Introduction
As the late summer sun begins to dip lower in the sky, dahlias often take center stage in the garden. These spectacular bloomers are famous for their productivity, offering a parade of color that lasts far longer than many other perennials. At Longfield Gardens, we know that the end of the flowering season isn't just a finish line; it’s an opportunity to set the stage for an even more beautiful display next year.
Whether you are enjoying your very first dahlia season or you have been growing these beauties for years, knowing how to handle the plants after they bloom is the secret to healthy tubers and repeat success. This guide covers everything from deadheading to winter storage, designed to help home gardeners navigate the transition from autumn flowers to winter dormancy. By following a few simple steps, you can ensure your favorite varieties return with even more vigor next spring.
Learning what to do after dahlias bloom will help you maximize your current harvest and protect your plants during the cold months ahead.
Maximizing Late-Season Blooms with Deadheading
Long before the first frost arrives, your dahlias will begin the natural process of finishing their individual blooms. To keep the plant focused on producing new flowers rather than setting seeds, you should practice regular deadheading. Deadheading is simply the process of removing spent or faded flowers.
For dahlias, deadheading can be a bit of a puzzle because the spent flower heads look remarkably similar to new buds. If you accidentally snip off a new bud, don’t worry—the plant is resilient—but you can avoid this by looking closely at the shape of the head.
How to Tell a Bud from a Spent Flower
- New Buds: These are typically round, firm, and compact. They look like tight little balls of color waiting to explode.
- Spent Flowers: Once the petals fall away, the remaining head becomes more pointed or conical in shape.
- The Squeeze Test: If you aren't sure, gently squeeze the head. A new bud feels hard and solid, while a spent flower head often feels squishy or hollow.
When you are ready to cut, follow the stem down to the next set of leaves or a side bud and make a clean snip. This keeps the plant looking tidy and prevents long, leafless "sticks" from poking out of your garden bed.
Key Takeaway: Regular deadheading signals the plant to keep producing flowers, extending your dahlia season right up until the first frost.
Watching for the First Frost
Dahlias will continue to bloom enthusiastically until the weather takes a sharp turn. In most regions, the official end of the blooming season is marked by the first "killing frost." This is when temperatures drop low enough to freeze the water inside the plant's cells.
You will know the frost has arrived when you look out at your garden and see the once-vibrant green foliage turned black or dark brown. While it might look a bit sad at first, this is actually a vital part of the dahlia life cycle. This sudden change tells the plant to stop sending energy to the leaves and flowers and instead pull all its remaining resources down into the tubers underground.
We recommend waiting a few days—or even up to two weeks—after the foliage turns black before you begin the next step. This brief waiting period allows the tubers to "cure" slightly in the ground and helps them toughen up for winter storage. For more detail, see this guide to when to dig dahlia tubers for winter storage.
What to do next:
- Monitor local weather reports for "Frost Advisories" or "Freeze Warnings."
- Enjoy the final blooms by cutting them for indoor bouquets before the frost hits.
- Check that your garden labels are still in place so you know which variety is which once the foliage is gone.
Cutting Back Dahlias for Winter
Once the frost has blackened the leaves and you’ve given the tubers a few days to settle, it’s time to cut the plants back. This step makes the garden look neat and prepares the tubers for lifting.
Using a sharp pair of bypass pruners or garden loppers, cut the main stems down so only about 4 to 6 inches of the stalk remains above the soil line. These short "stumps" will serve as convenient handles when it comes time to lift the tubers from the ground.
It is a good idea to clear away and compost (or discard) the blackened foliage. Leaving dead plant material on top of the soil can sometimes invite pests or diseases to linger over the winter. By clearing the area, you create a clean workspace for the digging process.
Deciding Whether to Lift or Mulch
In the United States, dahlia care over the winter depends largely on your USDA hardiness zone. Dahlias are generally considered hardy in zones 8 through 11. If you live in these warmer regions, you may be able to leave your tubers in the ground all year round.
Leaving Dahlias in the Ground
If you live in a warm climate, you can simply cut the plants back and cover the area with a thick layer of mulch, such as straw or wood chips. This protects the tubers from occasional cold snaps and keeps the soil moisture consistent.
Lifting Dahlias for Winter
For gardeners in zones 7 and colder, the ground will likely freeze deep enough to damage or kill the tubers. In these areas, lifting and storing the tubers indoors is the best way to ensure they survive. Even in zone 8, some gardeners choose to lift their tubers every couple of years to divide them and prevent the clumps from becoming too crowded.
Key Takeaway: If your soil freezes solid in the winter, you should plan to lift and store your dahlia tubers in a frost-free environment.
How to Dig and Lift Dahlia Tubers
Lifting dahlia tubers is a rewarding task that feels like a treasure hunt. Because the tuber clumps grow significantly during the summer, you might be surprised at how much larger they are than when you first planted them.
To lift the tubers without damaging them, we recommend using a sturdy garden fork rather than a shovel. A fork allows you to loosen the soil without the risk of slicing through the tubers.
- Find the Perimeter: Start by placing your garden fork about 12 inches away from the center stem.
- Loosen the Soil: Gently push the fork into the ground and pry upward. Move around the plant in a circle, loosening the soil from all sides.
- Lift Carefully: Once the soil is loose, use the fork to gently lift the entire clump out of the ground. You can use the 4-inch stem stump as a handle to help guide the clump out.
- Shake Off Excess Soil: Gently shake the clump or use your hands to brush away large chunks of dirt. Avoid banging the tubers against hard surfaces, as they can bruise or break.
Curing and Cleaning Your Tubers
Before you put your dahlias away for their winter nap, they need to be cleaned and "cured." Curing is simply a fancy word for letting the tubers dry out slightly so they don't rot in storage.
Some gardeners prefer to wash their tubers with a garden hose to remove all the soil. If you do this, be very gentle and make sure the tubers have plenty of time to dry completely afterward. Other gardeners prefer to let the soil dry and then brush it off. Either method works well as long as the tubers aren't soaking wet when they go into storage.
Place your cleaned tubers in a cool, dry, and airy spot—like a garage or a covered porch—for 1 to 3 days. They should be protected from frost during this time. The goal is for the outer skin to feel dry to the touch, which helps prevent mold and fungus from growing during the winter months.
Steps for a Successful Cure:
- Keep tubers out of direct sunlight while drying.
- Ensure good airflow around the clumps.
- Inspect each clump for signs of damage or soft spots and trim away any "rotten" bits with a clean knife.
Dividing Dahlia Tubers
Once the tubers are clean, you may notice small bumps near the "neck" of the tuber, where it meets the old stem. These are called "eyes," and they are where next year’s growth will come from.
Many gardeners choose to divide their dahlia clumps after lifting them. Dividing allows you to turn one large clump into several smaller plants, which is an easy way to expand your garden for free. However, if you are a beginner, it is perfectly fine to store the entire clump whole and wait until spring to divide it. By spring, the "eyes" are much easier to see.
If you do choose to divide now, ensure each piece you cut has at least one "eye" and a solid tuber attached. Use a clean, sharp knife and wipe it with rubbing alcohol between plants to prevent the spread of any garden diseases.
Safe Storage for Winter Dormancy
The most important part of dahlia care after they bloom is the storage environment. You want to keep the tubers in a "Goldilocks" zone: not too cold (which would freeze them), not too warm (which would make them sprout or shrivel), and not too wet (which would cause rot).
The Ideal Storage Environment
- Temperature: Between 38°F and 45°F is perfect. A frost-free garage, a cool basement, or an unheated crawl space usually fits the bill.
- Humidity: Aim for 75% to 85% relative humidity. If the air is too dry, the tubers will shrivel like old carrots.
Choosing a Storage Medium
To maintain the right moisture balance, we recommend packing the tubers in a storage medium. Common choices include:
- Vermiculite: Excellent for holding just the right amount of moisture.
- Peat-free compost or potting soil: Make sure it is slightly damp, but not wet.
- Wood shavings: Often used for animal bedding, these are affordable and effective.
- Cardboard boxes or plastic bins: You can use these to hold your medium. If using plastic bins, leave the lid slightly cracked to allow for some air exchange.
Place a layer of your chosen medium in the bottom of the container, nestle the tubers inside so they aren't touching each other, and cover them completely. This prevents rot from spreading if one tuber happens to go bad.
Monthly Winter Maintenance
Dahlias aren't quite "set it and forget it" during the winter. We suggest checking on your stored tubers about once a month. This quick check takes only a few minutes but can save your entire collection.
When you open your storage bins, look for two things: shriveling and rot.
- If the tubers look shriveled: They are losing too much moisture. Give the storage medium a very light misting with water to increase the humidity.
- If you see fuzzy mold or soft spots: This is a sign of rot. Immediately remove any affected tubers so the rot doesn't spread to the healthy ones. If the rot is only on a small tip, you can often cut it off with a clean knife and let the cut end dry before placing it back in storage.
By keeping a close eye on your tubers, you ensure they stay plump and healthy until it’s time to plant them again in the spring. For additional guidance, read how to overwinter dahlias.
Conclusion
Taking care of your dahlias after they bloom is one of the most rewarding parts of the gardening cycle. While the vibrant colors of summer may have faded, the work you do in the fall ensures that those same beautiful flowers—and often many more—will return to brighten your yard next season. From the simple act of deadheading to the careful storage of tubers, each step is a move toward a more successful garden.
At Longfield Gardens, we believe that gardening should be a source of joy and relaxation. Don't feel pressured to get every detail perfect in your first year. Gardening is a journey of observation and learning, and dahlias are incredibly forgiving plants. With a little bit of protection from the winter cold, your tubers will be ready to sprout and grow as soon as the spring soil warms up again.
- Keep deadheading until the first frost to maximize your flower harvest.
- Wait for the foliage to turn black before lifting tubers to ensure they are mature.
- Store tubers in a cool, dark, frost-free place with a moisture-balancing medium.
Success with dahlias is all about working with the seasons; once the flowers fade, simply give the tubers the protection they need to rest and recharge for next year.
For more inspiration and to find new varieties for your collection, feel free to explore our selection of premium dahlia tubers at Longfield Gardens when you're ready to plan your next spring planting.
FAQ
How long can I leave dahlias in the ground after the first frost?
It is best to leave them for about 3 to 14 days after the foliage turns black. This short window allows the tubers to finish maturing and prepare for dormancy without risking a deep ground freeze that could cause damage. See our guide to cutting dahlias back for winter for additional timing advice.
Do I have to wash the dirt off the tubers before storing them?
No, washing is optional. You can simply shake off the loose soil and let the rest dry, then brush it away. If you do choose to wash them, ensure they are completely dry before you pack them away in storage to prevent mold.
Can I store my dahlias in the refrigerator?
While the temperature of a refrigerator is often in the right range, the air inside is usually very dry, which can cause tubers to shrivel quickly. If you use a fridge, you must check them frequently and ensure they are packed in a moisture-retaining medium like damp vermiculite.
What happens if I don't dig up my dahlias in a cold climate?
In regions where the ground freezes (Zone 7 and colder), the water inside the dahlia tubers will freeze and expand, turning the tuber into a mushy, non-viable clump. To keep your favorite varieties alive in these areas, lifting and storing them indoors is necessary. For a closer look at cold tolerance, read how cold dahlias can tolerate.
