Table of Contents
- Introduction
- Why Planting on the Side is the Best Choice
- Identifying the "Eye" of the Tuber
- Preparing the Perfect Planting Site
- How to Plant Your Dahlias: Step-by-Step
- The "No Water" Rule for New Tubers
- Planting Dahlias in Containers
- Starting Tubers Early Indoors
- Handling Different Tuber Shapes and Sizes
- Common Planting Questions and Concerns
- Encouraging Healthy Growth After Planting
- Safety for Pets and Children
- Enjoying the Reward
- Summary of Success
- FAQ
Introduction
There is nothing quite like the excitement of unboxing a fresh shipment of dahlia tubers in the spring. These modest, potato-like roots hold the potential for some of the most spectacular blooms in the garden world, from massive dinnerplate varieties to intricate pompons. As you prepare your garden beds for a season of color, a common question often arises: what is the best way to place them in the ground?
Getting the orientation right is a simple step that sets your dahlias up for a successful growing season. At Longfield Gardens, we want to make sure you feel confident from the moment your tubers arrive at your door. To browse more options, see our dahlias for sale. Whether you are a first-time grower or a seasoned gardener looking to refine your technique, understanding the "how" and "why" of planting dahlias will help you achieve the lush, flower-filled garden you’ve been dreaming of.
In this guide, we will answer the question of whether to plant your dahlia tubers on their side and explain the practical reasons behind this traditional method. We will also cover site preparation, depth, and the simple care steps that follow planting. Our goal is to provide clear, actionable advice so you can focus on the reward of beautiful summer flowers.
Planting dahlia tubers horizontally is the most effective way to encourage healthy growth, prevent moisture issues, and help new sprouts reach the sun with ease.
Why Planting on the Side is the Best Choice
When you look at a dahlia tuber, it might not be immediately obvious which end is "up." Unlike a tulip or daffodil bulb, which has a clear pointed top and a flat bottom, a dahlia tuber is a cluster of storage roots. Planting these tubers on their side—or horizontally—is the standard recommendation for several practical reasons.
First, planting on the side mimics how these tubers naturally grow and multiply underground. Dahlias are native to the high-altitude regions of Mexico and Central America, where they grow in well-draining soil. By laying the tuber flat, you provide a stable base for the plant to establish its root system.
Second, the horizontal position is safer for the tuber in terms of moisture. When a tuber is planted vertically with the "neck" or sprout-end pointing straight up, water can sometimes collect in the hollow of the old stem. This standing water can lead to rot before the plant even has a chance to sprout. Laying the tuber on its side allows water to drain away from the crown more effectively.
Finally, planting on the side makes it easier for the "eye" of the dahlia to find its way to the surface. The eye is the small bump or sprout where the new stem will emerge. If the tuber is horizontal, the sprout can grow upward naturally without having to navigate around the bulk of the tuber itself.
Key Takeaway: The Goal of Horizontal Planting
Laying your dahlia tubers flat on their side provides the best balance of stability, drainage, and easy access for new sprouts to reach the light.
Identifying the "Eye" of the Tuber
Before you put your tubers in the ground, it helps to identify the "eye." This is the most important part of the dahlia because it is the only place where new growth can begin. If you have a tuber without an eye, it will not produce a plant, even if the tuber itself is large and healthy-looking.
The eye is located on the "crown" of the dahlia, which is the area where the individual tubers meet the old stem from the previous year. It looks like a tiny, swollen bump, much like the eye on a potato. In the spring, as the weather warms, these eyes often begin to sprout, showing a small green or pink "nub."
When you plant your tuber on its side, try to position it so the eye is facing upward. Don't worry if you can't see an eye yet; dahlias are very resilient. As long as you lay the tuber flat, the sprout will eventually find its way toward the warmth of the sun.
Preparing the Perfect Planting Site
Success with dahlias begins long before the tuber touches the soil. Like any plant, dahlias have specific preferences that help them thrive. Choosing the right spot and preparing the soil will make the physical act of planting much more rewarding.
Sunlight Requirements
Dahlias are sun-loving plants. For the best blooms and strongest stems, they need at least six to eight hours of direct sunlight each day. If they are planted in too much shade, the plants tend to become "leggy" as they stretch toward the light, and they will produce fewer flowers. In very hot southern climates, a bit of afternoon shade can be beneficial to prevent the flowers from wilting, but full sun is generally the rule.
Soil Drainage and Texture
"Drainage" is a term gardeners use to describe how fast water leaves the soil. Dahlias have a very low tolerance for "wet feet," which means they do not like to sit in soggy soil. If the soil stays too wet for too long, the tubers can rot.
The ideal soil for dahlias is loose, crumbly, and rich in organic matter. If you have heavy clay soil that stays wet after rain, you can improve the drainage by adding compost or planting in raised beds. We find that a well-prepared bed allows the tubers to breathe and grow a robust root system quickly.
Soil Temperature and Timing
Timing is one of the most important factors in dahlia success. It can be tempting to plant as soon as the first warm day of spring arrives, but dahlias are tropical plants that love warmth. They should not go into the ground until the soil temperature has reached at least 60°F and all danger of frost has passed. If you want to check your climate, our USDA Hardiness Zone Map can help.
A good rule of thumb is to plant your dahlias around the same time you would plant tomatoes in your garden. If the soil is too cold and wet, the tuber will sit dormant, making it more susceptible to rot. Waiting for the soil to warm up ensures that the tuber "wakes up" and starts growing immediately.
What to do next:
- Pick a spot with 6-8 hours of full sun.
- Check that the soil is loose and doesn't hold standing water.
- Wait for the soil to reach 60°F before planting.
- Add a few inches of compost to the area to boost nutrients.
How to Plant Your Dahlias: Step-by-Step
Once your site is ready and the weather is warm, it’s time to get your tubers in the ground. Following a few simple steps ensures they are at the right depth and have enough room to grow.
Step 1: Dig the Hole
For most dahlia varieties, you should dig a hole that is about 6 to 8 inches deep and wide enough to accommodate the tuber horizontally. If you are planting a large clump of tubers, make the hole a bit wider so they aren't cramped.
Step 2: Set the Stake (Optional but Recommended)
If you are growing decorative dahlias, it is a great idea to put your support stake in the ground at the time of planting. If you wait until the plant is large to drive a stake into the ground, you run the risk of piercing the tuber below. Placing the stake first allows you to plant the tuber right next to it safely.
Step 3: Place the Tuber
Lay the tuber flat on its side at the bottom of the hole. If you identified an eye or a sprout, make sure it is pointing toward the sky. If you are planting near a stake, place the crown (the end with the eye) closest to the stake.
Step 4: Cover with Soil
Gently fill the hole back in with soil. You want the tuber to be covered by about 4 to 6 inches of soil. Do not pack the soil down too hard; just a light pat will do to remove any large air pockets.
Step 5: Spacing
Dahlias need plenty of elbow room to allow for air circulation, which helps prevent disease.
- Large varieties: Space them 18 to 24 inches apart.
- Small or "border" varieties: Space them 12 to 15 inches apart.
The "No Water" Rule for New Tubers
One of the most surprising tips for new dahlia growers is that you usually should not water your tubers immediately after planting. This is a departure from how we treat most new plants, but there is a good reason for it.
Until the dahlia tuber has sent out roots and a sprout has emerged from the soil, it has no way to "drink" the water you provide. Adding extra water to the soil before the plant is active only increases the risk of the tuber rotting. In most regions, the natural moisture already present in the spring soil is more than enough to get the tuber started.
You should wait to start regular watering until you see the green sprouts appearing above the soil line. This usually takes about two to three weeks, depending on the temperature. Once the plant is growing and has leaves, you can begin a regular watering schedule, ensuring the soil stays consistently moist but not soggy.
Key Takeaway: Patience with the Watering Can
Avoid watering your dahlias until you see green growth above the ground. This simple step is one of the best ways to prevent tuber rot.
Planting Dahlias in Containers
If you don't have a large garden plot, you can still enjoy beautiful border dahlias by planting them in containers. The rules for planting on the side remain the same, but there are a few extra considerations for pot-grown flowers.
Choosing the Right Pot
A dahlia needs a large enough "house" to support its root system and its tall top growth. For most varieties, a 5-gallon container is the minimum size you should use. Ensure the pot has plenty of drainage holes at the bottom.
Soil for Containers
Use a high-quality potting mix rather than garden soil. Potting mix is designed to be lightweight and provide excellent drainage, which is crucial for dahlias in pots.
Planting Depth in Pots
In a container, you can plant the tuber slightly shallower than you would in the ground. Aim for about 4 inches of soil over the top of the tuber. Lay the tuber on its side just as you would in a garden bed.
Watering Pots
Unlike dahlias in the ground, dahlias in containers may need a small amount of water at planting time if the potting mix is bone-dry. Just a light sprinkle is enough to settle the soil. Once the plant is growing, remember that pots dry out much faster than the ground, so you will need to check them daily during the heat of summer.
Starting Tubers Early Indoors
For gardeners in northern climates with short growing seasons, starting dahlia tubers indoors can give the plants a helpful head start. This process is often called "pre-sprouting."
About 4 to 6 weeks before the last frost date, you can place your tubers in small pots or trays filled with slightly moist potting soil. Again, lay them on their side with the eye-end pointing up. Keep the pots in a warm spot (around 65-70°F) with plenty of light. For more background, see Dahlia Tubers: What You Need to Know.
By the time the soil outside is warm enough for planting, your dahlias will already have a strong root system and several inches of green growth. When you move them outside, be sure to "harden them off" by gradually introducing them to direct sunlight over several days to prevent the leaves from burning.
Handling Different Tuber Shapes and Sizes
When you receive your order from us, you might notice that tubers come in many different shapes. Some are long and skinny, while others are round and plump. Some varieties produce large clumps of several tubers joined together, while others arrive as a single, sturdy tuber.
The size of the tuber does not necessarily determine the size of the plant or the flower. A small, healthy tuber with a clear eye will often grow just as vigorously as a much larger one. For a broader overview, see All About Dahlias.
What if the tuber is very long?
If you have a particularly long tuber that doesn't fit easily in your planting hole, you can dig the hole a bit wider. It is better to give a long tuber the space to lie flat on its side than to try and stand it up vertically to make it fit.
What if the tuber is huge?
Occasionally, you might find a "mother tuber" that is exceptionally large. While it can be tempting to think bigger is better, a very large tuber can sometimes be slow to establish new roots because it is living off its own stored energy. You can still plant it on its side, just as you would a smaller one, but be extra careful not to overwater it.
Common Planting Questions and Concerns
Even with the best advice, it’s natural to have a few questions as you get started. Here are a few common scenarios gardeners encounter when planting dahlias.
"What if I accidentally plant it upside down?"
Don't worry! While planting on the side with the eye facing up is the "best" way, dahlias are incredibly determined. If a tuber is planted upside down or at an angle, the sprout will simply grow around the tuber and head toward the surface. It might take a few extra days for the sprout to appear, but the plant will usually be just fine.
"Can I mulch my dahlias?"
Mulching is a great way to keep weeds down and retain moisture, but you should wait until the dahlias are well-established. When you first plant the tubers, avoid covering the area with a thick layer of mulch. This can keep the soil too cool and trap too much moisture near the emerging sprout. Once the plants are about a foot tall, you can add a thin layer of mulch, keeping it a few inches away from the main stem.
"Do I need to fertilize at planting time?"
If your soil is already healthy and has been amended with compost, you don't necessarily need to add fertilizer the moment you plant. However, many gardeners like to mix a small amount of a low-nitrogen, high-phosphorus fertilizer into the bottom of the hole. This encourages strong root development and future blooms. Avoid fertilizers with high nitrogen (the first number on the package), as this can lead to lots of green leaves but very few flowers.
What to do next:
- Check the forecast to ensure no more frost is expected.
- Lay out your tubers to plan your spacing.
- Keep a garden journal to note where you planted each variety.
- Take a photo of the tags so you remember the names!
Encouraging Healthy Growth After Planting
Once your dahlias have sprouted and are about 12 inches tall, there is one more simple trick to ensure a spectacular display: "pinching."
Pinching is the process of snipping off the very top of the main stem. This might feel a bit scary, but it actually encourages the plant to grow more side branches. More branches mean a bushier, stronger plant and, most importantly, many more flowers! To pinch your dahlia, wait until it has three to four sets of leaves, then use your fingers or a clean pair of snips to remove the center growing point. For a complete walk-through, see How to Plant and Grow Dahlias for a Spectacular Garden.
As the season progresses, remember to keep your dahlias supported. Tall varieties can become top-heavy when they are covered in blooms. Use soft twine to tie the stems to your stakes as they grow. This protects the brittle stems from being broken by wind or heavy summer rain.
Safety for Pets and Children
It is important to note that dahlia tubers and foliage can be mildly toxic if eaten by pets or humans. They can cause skin irritation or upset stomachs in some cases. When planting, keep your tubers out of reach of curious dogs or cats, and wash your hands after handling the roots and plants. If you have pets that like to dig, you might want to place a small piece of chicken wire over the planting spot until the sprouts emerge to discourage them from uncovering the tubers.
Enjoying the Reward
Gardening is a journey of patience and observation. From that first moment you lay a tuber on its side in the warm spring soil to the day you cut a magnificent bloom for a vase, each step is a rewarding part of the process. Dahlias are some of the most generous plants in the garden, providing color and joy from mid-summer all the way until the first frost of autumn.
At Longfield Gardens, we are here to support you every step of the way. We take great care to ensure our tubers are healthy, true to variety, and ready to perform in your garden. By getting the basics right—like planting on the side, choosing a sunny spot, and waiting for the soil to warm—you are well on your way to a season filled with stunning flowers. For extra peace of mind, see our 100% Guarantee.
We look forward to hearing about your dahlia success! If you ever have questions about your order or need more gardening tips, our team is always ready to help. When you're ready to plan your next bed, browse our dahlia collections.
Summary of Success
- Orientation: Plant tubers horizontally (on their side).
- Depth: Aim for 4-6 inches of soil over the tuber.
- Timing: Wait for soil to reach 60°F and frost danger to pass.
- Watering: Hold off on watering until you see green sprouts.
- Support: Stake tall varieties at planting time to avoid root damage later.
"The simple act of planting a dahlia tuber is an investment in months of beauty. By giving them the right start, you’re ensuring a garden that glows with color all season long."
We look forward to hearing about your dahlia success! If you ever have questions about your order or need more gardening tips, our team is always ready to help.
FAQ
1. Do I need to soak dahlia tubers before planting them on their side?
Soaking is not strictly necessary, but some gardeners find that a short soak of one to two hours in lukewarm water can help "wake up" a very dry tuber. If your tubers look firm and healthy, you can skip this step and plant them directly in the warm soil.
2. Is it okay if some of the tubers in a clump are broken?
Yes, it is common for a few individual tubers in a cluster to get bent or broken during shipping or handling. As long as the "crown" (the area where the tubers connect to the stem) and the "neck" of the tuber with the eye are intact, the dahlia will grow perfectly fine. You can even snip off any completely detached tubers.
3. Can I plant dahlias on their side in a trench?
If you are planting a long row of dahlias for a cutting garden, digging a trench instead of individual holes can be a great time-saver. For more on harvesting stems, see our Expert Tips for Cutting and Arranging Dahlias. Dig the trench 6 inches deep, lay your tubers flat on their side at the recommended spacing, and then backfill the entire trench with soil.
4. Why is my dahlia taking so long to sprout?
Dahlias move at their own pace based on the temperature. If the weather has been cool or rainy, it can take three weeks or even longer for a sprout to appear above the soil. As long as the soil is well-drained and the weather is warming up, your tuber is likely busy growing roots underground and will appear soon.