Introduction
Walking through a garden filled with blooming dahlias is a highlight of the late summer season. These spectacular flowers offer an incredible range of colors, shapes, and sizes, from dainty pompons to massive dinnerplate varieties that can be larger than a dinner plate. If you are new to growing these beauties, you might find yourself asking a common question: are dahlia bulbs actually bulbs?
At Longfield Gardens, we love helping home gardeners discover the joy of growing these prolific bloomers. You can explore our collection of dahlias while learning how these plants grow. While many people use the term "bulb" as a catch-all for any plant that grows from an underground storage organ, there are some important technical differences that can help you become a more successful gardener. Understanding how these plants grow and what they need to thrive is the first step toward a garden full of stunning bouquets.
This guide will explain the technical nature of dahlia roots, how to identify healthy planting stock, and how to care for them from spring planting through fall harvest. Whether you are a beginner or a seasoned gardener, learning the simple rules for dahlia success will ensure your garden is the envy of the neighborhood. While they have a few unique needs, dahlias are incredibly rewarding and accessible for everyone.
The Technical Truth: Tubers vs. Bulbs
If you head to a garden center or browse an online shop, you will frequently see dahlias listed under the "summer bulbs" category. In the gardening world, "bulb" is often used as a general term for any plant that stores its life cycle in an underground structure. However, if we look at the science, dahlias are technically tubers, not bulbs.
A true bulb, like a tulip or a daffodil, is a complete underground "package" that contains a miniature plant and its food supply. When you cut a tulip bulb in half, you can see the layers of fleshy scales that store energy. A dahlia, on the other hand, grows from a tuberous root. These structures look more like a bunch of brown carrots or a cluster of fingerling potatoes than the rounded, onion-like shape of a true bulb.
Tubers are thickened parts of an underground stem or root used by the plant to store nutrients. While a bulb contains the entire blueprint for the next season’s flower, a dahlia tuber serves as the energy reserve to push out new growth once the soil warms up. This distinction matters because it changes how we handle, plant, and store the roots over the winter.
Understanding the Anatomy of a Dahlia Tuber
When you receive your order from us, you might notice that the tubers look a bit unusual. Unlike a symmetrical lily bulb, dahlia tubers come in various shapes and sizes depending on the variety. Some are long and thin, while others are round and chunky. Regardless of their shape, every viable dahlia unit needs three specific parts to grow into a healthy plant.
The Eye
The most critical part of the tuber is the "eye." This is a small, often pinkish or green bump where the new sprout will emerge. It is very similar to the eyes you see on a potato in your pantry. In dahlias, these eyes are located on the "crown," which is the area where the tuber attaches to the old stem. If a tuber does not have an eye, it will not produce a plant, even if the rest of the tuber looks healthy.
The Neck
The neck is the narrow portion that connects the body of the tuber to the crown. This area is quite fragile. It is important to handle your tubers gently because if the neck is broken or severely creased, the connection between the energy source (the tuber) and the growth point (the eye) is severed. A tuber with a broken neck usually will not grow, even if it has a visible eye.
The Body
The body is the fleshy part of the tuber. This is the storage tank for the plant's energy. Interestingly, the size of the body does not determine the size of the final plant. A small tuber about the size of an AA battery has plenty of energy to get a plant started. Once the plant develops its own root system and several sets of leaves, it stops relying on the mother tuber and starts producing its own energy through photosynthesis.
Key Takeaway: When inspecting your dahlias, look for a firm body and an intact neck. Don't worry if the tuber is small; as long as there is a visible eye or a piece of the crown attached, it has everything it needs to grow.
Clumps versus Individual Tubers
When you shop for dahlias, you might receive them in two different forms: individual tubers or "clumps." Both forms are excellent for planting, but they look a bit different in the packaging.
Individual Tubers
Many growers in the United States divide their dahlia clumps in the fall or spring. This involves carefully cutting the tubers apart so that each individual piece has at least one eye and a portion of the crown. Individual tubers are easier to store in small spaces and are the standard for many specialty flower farms.
Dahlia Clumps
In Europe and at Longfield Gardens, we often provide dahlia clumps. These are essentially the entire root system of a one-year-old plant grown from a cutting. A clump consists of several tubers still attached to a central stem. The primary advantage of a clump is that it usually contains multiple eyes. This provides a bit of "insurance"—if one sprout is accidentally damaged, there are others ready to take its place.
Whether you plant an individual tuber or a full clump, the result is the same: a vigorous, bushy plant that will bloom its heart out from mid-summer until the first frost. Neither is "better" than the other; they are just different ways of preparing the plant for your garden.
Does Tuber Size Affect Flower Size?
It is a common myth that a giant tuber will produce a giant flower. In reality, the size of the tuber is determined by the genetics of the specific variety and the growing conditions of the previous season.
For example, a "Dinnerplate" dahlia like the creamy-colored Cafe au Lait might produce relatively modest-sized tubers, while a smaller "Pompon" variety might produce massive, chunky clumps. The size of the bloom you see in August is governed by the variety's DNA and the care you provide during the growing season—not the size of the root you put in the ground in May.
If you receive a small tuber, do not be discouraged. As long as it is firm and has a healthy eye, it will grow into a full-sized plant. In fact, smaller tubers often sprout faster because they don't have as much bulk to hydrate before they begin growing.
When and How to Plant Your Dahlias
Timing is the most important factor when planting dahlias. Because they are tropical plants originally from Mexico, they have no tolerance for frost. If you plant them too early in cold, wet soil, the tubers may rot before they have a chance to sprout.
The Tomato Rule
A great rule of thumb for dahlia planting is to wait until you would normally plant your tomatoes or peppers. This usually means the danger of frost has passed, and the soil has warmed up to at least 60°F. If the ground is still chilly to the touch, it is better to wait a week or two.
Choosing the Right Spot
Dahlias are sun worshippers. To get the best blooms and strongest stems, they need at least six to eight hours of direct sunlight every day. If they are planted in too much shade, they will become "leggy" (tall and floppy) and produce fewer flowers.
Drainage is also key. "Drainage" simply means how fast water moves through the soil. Dahlias love consistent moisture, but they hate sitting in soggy ground. If you have heavy clay soil, consider planting them in raised beds or adding compost to help the water move through more easily.
Planting Depth and Spacing
For more detail on how deeply to plant dahlia tubers, follow these basic steps:
- Dig a hole about 4 to 6 inches deep.
- If you are planting tall varieties, place a stake in the hole now so you don't damage the tuber later.
- Lay the tuber or clump horizontally in the hole with the eyes facing up.
- Cover with soil, but do not water them yet!
Wait to water your dahlias until you see the first green sprouts poking through the soil. The tubers have enough stored moisture to get started. Adding too much water to a dormant tuber in cool soil is the most common cause of rot. Once the plant is a few inches tall, you can begin a regular watering schedule.
What to do next:
- Check your local frost dates to determine your planting window.
- Prepare your garden bed by removing weeds and adding a bit of compost.
- Source your stakes (bamboo, wood, or metal) before you start planting.
Essential Care for Better Blooms
Once your dahlias are up and growing, a few simple maintenance tasks will transform them from average garden plants into showstoppers. Dahlias are very "responsive" plants—they reward a little bit of extra attention with an abundance of flowers.
The Power of Pinching
One of the best tricks for a bushy dahlia plant is "pinching." When your plant is about 12 to 16 inches tall and has four sets of leaves, use your fingers or clean shears to snip off the very top of the center stem.
While it might feel strange to cut your plant, this actually signals the dahlia to stop growing one tall, thin stalk and instead send its energy to the side buds. This results in a much fuller plant with more branches and, ultimately, many more flowers. If you don't pinch, you'll get one very early bloom on a tall stem, but fewer flowers later in the season.
Staking for Support
Because dahlias can grow quite large—some reaching four or five feet tall—and their flowers are often heavy, they need support. Wind and heavy rain can easily topple a full-grown dahlia.
You can use individual stakes for each plant, tying the main stem to the stake with soft twine as it grows. Alternatively, if you are growing a row of dahlias, you can use the "corralling" method by placing stakes at the corners of the bed and running twine around the perimeter to keep the plants upright.
Watering and Feeding
Dahlias are hungry and thirsty plants. Once they are established, they prefer deep watering two or three times a week rather than a light sprinkle every day. This encourages the roots to grow deep into the soil.
Regarding fertilizer, a balanced garden food or one slightly lower in nitrogen is ideal. Avoid high-nitrogen fertilizers later in the season, as this can encourage lots of green leaves but very few flowers. A fertilizer designed for flowers or vegetables (like a 5-10-5 or 10-10-10) works perfectly. Always follow the instructions on the product label for the best results.
Dahlias as Cut Flowers
One of the main reasons gardeners love dahlias is for the incredible bouquets they provide. Longfield Gardens’ cut-flower bulb collection offers more ideas for flowers suited to arrangements. Unlike many other flowers, dahlias do not open much once they are cut, so timing is important.
Pick your flowers when they are almost fully open but before the back petals start to wilt or turn brown. The best time to cut is in the cool of the early morning or evening when the plant is most hydrated. Place the stems immediately into a bucket of clean, room-temperature water.
The more you cut dahlias, the more they bloom! This is because the plant’s goal is to produce seeds. By cutting the flowers for bouquets (or "deadheading" faded blooms by cutting them back to a side shoot), you prevent the plant from making seeds and encourage it to keep producing new buds.
End of Season: Digging and Storing
In USDA zones 8 and warmer, dahlia tubers can often stay in the ground over the winter if the soil drains well and you provide a thick layer of mulch. For help identifying your region, consult Longfield Gardens’ hardiness zone map. However, for most of the United States (zones 3 through 7), dahlias must be dug up and stored indoors because the freezing temperatures will kill the tender tubers.
When to Dig
Wait for a "killing frost" to hit your garden. You will know it has happened because the dahlia foliage will turn black or dark brown overnight. This frost signals the plant to go into dormancy and move its remaining energy down into the tubers for storage.
After the frost, cut the stems down to about 4 inches above the ground. You can leave the tubers in the soil for another week to "cure," which helps the skins toughen up for storage.
How to Lift and Store
For a detailed walkthrough, see this guide to dividing and storing dahlia tubers.
- Use a garden fork to gently loosen the soil about a foot away from the stem to avoid piercing the tubers.
- Lift the clump and shake off the excess soil.
- Rinse the tubers with a hose if you prefer to store them clean, but make sure they dry completely in a shaded, frost-free area for a day or two.
- Store the tubers in a breathable container, such as a cardboard box or a plastic bin with holes.
- Surround the tubers with a packing material like peat moss, vermiculite, or slightly damp wood shavings. This keeps them from drying out too much while preventing rot.
Keep your stored tubers in a cool, dark, and dry place that stays between 40°F and 50°F. A basement, crawlspace, or insulated garage is usually perfect. Check on them once or twice during the winter to make sure they aren't shriveling or showing signs of mold.
Common Myths About Dahlia "Bulbs"
As you explore the world of dahlias, you might come across some confusing advice. Let’s clear up a few common misconceptions so you can garden with confidence.
Myth: You need a giant tuber for a big plant.
As discussed earlier, a tuber the size of a finger can produce a massive plant. The "eye" is the brain of the operation; the tuber is just the lunch box. Once the plant has leaves, it makes its own food.
Myth: Dahlias are "hard" to grow.
Dahlias are actually quite easy! They follow the same basic needs as a tomato plant: sun, water, and a bit of support. While digging them up in the fall is an extra step, many gardeners find it a small price to pay for months of spectacular color.
Myth: You must water them every day.
Overwatering is the fastest way to kill a dahlia tuber, especially early in the season. Deep, infrequent watering is much better for the plant’s health.
Myth: Dahlias are deer-proof.
While dahlias aren't the first choice for deer (they usually prefer hostas or lilies), a hungry deer will eat almost anything. If you have heavy deer pressure, a simple fence or a repellent spray is a good idea.
Why We Love Dahlias
Dahlias represent the grand finale of the gardening year. While spring bulbs like tulips bring the first burst of hope, and summer perennials provide steady color, dahlias offer a sense of abundance and drama that is hard to match. They bridge the gap between late summer and the first hints of autumn, providing nectar for pollinators and endless material for flower arrangements.
Working with us at Longfield Gardens, you’ll find that we choose varieties that are known for their beauty and reliable performance. We take pride in ensuring that the tubers we ship are healthy and ready to grow. Gardening is meant to be a rewarding experience, and there is nothing quite like the feeling of seeing those first sprouts emerge from the soil after a winter of waiting.
Whether you choose the classic elegance of a white Fleurel dahlia or the vibrant, prickly petals of a cactus variety, you are investing in a season of joy. Every year that you grow and store your tubers, you learn a little more about the rhythm of your garden.
Conclusion
So, are dahlia bulbs truly bulbs? Technically no—they are tubers—but the joy they bring to the garden is universal. By understanding that these plants grow from energy-storing roots rather than layered bulbs, you can provide the specific care they need to thrive. Remember to wait for warm soil, provide plenty of sun, and don't be afraid to pinch them back for more blooms.
Growing dahlias is a journey that connects you to the seasons. From the quiet wait for spring planting to the vibrant explosion of late-summer color, these plants offer a unique kind of garden magic. With a little bit of patience and the right basics, you can grow professional-quality flowers right in your own backyard.
- Wait for the soil to reach 60°F before planting.
- Ensure your planting site receives at least 6 hours of full sun.
- Pinch the center stem when the plant is 12 inches tall for a bushier shape.
- Deadhead or cut flowers regularly to keep the plant blooming.
"Dahlias are the ultimate reward for the patient gardener, offering more color and variety per square foot than almost any other summer flower."
We are here to support you in creating the beautiful garden you've always imagined. Start small with a few of your favorite colors, and before you know it, you’ll be a dahlia expert.
FAQ
Is it better to plant dahlia clumps or individual tubers?
Both work exceptionally well and will produce the same size plant by mid-summer. Clumps offer a bit more "insurance" because they usually have multiple eyes, while individual tubers are easier to handle and take up less space in storage. At Longfield Gardens, we provide high-quality stock in the form that best suits each specific variety.
Can I grow dahlias in pots or containers?
Yes, dahlias grow beautifully in containers! Choose a pot that is at least 12 to 15 inches in diameter and has good drainage holes. Smaller "border" or "gallery" dahlia varieties are particularly well-suited for pots, though even larger varieties can thrive if the container is heavy enough to prevent tipping. You can browse the dahlia best sellers for compact and container-friendly options.
Why aren't my dahlia tubers sprouting?
The most common reasons for a delay in sprouting are cold soil or planting too deep. Dahlias are slow to wake up if the soil temperature is below 60°F. If your soil is warm and you still see nothing after three weeks, check to ensure the soil isn't overly saturated, which can cause the tuber to rot. This guide to what to do with dahlia tubers offers additional troubleshooting help.
Do I really have to dig up my dahlias every year?
If you live in a climate where the ground freezes (USDA zones 7 and colder), the tubers will turn to mush and die if left in the ground. Digging them up allows you to save your favorite varieties and even multiply your collection, as one tuber planted in the spring will often turn into a clump of five or more by the fall. For additional storage advice, see how to store dahlia tubers.
