Dahlias are popular tuberous flowering plants that produce beautiful blooms in a wide range of colors and forms. They grow from tubers that develop underground storage organs called tubers. As dahlia plants grow over time, the tubers multiply and form clumps. This leads many gardeners to wonder – should I divide my dahlia tubers?
Dividing dahlia tubers has pros and cons. On the plus side, dividing dahlias helps stimulate growth, encourages larger blooms, prevents overcrowding, and results in more plants. However, it also takes time and care to properly divide tubers. Additionally, dividing is not always necessary every year.
Here is a quick overview of the key factors to consider when deciding whether to divide dahlia tubers:
Pros of Dividing Dahlia Tubers
– Promotes growth and larger blooms – Dividing tubers provides more energy and nutrients to each new growth.
– Prevents overcrowding – Dividing congested tubers prevents competition for resources.
– Multiplies your collection – Dividing results in more tubers and therefore more plants.
Cons of Dividing Dahlia Tubers
– Time consuming – It takes time and care to properly dig up, divide, and replant tubers.
– Can damage tubers – Dividing can accidentally damage tubers, especially if done carelessly.
– Not always needed – Dividing is not crucial every year for healthy plants.
When to Divide Dahlia Tubers
The ideal time to divide dahlia tubers is in early spring before new growth begins. This minimizes stress on the plant. Fall is another option, after the first frost has killed back foliage. Avoid dividing when plants are actively growing.
Signs It’s Time to Divide Dahlias
– Clumps are crowded with decreased blooms.
– The center of the clump is dead and growth is only around the edges.
– Tubers are small (smaller than 2 inches).
– You want to propagate your plant collection.
Steps for Dividing Dahlia Tubers
1. Dig up entire dahlia clump after frost or before spring growth.
2. Shake off excess soil but do not wash tubers.
3. Carefully break apart clump and divide tubers.
4. Discard any rotted or damaged tubers.
5. Cut tops of remaining tubers to 2 inches with clean shears.
6. Allow cuts to dry out for a day before replanting.
7. Replant tubers horizontally 4-6 inches deep, eye/sprout side up.
The Benefits of Dividing Dahlia Tubers
Dividing dahlia tubers has some key benefits that can result in healthier, more prolific plants.
Stimulates New Growth
Dividing up congested tuber clumps into smaller sections disturbs their dormancy and stimulates new, invigorated growth. The process of digging them up, separating tubers, and replanting mimics spring conditions. This interruption causes the tubers to break dormancy and initiate new sprouts and roots.
Each newly divided tuber has more access to moisture, nutrients, and space to focus energy on developing one or two strong new stems. Without competition from a congested clump, the separated tubers tend to produce bushier, stronger plants.
Encourages Larger Blooms
Another benefit of dividing dahlia tubers is larger, showier blooms on each stem. Every dahlia plant has a certain amount of energy and nutrients to put towards flowering. In an overcrowded clump, this energy is spread across many stems and results in smaller blooms.
By dividing the tubers and reducing competition, more energy goes to each new plant, supporting the production of bigger, brighter blooms. Dividing every couple years helps maintain an ideal balance between number of stems and bloom size.
Prevents Overcrowding
Dahlia tubers naturally multiply each year, forming expanding clumps. If clumps become too dense, interior tubers are shaded and poorly aerated, making them prone to rot. Dividing up the congested clump gives each portion enough space to access sunlight, moisture, and soil nutrients. It prevents inner crowding and die out of central tubers.
Results in More Plants
Dividing dahlia tubers is an easy, low cost way to increase your number of plants. Mature, healthy tubers that are split up can double or triple your plant collection. Having more young plants also allows you to selectively cull weaker ones prior to planting. The result is more robust, healthy plants obtained at minimal expense compared to buying new tubers.
Potential Drawbacks of Dividing Dahlias
While dividing dahlia tubers has many advantages, there are also some potential drawbacks to consider.
Time and Labor
It takes time, care, and physical effort to properly dig, divide, and replant dahlia tubers. The tasks of digging up clumps, breaking apart sections, discarding dead tubers, cutting tops, and then replanting is labor intensive. For large gardens with many dahlia plants, this can become a major time commitment.
Risk of Damage
When digging and separating old clumps there is significant risk of accidentally damaging or stressing the tubers. Cuts and nicks to tubers can allow decay to set in. Over-handling during washing or excessive removal of eyes/sprouts can harm tubers. Any damage done while dividing increases risk of problems when replanting.
Not Always Necessary
While dividing is recommended every few years under optimal conditions, it is not mandatory to divide dahlias annually. Mature, healthy tubers often carry over well for several years without division. Tubers only need dividing if plants are clearly underperforming due to overcrowding, pests, or disease.
Challenging Timing
The timing required for dividing dahlias can also be a challenge. Digging up plants before spring growth begins is ideal, but this must be planned in advance. Other good times are after first frost or during dormant winter months, when gardens may be muddy or frozen.
When to Divide Dahlia Tubers
Dividing dahlias at the right time is important for success. The best time to divide tubers is early spring or fall when plants are dormant.
Early Spring
Dividing dahlia tubers in early spring as new growth is beginning to emerge is ideal timing. Digging up and dividing clumps as shoots first appear causes minimal stress. The newly divided tubers only have to re-initiate sprouting rather than fully break dormancy.
Target late March to early April for spring division, about 2-4 weeks before your expected last frost date. The window for spring division can be short before growth advances too far. Beginning while ground is still workable but prior to active growth is key.
After First Fall Frost
The other optimal window for dividing dahlias is in fall after the plants have been killed back by first light frost. Plants naturally start going dormant as day length shortens in fall. A light frost fully kills back the foliage and sends the tubers into winter dormancy.
The advantage of fall division is drier soil conditions compared to spring. Cut off dead foliage and carefully dig up and divide tubers October through November. Let the freshly divided tubers air dry for a day before packing them up in storage medium.
During Winter Months
If needed, dahlias can also be divided while fully dormant during winter months. However, soil may be wet or frozen, making the task more challenging. Tubers need several weeks in a cool, dry spot to re-acclimate before spring planting.
Target February or March for winter dividing to get replanted 1-2 months before your spring planting date. Otherwise store the tubers until ready to plant them in spring.
Signs It’s Time to Divide Dahlia Tubers
Certain visible signs indicate when mature dahlia plants are due for division. Look for these cues to know it’s time to divide and rejuvenate tubers.
Overcrowded Clump
A clear indicator dahlia tubers need dividing is when the original clump becomes a congested tangle of old and new tubers. Growth may only emerge around the edges while the interior tubers decay. Digging up reveals a tight mass of tubers competing for space.
Decreased Blooms
When an established dahlia plant that previously bloomed well begins producing smaller flowers on shorter stems, it likely needs dividing. Nutrients are lacking within a dense clump, resulting in reduced flowering.
Mostly Small Tubers
If digging up mature plants reveals a majority of tubers are only peanut-sized, division is overdue. Healthy, happy dahlia tubers grow to golf ball size or larger. Miniature tubers signal overcrowding.
Desire to Propagate
You may opt to divide healthy dahlias simply to propagate your collection and obtain more plants. Division accomplishes propagation at low cost.
How to Divide Dahlia Tubers
Here is an overview of the step-by-step process for properly dividing dahlia tubers:
Dig and Remove Clump
– Dig around and under clump to lift entire plant
– Shake off loose soil but do not wash
– Remove attached stakes and tags
Break Apart Clump
– Gently pull apart sections of the clump
– Try to break along natural divisions
– Retain growth eyes/sprouts if possible
Discard Unhealthy Tubers
– Inspect each tuber and discard any that are:
– Moldy, mushy, or damaged
– Too small to sustain growth
– Hollowed out or rotting in center
Trim Tubers
– Using clean shears, trim each remaining tuber
– Make straight cut 2-3 inches below eyes/sprouts
– Disinfect shears between clumps
Allow Drying
– Set trimmed tubers aside for 24 hours
– Air drying reduces rot risk
– Avoid direct sun to prevent dehydration
Replant Tubers
– Carefully replant individually
– Bury horizontally 4-6 inches deep
– Place eye/sprout side facing up
– Space 12-24 inches apart
| Tool | Purpose |
|---|---|
| Garden fork | Lifting clumps from soil |
| Pruners/shears | Trimming tuber tops |
| Hand trowel | Planting individual tubers |
| Container/tray | Holding tubers while working |
| Fungicide | Disinfecting tools between clumps |
| Tags | Labeling tuber varieties |
Having the right tools makes dividing dahlia tubers much easier. Use a garden fork to loosen soil and lift each clump. Pruners or garden shears trim tops cleanly. A hand trowel works best for replanting individual tubers. Have fungicide and tags on hand too.
Caring for Divided Tubers
Proper care of freshly divided dahlia tubers ensures they will grow vigorously after replanting. Here are some tips for handling divided tubers:
Let Dry Before Storing
If tubers won’t be planted right away, let them dry out for 1-2 days after division before packing for storage. Air drying reduces the chance of rot developing. Lay tubers in a single layer in trays out of direct sun.
Store in Cool, Dry Location
Keep divided tubers dormant by storing in a frost-free but cool (40-50°F) spot. A basement, unheated garage, or refrigerator works well. Ensure tubers do not freeze or overheat.
Use Medium Like Vermiculite
Pack stored tubers in trays or boxes with vermiculite, peat moss, sawdust, or other medium that retains some moisture while staying light and airy. Avoid sealing in plastic that can cause condensation.
Check Periodically for Issues
Check stored dahlia tubers occasionally for signs of rotting, shriveling, or sprouting. Remove any damaged tubers and mist others with water if drying out. Watch for early sprouting.
Pot Up Prior to Planting
If tubers begin sprouting in storage, pot them up in soil ahead of planting time. Keep pots cool until ready to plant in ground. This avoids breaking fragile new shoots later.
Reasons to Avoid Dividing Dahlias
While division benefits mature dahlia plants in many cases, there are times when leaving tubers undisturbed may be better.
When Plants are Performing Well
If your dahlias are blooming prolifically with no signs of disease, decline, or overcrowding, don’t divide simply for the sake of dividing. Well-performing, healthy tubers often carry over fine for several years without division.
After Harsh Winters
In regions with very cold winters, dahlia tubers may need extra recovery time in spring if they suffered freeze damage. Dividing right after an extreme winter adds stress; give plants a year to rebound first.
When Storing Tubers Over Winter
Where winters are too cold to leave tubers in ground, don’t divide them right before digging for storage. Undivided clumps store better. Divide in spring after taking them out of storage.
With Rare or Prized Varieties
Dividing risks damage, so avoid disturbing prized dahlia varieties you only have a limited number of tubers for. Only divide them when essential to propagate for more plants.
When Time is Too Short
If spring arrives and you don’t have time to properly dig, divide, and replant dahlias, it’s better to leave them undivided rather than rush the job. Divide in fall instead.
Storing Undivided Dahlia Tubers Over Winter
In climates where dahlias can’t be left in the ground through winter, you must dig up and store the tubers until spring planting. Here are tips for storing undivided tuber clumps:
Allow Plants to Mature
Leave dahlias in ground until after a light frost kills the foliage, usually October or November. Let them fully mature and go dormant on their own.
Dig Carefully with Clumps Intact
Dig tubers using a garden fork, lifting out whole clumps carefully to avoid breaks and damage. Shake off excess soil.
Allow Clumps to Air Dry
Set clumps aside for 1-2 days in a frost-free place to surface dry before storage. Avoid direct sun.
Pack in Storage Medium
Place dry clumps spaced apart in boxes of vermiculite, peat, or sawdust that retains some moisture. A cool basement or unheated garage works for storage.
Inspect Periodically
Check clumps occasionally over winter. Look for rotting or shriveling. Mist sparingly if they are drying out. Discard any that show decay.
Divide After Overwintering
In spring, divide stored clumps when you take them out of storage. Let divisions further dry before replanting in garden.
Conclusion
Dividing congested dahlia tubers encourages vigorous growth, larger blooms, and propagation of new plants. But it also takes time and care to complete properly. Consider the age and performance of your plants, as well as your climate and workload, when deciding whether to divide each year. In general, plan to divide mature, multi-year plants every 2-3 years for optimal results and to rejuvenate your dahlias.
