Introduction
There is nothing quite like the late-summer theater of a dahlia garden. From the massive, pillow-like blooms of dinnerplate dahlias to the intricate, geometric petals of pompons, these plants offer a color palette and scale that few other flowers can match. As the season winds down and the first crisp autumn air arrives, many gardeners ask us the same question: do you have to lift dahlia tubers, or can they stay in the ground until spring?
At Longfield Gardens, we want to help you enjoy these spectacular dahlias year after year without the guesswork. Deciding whether to dig up your tubers depends on several factors, including your local climate, your soil type, and how much effort you want to put into your garden’s winter nap. This guide is designed to help you make the best choice for your specific backyard conditions.
Understanding your hardiness zone and the needs of the dahlia plant is the first step toward a successful bloom season next year.
Understanding the Dahlia's Natural Cycle
Dahlias are native to the high plains of Mexico and Central America. In their natural habitat, they experience warm days and cool, dry winters. They are perennial plants, but they are not built to survive the deep-freezing temperatures found in many parts of the United States.
The dahlia stores its energy in a cluster of starchy roots called tubers. These tubers act like a battery, holding all the nutrients and moisture the plant needs to sprout again when the weather warms up. However, these tubers are approximately 80% water. When the ground freezes, the water inside the tuber expands and turns to ice. This process ruptures the plant's cells, causing the tuber to turn into a mushy, unusable mess once it thaws.
Because of this, the decision to lift is primarily a protection mission. You are essentially "rescuing" the plant from the cold and keeping it in a dormant, protected state until the danger of frost has passed.
The Role of USDA Hardiness Zones
The most important factor in deciding whether to lift your dahlia tubers is your USDA hardiness zone. These zones are based on the average minimum winter temperature in your area.
Zones 8 and Warmer
If you live in USDA Zone 8, 9, 10, or 11, you are in luck. In these regions, the ground rarely freezes deep enough to reach the tubers. Most gardeners in these zones can leave their dahlias in the ground year-round. However, even in these warm areas, a heavy layer of mulch is a smart "insurance policy" to protect the crowns from an unexpected cold snap.
Zones 7 and Colder
For gardeners in Zone 7 and below, the ground typically freezes deep enough to kill dahlia tubers. If you live in a place like Chicago, New York, or Denver, lifting your tubers is a standard part of the autumn gardening routine. While some gardeners in Zone 7 might find success leaving tubers in the ground during a particularly mild winter, it is a gamble. If you have a variety you truly love, we recommend lifting it to be safe.
Key Takeaway: If your winters involve consistently frozen ground (typically Zone 7 and below), lifting your tubers is the only way to ensure they return the following spring.
Soil Drainage and Winter Survival
Temperature isn't the only thing that affects a dahlia's survival; moisture is just as important. In fact, many dahlias that die over the winter in warmer zones are actually victims of rot, not cold.
Dahlias prefer to stay relatively dry during their dormant period. If your garden has heavy clay soil that holds onto water, the tubers are likely to rot if left in the ground during a wet winter. Even in Zone 8, if you have a very rainy winter season and slow-draining soil, you might find that lifting your tubers leads to better results.
If you have sandy or well-draining soil, the tubers have a much higher chance of surviving in the ground. Before you decide to leave them, consider how water moves through your garden. If you see puddles that linger for hours after a rainstorm, that spot is likely too wet for wintering dahlias.
The Benefits of Lifting Dahlia Tubers
While lifting tubers requires a bit of work, there are several reasons why many gardeners choose to do it even if they live in a borderline zone.
Opportunities for Division
One of the most exciting parts of growing dahlias is how much they multiply. A single tuber planted in the spring will often grow into a massive clump of 5 to 20 new tubers by the fall. If you leave these in the ground year after year, the clump becomes overcrowded. Overcrowding leads to smaller flowers and weaker stems because the plants are competing for the same nutrients. By dividing the clump, you can turn one plant into a dozen.
Quality Control
When you lift your tubers, you get a "health check" on your plants. You can see if any tubers have started to rot or if there are signs of pests. This allows you to discard any unhealthy material and only store the best, most vigorous tubers for the next year.
Flexibility in Garden Design
Gardening is an evolving art. Maybe that Thomas Edison variety would look better next to your dahlias.
Or perhaps you want to try a new color scheme altogether with Kelvin Floodlight dahlias. When they are in storage, you are the master of next year's layout.
When Is the Best Time to Lift?
Timing is everything when it comes to lifting dahlias. If you dig them up too early, the tubers may not have had enough time to fully mature and store the energy they need for a long winter sleep.
The best signal to start the process is the first killing frost. This is the frost that turns the lush green foliage of your dahlias to a dark brown or black color. While the top of the plant looks dead, the tubers underground are perfectly fine.
Many experienced gardeners wait about a week or two after this first frost before digging. This short waiting period encourages the plant to go into a deep dormancy and helps the "eyes" (the small bumps where next year's growth will come from) become more visible. However, you must dig them before the ground itself freezes solid.
Steps to Take After the First Frost:
- Cut the stems: Use sharp pruners to cut the stalks down to about 4 to 6 inches above the ground.
- Label your plants: Before you dig, make sure you know which variety is which. It is easy to tell a Cafe au Lait from a Labyrinth when they are blooming, but they all look the same once they are just brown stalks. Use a waterproof tag or write the name directly on the stalk with a marker.
- Let them rest: Some gardeners like to let the cut stalks sit for a few days to "cure," which can help the skin of the tubers toughen up slightly.
How to Lift Dahlias Safely
When you are ready to dig, the goal is to get the entire clump out of the ground without damaging the "necks" of the tubers. The neck is the narrow part where the tuber connects to the main stalk. If the neck is broken or cracked, the tuber usually won't grow.
The Right Tools
A garden fork is generally better than a shovel for this task. A shovel has a sharp edge that can easily slice through a tuber, whereas the tines of a fork can slide around the roots more easily.
The Digging Process
Start by digging a wide circle around the plant. Most dahlia clumps grow outward as well as downward. We recommend starting your fork about 12 inches away from the main stem. Gently pry upward from several sides of the plant to loosen the soil.
Once the clump feels loose, use the remaining stem as a handle to gently lift it out of the earth. Don't worry if a few of the very long, thin feeder roots break off; the plant doesn't need those for storage.
Key Takeaway: Treat your dahlia clumps like a box of eggs. They are surprisingly heavy but quite fragile at the "neck" where the growth happens.
Preparing Tubers for Storage
Once the dahlia tubers are out of the ground, they need a little bit of spa treatment before they go into the dark for the winter.
Cleaning the Tubers
Gently shake off the loose soil. You can use your hands or a small wooden stick to poke away clumps of dirt from the center of the root mass. Some gardeners prefer to wash their tubers with a garden hose to get them perfectly clean. This makes it easier to see the "eyes" and any potential rot. If you do wash them, it is vital that you let them dry completely before moving to the next step.
The Drying (Curing) Phase
Lay your tubers out in a frost-free, shaded area with good air circulation. A garage or a covered porch works well. Let them dry for 24 to 48 hours. You want the outside skin to feel dry and the remaining soil to be powdery. Do not leave them in direct sunlight, as this can cause the tubers to shrivel.
To Divide or Not to Divide?
You can divide your dahlia clumps in the fall or in the spring.
- Fall Division: The tubers are softer and easier to cut, but the "eyes" can be harder to see.
- Spring Division: The "eyes" are very prominent and easy to spot, but the tubers are much tougher and harder to cut.
If you are a beginner, we often suggest waiting until spring to divide so you can clearly see where the new growth will emerge.
Best Practices for Winter Storage
The goal of winter storage is to keep the tubers in a "Goldilocks" environment: not too cold, not too warm, not too wet, and not too dry.
The Ideal Temperature
The perfect storage temperature is between 40°F and 50°F. If it gets much colder, they might freeze. If it gets much warmer, they might start to sprout prematurely or dry out too quickly. An unheated basement, a root cellar, or an insulated crawl space is usually the best spot.
Choosing a Storage Medium
To prevent the tubers from shriveling, you need to surround them with a material that regulates moisture. Common choices include:
- Peat moss: Excellent at holding a tiny bit of moisture while remaining airy.
- Vermiculite: A sterile mineral that works very well for keeping tubers plump.
- Wood shavings: Often used for animal bedding, these provide good airflow.
- Newspaper: Wrapping tubers individually in newspaper is a low-cost method that works well in humid basements.
The Packing Process
Use a breathable container like a cardboard box, a plastic bin with holes drilled in the sides, or a wooden crate. Place a layer of your storage medium at the bottom, then lay the tubers in so they aren't touching each other. Cover them with more medium and repeat the process.
Key Takeaway: Storing tubers so they don't touch is an important safety measure. If one tuber starts to rot, the dry medium between them will act as a firebreak, preventing the rot from spreading to the rest of the collection.
Monitoring Your Tubers During Winter
Your job isn't quite finished once the boxes are tucked away. We recommend checking on your tubers about once a month throughout the winter.
If you notice a tuber feels soft or mushy, or if it has a fuzzy mold growing on it, remove it immediately and throw it away. This protects the rest of the box.
If the tubers look shriveled and wrinkled like a prune, they are getting too dry. Give the storage medium a very light misting of water with a spray bottle. You don't want it to be wet—just a tiny bit of humidity is enough to perk them back up.
What to Do If You Decide to Leave Them in the Ground
If you live in Zone 8 or warmer, or if you simply want to take a chance in Zone 7, you can prepare your dahlias for an "in-ground" winter. This is often referred to as winterizing.
The Mulching Method
Once the foliage has died back and you have cut the stalks down to the ground, you need to provide an insulating blanket.
- Clear the area: Remove any fallen leaves or debris that might harbor pests.
- Apply a heavy mulch: Cover the crown of the plant with 4 to 6 inches of mulch. You can use wood chips, straw, shredded bark, or even a mound of well-drained compost.
- Cover with a dome: Some gardeners place an upside-down bucket or a piece of heavy plastic over the mulch to keep the area dry during winter rains. Just make sure there is still some air movement so the soil doesn't become stagnant.
Mark the Spot
It is incredibly easy to forget where a dahlia was planted once the ground is bare in January. Use a sturdy garden stake to mark the location so you don't accidentally dig it up or plant something else on top of it in the spring.
Moving Toward a Successful Spring
Whether you choose to lift your tubers or leave them in the earth, the goal is the same: a spectacular show of flowers next summer. Lifting tubers is one of those gardening tasks that can feel like a lot of work the first time you do it, but it quickly becomes a rewarding ritual. There is a deep satisfaction in "putting the garden to bed" and knowing that your favorite plants are safe and sound.
At Longfield Gardens, we have spent years trialing different dahlia varieties and storage methods. We know that every garden is a little bit different. Your soil, your local weather, and even the microclimates near your house all play a role in what works best. Don't be afraid to experiment! Maybe you lift half of your tubers and leave the other half to see what happens.
If things don't go perfectly, don't worry. Gardening is a constant learning process. We stand behind our plants with a 100% quality guarantee, and we are always here to help you troubleshoot or plan your next garden masterpiece.
Next Steps: As spring approaches, keep an eye on your storage boxes. When you see tiny green sprouts beginning to poke out from the eyes of your tubers, it’s time to start thinking about your planting layout for the new season!
FAQ
Can I leave my dahlias in pots over the winter?
It is possible, but it is often riskier than leaving them in the ground. Because the soil in a pot is elevated, it is exposed to the cold from all sides and will freeze much faster than the ground. If you want to keep them in pots, move the entire container into a frost-free garage or basement and keep the soil almost completely dry until spring.
What happens if I don't lift my dahlias in Zone 5 or 6?
In these colder zones, the tubers will almost certainly freeze and die. By springtime, you will likely find that the tubers have decomposed and turned into a watery, dark substance. To have dahlias in these zones next year, you must either lift the tubers or buy new ones to plant in the spring.
Do I need to treat my tubers with fungicide before storage?
While not strictly necessary for home gardeners, some people like to dust their tubers with sulfur powder or a garden fungicide to prevent rot. If you have had issues with rot in the past, or if your storage area is particularly damp, this can be a helpful preventative step. However, ensuring the tubers are dry and stored in a breathable medium is usually sufficient.
How do I know if a tuber is still alive in the spring?
Healthy tubers should feel firm, similar to a potato. If you see a "bud" or a small green sprout (the "eye") near the neck, the tuber is definitely alive. If a tuber is hollow, papery, or completely mushy, it has likely not survived the winter and should be discarded before planting.
