Table of Contents
- Introduction
- Tubers vs. Bulbs: What Is the Difference?
- The Anatomy of a Dahlia Tuber
- Buying Dahlias: Clumps vs. Individual Tubers
- Selecting the Right Spot for Your Dahlias
- When to Plant Your Dahlias
- How to Plant Dahlia Tubers Step-by-Step
- Caring for Your Dahlias as They Grow
- Popular Dahlia Varieties to Explore
- Dealing with Common Challenges
- What to Do When the Season Ends
- Creating a Beautiful Garden with Longfield Gardens
- FAQ
Introduction
There is something truly magical about the moment a dahlia bud finally opens in late summer. These plants are the stars of the garden, offering an incredible variety of colors, shapes, and sizes that few other flowers can match. If you are browsing our Dahlia Collections at Longfield Gardens, you might notice that they are often grouped with spring-planted bulbs.
This often leads to a common question: do dahlias actually have bulbs? While many gardeners use the term "bulb" as a general name for any plant that grows from an underground storage organ, the answer is a bit more nuanced. This guide will help you understand the unique way dahlias grow and why knowing the difference between a bulb and a tuber makes gardening easier. Understanding how these plants store energy is the best way to ensure your garden is filled with vibrant, healthy blooms all season long.
Tubers vs. Bulbs: What Is the Difference?
In the gardening world, "bulb" is often used as a catch-all term for several different types of underground structures, including corms, rhizomes, and tubers. However, from a botanical standpoint, dahlias do not have bulbs. They grow from what are known as dahlia tubers or "tuberous roots."
A true bulb, like a tulip or an onion, is actually a modified leaf bud. If you cut a tulip bulb in half, you will see layers of fleshy scales that contain a tiny, immature flower and leaves protected inside. These scales store all the food the plant needs to sprout and bloom.
Tubers, like dahlias and potatoes, are different. They are thickened parts of the root or stem that store nutrients and water. Unlike a bulb, a tuber does not have protective layers or scales. It is a solid, fleshy mass of energy. While a tulip bulb is like a pre-packaged survival kit for a flower, a dahlia tuber is more like a battery that powers the plant's growth once the conditions are right.
Why the Name "Bulb" Sticks Around
Most people continue to call them dahlia bulbs because it is a simple way to describe how we buy and plant them. We sell them alongside lilies and gladiolus because they share the same spring planting window. Whether you call them bulbs or tubers, the care they need remains the same. Recognizing that they are tubers simply helps you understand their anatomy better so you can plant them with confidence.
Key Takeaway: Dahlias grow from fleshy structures called tubers, not true bulbs. While the names are often used interchangeably, tubers are solid energy stores similar to potatoes.
The Anatomy of a Dahlia Tuber
To get the best results from your garden, it helps to know what a healthy dahlia tuber looks like. If you have ever looked at a potato that has been sitting in your pantry too long, you have already seen a tuber in action. Just like a potato, a dahlia tuber needs a specific part to grow a new plant: the "eye."
A dahlia tuber is generally made up of three parts: the body, the neck, and the crown.
The Body
The body is the large, fleshy part of the tuber. This is where the plant stores the energy it needs to grow. Tubers come in many shapes and sizes. Some look like long, thin carrots, while others are round and plump like a small potato. The size of the body does not necessarily dictate the size of the final plant. A small tuber often grows into a massive, bloom-heavy plant just as well as a large one.
The Neck
The neck is the narrow portion that connects the body of the tuber to the crown. This part is quite delicate. If the neck is broken or badly creased, the energy stored in the body cannot reach the sprout. When handling your tubers, it is always best to be gentle to keep the neck intact.
The Crown and the Eye
The crown is the area where the neck meets the old stem from the previous year. This is where the "eyes" are located. An eye is a small bump or growth point where the new sprout will emerge.
Unlike potatoes, which have eyes all over their surface, dahlias only grow eyes on the crown. If a tuber is detached from the crown and has no eye, it will stay firm in the ground, but it will never sprout a plant. When you receive your order, you might see a tiny green sprout or just a small, pale bump. Both are signs of a healthy, viable tuber.
Buying Dahlias: Clumps vs. Individual Tubers
When you shop for dahlias, you may notice they are sold in two different ways: as individual tubers or as clumps. Both versions produce beautiful flowers, but they look a bit different in the packaging.
Individual Tubers
Many growers in the United States sell dahlias as individual tubers. This means one single tuber has been carefully cut away from a larger group. To be successful, this single tuber must have a piece of the crown attached and at least one visible eye. These are popular because they are easy to ship and take up very little space in the garden shed before planting.
Dahlia Clumps
In many parts of Europe and at Longfield Gardens, dahlias are often sold as clumps. A clump is a group of tubers still attached to a piece of the original stem.
Clumps offer a little extra insurance for the home gardener. Because a clump usually has multiple tubers and several eyes, you often get multiple sprouts from the start. This can lead to a slightly bushier plant earlier in the season. If one tuber in the clump happens to get damaged, the others are there to support the plant.
Does Tuber Size Matter?
It is a common myth that a bigger tuber leads to a bigger flower. In reality, the size of the tuber is mostly determined by the variety of dahlia and the weather during the previous growing season. For example, some "Dinnerplate" dahlias naturally produce smaller tubers, while some smaller pompon varieties produce huge ones. As long as the tuber is firm and has a healthy eye, it has everything it needs to succeed.
What to Do Next:
- When your shipment arrives, open the bags to let the tubers breathe.
- Check each tuber or clump to ensure it feels firm, not mushy.
- Look for the "eye" or a small sprout at the crown.
- If you aren't ready to plant, store them in a cool, dark place (around 45–50°F).
Selecting the Right Spot for Your Dahlias
Success with dahlias starts with "right plant, right place." Because these plants are native to the high plains of Mexico and Central America, they have specific preferences for sun and soil.
The Power of Sunlight
Dahlias are sun-worshippers. To produce those famous, vibrant blooms, they need a lot of energy from the sun. We recommend choosing a spot that receives at least six to eight hours of direct sunlight every day. If they are planted in too much shade, the stems will become "leggy" as they stretch toward the light, and they will produce far fewer flowers.
Soil and Drainage
"Drainage" simply refers to how fast water leaves the soil. Dahlias have a very simple rule: they like to be hydrated, but they hate having "wet feet." If the soil stays soggy for too long, the fleshy tubers can rot before they even have a chance to grow.
If you have heavy clay soil that stays wet after a rain, consider planting your dahlias in raised beds. This is one of the easiest wins in gardening. Raised beds allow you to control the soil quality and ensure that excess water drains away quickly. If planting in the ground, adding some compost can help improve the soil structure for better drainage.
When to Plant Your Dahlias
Timing is more important than almost any other "trick" when it comes to dahlias. Because these are tropical plants, they are very sensitive to cold.
The Golden Rule: Wait for the Warmth
A common mistake is planting dahlias too early in the spring while the soil is still cold and damp. If the soil temperature is below 60°F, the tuber will sit dormant, making it more vulnerable to rot.
A great rule of thumb is to plant your dahlias at the same time you would plant tomatoes or peppers. In most parts of the United States, this is usually between late April and early June, depending on your local climate. There is no rush; dahlias grow incredibly fast once the weather warms up, and they will easily catch up even if planted in June.
Hardiness Zones and Shipping
Dahlias are considered "tender perennials." This means they can stay in the ground year-round in warm climates (USDA zones 8–11), but in colder regions (zones 3–7), the tubers will freeze and die if left in the ground over winter. We time our shipping based on your USDA hardiness zone so your tubers arrive when it is nearly time to plant. This helps prevent them from sitting in a box for too long. For complete details, see our Shipping Information.
How to Plant Dahlia Tubers Step-by-Step
Planting dahlias is a straightforward process. Once the danger of frost has passed and your soil is warm, follow these simple steps for the best results.
1. Dig the Hole
Dig a hole about 4 to 6 inches deep. If you are planting a tall variety, such as a Dinnerplate dahlia, space the holes about 18 to 24 inches apart. Smaller border dahlias can be spaced closer together, about 12 inches apart.
2. Add Support Early
Most dahlias grow to be 3 to 5 feet tall and produce heavy flowers. They will need support so they don't tip over in a summer breeze. It is much easier to put a stake in the ground at the time of planting than it is to try to do it later when the plant is large. Driving a stake into the ground after the plant is grown can accidentally pierce the tubers below.
3. Place the Tuber
Lay the tuber or clump horizontally in the hole. If you can see the "eye" or a sprout, point it upward. Don't worry if you can't tell which way is up; the plant is smart enough to find its way to the surface.
4. Cover with Soil
Fill the hole back in with soil. You do not need to mound the soil; just level it with the surrounding ground.
5. Hold the Water
This is a critical step that often surprises new gardeners. Unless your soil is bone-dry, do not water your dahlias immediately after planting. The tuber has enough moisture stored inside to start growing. Wait until you see the first green sprouts poking through the soil before you begin a regular watering schedule. This simple step is the best way to prevent rot.
Key Takeaway: Plant dahlias 4-6 inches deep in warm soil (60°F). Place the eye facing up and avoid watering until you see green growth to ensure the tuber stays healthy.
Caring for Your Dahlias as They Grow
Once your dahlias have sprouted, they are relatively low-maintenance, but a few simple habits will reward you with a spectacular display of flowers. For a fuller care refresher, see 8 Tips for Growing Better Dahlias.
Deep Watering
As the plants grow larger and the summer heat sets in, dahlias will need more water. Instead of a light sprinkle every day, give them a deep soaking two or three times a week. This encourages the roots to grow deeper into the soil, making the plant more stable and drought-resistant. If you are growing dahlias in containers, they will need more frequent watering since pots dry out faster than the ground.
The Secret of "Pinching"
If you want a bushier plant with twice as many flowers, you should "pinch" your dahlias. When the plant is about 12 to 16 inches tall and has four sets of leaves, use your fingers or a pair of clean shears to snip off the very top of the center stem.
This might feel a bit scary, but it is one of the best things you can do for the plant. Pinching signals the dahlia to stop growing one tall, lanky stem and instead start growing multiple side branches. More branches mean more flowers! For step-by-step help, see How to Pinch and Stake Dahlias.
Deadheading for More Blooms
To keep the flowers coming all the way until the first frost, you should "deadhead" the plants. This simply means cutting off faded blooms. When a dahlia finishes blooming, it starts to put energy into producing seeds. By removing the old flowers, you tell the plant to keep putting that energy into making new buds instead.
Popular Dahlia Varieties to Explore
Dahlias come in an amazing array of styles. When you are looking for "bulbs" to add to your garden, consider a mix of these popular types:
- Dinnerplate Dahlias: These are the giants of the garden. Varieties like Dahlia Dinnerplate Cafe Au Lait produce blooms that can be 8 to 10 inches across—literally the size of a dinner plate.
- Varieties like Dahlia Dinnerplate Kelvin Floodlight also produce blooms that can be 8 to 10 inches across.
- Decorative Dahlias: These have the classic dahlia look with broad, flat-tipped petals. They come in every color imaginable and are excellent for cutting. For a romantic example, see Dahlia Decorative Labyrinth & Great Silence.
- Cactus Dahlias: These unique flowers have narrow, pointed petals that give them a spiky, starburst appearance. They add wonderful texture to garden beds. A standout option is Dahlia Cactus Purple Gem & Jura.
- Ball and Pompon Dahlias: These are perfectly symmetrical, globe-shaped flowers with petals that roll inward. They are incredibly sturdy and have a very long vase life, making them favorites for floral arrangements. Browse PomPon Dahlia if you love this form.
- Border Dahlias: If you have a small space or want to grow dahlias in pots, these shorter varieties are a perfect choice. They stay compact but still produce plenty of color. For a border-friendly combo, try Dahlia Border Decorative Gallery Art Deco & Gallery Singer.
Dealing with Common Challenges
While dahlias are generally robust, you might run into a few common issues. Most can be solved with simple, proactive steps.
Slugs and Snails
Young dahlia sprouts are like candy to slugs. If you see jagged holes in the leaves or silver trails on the ground, you likely have slugs. The easiest win is to use a pet-safe slug bait or organic barriers around the base of the plant when they first emerge. Once the plants are about a foot tall, they are usually tough enough to handle a little nibbling.
Powdery Mildew
In the late summer, you might notice a white, flour-like dust on the leaves. This is powdery mildew, a common fungus that thrives in humid weather. You can help prevent this by giving your plants plenty of space for air to circulate and by watering at the base of the plant rather than over the leaves.
Why Didn't My Dahlia Bloom?
If your plant is big and green but has no flowers, the most common reason is a lack of sunlight. Dahlias need that direct sun to trigger bud production. Another possibility is using a fertilizer that is too high in nitrogen, which encourages leaf growth but can discourage flowers. A balanced, all-purpose fertilizer is usually the best choice.
What to Do When the Season Ends
Because dahlias grow from tubers rather than hardy bulbs, they need a little help to survive the winter in cold climates.
Lifting the Tubers
Once a hard frost hits your area, the dahlia foliage will turn black. This is the signal that the growing season is over. Cut the stems down to about 4 inches above the ground and wait about a week. This allows the tubers to "cure" and prepare for dormancy.
Gently use a garden fork to lift the clump out of the ground. Be careful not to poke the tubers or snap the necks. Shake off the excess soil and let them dry in a protected, frost-free area for a day or two.
Winter Storage
To keep your tubers healthy until next spring, store them in a cool, dark, and dry place. A basement or an unheated garage that stays above freezing is ideal. You can tuck the tubers into a box filled with slightly damp peat moss, vermiculite, or wood shavings. This keeps them from drying out completely without making them wet enough to rot. For step-by-step digging and storage, see How to Lift and Store Dahlia Bulbs.
Check on your tubers once or twice during the winter. If they look shriveled, give them a tiny spritz of water. If any look mushy, remove them so the rot doesn't spread to the healthy ones.
What to Do Next:
- Wait for the first frost to turn the foliage black before digging.
- Clean off the soil and let the tubers dry for 48 hours.
- Pack them in breathable material like wood shavings or peat moss.
- Store in a cool (40–50°F) spot until spring.
Creating a Beautiful Garden with Longfield Gardens
Gardening should be a rewarding and joyful experience, and dahlias are one of the most satisfying plants you can grow. By understanding that these "bulbs" are actually tubers with specific needs for warmth and drainage, you are already well on your way to success.
We are here to support your journey from the moment you pick out your favorite varieties to the day you cut your first bouquet. Our team works with expert growers to ensure you receive high-quality, healthy tubers that are true to variety and ready to perform. We stand behind our plants with a 100% quality guarantee, so you can plant with peace of mind.
Whether you are a seasoned gardener or just starting your first flower bed, dahlias offer an accessible way to bring professional-level beauty to your backyard. With a little sun, some well-drained soil, and a bit of patience, you will soon see why these spectacular flowers are a favorite for so many.
"A dahlia tuber is a small investment that pays out in months of spectacular color and endless bouquets for your home."
For more tips on planning your garden and choosing the right varieties, explore our other guides and articles. We look forward to helping you grow something beautiful this season.
FAQ
Can I leave my dahlia tubers in the ground all winter?
This depends on your USDA hardiness zone. If you live in a warm climate (Zone 8 or higher), you can often leave dahlias in the ground with a thick layer of mulch for protection. In colder climates (Zone 7 and lower), the ground will freeze deep enough to kill the tubers, so they must be dug up and stored indoors for the winter. If you're not sure of your zone, use our Hardiness Zone Map.
Why are my dahlia tubers soft or mushy?
Soft or mushy tubers are usually a sign of rot, which is caused by excess moisture. This can happen if the soil doesn't drain well, if you water the tubers too early after planting, or if they were stored in conditions that were too damp. If a tuber is completely mushy, it cannot be saved and should be discarded to prevent the rot from spreading. For a refresher on healthy tubers, see Dahlia Tubers: What You Need to Know.
How many flowers will I get from one dahlia tuber?
One healthy tuber or clump will grow into a single large plant. Depending on the variety and how often you cut the flowers, one plant can produce anywhere from 20 to over 50 blooms throughout the season. The more you cut dahlia flowers for bouquets, the more the plant will produce to replace them!
Do I have to separate dahlia clumps every year?
No, you do not have to divide them every year. You can replant the entire clump you dug up the previous fall. However, as the clumps get larger over several years, they can become crowded and produce smaller flowers. Dividing them every year or two is an easy way to get "free" plants to expand your garden or share with friends.