master Gardeners of San Luis Obispo County

Dahlias: Digging, Dividing, and Storing

Dahlia Tubers: Digging, Dividing and Storing

By Carol Moore, UC Master Gardener

1

Photo credit: Carol Moore
UC Master Gardener

 
2

Photo credit: Kim Wilson
UC Master Gardener

What Is a Tuber?

A dahlia tuber is the tuberous root of a dahlia plant. It consists of three parts: the body, the neck and the crown.

The Body: The swollen body contains carbohydrates, water and nutrients. It provides energy until roots and shoots are established, after which the plant is fueled by photosynthesis.

Each year the mother tuber (the original planted tuber) produces new tubers. The number varies depending on growing conditions. Ideal conditions result in larger and more numerous tubers.

The Neck: Connects the tuber body to the crown. If the neck is broken, the tuber is not viable.

The Crown: On top of the neck sits the crown. Dahlia eyes sprout from the crown and are the source of shoots. The crown must have at least one eye to produce a plant. Some tubers take time to “eye up,” especially late-blooming varieties.

3

Photo credit: Carol Moore
UC Master Gardener

Does Tuber Size Matter?

Tubers vary in size and shape. To grow a flowering plant, a tuber should be larger than your pinky finger or a AAA battery. Some varieties produce large tubers that flower well but may not generate additional tubers by fall. To prompt additional growth, cut off the back of the tuber before storing.

Why and When to Dig Up Tubers

Dahlia tubers are fleshy and thin-skinned. They may freeze or rot if left in the ground over winter. In colder climates, where soil freezes 4–6”, dig dahlias by November 15th or after the first killing frost.

If left undivided, dahlias form massive clumps that produce weak stalks and smaller blooms. Divide every 2–3 years at minimum.

Fall Digging

Wait until foliage turns yellow and brown. This allows nutrients from leaves to move into the tubers.

Pros:

  • Easier harvest in drier soil.
  • Softer tubers, easier to divide.
  • Frees garden space for winter crops.
  • Protects from predators such as gophers.
  • Allows controlled planting timing.

Cons:

  • Thin skins may lead to 20% storage loss from rot or dehydration.
  • Requires suitable cold, dark storage space.
  • Requires winter monitoring.

Spring Digging

If digging in spring, cut stems to crown level and cover with 4” mulch (compost, alfalfa, straw or pine needles). Do not water during winter.

Pros:

  • Dig, divide and replant immediately.
  • No winter storage required.

Cons:

  • Woodier tubers are harder to divide.
  • Higher rot risk from winter moisture or freeze.
  • Replacement options limited if losses occur.

Digging and Washing Tubers

Equipment

  • Shovel or garden fork
  • Gloves, boots, waterproof clothing
  • Sanitizing solution (1 part bleach to 10 parts water, or 5 tsp dish soap to 4 cups water)
  • Large buckets
  • Holding containers (flats, baskets, boxes)
  • Waterproof labels and markers

Before Digging

  • Discard diseased plants (do not compost).
  • 1–2 weeks before fall digging, cut stems to 5–6” to use as handles and promote eye growth.

Always sterilize cutting tools between plants.

Digging

  • Dig about 12” from stem, encircling plant.
  • Gently rock and lift clump.
  • Shake off excess soil carefully.
  • Label immediately.
  • Discard tubers with crown or leafy gall (do not compost).

Washing

  • Wash gently with hose.
  • Dip briefly in sanitizing solution.
  • Air-dry 24–48 hours (not on concrete).
  • Balance drying — too much causes shrivel, too little causes rot.

Dividing Tubers

The division process is the same in fall or spring.

Always sterilize tools between clumps.

  1. Remove stems, fibrous roots, rotted or broken tubers.
  2. Save healthy mother tuber if a new crown is attached.
  3. Cut large crowns in half with pruners.
  4. Each tuber needs ¼–½ square inch of crown with at least one eye.
  5. Remove extra stem tissue.
  6. Check for rot. White flesh is healthy. Cut out brown spots and dust with antifungal powder.

Storing Tubers

  • Location: Cool, dry, dark area (garage, basement, attic, closet).
  • Temperature: 40–50°F with ~70% humidity.
  • Storage Medium: Peat moss, vermiculite or wood shavings.
  • Layer 1–2” medium, tubers not touching, repeat layers and label.
  • Check every few weeks. Remove rotted tubers.
  • If shriveled, move to more humid area.
  • If mold appears, brush off and move to drier location.
4

Photo credit: Carol Moore, UC Master Gardener

5

Photo credit: Kim Wilson
UC Master Gardener

6

Photo credit: Kit Long

7

Photo credit: Carol Moore
UC Master Gardener

References

Crown Gall. https://ipm.ucanr.edu/PMG/GARDEN/FLOWERS/DISEASE/crowngall.html

Plakos, Lori. All About Dahlias. UC ANR. All About Dahlias

Plakos, Lori. All About Dahlias, Part 2. UC ANR. Part 2

Digging, Dividing and Storing Tubers. American Dahlia Society