Introduction
At Longfield Gardens, we want you to enjoy dahlias year after year. Whether you grow petite pompons or dinnerplate varieties, harvesting your own bouquets is a highlight of the season.
Caring for your plants after they bloom is the secret to keeping the display vibrant all summer and ensuring the plants return even stronger next year. This guide covers the essential steps for maintaining your dahlias during their flowering cycle and best practices for handling them once the first frost arrives, from deadheading to overwintering tubers.
Quick Answer: To keep dahlias blooming, you should regularly deadhead spent flowers and cut stems for bouquets throughout the summer. Once the first hard frost turns the foliage black, the plants should be cut back and, in colder climates, the tubers must be lifted and stored in a cool, frost-free environment for the winter.
Caring for Dahlias During the Flowering Season
When your dahlias start blooming in mid-to-late summer, "after-bloom" care begins immediately. Maintaining the plant while it is actively flowering ensures it continues to produce new buds rather than putting energy into seed production.
The Art of Deadheading
Deadheading is the practice of removing faded or spent flowers to signal the plant to keep producing more blooms.
- Identification: Dahlia buds are usually round and firm, while spent flowers are pointed or cone-shaped and feel soft or squishy.
- Technique: Follow the stem of the faded flower down to the next set of leaves or buds and make a clean cut.
Cutting Flowers for Bouquets
Dahlias are unique because the more you cut them, the more they bloom. Cutting stimulates the plant to branch out and produce more stems.
- Timing: Cut in the cool of the morning when plants are hydrated.
- Selection: Look for flowers that are three-quarters open; dahlias do not open much further once cut.
- Care: Use sharp, clean snips and place stems immediately into room-temperature water.
Maintaining Water and Nutrients
As heavy feeders, dahlias have specific needs once they are in full flower:
- Watering: Continue to water deeply at the base. Dahlias prefer a "deep soak then dry" routine. Avoid wetting the foliage to prevent powdery mildew.
- Fertilizing: Use a low-nitrogen fertilizer where phosphorus and potassium are higher than nitrogen. This supports flower production and tuber health.
- Support: Check stakes and ties regularly. The weight of big blooms, especially after rain, can cause stems to snap.
Key Takeaway: Consistent deadheading and frequent cutting redirect the plant's energy into creating a continuous supply of new buds rather than seeds.
Transitioning to Late Autumn
As days shorten and temperatures dip, dahlias slow down to store energy in their tubers.
Slowing Down Maintenance
In early-to-mid autumn, stop fertilizing to prevent tender green growth that cold weather would damage. Reduce watering frequency; the soil stays moist longer in the fall, and soggy conditions can lead to tuber rot.
Watching for the First Frost
The most significant signal for dahlia care is the first hard frost, which turns the foliage black or dark brown. You do not need to dig the tubers immediately. Waiting several days to a week after the first hard frost allows the "eyes" (growth points) to become more visible and lets the plant move final nutrients into the tubers.
Cutting Back the Foliage
Once the foliage has blackened and you have waited a few days, use loppers or a garden saw to cut the stems down to about 4 to 6 inches above the ground. This "handle" makes it easier to lift the tubers and marks their location.
Quick Summary:
- Continue deadheading and cutting flowers to maximize the blooming season.
- Reduce watering and stop fertilizing in early autumn to prepare the plant for dormancy.
- Wait for the first hard frost to blacken the foliage before cutting stems back to 4 to 6 inches.
- Lift tubers in USDA zones 7 and colder to prevent them from freezing.
- Store tubers in a cool, dry place, checking them monthly for signs of rot or shriveling.
Lifting and Digging Dahlia Tubers
In USDA hardiness zones 8 or warmer, you may leave tubers in the ground with thick mulch. In zones 7 and colder, tubers must be lifted and stored indoors.
How to Lift Tubers Safely
The goal is to remove the entire clump without breaking the "necks" where they attach to the main stem. A broken neck usually means the tuber cannot grow next year.
- Clear the Area: Remove mulch or debris from the base.
- Loosen the Soil: Dig with a garden fork about 12 inches away from the center to avoid the wide tuber clump.
- Lift Gently: Pry upward from all sides until the clump is loose.
- Remove by Hand: Reach under the clump to lift. Avoid pulling on the stems.
Cleaning the Tubers
Remove excess soil by shaking the clumps or using a small stick. If you have heavy clay soil, you can wash them with a hose to see the eyes more clearly. If washed, they must dry completely before storage to prevent rot.
What to do next:
- Identify each variety with tied-on tags or waterproof markers.
- Inspect clumps for damage or soft spots.
- Cut away thin, hair-like feeder roots.
- Drain any water trapped in the stem "handle."
Curing and Preparing for Storage
Curing allows the tuber skin to toughen, protecting it from moisture loss during winter.
The Drying Process
Place cleaned tubers in a frost-free, shaded area with good circulation, such as a garage or basement. Lay them upside down (stems pointing down) on newspaper or mesh for 1 to 3 days. The surface should look dull and feel dry, but the tuber should remain firm.
To Divide or Not to Divide?
| Timing | Pros | Cons |
|---|---|---|
| Fall Division | Tubers are softer and easier to cut. | The "eyes" are very difficult to see. |
| Spring Division | Eyes are prominent and easy to identify. | Tubers are tougher and require more effort to cut. |
If you are a beginner, wait until spring to divide your dahlia clumps to ensure each piece has a viable "eye" located on the crown.
Best Practices for Winter Storage
Successful storage requires a cool, dormant state without freezing or rotting.
Ideal Storage Conditions
The target temperature is between 38°F and 45°F.
- Above 50°F: Tubers may sprout too early.
- Below 32°F: Tubers will freeze and turn to mush.
Choosing a Storage Medium
Use a packing medium in a cardboard box or a ventilated plastic bin:
- Coarse Vermiculite: Holds minimal moisture while allowing air exchange.
- Wood Shavings: Breathable and provides insulation.
- Peat Moss: Must be slightly damp, not wet.
- Newspaper: Useful for wrapping individual tubers.
Arrange tubers so they do not touch and cover them with the medium. If using plastic bins, leave the lid cracked for ventilation.
Monthly Check-ins
- If you see rot: Remove the affected tuber immediately. Surface mold can often be brushed off.
- If they are shriveling: Give the storage medium a very light misting with water.
Key Takeaway: Storage should mimic cool, slightly damp soil conditions. Monthly checks are essential to catch moisture issues before they spread.
Safety and Practical Considerations
Toxicity Awareness
Dahlia tubers can be mildly toxic to pets. Store them where dogs or cats cannot reach them. The sap may also cause mild skin irritation; wearing gloves is recommended.
Labeling is Vital
Write the variety name directly on the skin with a permanent marker or use durable tags. This makes garden planning much easier in the spring.
Soil and Weather Variations
Timing depends on your local climate. If your soil is exceptionally wet in the fall, you may want to lift tubers earlier to prevent rot, even if a frost has not occurred yet.
Preparing for Next Spring
When the soil warms to about 60°F, bring your tubers out of storage. The eyes should be visible as small pink or white bumps. You can then divide large clumps, ensuring each piece has at least one eye. For a refresher on varieties, see our Planning Guide for Dahlias.
Conclusion
Caring for dahlias after they bloom protects your investment and ensures your garden continues to thrive.
- Deadhead regularly to keep flowers coming all summer.
- Wait for the first frost before digging tubers.
- Store in a cool, dark place with a moisture-regulating medium.
- Check monthly to prevent rot.
The care you give your plants today is the foundation for a spectacular garden next year. Explore our new varieties at Longfield Gardens to expand your collection.
"Gardening is a journey through the seasons, and the care we give our plants today is the foundation for the beauty we will see tomorrow."
FAQ
When should I stop deadheading my dahlias?
You should continue deadheading as long as the plant is actively producing new buds. Once the first hard frost hits and turns the foliage black, the blooming season is officially over, and you can stop deadheading and prepare to cut the plant back for the winter.
Can I leave my dahlias in the ground if I live in a cold climate?
In regions where the ground freezes (USDA zones 7 and colder), dahlia tubers will likely perish if left in the ground. To ensure they return next year, it is best to lift them after the first frost and store them in a frost-free environment like a basement or garage.
How do I know if my stored dahlia tubers are still good?
Healthy tubers should feel firm to the touch, similar to a fresh potato. If a tuber is mushy, smells bad, or is completely shriveled and brittle, it is likely no longer viable. A small amount of surface mold is usually fine and can be brushed off.
What is the best material to store dahlia tubers in?
Most gardeners find success using coarse vermiculite, wood shavings (pet bedding), or slightly damp peat moss. These materials help maintain a consistent humidity level around the tubers while allowing for the necessary air circulation to prevent rot.
