Introduction
The late summer garden is often at its most vibrant when dahlias are in full swing. These spectacular flowers offer a color palette and variety of shapes that few other plants can match, providing armloads of blooms for indoor bouquets. As the season begins to shift toward autumn, you may find yourself wondering how to transition these garden stars from their peak performance into their next phase of life.
At Longfield Gardens, we believe that the end of the blooming season is just the beginning of a rewarding cycle that keeps your garden beautiful year after year. Whether you are growing dinnerplate dahlias for their size or petite pompon varieties for their charm, knowing how to handle the plants after the flowers fade is the key to a successful return next spring.
This guide will walk you through the essential steps for dahlia care once the flowering window begins to close. We will cover how to extend the blooming period through the first frost, the correct way to handle foliage, and the simple steps for lifting and storing your tubers for the winter.
By following a few straightforward steps, you can ensure your plants stay healthy and ready for another spectacular show next year.
Extending the Season with Deadheading
The most important thing to do with dahlias immediately after they bloom is to encourage them to bloom again. Dahlias are prolific producers, and they will continue to send up new buds as long as the weather stays mild and you remove the old flowers. This process is called deadheading, and it tells the plant to keep putting its energy into flowers rather than producing seeds.
One of the most common questions gardeners have is how to tell the difference between a new bud and a spent flower head. At first glance, they can look quite similar, but there are two easy ways to tell them apart.
Identifying Buds vs. Spent Heads
A new dahlia bud is almost perfectly round, like a small marble. It will feel firm to the touch when you give it a gentle squeeze. As the bud develops, you might even see the compressed petals beginning to show through the green casing.
In contrast, a spent flower head—one that has already bloomed and lost its petals—is usually more conical or pointed in shape. If you squeeze it, it will feel squishy or soft rather than firm. If you see a pointed, soft head on the plant, it is time to remove it.
Where to Make the Cut
When you are ready to remove a spent bloom, do not simply snip the head off at the top. This leaves a bare, unsightly stem that will eventually turn brown. Instead, follow the stem down to the first or second set of healthy leaves.
Make your cut just above where the flower stem intersects with the leaves. This keeps the plant looking tidy and encourages the dahlia to branch out, which often results in even more flowers. Using a sharp pair of garden scissors or bypass pruners ensures a clean cut that heals quickly.
Key Takeaway: Regular deadheading keeps dahlias blooming longer. Look for pointed, squishy heads to remove and keep the round, firm buds to enjoy later.
Preparing for the First Frost
As autumn progresses, you will notice the growth of your dahlias slowing down. The nights get cooler, and the plants may not produce flowers as quickly as they did in July. This is a natural part of the plant's life cycle. During this time, you should continue to water them if the soil is dry, but you can stop any regular fertilizing.
The "finish line" for dahlia blooms is the first hard frost. A light frost might nip the top leaves, but a hard frost will turn the entire plant black or dark brown almost overnight. While this might look a bit sad at first, it is actually a helpful signal from nature.
Why Wait for the Frost?
It is best to leave your dahlias in the ground until the frost arrives. When the foliage dies back, the plant stops growing upward and starts focusing all its energy on the tubers underground. These tubers are the starchy, root-like structures that store energy for next year.
Allowing the plant to stand for a few days (or even up to two weeks) after the frost helps the tubers "cure" slightly while still in the soil. This short waiting period can make the tubers more resilient during winter storage. For additional guidance, see this guide to when to store dahlia tubers.
What to Do Next
- Monitor local weather reports for frost warnings.
- Keep deadheading until the plant is hit by frost to enjoy every last bloom.
- Gather your tools, including a garden fork and labels, so you are ready when the time comes.
Cutting Back the Foliage
Once the frost has turned the foliage black, the next step is to remove the top growth. This is a simple task, but doing it correctly helps protect the health of the tubers.
Use a sharp pair of pruners or a garden saw to cut the main stems. You want to leave about 3 to 6 inches of the stem protruding above the soil line. This remaining stem serves as a handle when you eventually lift the tubers, and it also helps you keep track of where each plant is located in the garden bed.
After cutting the foliage, it is a good idea to remove the old leaves and stems from your garden area. Compost them if they are healthy, or dispose of them if you noticed any powdery mildew or pest issues during the summer. Cleaning up the area helps prevent diseases from overwintering in the soil.
Lifting the Dahlias
If you live in a region where the ground freezes (typically USDA zones 7 and colder), you will need to lift your dahlia tubers and store them indoors. If you leave them in frozen soil, the water inside the tubers will freeze, causing the cells to burst and the tuber to rot. Learn more about overwintering dahlias.
Using the Right Tools
The best tool for lifting dahlias is a garden fork. Shovels and spades can work, but they have a solid blade that is more likely to accidentally slice through a tuber. A garden fork allows you to loosen the soil around the plant with less risk of damage.
The Lifting Process
To lift the tubers safely, start by inserting your garden fork into the soil about 12 inches away from the main stem. You want to avoid the "crown" of the plant, which is where the tubers meet the stem.
Gently pry upward to loosen the soil, then move the fork to the opposite side of the plant and repeat the process. Work your way around the plant in a circle until the entire clump of tubers feels loose. Once the soil is loose, you can gently lift the clump out of the ground by the stem handle you left behind.
Key Takeaway: Always lift dahlias by working in a wide circle around the plant. This protects the delicate "necks" of the tubers from breaking.
Cleaning and Curing Tubers
Once the tubers are out of the ground, they will likely be covered in garden soil. Before they can go into storage, they need to be cleaned and dried. This stage is often called "curing," and it is essential for preventing rot and mold.
Removing Soil
Gently shake the clump to remove large chunks of dirt. You can also use your hands or a soft brush to brush away loose soil. Some gardeners prefer to wash their tubers with a garden hose to get them completely clean. This makes it much easier to see the "eyes" if you plan on dividing them later.
If you do wash them with water, make sure you do it on a sunny or breezy day so the tubers can dry quickly. Leaving wet tubers in a pile can lead to fungal issues.
The Drying Phase
Find a cool, dry place out of direct sunlight—such as a garage, shed, or covered porch—to let the tubers dry. Lay them out in a single layer, perhaps on top of some newspaper or cardboard.
The goal is to let the outer skin of the tuber dry out and toughen up slightly. This usually takes between one and three days. You do not want to leave them out so long that the tubers begin to shrivel or look like wrinkled raisins. They should still feel firm, like a fresh potato.
For more detailed instructions, read how to store dahlia bulbs over winter.
What to Do Next
- Gently remove soil from the lifted clumps.
- Check for any damaged or rotten tubers and trim them off with clean pruners.
- Label each clump immediately with a permanent marker or a tag so you don't forget which variety is which.
Dividing Your Dahlias
Dividing your dahlias is an optional step, but it is a great way to increase your flower collection for free. Each year, a single dahlia tuber grows into a larger clump. If you divide that clump, you can turn one plant into three, four, or even more.
When to Divide
You can divide your dahlias in the fall right after lifting them, or in the spring before planting. Fall division is often easier because the tubers are softer and easier to cut. However, many gardeners wait until spring because the "eyes" are much easier to see once the tubers begin to wake up.
Finding the Eye
An "eye" is a small bump or growth point located on the crown of the tuber, near where it connects to the main stem. This is where the new sprout will emerge next year. For a tuber to grow into a successful plant, it must have at least one healthy eye.
If a tuber breaks off without any part of the crown attached, it will not have an eye and will not grow, even if the tuber itself looks healthy.
Making the Cut
Use a clean, sharp knife or garden pruners to separate the tubers. Ensure that each piece you cut away has a portion of the crown and at least one eye. We find that a good rule of thumb is to leave at least a small section of the crown—about the size of half a dime—attached to each tuber.
To prevent the spread of garden diseases, it is helpful to dip your cutting tool in a solution of rubbing alcohol or a mild bleach solution between different plants.
Winter Storage Methods
The biggest challenge in keeping dahlias over the winter is finding the right balance of moisture. If the storage area is too wet, the tubers will rot. If it is too dry, they will shrivel up and die.
The Ideal Environment
The perfect storage spot is cool, dark, and slightly humid. You are looking for a temperature between 38°F and 45°F. This is cold enough to keep the plants dormant (sleeping) but warm enough to prevent freezing. For more guidance, see what temperature to store dahlia tubers.
Many people find that an unheated basement, a root cellar, or an insulated garage works well.
Choosing a Storage Medium
You should not store tubers completely exposed to the air, as they will lose moisture too fast. Instead, tuck them into a container filled with a storage medium. Common choices include:
- Vermiculite: This is a mineral that holds onto a bit of moisture and provides excellent insulation.
- Peat Moss: A classic choice that is easy to find, though it can be quite dusty.
- Pine Shavings: Often sold as animal bedding, these are affordable and provide good airflow.
- Perlite: Similar to vermiculite, this helps regulate moisture levels.
Place a layer of your chosen material in the bottom of a cardboard box, plastic bin, or paper bag. Lay the tubers on top, then cover them with more material. If you use plastic bins, keep the lids slightly ajar or drill a few small holes in the sides to allow for air circulation.
For additional advice, read this guide to storing dahlia tubers.
The Plastic Wrap Method
An alternative method used by some gardeners involves wrapping individual, cleaned tubers tightly in plastic kitchen wrap. This seals the moisture inside the tuber itself. If you try this, make sure the tubers are completely clean and dry before wrapping to prevent trapping soil-borne bacteria.
Key Takeaway: Storage is all about balance. Aim for a "Goldilocks" environment—not too cold, not too warm, and just enough humidity to keep the tubers firm.
Monitoring Your Tubers Mid-Winter
What you do with dahlias after they bloom doesn't end once they are in the box. It is a good idea to check on your stored tubers once a month during the winter. This allows you to catch any potential problems before they ruin the entire batch.
Handling Rot
If you find a tuber that feels soft or mushy, or one that has fuzzy mold growing on it, remove it immediately. If only a small part of a tuber is rotten, you can often cut that section away with a clean knife and let the cut end dry out before returning the rest to storage.
Handling Dehydration
If the tubers look shriveled or feel very light, they are losing too much moisture. You can lightly mist the storage medium with a spray bottle of water to add a touch of humidity. Be careful not to make the material soaking wet; a very light mist is usually enough.
Overwintering Dahlias in the Ground
If you are lucky enough to live in USDA zones 8 through 11, you may not need to lift your dahlias at all. In these warmer climates, the ground does not freeze deep enough to kill the tubers.
Preparing the Bed
Even in warm areas, a bit of winter protection is a good idea. After cutting the foliage back to the ground, cover the dahlia bed with a thick layer of mulch. Use 4 to 6 inches of straw, wood chips, or shredded leaves. This acts as a blanket, keeping the soil temperature consistent and protecting the tubers from heavy winter rains.
Drainage Matters
The biggest threat to dahlias left in the ground isn't the cold; it's the wet. If your soil doesn't have good drainage—meaning water stays in the soil for a long time after a rain—the tubers are likely to rot in the winter. "Drainage" simply refers to how fast water leaves the soil. If you have heavy clay soil, you may still want to lift your tubers even in a warm zone to keep them dry until spring.
Summary of After-Bloom Care
Managing dahlias after they bloom is a process that rewards patience and attention to detail. By transitioning the plants through deadheading, frost, and eventually into a stable storage environment, you are protecting your investment in your garden's beauty.
Most gardening success comes from getting these few basics right. You don't need fancy equipment or a professional greenhouse to keep your dahlias healthy. A simple garden fork, some cardboard boxes, and a cool corner of the basement are often all you need to ensure a repeat performance.
The cycle of the seasons is part of what makes gardening so enjoyable. As your dahlias go to sleep for the winter, you can spend the colder months planning where their colorful faces will shine in your garden next summer.
Action Steps for Success
- September/October: Continue deadheading to maximize the bloom season.
- After First Frost: Cut stalks to 4-6 inches and wait a few days before lifting.
- Lifting: Use a garden fork to gently remove tuber clumps from the soil.
- Storage: Clean, dry, and pack tubers in a cool, dark place (38-45°F).
"The work you do in the autumn ensures the beauty of the spring. Taking the time to properly store your dahlia tubers is an act of optimism for next year's garden."
At Longfield Gardens, we want every gardener to feel confident in their ability to grow and maintain these stunning plants. By following these simple steps for after-bloom care, you can enjoy the satisfaction of seeing your favorite dahlias return bigger and better year after year.
FAQ
How soon after the flowers fade should I deadhead my dahlias?
You should deadhead as soon as you notice the flower petals beginning to wilt or drop. Removing the spent blooms quickly prevents the plant from starting seed production and keeps its energy focused on producing new flower buds. Checking your plants once or twice a week is usually sufficient to keep them looking their best.
Can I leave my dahlias in the ground if I live in a cold climate?
In regions where the ground freezes (Zone 7 and colder), leaving dahlias in the ground usually results in the tubers rotting and dying. While a very mild winter or a heavily protected microclimate might occasionally allow them to survive, it is much safer to lift and store them indoors. The effort of digging them up is small compared to the reward of saving your favorite varieties. If you are unsure of your region, check the Hardiness Zone Map.
Do I have to wash the soil off the tubers before storing them?
While it isn't strictly mandatory to wash them, cleaning the tubers makes it much easier to inspect them for damage, rot, or pests. It also makes the "eyes" visible if you intend to divide the clumps. If you choose not to wash them, at least brush off as much loose soil as possible to prevent excess moisture from being trapped against the tubers in storage.
What should I do if my stored tubers start to sprout in February?
If your tubers start to sprout early, it usually means the storage temperature is a bit too warm. Move them to a slightly cooler spot if possible. If the sprouts are small, you can simply leave them alone until planting time. If they become very long and spindly, you can carefully snip them off, and the tuber will usually produce a new, stronger sprout once it is planted in warm soil in the spring.
