Introduction
There is nothing quite like the excitement of unboxing a fresh shipment of dahlias. These unassuming, potato-like roots hold the promise of spectacular, dinnerplate-sized blooms and vibrant colors that last from midsummer until the first frost. At Longfield Gardens, we know that the first step to a successful growing season is getting your tubers in the ground with confidence.
Whether you are a first-time gardener or a seasoned pro adding new varieties to your collection, the question of which way is "up" can be a bit confusing, especially with dinnerplate dahlias. Unlike a traditional flower bulb, a dahlia tuber has a unique anatomy that determines how it should be positioned in the soil. This guide is designed to help home gardeners understand the best orientation for planting to ensure strong, healthy growth.
We will cover how to identify the "eye" of the tuber, why horizontal planting is the preferred method, and the simple steps you can take to prepare your soil. For a broader look at what Longfield offers, browse our dahlia collections. By focusing on a few basic rules of anatomy and timing, you can set your dahlias up for a season of incredible performance. Getting the orientation right is the first step toward a garden full of stunning cut flowers.
Understanding Dahlia Tuber Anatomy
Before you dig your first hole, it helps to understand what a dahlia tuber actually is. Our Planning Guide for Dahlias can help you compare flower sizes and styles. While many people call them "bulbs," they are technically tuberous roots. They function much like a potato, storing energy and moisture to fuel the plant’s growth until it can establish a permanent root system.
A viable dahlia tuber consists of three main parts: the body, the neck, and the crown. The body is the fat, starchy part of the tuber. The neck is the narrow portion that connects the body to the crown. The crown is the most important part because this is where the "eyes" are located. For more on how tubers work, see Dahlia Tubers: What You Need to Know.
The "eye" of a dahlia is a small, sometimes slightly raised bump. It looks very much like the eye on a kitchen potato. This is the growth point where the sprout will emerge. If a tuber is broken at the neck and loses its connection to the crown, it will not grow, even if the body looks healthy. This is why we always handle tubers with care during the planting process.
How to Find the Eye
Identifying the eye is the key to knowing which way to plant your dahlia. If you want to see the process in action, our How to Plant Dahlias video is a helpful companion. In the early spring, eyes can be quite small and difficult to see. They are always located on the crown, which is the area where the tuber was originally attached to the main stem of the previous year's plant.
If you are having trouble spotting the eye, do not worry. Sometimes the eyes are "dormant" and haven't started to swell yet. You can encourage them to show themselves by placing the tubers in a warm, bright room for a few days. As the tuber senses warmth, the eye will begin to sprout, often turning a light pink or green color.
In some cases, you may receive a tuber that already has a visible sprout. This makes your job much easier. If there is no sprout and no obvious bump, look for the "head" of the tuber where the old stem material is. That end is the "top," and the eyes will always be located there.
The Best Orientation: Laying Them Flat
The most common question we hear is whether the tuber should stand up vertically or lie down horizontally. While some gardeners plant them at a slight angle, the most reliable method for success is to plant dahlia tubers horizontally.
Laying the tuber on its side is the most natural position for the plant. In this horizontal position, the sprout that emerges from the eye has a clear, easy path to the surface of the soil. It also allows the new root system to develop evenly from the crown area.
When you lay the tuber flat, make sure the eye is facing upward or toward the center of the hole. If the eye is pointing down, the sprout will eventually find its way around the tuber and head toward the light, but it may take longer to emerge. Placing the eye facing up gives the plant a head start.
Key Takeaway: Always plant dahlia tubers horizontally (on their side) with the "eye" or sprout facing upward to give the plant the quickest path to the sun.
Step-by-Step Planting Guide
Once you have identified the eye and the correct horizontal orientation, you are ready to plant. Following a consistent process helps ensure the tuber is at the right depth and has the support it needs to thrive.
Prepare the Hole
Start by digging a hole that is about 6 inches deep and 12 inches wide. Dahlias love loose soil that allows their roots to spread easily. If your soil is very heavy or stays wet for a long time, you can mix in a bit of compost to improve the structure. For more help, see How to Prepare Soil for Planting.
Set the Stake
If you are planting tall varieties, such as dinnerplate or decorative dahlias, it is a smart move to put a stake in the ground right now. A classic dinnerplate choice is Dahlia Dinnerplate Cafe Au Lait. Driving a stake into the ground after the plant has started growing can accidentally pierce the tuber or damage the roots. Place a sturdy wooden or metal stake at the edge of your 6-inch hole before you put the tuber in.
Place the Tuber
Lay your dahlia tuber horizontally in the bottom of the hole. Ensure the crown—the end with the eye—is closest to your stake. Position the tuber so the eye is facing up. If you are planting a clump of tubers rather than a single tuber, lay the entire clump flat in the bottom of the hole with the old stem pointing upward.
Cover with Soil
Gently fill the hole with soil until the tuber is covered by about 4 to 6 inches of earth. Do not pack the soil down too hard; a light firming with your hands is enough to remove large air pockets. The sprout needs to be able to push through the soil without meeting too much resistance.
What to Do Next:
- Confirm your last frost date has passed before planting.
- Check that the soil temperature is at least 60°F.
- Identify the crown and the eye on each tuber.
- Lay the tuber flat in a 6-inch deep hole.
- Place the eye so it faces the sky.
The Importance of Planting Depth
Getting the depth right is just as important as the orientation. If you plant a dahlia too shallow, the plant may struggle to stay upright as it grows tall and heavy with blooms. If you plant it too deep, the sprout may run out of energy before it reaches the surface.
A depth of 4 to 6 inches is the "sweet spot" for most varieties. This provides enough soil coverage to keep the tuber cool and moist during the hot summer months. It also provides a stable foundation for the roots. For smaller, dwarf varieties, 4 inches is usually sufficient, while the largest varieties benefit from the full 6 inches of depth.
Remember that the measurement is taken from the top of the tuber to the surface of the soil. When you are finished, the area should look level with the rest of your garden bed.
Timing and Soil Temperature
One of the most common mistakes in dahlia gardening is planting too early. Because dahlia tubers are full of moisture, they are very sensitive to cold, wet soil. If they are tucked into the ground while it is still chilly and damp, they may rot before they ever have a chance to sprout.
Patience is a virtue when it comes to dahlias. We recommend waiting until all danger of frost has passed and the soil has warmed up to at least 60°F. If you're not sure about your area, check our Hardiness Zone Map before planting. A good rule of thumb is to plant your dahlias at the same time you would plant your tomatoes or peppers. These "warm-weather" plants all share the same preference for cozy soil.
If you live in a region with a short growing season, you can give your dahlias a head start by "potting them up" indoors. About four to six weeks before the last frost, plant the tubers in containers and keep them in a warm, sunny spot. By the time the weather is right for outdoor planting, you will already have established green growth.
Water Correctly, Not Constantly
When it comes to watering newly planted dahlia tubers, the rule is simple: less is more. Until you see green growth poking through the soil, you generally do not need to water at all.
The tuber has enough stored energy and moisture to begin the sprouting process on its own. Adding extra water to the soil before the plant has roots can lead to rot. Once the sprout is a few inches tall and has its first set of "true leaves," you can begin a regular watering schedule.
When you do start watering, aim for deep soakings rather than frequent light sprinkles. This encourages the roots to grow deep into the soil where it is cooler and more stable. If you want a quick refresher on the rest of the care routine, see 8 Tips for Growing Better Dahlias. In sandy soil, you may need to water more often, while clay soil stays wet longer and requires more caution.
Choosing the Right Location
Dahlias are sun worshippers. To produce those famous, high-petal-count flowers, they need plenty of fuel from the sun. Choose a spot in your yard that receives at least six to eight hours of direct sunlight every day.
Morning sun is particularly beneficial because it helps dry the dew off the leaves, which keeps the plants healthy. If you live in an extremely hot climate, a little bit of afternoon shade can help prevent the blooms from wilting in the peak heat of the day, but full sun is still the standard for the best results.
In addition to sun, consider wind protection. Because dahlias can grow quite tall and have hollow stems, they can be vulnerable to heavy summer storms. For a decorative variety with strong stems and beautiful color, Dahlia Decorative Great Silence is a nice one to keep in mind. Planting them near a fence or a building can provide a natural windbreak. If that isn't an option, our earlier advice about staking becomes even more important.
Soil and Drainage Basics
Dahlias are not overly picky about soil type, but they absolutely insist on good drainage. "Drainage" is simply a way of describing how fast water moves away from the plant's roots. If water sits in a spot for hours after a rainstorm, that area has poor drainage.
To give your dahlias the best home, look for soil that is rich and loose. If you have heavy clay soil, which feels sticky and holds water, you can improve it by adding organic matter like compost or aged manure. This creates air spaces in the soil, allowing roots to breathe and water to flow. If you want another decorative option with dark foliage, Dahlia Decorative David Howard is worth a look.
If your garden has very poor drainage and you find it difficult to fix, consider planting your dahlias in raised beds. Raised beds allow you to control the soil quality and ensure that the tubers never sit in soggy conditions. Many of our most successful gardeners prefer this method because it takes the guesswork out of soil management.
Dealing with Small or Shriveled Tubers
When you receive your shipment, you may notice that some tubers are much larger than others. It is a common misconception that a bigger tuber produces a bigger plant. In reality, size does not determine the quality of the bloom.
A dahlia tuber only needs to be about the size of a AA battery to have enough energy to grow a successful plant. Some varieties naturally produce small, slim tubers, while others produce large, chunky ones. As long as the tuber is firm and has an intact neck and crown with an eye, it will perform beautifully.
If a tuber looks a bit shriveled or wrinkled, do not be discouraged. Dahlias are remarkably resilient. You can soak a slightly dehydrated tuber in a bucket of room-temperature water for an hour or two before planting to help it rehydrate. Once it is in the warm soil, it will typically plump up and begin growing without any issues.
Staking for Success
Because dahlia plants can grow anywhere from three to five feet tall, they need a little extra support to stay upright. The weight of the large flowers, especially after a rain, can cause the stems to bend or break.
As mentioned, the best time to install a stake is at the time of planting. This allows you to place the stake exactly where you need it without worrying about hitting the tuber underground. You can use wooden stakes, bamboo poles, or sturdy metal green stakes.
As the plant grows, use soft twine or garden ties to loosely secure the main stem to the stake every 12 inches. Do not tie it too tightly; the stem will thicken as the season progresses, and it needs room to expand. This simple step ensures that your beautiful blooms stay off the ground and in plain sight where you can enjoy them.
Watching for the First Sprouts
The "waiting game" is often the hardest part of gardening. After you have planted your tubers at the correct depth and in the right orientation, it can take anywhere from two to four weeks for the first green shoots to appear.
The speed of sprouting depends entirely on the soil temperature and the specific variety. Some dahlias are "early birds," while others take their time to wake up. As long as the soil is warm and not overly wet, there is no need to worry if you don't see growth immediately.
When the sprouts do emerge, they often look like small, purple or green triangles pushing through the dirt. This is a very exciting moment! Once they reach about six inches in height, you can begin to treat them like established plants, providing regular water and monitoring for any garden visitors like snails or slugs who might be interested in the tender new leaves.
Managing Pests and Early Care
Dahlias are generally easy to care for, but they are a favorite snack for slugs and snails, especially when the plants are young and the leaves are soft. Keeping the area around your dahlias free of weeds and debris can help reduce the hiding spots for these pests.
If you notice small holes in the new leaves, a simple application of organic slug bait can protect your plants during this vulnerable stage. As the plants grow taller and the stems become woodier, they become much less attractive to slugs.
Another early care tip is to "pinch" your dahlias. When the plant is about 12 to 16 inches tall and has several sets of leaves, you can snip off the very top of the center stem. This might feel like you are hurting the plant, but it actually encourages the dahlia to branch out. This results in a bushier plant with many more flowers rather than one single, tall stalk.
Realistic Expectations for Your Garden
Gardening is a partnership with nature, and results can vary based on your local microclimate, soil health, and the weather. Some years might bring a long, hot summer that dahlias love, while other years might be cooler and rainier.
It is important to remember that dahlias are tropical plants at heart. They thrive in the warmth and give their best performance when they are well-fed and well-watered during the height of summer. If a particular variety takes a little longer to bloom, enjoy the lush green foliage in the meantime. The wait is almost always worth it when those first massive flowers finally open.
At Longfield Gardens, we want every gardener to feel the joy of a successful harvest. If you follow the basics—right orientation, right depth, and right timing—you are well on your way to a spectacular display. Dahlias are generous plants, and with just a little bit of care at the start, they will reward you with armloads of flowers for your kitchen table.
Summary of the "Horizontal Rule"
If you remember nothing else from this guide, remember to lay your tubers flat. This single decision solves most orientation problems. Whether the eye is on the left, right, or top, a horizontal position allows the plant to find its way to the surface efficiently.
Combined with a planting depth of 6 inches and a commitment to waiting for warm soil, the horizontal orientation is the foundation of dahlia success. It protects the tuber, supports the future root system, and simplifies the planting process for gardeners of all skill levels.
Key Takeaway: Success starts with patience. Wait for warm soil, plant your tubers horizontally at a depth of 6 inches, and avoid watering until you see green shoots.
Conclusion
Planting dahlias is a rewarding activity that brings incredible beauty to any backyard. By taking the time to understand which way to plant a dahlia tuber, you are giving your garden the best possible start. Remember to look for the eye, lay the tuber horizontally, and place it about 6 inches deep in warm, well-draining soil. These simple steps, backed by the quality tubers we provide at Longfield Gardens, ensure that your summer will be filled with vibrant color.
We stand behind the quality of our plants and want you to have a wonderful experience. If you ever have questions about your delivery or the performance of your plants, our Shipping Information page explains how orders are scheduled and shipped. Gardening is an ongoing journey of learning and discovery, and we are honored to be a part of yours.
- Check your soil temperature before planting (60°F is ideal).
- Always plant horizontally with the eye facing up.
- Don't water until you see the first green sprouts.
- Stake tall varieties at the time of planting to protect the tuber.
"Dahlias are the workhorses of the late-summer garden, providing endless color and beauty if you simply get the basics right at the start."
FAQ
Should the dahlia tuber eye be at the top or the bottom?
The eye should ideally be at the top or facing upward. This allows the sprout to grow directly toward the soil surface, saving the plant energy and helping it emerge faster. If you plant the eye facing down, the sprout will still grow, but it will have to curl around the tuber to find the light.
What happens if I plant a dahlia tuber upside down?
Dahlias are quite resilient, and the sprout will eventually find its way to the surface even if planted upside down. However, it will take much longer for the plant to emerge, and it may be weaker during its early stages. To avoid this, look for the "crown" or the old stem end and ensure that end is facing up or to the side.
Can I plant my dahlia tubers vertically instead of horizontally?
While you can plant them vertically with the eye pointing up, horizontal planting is generally preferred. Laying the tuber flat on its side provides a more stable base for the root system and prevents the tuber from being buried too deep or too shallow. It also mimics how the tubers naturally grow in a clump.
How deep should the eye of the dahlia tuber be buried?
The eye should be buried about 4 to 6 inches below the surface of the soil. This depth provides a good balance between protecting the tuber from temperature fluctuations and allowing the sprout to reach the sun easily. For large varieties, aim for the full 6 inches to provide better support for the heavy stems.
