Introduction
There is nothing quite like the feeling of seeing your first dinnerplate dahlia unfurl its petals in late summer. These magnificent flowers are the stars of the garden, offering a variety of colors and shapes that feel almost too beautiful to be real. Many gardeners find themselves so enamored with these blooms that they immediately wonder if they can enjoy them again next year. At Longfield Gardens, we believe that every gardener should have the chance to see their favorite varieties return season after season.
The short answer is that dahlias can indeed come back, but the way they return depends heavily on where you live and how you care for them. While they are often treated as annuals in many parts of the United States, they are technically tender perennials. This means they have the potential to live for many years if they are protected from freezing temperatures.
This guide will help you understand the simple steps needed to ensure your dahlias have a successful winter. Whether you live in a warm climate where they can stay in the ground or a cooler region where they need a little extra help, we have the practical advice you need. The key to success is matching your winter care to your local environment.
Understanding Dahlia Tubers and Hardiness
To understand if your dahlias will come back, it helps to know a little bit about how the plant grows. Although many people refer to them as "dahlia bulbs," they actually grow from underground structures called tubers. These tubers look a bit like a bunch of sweet potatoes or carrots clustered together. They act as a storage tank, holding all the energy the plant needs to sprout and bloom the following year.
In their native environment of Mexico and Central America, dahlias grow as perennials. They sprout when the rains come and go dormant during the dry season. In the United States, their "dry season" is our winter. Because they evolved in a warm climate, these tubers are full of water and are very sensitive to freezing. If the water inside the tuber freezes, it turns to mush, and the plant will not return.
Whether a dahlia is considered a perennial or an annual in your yard depends on your USDA hardiness zone. This is a standard way of measuring how cold your winters typically get. Knowing your zone is the most important piece of information for deciding how to handle your plants in the fall.
Key Takeaway: Dahlias are tender perennials that grow from tubers. They can return every year if the tubers are protected from freezing temperatures and excess moisture during their dormant period.
The Role of USDA Hardiness Zones
Your local weather is the primary factor in determining how your dahlias will behave. In the United States, gardeners generally fall into two categories when it comes to dahlia care.
Warm Climates (Zones 8 and Higher)
If you live in USDA zones 8, 9, or 10, your dahlias are very likely to come back on their own. In these regions, the ground rarely freezes deep enough to reach the tubers. You can usually leave the tubers right where they are. With a little bit of mulch for insulation, they will rest through the winter and begin growing again once the soil warms up in the spring.
Cool Climates (Zones 7 and Lower)
For gardeners in zones 3 through 7, the winter air and soil temperatures often drop well below freezing. In these areas, dahlias will not survive the winter if left unprotected in the garden. To see them again, you have two choices: you can treat them as annuals and buy fresh tubers each spring, or you can dig up the tubers and store them indoors.
Some gardeners in zone 7 find success by using heavy layers of mulch and planting in very well-drained soil, but digging them up is the only way to be certain they will survive.
Helping Dahlias Return in Warm Climates
If you are lucky enough to live in a warm region, your fall garden tasks are quite simple. You don't need to dig up your plants, but a little bit of preparation will help ensure they return healthy and strong.
First, wait for the plant to start slowing down in late autumn. You will notice the foliage beginning to yellow or fade. Once the plant has finished blooming and the weather cools, you can cut the stems down. Leave about three to four inches of the stem visible above the soil line so you don't lose track of where the plant is located.
The biggest threat to dahlias in warm climates isn't usually the cold—it’s the wet. If your winters are very rainy, the tubers can sit in cold, soggy soil and rot. To prevent this, make sure your dahlias are planted in a spot with excellent drainage.
Steps for over-wintering in the ground:
- Cut stems down to 4 inches after the first light frost or in late fall.
- Clear away any fallen leaves or debris from around the base of the plant to prevent pests.
- Apply a 4-to-6-inch layer of bark mulch, straw, or pine needles over the top of the plant.
- Avoid extra watering during the winter months while the plant is dormant.
Saving Dahlias in Colder Climates
For those of us in the North, the process of bringing dahlias back requires a bit more hands-on care. Digging up tubers is a rewarding ritual that allows you to multiply your collection over time. Because the tubers grow and expand during the summer, one tuber planted in May often becomes a large clump by October.
The process begins after the first "killing frost." This is the frost that turns the green leaves of your dahlia to black or brown. While it might look a bit sad, this is actually a good thing. The cold signals to the plant that it is time to go to sleep and move all its energy down into the tubers.
It is often helpful to wait about a week after this first frost before you start digging. This short wait helps the eyes (the sprouts for next year) become more visible and allows the skin of the tuber to "cure" or toughen up slightly.
What to do next: Before the first frost hits, make sure you have labeled your plants. Once the foliage turns black, it is impossible to tell a "Cafe au Lait" from a "Sweet Fabienne." Use waterproof tags or survey tape tied to the base of the stem.
Step-by-Step: Digging and Storing Your Tubers
Digging up your dahlias is a straightforward process that only takes a few minutes per plant. You will need a sturdy shovel or a garden fork and a pair of loppers or hand pruners.
1. Cutting Back
Start by cutting the stalks down to about 4 inches above the ground. This gives you a "handle" to hold onto while you work, but keeps the bulk of the plant out of your way. Be careful not to tug on the stems, as the connection between the stem and the tuber is very fragile.
2. Lifting the Clump
Position your shovel or fork about 12 inches away from the center of the plant. You want to avoid slicing into the tubers. Gently push the tool deep into the soil and pry upward. Work your way around the plant in a circle, loosening the soil from all sides. Slowly lift the entire root ball out of the ground.
3. Cleaning and Drying
Shake off the excess soil. You can use your hands or a small tool to gently remove large clumps of dirt. Some gardeners like to wash their tubers with a hose, while others prefer to leave a little soil on them for protection. If you do wash them, make sure they dry completely before moving to the next step.
Place the tubers in a frost-free, shaded area like a garage or shed for a day or two. This "curing" period allows any surface moisture to evaporate. If you store them while they are soaking wet, they will likely rot.
4. Preparing for Storage
Once the tubers are dry to the touch, you can prepare them for their winter nap. You want to create an environment that is cool, dark, and slightly humid. The goal is to keep the tubers from drying out completely without letting them get so wet that they mold.
Common storage mediums include:
- Peat moss: Excellent for holding just enough moisture.
- Vermiculite: A clean, lightweight mineral that helps regulate humidity.
- Wood shavings: Simple and effective, often found at pet supply stores.
- Cardboard boxes or plastic bins: These hold the storage medium and the tubers.
At Longfield Gardens, we suggest checking your tubers once a month during the winter. This simple habit allows you to catch any issues early and ensures your dahlias come back beautifully in the spring.
Winter Care: Maintaining Stored Tubers
Storing tubers isn't a "set it and forget it" task. Throughout the winter, the tubers are still alive; they are just resting. The ideal temperature for storage is between 40°F and 50°F. An unheated basement, a crawl space, or a cool closet in a garage usually works well. If the area gets too warm, the tubers might try to sprout too early. If it gets too cold (below freezing), the tubers will die.
During your monthly check-ins, look for two things: rot and shriveling.
If you see a tuber that feels soft or mushy, or one that has a fuzzy mold growing on it, remove it immediately. Rot can spread from one tuber to the next, so taking out the "bad apple" protects the rest of the bunch. If the storage medium feels very wet, leave the lid off the box for a few days to let it dry out.
On the other hand, if the tubers look very wrinkled and feel light, like a dried-out sponge, they are losing too much moisture. You can fix this by lightly misting the storage medium with a spray bottle of water. You don't want it to be wet, just slightly damp, like a wrung-out sponge.
Replanting in Spring: Giving Them a Fresh Start
As the days get longer and the soil begins to warm, it is time to think about bringing your dahlias back into the garden. This is the most exciting part of the process. In most parts of the country, the best time to plant is mid-to-late May, or whenever the soil has reached about 60°F and the danger of frost has passed.
Before you head out to the garden, take your tubers out of storage and inspect them. A healthy tuber should feel firm, similar to a fresh potato. You may even see tiny green or white sprouts starting to emerge from the top of the clump. These are called "eyes."
Finding the Eyes
The eyes are the growth points where the new stems will emerge. They are located on the "neck" of the tuber, right where it attaches to the old stem. If you don't see any eyes yet, don't worry. Sometimes they just need a little warmth to wake up. You can place the tubers in a warm, bright room for a week or two before planting to encourage the eyes to sprout.
Dividing Your Tubers
If your dahlia clumps have become very large, you can divide them. Each piece you cut must have at least one eye and one healthy tuber. Using a clean, sharp knife, carefully cut the clump into smaller sections. This is a great way to turn one favorite plant into three or four separate plants to share with friends or fill more space in your borders. For more guidance, see this guide to splitting and storing dahlia tubers.
Planting Basics
When you are ready to plant, choose a spot with at least six to eight hours of direct sunlight. Dahlias are sun-lovers and need plenty of energy to produce those big, beautiful blooms.
- Dig a hole about 4 to 6 inches deep.
- Lay the tuber on its side in the hole.
- If you are planting a tall variety, place a stake in the ground now so you don't damage the tuber later.
- Cover with soil and wait.
- Important Tip: Do not water your dahlias until you see the first green sprouts poking through the soil. The tubers have enough moisture to get started, and extra water in cold spring soil can cause them to rot before they even grow.
When to Treat Dahlias as Annuals
While we love seeing our dahlias come back, it is perfectly okay to treat them as annuals. Gardening should be a source of joy, not a source of stress. If the idea of digging and storing tubers feels overwhelming, or if you simply don't have a cool spot to keep them over the winter, don't feel guilty.
Treating dahlias as annuals allows you to try new colors and styles every single year. One year you might want a garden filled with soft pastels and "dinnerplate" varieties, and the next you might opt for vibrant "cactus" types or dark-foliaged "bishop" varieties.
Many gardeners choose to save only their absolute favorite, most expensive, or hardest-to-find varieties and buy fresh tubers for the rest of their display. This balances the satisfaction of overwintering with the ease of starting fresh. If you are ready to explore new options, browse the dahlia collections.
Key Takeaway: Whether you dig them up or buy new ones, dahlias are a high-reward plant. Choose the method that fits your schedule and your gardening style.
Common Myths About Returning Dahlias
There is a lot of advice on the internet about how to make dahlias come back, and not all of it is accurate. Let’s clear up a few common misconceptions so you can focus on what actually works.
Myth 1: They Need to Be "Fed" Over Winter
Dormant tubers do not need fertilizer. In fact, adding fertilizer during the winter or even at the time of planting can do more harm than good. The tuber already contains the food the plant needs to start growing. Wait until the plant is about a foot tall before you start a regular feeding routine.
Myth 2: You Must Wash Every Bit of Soil Off
While some professional growers wash their tubers to inspect them for disease, it isn't strictly necessary for the home gardener. Leaving a little bit of native soil on the clump can actually help protect the tubers from drying out too quickly in storage. As long as the clump is dry before it goes into the box, a little dirt is perfectly fine.
Myth 3: If They Shrivel, They Are Dead
Not necessarily! A slightly wrinkled tuber is often still very viable. As long as it isn't bone-dry or mushy, it will likely rehydrate once it hits the moist soil of spring. Use the "firmness test"—if it feels like a soft carrot rather than a dried-out twig, give it a chance.
Conclusion
Dahlias are among the most rewarding flowers you can grow, and the fact that they can come back year after year makes them a wonderful investment for your landscape. By understanding your USDA zone and providing the right winter care, you can enjoy these spectacular blooms for many seasons to come. Whether you are mulching them in a warm zone 9 garden or tucking them into peat moss in a zone 5 basement, the effort is always worth it when those first buds appear in mid-summer.
At Longfield Gardens, we are here to support your gardening journey every step of the way. From choosing the perfect varieties to helping you through your first winter storage, our goal is to make gardening feel accessible and successful.
Next Steps for Your Dahlias:
- Check your USDA hardiness zone to determine if you need to dig or mulch.
- Label your favorite varieties while they are still in bloom.
- Prepare your storage supplies (boxes and peat moss) in early autumn.
- Plan your spring garden layout to include space for your returning favorites.
- Explore bulk dahlia offers if you want to plant a larger display.
Gardening is a partnership with nature. By giving your dahlia tubers a safe place to rest during the winter, you are setting the stage for a magnificent encore performance next summer.
FAQ
Can I leave my dahlias in the ground if I live in Zone 7?
It is possible, but risky. In Zone 7, dahlias may survive a mild winter if the soil is very well-drained and you apply a thick (6-8 inch) layer of mulch. However, if the winter is unusually cold or wet, the tubers may rot or freeze. For valuable varieties, we recommend digging them up to be safe.
How do I know if my stored dahlia tubers are still alive?
Check the texture and look for "eyes." A healthy tuber should feel firm to the touch, like a fresh potato. In late winter or early spring, you should see small, pimple-like bumps or tiny green sprouts (eyes) near the top of the tuber where it meets the stem. If the tuber is mushy or crumbles like dust, it is no longer viable.
Do I have to wait for a frost before digging up my dahlias?
While you don't have to wait for a frost, it is highly recommended. The frost tells the plant to stop growing and send its sugars down into the tubers, which helps them survive storage. If you must dig them early due to travel or scheduling, try to wait as late into the autumn as possible. This step-by-step guide to digging up dahlia bulbs provides additional timing and handling advice.
What is the best container for storing dahlia tubers?
Cardboard boxes, wooden crates, or plastic bins with loose-fitting lids all work well. The key is to allow for some air circulation. If using plastic bins, do not snap the lid on tight, as this can trap too much moisture and cause rot. Many gardeners find that open-topped boxes stored in a humid basement provide the perfect balance. For more detailed storage instructions, see how to store dahlia tubers over the winter.
