Introduction
There is nothing quite like the excitement of unboxing a fresh shipment of dahlia tubers. These remarkable plants produce some of the most spectacular blooms in the summer garden, ranging from tiny pompons to massive dinnerplate varieties. At Longfield Gardens, we know that while dahlias look exotic and complex, they are actually quite simple to grow once you understand a few basic principles.
Whether you are a seasoned gardener or a beginner planting your very first flower bed, the most common question we hear is about orientation. Looking at a dahlia tuber for the first time can be a bit confusing because they don't look like a typical "pointed" bulb. This guide will show you exactly how to identify the right side up and how to plant your dahlias for the best possible results.
Getting the orientation right ensures your plants emerge quickly and develop a strong root system. While dahlias are resilient, taking a moment to position them correctly in the soil sets the stage for a season full of vibrant color and abundant stems for cutting. By following a few simple steps, you can plant with confidence and look forward to a stunning late-summer display.
Understanding Dahlia Anatomy
Before we dig into the planting process, it helps to know what you are looking at. While many people refer to them as "dahlia bulbs," they are technically tubers. They function similarly to a potato, storing energy and nutrients to fuel the plant's growth throughout the season.
A viable dahlia tuber consists of three main parts: the body, the neck, and the crown. The body is the fat, sausage-like part of the tuber. The neck is the narrower portion that connects the body to the crown. The crown is the area where the "eyes" or growth points are located.
It is important to handle these tubers with care. The neck is the most fragile part of the plant. If the neck is broken or severely creased, the energy stored in the body cannot reach the eye, and the tuber may not grow. When you receive your order from us, you will notice the tubers are firm and healthy, ready to be tucked into the ground.
Identifying the Growing Eye
The "eye" is the most important part of the dahlia tuber. This is the small bump or sprout where the new stem will emerge. It is located on the crown, right at the base of the old stem from the previous year.
Sometimes the eyes are very easy to see, especially if the tuber has already started to sprout. They look like tiny green or pinkish buds, similar to the eyes on a potato. If you don't see a sprout yet, look for a small, slightly raised "pimple" on the crown area.
If you can't find an eye right away, don't worry. Sometimes they are "blind" or dormant until they feel the warmth of the soil. As long as the tuber has a crown and an intact neck, it is a healthy plant that is ready to grow.
Tuber Shapes and Sizes
Dahlia tubers come in many different shapes and sizes. Some are long and thin, while others are short and round. You might receive a single tuber or a small clump of them joined at a single crown.
The size of the tuber does not determine the size of the flower. A tiny tuber can produce a massive plant, and a large tuber might produce a compact variety. The tuber is simply a starter kit of energy. Once the plant develops its first few sets of leaves, it will begin to grow its own root system and eventually produce a new "clump" of tubers underground for the following year.
Key Takeaway: A healthy dahlia tuber needs an intact neck and at least one "eye" located on the crown to grow successfully.
The Best Way Up: Horizontal vs. Vertical
When it's time to put your dahlias in the ground, the goal is to make it as easy as possible for the sprout to find the surface and for the roots to anchor the plant.
The most effective way to plant a dahlia tuber is horizontally. Instead of trying to stand the tuber up on one end, lay it flat on its side at the bottom of the planting hole. For additional guidance, see this guide to positioning dahlia tubers.
Why Horizontal is Better
Planting horizontally is the preferred method for several reasons:
- Stability: A tuber lying flat has a broader base, which helps the plant stay anchored as it grows tall and heavy with blooms.
- Sprout Access: When laid flat, the eye (which should be facing upward or slightly to the side) has a direct path to the surface.
- Root Development: Roots will emerge from the crown area and the base of the new stem. A horizontal position allows these roots to spread out easily into the surrounding soil.
If you happen to plant a tuber vertically with the eye facing up, it will still grow. However, horizontal planting is more natural and typically results in a more vigorous start for the plant.
Positioning the Eye
When you lay the tuber on its side, try to position it so the eye is facing toward the sky. If the eye is on the side of the crown, that is perfectly fine too. The sprout is naturally programmed to grow toward the light, so it will find its way up regardless of the exact angle, as long as it isn't pointed directly into the bottom of the hole.
If you are planting a clump of tubers rather than a single tuber, the same rule applies. Lay the entire clump flat so that the old stem (the center point where the tubers meet) is pointing upward.
Step-by-Step Planting Guide
Now that you know which way is up, you can move forward with the actual planting. Following a consistent process will help ensure your dahlias thrive from day one.
1. Choose the Right Spot
Dahlias are sun-lovers. They need at least six to eight hours of direct sunlight every day to produce those famous blooms. If they are planted in too much shade, the stems will become "leggy" and weak, and you will see fewer flowers.
Good drainage is also essential. Dahlias don't like "wet feet." If your soil stays soggy after a rain, the tubers may rot before they have a chance to grow. If you have heavy clay soil, consider planting in raised beds or amending the soil with compost to improve the way water moves through it. This guide to choosing where to plant dahlias offers additional site-planning advice.
2. Dig the Hole
For most dahlia varieties, you should dig a hole about 4 to 6 inches deep. This depth protects the tuber from temperature fluctuations and provides enough soil coverage to support the heavy stems later in the season.
Space your holes about 12 to 24 inches apart. Smaller "border" dahlias can be closer together, but large dinnerplate varieties need at least 2 feet of space to allow for good airflow and room to branch out. See this dahlia spacing guide for more details.
3. Place the Tuber
Place your dahlia tuber in the hole horizontally. Check one last time to ensure the neck is intact and the eye is facing up or to the side.
If you are planting tall varieties, this is also the perfect time to place a stake in the hole. Driving a stake into the ground after the plant is growing can accidentally pierce the tuber. By putting the stake in now, you know exactly where the plant is and can avoid any damage.
4. Cover and Label
Fill the hole with soil, gently firming it down with your hands. Avoid packing it too tightly, as the sprout needs to be able to push through easily.
We highly recommend labeling your dahlias at the time of planting. It is very easy to forget which color is which once they are buried! Use a waterproof marker and a sturdy garden label to keep your varieties organized.
What to Do Next
- Check your soil temperature to ensure it is at least 60°F.
- Dig holes 4–6 inches deep and space them according to the variety size.
- Lay the tubers flat (horizontally) with the eye facing up.
- Place stakes for tall varieties at the time of planting to protect the tubers.
- Cover with soil and label each spot immediately.
Timing Your Planting
Timing is perhaps the most critical factor in dahlia success. Because these plants are native to the warm climates of Mexico and Central America, they have no tolerance for frost.
Wait for Warm Soil
At Longfield Gardens, we ship our tubers based on your USDA hardiness zone so they arrive at the appropriate time for your area. However, local weather can be unpredictable. You should wait until all danger of spring frost has passed before putting your tubers in the ground.
Beyond just the air temperature, pay attention to the soil temperature. Dahlias will sit dormant and may rot if the soil is cold and wet. Wait until the soil has warmed to about 60°F. A simple way to tell if the ground is ready is when you see local farmers planting corn or when you are ready to set out your tomato plants.
Starting Early Indoors
If you live in a region with a very short growing season, you can give your dahlias a head start by "waking them up" indoors. About four to six weeks before the last frost date, you can place the tubers in pots with slightly damp potting soil.
Keep the pots in a warm, sunny spot. This allows the eyes to sprout and the root system to begin developing. When the weather is finally warm enough, you can transplant the entire root ball into the garden. This method often results in blooms several weeks earlier than direct planting.
Watering and Initial Care
One of the most common mistakes gardeners make is overwatering dahlias immediately after planting. Until the plant has sprouted and has green leaves above the ground, it does not have a way to process large amounts of water.
The "Wait to Water" Rule
When you first plant your dahlia tubers, the soil should be slightly moist but not saturated. In most cases, you do not need to water them at all until you see the first green shoots poking through the soil.
The tuber contains all the moisture and energy needed to send up that first sprout. Adding too much water to the soil before the sprout appears can lead to rot. If your region is experiencing an extreme dry spell or your soil is bone-dry, a very light watering is okay, but generally, let nature take its course until the plant is established.
Watching for Sprouts
It can take anywhere from two to four weeks for a dahlia sprout to emerge from the ground. Be patient! The plant is busy growing roots under the surface before it focuses on upward growth. Once the green leaves appear, you can begin a regular watering schedule, ensuring the plants get about an inch of water per week.
Key Takeaway: Resist the urge to water your dahlias until you see green growth above the soil line to prevent the tubers from rotting in the ground.
Support and Growth Habits
As your dahlias begin to grow, they will need a little bit of guidance to reach their full potential. Dahlias are fast growers, and some varieties can reach heights of 4 to 5 feet.
Staking and Tying
Because dahlia stems are hollow, they can be somewhat brittle. The weight of large flowers, combined with wind or heavy rain, can cause the plants to topple over.
If you placed your stakes at planting time, simply use garden twine or soft ties to secure the main stem to the stake every 12 inches or so as the plant grows. For large groupings of dahlias, some gardeners use the "corral" method, where stakes are placed at the corners of the bed and twine is wrapped around the entire perimeter to hold the plants upright.
Pinching for More Blooms
If you want a bushier plant with more flowers, we recommend "pinching" your dahlias. When the plant is about 12 to 16 inches tall and has four sets of leaves, snip off the very top of the center stem.
This might feel counterintuitive, but it signals the plant to stop growing upward and start sending out side branches. This results in a stronger, more compact plant and significantly more blooms throughout the season. If you prefer one single, giant flower (often done for competitions), you can skip the pinching, but for the home garden, pinching is almost always the best choice.
Protecting Your Plants
While dahlias are generally easy to care for, they do have a few fans in the insect world. Keeping an eye on your plants early in the season will help them stay healthy.
Slugs and Snails
The tender green shoots of a newly emerged dahlia are a favorite snack for slugs and snails. If you notice holes in the leaves or missing sprouts, these are the likely culprits. You can use organic slug bait or physical barriers to protect your young plants until they are large enough to withstand a little nibbling.
Earwigs and Aphids
Later in the season, you may see earwigs or aphids. Earwigs like to hide inside the petals of the flowers, while aphids usually cluster on the new growth or the undersides of leaves. In most cases, a strong blast of water from the garden hose is enough to dislodge these pests. For persistent issues, consult your local extension office for advice on the best environmentally friendly treatments for your specific area.
Dahlias in Containers
If you don't have a large garden plot, you can still enjoy dahlias! Many varieties grow beautifully in pots and containers. This is a great way to add color to a patio or balcony.
Choosing the Right Pot
When growing dahlias in containers, the "which way up" rule remains the same—plant the tuber horizontally. However, you must ensure the pot is large enough. A 5-gallon container is the minimum size for most dahlias. Larger varieties may need even more space.
Ensure the container has excellent drainage holes. Use a high-quality potting mix rather than garden soil, as potting mix is designed to drain well and provide the right balance of air and moisture for roots in a confined space.
Container Maintenance
Plants 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. Additionally, because the roots are confined, they will use up the nutrients in the potting soil quickly. Applying a balanced, water-soluble fertilizer every two weeks will keep your container dahlias blooming vigorously until the first frost.
Harvesting and Enjoying Your Flowers
The best part of growing dahlias is the flowers! These plants are incredibly productive, and the more you cut them, the more they will bloom.
When to Cut
Unlike some flowers that continue to open after they are harvested, dahlias should be cut when they are nearly fully open. Look at the back of the flower head; the petals should be firm and lush. If the petals on the back are starting to look papery or limp, the flower is past its prime.
Cut your stems in the cool of the morning for the longest vase life. Use clean, sharp snips and place the stems immediately into a bucket of water.
Deadheading
If you choose not to cut your flowers for bouquets, you still need to "deadhead" the plant. This means removing the faded blooms before they start to produce seeds. This tells the plant to keep putting its energy into making new flowers rather than finishing its life cycle for the year.
To deadhead correctly, don't just pull off the flower head. Follow the stem down to the next set of leaves or buds and make your cut there. This keeps the plant looking tidy and encourages new growth.
Preparing for Winter
In most parts of the United States, dahlias are not hardy enough to stay in the ground over the winter. They are treated as annuals or as tender perennials that need to be "lifted" and stored. This winter-care guide explains the process in more detail.
Lifting the Tubers
After the first hard frost kills the foliage, the plant will turn black. This is your signal that it's time to act. Cut the stems down to about 4 inches above the ground and wait about a week. This allows the tubers to go into a dormant state.
Gently dig around the plant, being careful not to pierce the tubers with your shovel. Lift the entire clump out of the ground and shake off the excess soil.
Storage Basics
Once lifted, let the tubers dry in a protected, frost-free area for a few days. You can then store them in a cool, dark, dry place (like a basement or crawlspace) where temperatures stay between 40°F and 50°F. Many gardeners pack them in peat moss, vermiculite, or wood shavings to keep the moisture levels stable.
Check on your stored tubers once a month during the winter. If they look shriveled, give them a tiny mist of water. If any show signs of rot, remove them immediately to keep the rest of the clump healthy.
Conclusion
Growing dahlias is one of the most rewarding experiences a gardener can have. By simply placing your tubers horizontally with the eye facing up, you give these plants the best possible start. Remember to wait for warm soil, resist the urge to overwater early on, and provide plenty of sunlight.
At Longfield Gardens, we take pride in providing high-quality tubers that are ready to burst into life in your garden. With a little bit of patience and the right planting technique, you will soon be rewarded with a spectacular display of color that lasts from midsummer right through the first frost of autumn.
"Dahlias are the workhorses of the late-summer garden, providing endless color and beauty with just a small amount of initial care."
- Plant horizontally for the best stability and sprout growth.
- Wait for the soil to reach 60°F before planting to avoid rot.
- Don't water until you see the first green shoots emerge.
- Pinch the stems when they are 12 inches tall for a bushier, more productive plant.
FAQ
Can I plant a dahlia tuber vertically if it is very long?
While horizontal planting is ideal, you can plant a tuber at a slight angle if the hole isn't wide enough. Just ensure the crown with the eye is at the correct depth (4–6 inches) and the eye is generally pointing toward the surface.
What happens if I accidentally plant my dahlia bulb upside down?
Dahlias are surprisingly clever and the sprout will eventually turn itself around to grow toward the light. However, it will take much longer for the plant to emerge, and it may be weaker. If you realize your mistake early, it is perfectly fine to gently dig it up and reposition it.
Do I need to soak dahlia tubers before planting?
No, it is not necessary or recommended to soak dahlia tubers. Unlike some bulbs or corms, dahlia tubers contain plenty of moisture. Soaking them can actually increase the risk of rot, especially if the soil is also damp.
Why hasn't my dahlia sprouted after three weeks?
It can take up to four weeks for a sprout to appear, especially if the soil is still on the cooler side. As long as the tuber was firm when planted and the soil isn't soaking wet, it is likely just taking its time to establish roots first. Be patient and wait for the soil to warm up further.
