Table of Contents
- Introduction
- Understanding the Lifecycle of a Dahlia
- Dahlias in Different Climates
- How to Overwinter Dahlias as Perennials
- Planting for Long-Term Success
- Watering and Feeding Your Dahlias
- Growing Dahlias in Containers
- Dividing Your Dahlias to Multiply Your Garden
- Choosing Varieties for Performance
- Simple Troubleshooting for Better Returns
- Conclusion
- FAQ
Introduction
Few moments in the garden compare to the excitement of seeing your first dinnerplate dahlia begin to unfurl. These spectacular blooms offer a variety of colors and shapes that can transform any backyard into a floral destination. At Longfield Gardens, we want every gardener to experience the joy of these late-summer stars. One of the most common questions we receive is whether these plants will come back on their own next year.
The answer is both simple and exciting: dahlias are indeed perennials. While they are native to the warm climates of Mexico and Central America, you can enjoy them year after year in almost any location with just a little bit of knowledge. Whether you live in a frost-free zone or a region with snowy winters, you can treat these plants as a long-term investment in your garden's beauty. This guide will show you exactly how to manage your dahlias so they return even stronger each season.
Understanding the Lifecycle of a Dahlia
To understand why dahlias are perennials, it helps to look at what is happening beneath the soil. Although many people refer to them as "dahlia bulbs," they are actually dahlia tubers. A tuber is a thickened, underground part of the stem or root that stores energy for the plant. You can think of a dahlia tuber much like a potato. It holds all the nutrients and water the plant needs to survive a period of rest and then push out new growth when conditions are right.
In their native habitat, dahlias follow a natural cycle of growth and dormancy. When the weather is warm and water is plentiful, the tubers send up stems and produce flowers. When the season changes and the weather becomes drier or cooler, the top of the plant dies back, but the tuber remains alive underground. This stored energy allows the plant to return the following year.
In a home garden, we replicate this cycle. Because dahlias are "tender" perennials, they cannot survive being frozen. If the ground freezes where the tubers are buried, the water inside the tuber will turn to ice, damaging the plant tissue and causing it to rot. This is why your local climate determines exactly how you will care for your dahlias during the winter months.
Dahlias in Different Climates
The way you treat your dahlias depends largely on your USDA hardiness zone. These zones are a helpful way to understand your local climate and which plants will survive the winter in your soil.
Dahlias in Warm Climates (Zones 8-11)
In USDA zones 8 through 11, dahlias are truly "plant it and forget it" perennials. In these regions, the ground rarely freezes deep enough to reach the tubers. You can leave your dahlias in the garden year-round. After the first frost, the foliage will turn brown and die back. You can simply cut the stems down to a few inches above the soil.
In these warmer zones, the tubers will rest quietly in the soil through the winter. When the soil warms up again in the spring, new sprouts will emerge from the ground. To give them a little extra protection, we recommend adding a 2- to 3-inch layer of mulch, such as shredded bark or straw, over the planting site. This helps keep the soil temperature stable and protects the tubers from any unusual cold snaps.
Dahlias in Cold Climates (Zones 3-7)
If you live in a region where the ground freezes, your dahlias will behave like annuals if left alone. However, you can still grow them as perennials by "overwintering" them. This is the process of digging up the tubers in the fall and storing them in a frost-free place until spring.
Many gardeners in the North find this process very rewarding. It allows you to save your favorite varieties, like the stunning 'Cafe au Lait' or the bold 'Thomas Edison,' without having to buy new ones every year. While it requires a few extra steps, the process is straightforward and ensures your garden stays filled with the varieties you love most.
Key Takeaway: Dahlias are naturally perennials that store energy in underground tubers. In warm zones (8-11), they stay in the ground. In colder zones (7 and below), you must dig them up to save them for next year.
How to Overwinter Dahlias as Perennials
If you live in a cold climate, the goal of overwintering is to keep the tubers dormant, cool, and dry—but not so dry that they shrivel up. Here is the simple process we use to ensure our tubers stay healthy through the winter.
Timing the Harvest
Wait for the first frost of the season to hit your garden. You will know it has happened because the dahlia foliage will turn black or dark brown almost overnight. This might look disappointing, but it is actually a good thing. The cold temperature signals to the plant that it is time to send all its remaining energy down into the tubers for storage.
Wait about a week after this first frost before you start digging. This short wait helps the "eyes" (the small bumps where next year's stems will grow) become more visible. If you cannot wait due to a hard freeze being in the forecast, you can dig them up sooner, but that one-week wait is ideal.
Digging and Cleaning
Carefully use a garden fork or a shovel to lift the tuber clumps out of the ground. Start digging about a foot away from the main stem to avoid accidentally slicing through the tubers. Once the clump is loose, lift it gently by the base of the stem.
Shake off the excess soil. You can use a garden hose to wash the rest of the dirt away, which makes it easier to see the health of the tubers. After washing, cut the main stem down to about an inch or two. At this stage, you should inspect the clump. If any tubers are broken or feel soft and mushy, remove them. Healthy tubers should feel firm, similar to a fresh potato.
Curing and Storing
Before putting the tubers away for the winter, they need to "cure." Place them in a cool, shaded, and well-ventilated area (like a garage or a covered porch) for two to three days. This allows the outer skin to toughen up slightly, which prevents rot.
For storage, you need a container that breathes. Cardboard boxes, paper bags, or plastic bins with holes drilled in the sides work well. Place the tubers in the container and cover them with a packing medium. We suggest using slightly damp peat moss, vermiculite, or coarse sawdust. This medium acts as insulation and prevents the tubers from drying out completely.
Store the containers in a cool, dark place where the temperature stays between 40°F and 50°F. An unheated basement, a crawl space, or a cool closet is usually perfect. Avoid areas that might freeze, like an uninsulated shed, and areas that are too warm, like a furnace room.
What to do next:
- Check your tubers once a month during the winter.
- If they look shriveled, lightly mist the packing medium with water.
- If you see any soft spots or mold, cut those parts away immediately.
- Keep the storage area dark to prevent the tubers from sprouting too early.
Planting for Long-Term Success
Whether you are planting new tubers or those you saved from last year, getting the basics right is the best way to ensure your dahlias thrive as perennials. Success starts with the "right plant, right place" principle.
Choosing the Best Spot
Dahlias are sun-lovers. To get the most blooms, they need at least six to eight hours of direct sunlight every day. If they are planted in too much shade, the stems will become tall and "leggy" as they reach for the light, and you will see fewer flowers.
Drainage is the other essential factor. "Drainage" is simply how fast water leaves the soil. Dahlias do not like to have "wet feet." If the soil stays soggy, the tubers can rot before they even start to grow. If you have heavy clay soil that stays wet, consider planting your dahlias in raised beds or containers to ensure the water moves away from the tubers.
Proper Timing
Timing is more important than almost any other tip. Many gardeners are eager to get their dahlias in the ground as soon as the snow melts, but dahlias need warm soil. We recommend waiting until the soil temperature reaches about 60°F. A good rule of thumb is to plant your dahlias at the same time you would plant tomatoes or peppers.
In most parts of the country, this is usually mid-to-late May. If you plant too early in cold, wet soil, the tuber will sit idle and may rot. Waiting for the right temperature leads to faster, healthier growth.
Depth and Spacing
When you are ready to plant, dig a hole about 4 to 6 inches deep. Lay the tuber horizontally on its side. If you can see the "eye" (the little bump at the neck of the tuber), point it upward, but don't worry too much—the plant will find its way to the surface.
Cover the tuber with soil, but do not water it yet. This is a common mistake! The tuber has enough moisture stored inside to start its roots. If you add too much water before the plant has leaves to process it, you risk rot. Wait until you see the first green sprouts poking through the soil before you start a regular watering schedule.
For spacing, give your dahlias plenty of room to breathe.
- Small border dahlias: 12 to 18 inches apart.
- Medium "decorative" dahlias: 2 feet apart.
- Large "dinnerplate" dahlias: 3 feet apart.
Good spacing allows air to circulate around the leaves, which helps prevent common issues like powdery mildew (a white, dusty-looking fungus).
Watering and Feeding Your Dahlias
Once your dahlias are growing, they need consistent care to produce those famous blooms. Following a simple routine will keep the plants healthy and help the tubers grow large enough to survive the next winter.
The Right Way to Water
Dahlias prefer deep, infrequent watering over light daily sprinkles. When the plants are established, aim for a deep soak two or three times a week. You want the water to reach the root zone, which is several inches underground.
If you have sandy soil, you may need to water more often because sandy soil doesn't hold moisture well. If you have heavier soil, you can water less frequently. The goal is to let the top inch of soil dry out slightly between waterings. This encourages the roots to grow deeper into the ground, making the plant more resilient.
Fertilizing for Blooms
Dahlias are heavy feeders because they grow so much in a single season. However, the type of fertilizer you use matters. Avoid fertilizers that are very high in nitrogen. Nitrogen encourages a lot of green, leafy growth but can result in fewer flowers and weak tubers.
Instead, look for a balanced fertilizer or one that is slightly higher in phosphorus and potassium. These nutrients support flower production and tuber health. We recommend applying fertilizer about 30 days after planting and then once a month until the end of summer. Always follow the instructions on the product label for the best results.
Growing Dahlias in Containers
If you have limited space or poor soil, you can still enjoy dahlias as perennials by growing them in containers. This is also a great way for gardeners in cold climates to get a head start on the season.
Selecting the Right Pot
The pot needs to be large enough to hold the root system of a full-grown plant. For a standard dahlia, a 5-gallon container is the minimum size we recommend. Make sure the pot has plenty of drainage holes in the bottom.
Use a high-quality potting mix rather than garden soil. Potting mix is lighter and provides the excellent drainage that dahlias require. You can add a handful of compost to the mix to provide extra nutrients.
Container Care
Dahlias in pots dry out much faster than those in the ground. During the heat of the summer, you may need to water your container dahlias every day. Check the soil by sticking your finger an inch deep; if it feels dry, it is time to water.
One of the benefits of container growing is that you can move the pots. If a big storm is coming, you can move them to a sheltered spot. In the fall, you can move the entire pot into a garage or basement for the winter. Just let the soil dry out, cut the stems back, and keep the pot in a cool, dark place until spring.
Key Takeaway: Containers are a perfect solution for gardeners with heavy soil. They allow for better control over drainage and make it easy to move plants to a frost-free area for the winter.
Dividing Your Dahlias to Multiply Your Garden
One of the best things about dahlias being perennials is that the clumps grow larger every year. A single tuber planted in the spring will turn into a clump of several tubers by the fall. You can "divide" these clumps to create even more plants for your garden or to share with friends.
How to Divide
The best time to divide dahlias is in the spring, just before planting. At this time, the "eyes" are starting to wake up and are much easier to see. An eye looks like a tiny pink or green bump, similar to the eye on a potato.
To divide a clump:
- Use a sharp, clean pair of garden snips or a knife.
- Look for an eye on the neck of the tuber (the narrow part where it connects to the main stem).
- Cut the tuber away from the clump, ensuring that each individual tuber has at least one eye and a piece of the neck.
- If a tuber does not have an eye, it will not grow a new plant, even if the tuber itself is large and healthy.
Don't feel like you have to separate every single tuber. Often, cutting a large clump into halves or quarters is the safest way for a beginner to ensure each piece has a healthy growing point.
Dealing with Tuber Size
It is a common myth that a bigger tuber will produce a bigger plant. In our experience, this isn't true! As long as the tuber has a healthy eye and enough stored energy to get the first few leaves started, it will grow into a full-sized, beautiful plant. Some dahlia varieties naturally produce small, skinny tubers, while others produce large, round ones. Both will perform beautifully if the soil and sun are right.
Choosing Varieties for Performance
We maintain a trial garden at Longfield Gardens to evaluate how different varieties perform. If you are looking for dahlias that are easy to grow and provide a big impact, here are a few types we highly recommend.
Dinnerplate Dahlias
These are the giants of the dahlia world. Dinnerplate dahlias like 'Kelvin Floodlight' produce massive, sunny yellow blooms that can be 10 inches across. They are a "wow" plant and make incredible cut flowers. Because the blooms are so heavy, these varieties always need to be supported with a sturdy stake.
Decorative Dahlias
These are the classic dahlias most people recognize. They have broad, flat-tipped petals and come in every color imaginable. Decorative Dahlias like 'Thomas Edison' are a long-time favorite for their deep purple color and reliable performance. These are excellent for the middle of a flower border.
Cactus and Semi-Cactus Dahlias
If you want something unique, cactus dahlias feature narrow, pointed petals that give them a "spiky" look. They add wonderful texture to garden beds and floral arrangements. 'Black Narcissus' is a stunning example with its dark, moody red petals.
Simple Troubleshooting for Better Returns
Gardening is a learning process, and sometimes things don't go exactly as planned. If your dahlias aren't blooming as much as you'd like, or if the plants look a bit tired, the fix is usually very simple.
Deadheading for More Blooms
"Deadheading" is the process of removing flowers as they begin to fade. If you leave the old flowers on the plant, the dahlia will start to put its energy into producing seeds. By cutting off the faded blooms, you tell the plant to keep making more flowers instead.
To deadhead correctly, don't just pull the flower head off. Follow the stem down to the next set of leaves and make a clean cut there. This keeps the plant looking tidy and encourages new branches to form.
Support for Tall Plants
Most dahlias grow between 3 and 5 feet tall. As they get larger and start producing heavy flowers, the stems can bend or break, especially during summer rainstorms.
The easiest win is to put a stake in the ground at the time of planting. This way, you don't risk driving a stake through the tuber later in the season. As the plant grows, use soft twine or garden ties to gently secure the main stem to the stake every 12 inches.
Healthy Leaves
If you notice the leaves of your dahlias are starting to look yellow or have spots, first check your watering. Soil that stays too wet can cause yellowing leaves. If the watering is correct, check for air circulation. If the plants are too crowded, simply thinning out some of the lower leaves can help more air reach the center of the plant, which keeps the foliage green and healthy.
Conclusion
Dahlias are one of the most rewarding perennials you can add to your garden. Whether you live in the sunny South where they stay in the ground all year, or in the North where you save them in the cellar, these plants offer incredible beauty for very little effort. By focusing on the basics—sun, drainage, and timing—you can enjoy a spectacular display from mid-summer right up until the first frost.
At Longfield Gardens, we take pride in providing high-quality tubers that are true to variety and ready to grow. We stand behind our plants with a 100% quality guarantee. If you ever have a question about your order or need help with a plant, our team is here to support you. We believe that gardening should be a source of joy, and we are honored to be a part of your garden journey.
- Dahlias are perennials that grow from energy-storing tubers.
- In cold zones, dig tubers after the first frost and store them in a cool, dry place.
- Wait for 60°F soil temperatures before planting in the spring.
- Provide at least 6-8 hours of sun and ensure the soil has good drainage.
"Dahlias are a long-term investment in your garden's beauty. With a little winter care, a single tuber can provide a lifetime of stunning summer blooms."
We hope this guide gives you the confidence to start your own dahlia collection. Whether you are planting your very first 'Thomas Edison' or dividing a massive clump of 'Cafe au Lait,' the results are always worth the wait. Happy gardening!
FAQ
Can I leave my dahlias in the ground if I live in Zone 7?
Zone 7 is a "borderline" zone for dahlias. In a mild winter, they may survive if you apply a very thick layer of mulch (6-8 inches) to protect them. However, for the best results and to ensure your favorite varieties return, we recommend digging them up and storing them indoors.
Do dahlia tubers need to be dried before they are stored for winter?
Yes, this process is called "curing." After you dig them up and wash them, let the tubers sit in a cool, shaded area with good airflow for two to three days. This allows the skin to dry and toughen, which helps prevent rot and mold while they are in storage.
Why didn't my dahlias bloom even though the plants grew very tall?
The two most common reasons for this are too much shade and too much nitrogen. Dahlias need at least six hours of direct sunlight to produce flowers. Also, using a fertilizer with a high first number (nitrogen) will produce lots of leaves but very few blooms.
Should I soak dahlia tubers in water before planting them in the spring?
No, we do not recommend soaking dahlia tubers. Unlike some other bulbs, dahlia tubers are very sensitive to excess moisture before they start growing. The tubers already contain enough moisture to get started. Soaking them often leads to rot rather than faster growth.