When To Dig Up Dahlia Bulbs

Knowing when to dig up dahlia bulbs is the single most important factor for successful winter storage. Get the timing right, and you’ll protect your precious tubers from cold damage, ensuring they return healthy and vigorous next spring. This guide gives you the clear, simple signals to watch for in your garden.

Dahlias are not true bulbs; they are tender tuberous roots. This means they cannot survive freezing temperatures in the ground. To save them for another year, you must lift and store them. But timing this task correctly is a balance between letting the tubers fully mature and beating the first hard frost.

Your main cue comes from the weather, not the calendar. While dates vary by climate, the principle is universal. You are waiting for the plants to finish their season naturally, triggered by cooler nights.

The Primary Signal: The First Killing Frost

This is your most reliable indicator. A killing frost (also called a hard frost) is when temperatures drop below 28°F (-2°C) for several hours. This frost will blacken and wilt the dahlia’s foliage. Once the leaves and stems are visibly damaged, the plant’s growth cycle is complete.

Do not dig immediately after the frost. Wait about one week.
This short waiting period allows the tubers to receive a final signal from the dying foliage, which helps them cure and develop better skins for storage.
If you here a forecast for a severe freeze and your dahlias are still green, you can cover them with a thick blanket or cardboard overnight as a temporary shield.

What If You Don’t Get a Frost?

In mild winter regions, you may not experience a hard frost. In this case, you must use the plant’s natural cycle and daylight as your guide.

Watch for the foliage to start yellowing and dying back naturally in late autumn.
Growth will slow and flowers will become sparse.
Once the plant looks tired and is clearly declining—usually after several weeks of shorter days—it’s time to dig.

Regional Timing Guidelines

These are general estimates. Always prioritize the condition of your plants and local forcasts.

Northern U.S. & Canada (Zones 3-5): Typically late October to early November. Be prepared for early frosts.
Midwest & Northeast (Zones 5-7): Often from mid-October to early November.
Pacific Northwest (Zones 7-8): Usually late November, sometimes into December if winters are mild.
Mild Coastal & Southern Regions (Zones 9+): You may choose to dig in late December or even leave tubers in the ground with heavy mulch. Digging is still recommended for best tuber health.

Why Timing is So Critical

Digging too early or too late causes problems.

Too Early (Before Frost): Tubers are still immature. They haven’t developed the thick, protective skin needed for storage, making them prone to shriveling or rotting. You also sacrifice potential late-season blooms.
Too Late (After Ground Freezes): This is the real danger. If the ground freezes solid, the tubers inside can freeze and turn to mush. Once frozen, they are unrecoverable. It’s better to dig a little early than too late.

Pre-Dig Prep: Making the Job Easier

A little preparation the day before you dig makes the process smoother.

Cut Back the Stalks: Using sharp pruners, cut the dahlia stems down to about 4-6 inches above the soil. This removes the bulky foliage so you can see what your doing.
Label Your Plants: If you know the variety names, tie a weatherproof tag to the remaining stump. It’s easy to mix them up once they’re out of the ground!
Gather Supplies: Have a digging fork, garden trowel, buckets or crates, and marking pens ready.

The Step-by-Step Digging Process

Handle your dahlia tubers gently; they are living storage organs and can bruise easily.

Loosen the Soil: Insert a digging fork into the soil about 12 inches away from the central stalk. Gently rock it back and forth to loosen the soil in a wide circle around the plant. Avoid driving the fork directly into the tuber clump.
Lift the Clump: Once the soil is loose, work the fork under the clump and carefully lift it from the ground. Shake off the excess soil gently.
Initial Cleaning: Use a gentle stream from your hose to wash off the majority of the soil. This makes it easier to inspect and divide the tubers later.

Post-Digging: The Essential Curing Step

Do not skip curing! This step is non-negotiable for preventing rot during storage.

Place the washed tuber clumps in a well-ventilated, dry, and shaded spot—like a garage, garden shed, or covered porch.
Let them air-dry upside down (with the stems down) for 24 to 48 hours. This allows any moisture in the hollow stems to drain out.
The tubers should feel dry to the touch, and the skin will slightly toughen. Any remaining soil on them will brush off easily now.

Dividing Tubers (Optional Now or Later)

You can divide in the fall or wait until spring. Fall division lets you see the growth eyes (located near the stem base) more clearly before they swell.

Using a sharp, clean knife, cut the clump apart, ensuring each division has at least one visible “eye” and a piece of the original stem crown attached.
Dust the cut surfaces with sulfur powder or let them dry for another day to form a callus. This seals the wound against pathogens.

Choosing Your Winter Storage Method

The goal is to keep tubers cool, dark, and just barely moist. Ideal conditions are around 40-50°F (4-10°C) with moderate humidity.

Method 1: The Cardboard Box & Packing Material

This is a simple and effective method.

Line a cardboard box with newspaper or kraft paper.
Place a layer of slightly damp (not wet) packing material in the bottom. Peat moss, vermiculite, or wood shavings work well.
Lay tubers in a single layer, ensuring they do not touch eachother.
Cover completely with more packing material. Close the box and label it clearly.

Method 2: Paper Bags or Mesh Bags

Good for smaller collections and improves air flow.

Place tubers in paper bags with a handful of slightly damp peat moss or wood shavings.
Fold the top over and staple it shut. Label the bag.
Store these bags in a cool, dark place like a basement or cellar.

Winter Storage Check-Ups

Check on your tubers once a month through the winter.

Look for any signs of shriveling (too dry) or mold/soft spots (too moist).
If tubers are shriveling, lightly mist the packing material with water.
If you find rot, cut it away with a clean knife, dust with sulfur, and move the tuber to drier material. Discard any completly soft tubers.

Common Storage Mistakes to Avoid

Storing in Plastic Bags: This traps moisture and leads to certain rot. Always use breathable materials.
Storing in a Warm Place: Heat causes tubers to dehydrate rapidly or sprout too early.
Packing Material Too Wet: Slightly damp is the key. If you can squeeze water out of it, it’s too wet.
Forgetting to Label: You will not remember every variety come spring. Trust me.

FAQ: Your Dahlia Digging Questions Answered

Can I leave dahlia bulbs in the ground over winter?

Only if you live in a climate where the ground never freezes (USDA Zone 10 or higher). Even then, heavy winter wet can cause rot. In all other zones, digging is recommended for reliable results.

What is the best month for digging up dahlias?

The best month depends entirely on your local frost date. For most gardeners, it’s October or November. Focus on the plant’s condition and the weather forcast, not the calendar.

How do you know when dahlias are ready to dig?

They are ready after the foliage has been blackened by a killing frost, or has naturally died back after several weeks of cold, short days in autumn.

Is it better to divide dahlia tubers in fall or spring?

Both times have advantages. Fall division is easier when the eyes are visible on the fresh crown. Spring division is often preferred because the eyes have swollen and are obvious, and cut surfaces heal quickly as growth begins.

My tubers shriveled in storage. What happened?

Shriveling means the storage environment was too warm and/or too dry. The tubers lost there moisture. Next year, store them in a cooler location and ensure your packing material is slightly damp at the start.

By following these clear guidelines for when to dig up dahlia bulbs, you give your garden favorites the best chance to rest peacefully through the winter. With proper timing and care, you’ll be rewarded with a thriving dahlia patch season after season, all from your own successfully stored tubers.