Introduction
There is nothing quite like the feeling of seeing your first dahlias of the season begin to unfurl. Dinnerplate dahlias are the crown jewels of the summer garden, offering a variety of colors and shapes that few other plants can match. Whether you are dreaming of massive dinnerplate blooms or charming pompons, the journey to a beautiful garden starts with a single, simple step: getting the tuber in the ground.
At Longfield Gardens, we want to help you feel confident as you start your planting journey. One of the most common questions we hear from home gardeners is which way is up when it is time to plant dahlias. It is a natural question to ask, as dahlia tubers have a unique shape that does not always make the answer obvious.
This guide will help you identify the right parts of the tuber and show you exactly how to position them for the best results. By following a few basic steps, you can ensure your dahlias have the strongest possible start. Understanding the correct orientation for your tubers makes the planting process faster and helps your plants emerge with ease.
Identifying the "Eye" of a Dahlia Tuber
Before you can decide which way is up, you need to know what you are looking for. Every dahlia tuber or clump has a specific point where the new growth will begin. This point is called the "eye." If you have ever looked at a potato before planting it, you have seen something very similar.
The eye is a small, slightly raised bump or a tiny green or pink nub. It is located on the "crown" of the dahlia, which is the area where the individual tubers meet the old stem from the previous year. You will not find eyes on the round, fleshy body of the tuber or at the very tips. They only appear on the crown.
Sometimes, eyes are very easy to see, especially if the tuber has already started to sprout. In other cases, they can be quite dormant and look like a tiny, inconspicuous pimple. If you are having trouble spotting them, do not worry. You can place your tubers in a warm, bright spot for a week or two before planting. This often "wakes up" the eyes, making them swell and turn a light pink or green color.
Key Takeaway: The eye is the most important part of the tuber because it is the only place where a new stem can grow. Always look for this small bump near the old stem or crown before you head out to the garden.
Which Way Up? The Horizontal Rule
The most straightforward answer to the question of orientation is to plant the tuber horizontally. While some bulbs, like tulips or daffodils, have a very clear "pointy side up" rule, dahlias are a bit different. In a professional setting and in our own trial gardens, we find that laying the tuber on its side is the most effective method.
When you lay the tuber horizontally, you should ensure that the eye is facing toward the sky. If you are planting a clump of tubers that are still attached to a central stem, the stem should be pointing upward, with the individual tubers spreading out sideways.
There are several benefits to this horizontal approach:
- Easier Path to the Surface: When the eye is facing up, the new sprout has the shortest and most direct path to the sunlight.
- Better Root Distribution: Placing the tuber on its side allows roots to grow out from the crown and the neck of the tuber more evenly into the surrounding soil.
- Natural Growth Pattern: This positioning mimics how dahlias naturally grow and expand over time.
If you happen to plant a tuber upside down, the sprout will eventually find its way toward the light. Plants are very resilient and have a natural sense of direction. However, the sprout will have to grow in a "U" shape to get around the tuber. This uses up extra energy and can delay the time it takes for your dahlia to poke through the soil. Planting it correctly from the start gives the plant a little "head start" on the season.
Choosing the Best Spot for Your Dahlias
Success with dahlias depends on matching the plant to the right environment. Before you dig your first hole, take a look at your yard to find a location that meets these two simple requirements: plenty of sun and good drainage. You can also get a helpful overview of where dahlias grow well before you decide on a planting spot.
The Importance of Sunlight
Dahlias are sun-loving plants. To produce those famous, heavy blooms, they need at least six to eight hours of direct sunlight every day. More sun usually leads to stronger stems and more flowers. If they are planted in too much shade, the plants may become "leggy" as they stretch toward the light, and you will likely see fewer blooms.
Understanding Drainage
Drainage refers to how fast water leaves the soil after a rain or watering. Dahlias have fleshy tubers that store a lot of moisture. Because of this, they do not like to sit in "wet feet." If the soil stays soggy for too long, the tubers can rot before they even have a chance to grow.
To check your drainage, observe your garden after a heavy rain. If puddles remain for several hours, the soil may be too heavy or compacted. You can improve drainage by adding compost or planting in raised beds. A simple rule is that if the spot is good for a vegetable garden, it is likely a great spot for dahlias.
Timing Your Planting
When it comes to dahlias, timing is everything. For a fuller guide, see our When Should I Plant Dahlia Tubers? Best Planting Guide.
These are tropical plants that originated in warm climates, which means they have no tolerance for frost. Planting too early in cold, wet soil is one of the most common reasons tubers fail to sprout.
The best time to plant is when the soil has warmed up to at least 60°F and all danger of spring frost has passed. For most gardeners, this is around the same time you would plant tomatoes or peppers. A simple way to check is to feel the soil with your hand; if it feels cold and clammy, it is better to wait a week or two.
If you live in a region with a short growing season, you can start your dahlias indoors in pots about four to six weeks before the last frost. This gives them a head start so they are already growing when you move them outside. If you do this, just remember to move them outdoors gradually so they can get used to the sun and wind.
Step-by-Step Planting Process
Once your soil is warm and you have found a sunny spot, you are ready to plant. Following a consistent process helps ensure that every tuber is at the right depth and has the space it needs to thrive.
- Prepare the Soil: Loosen the soil to a depth of about 10 to 12 inches. This makes it easier for the new roots to spread out. You can mix in some compost at this stage to add organic matter.
- Dig the Hole: Dig a hole that is about 4 to 6 inches deep. For smaller border varieties, 4 inches is usually sufficient. For large dinnerplate varieties, a 6-inch depth is better to provide more stability for the tall stems.
- Place the Tuber: Lay the tuber horizontally in the bottom of the hole. Ensure the eye or the sprout is facing upward.
- Add a Support: If you are planting tall varieties, it is a great idea to place a stake in the ground right now. See our How to Pinch and Stake Dahlias guide.
- Cover with Soil: Gently fill the hole back in with the soil you removed. Do not pack it down too hard; a light touch is all that is needed to close up any large air pockets.
What to Do Next:
- Mark your planting spot with a label so you don't accidentally dig it up later.
- Set up your stakes or supports immediately for tall varieties.
- Check the soil temperature one last time before you begin.
- Keep your garden tools clean to prevent the spread of soil-borne issues.
Spacing and Depth Requirements
Giving your dahlias enough room to breathe is essential for plant health. Airflow between plants helps keep the leaves dry and prevents common issues like powdery mildew. The amount of space you need depends on how large the variety will grow.
- Large Varieties (Dinnerplate and Decorative): These plants can grow 3 to 4 feet wide. Space the tubers about 18 to 24 inches apart. For colorful mixed plantings, decorative dahlias are a fun option.
- Medium Varieties (Cactus and Ball): These generally need about 12 to 18 inches of space. Cactus dahlias bring a spikier flower form to the garden.
- Small Varieties (Border and Mignon): These compact plants can be spaced as close as 12 inches apart. Border dahlias are especially useful at the front of a bed.
Regarding depth, the goal is to have the top of the tuber covered by about 2 to 3 inches of soil once the hole is filled. If you plant them too shallow, the heavy plants might tip over later in the summer. If you plant them much deeper than 6 inches, the sprout may struggle to reach the surface. Staying in that 4-to-6-inch range is the "sweet spot" for most dahlias.
Post-Planting Care: Water and Patience
One of the most important rules for new dahlia growers is to avoid watering the soil immediately after planting. This might feel counterintuitive, as we usually water new plants right away. However, dahlia tubers are dormant when they go into the ground. Without leaves or a root system, they cannot "drink" the water.
Excess moisture in the soil before the tuber has sprouted can lead to rot. In most cases, the natural moisture in the soil is more than enough to get the tuber started. You should wait to start a regular watering schedule until you see the first green shoots poking through the soil. For more on this, read Should Dahlia Bulbs Be Soaked Before Planting?
Once the plants are about 6 to 12 inches tall and have established leaves, they will need consistent moisture. At that point, you can transition to deep watering once or twice a week. It is always better to water deeply and less often than to give them a light sprinkle every day. Deep watering encourages the roots to grow further down into the soil, making the plant more stable and drought-resistant.
Encouraging More Blooms Through Pinching
Once your dahlias are growing happily, there is one simple trick you can use to get even more flowers: pinching. Pinching sounds a bit harsh, but it is actually a way to help the plant become bushier and more productive.
When your dahlia plant is about 12 inches tall and has four sets of leaves, you can "pinch out" the very top of the center stem. You can do this with your fingers or a clean pair of garden snips. Removing that center growing point signals the plant to start growing from the side buds.
Instead of one tall, lanky stem, the plant will produce multiple side branches. This results in a sturdier plant that is less likely to blow over in the wind. Most importantly, more branches mean more places for flower buds to form. You will end up with a much more colorful display in your garden.
Supporting Your Tall Dahlias
Because dahlia stems are often hollow and the flower heads can be very heavy, many varieties need a little extra support. This is especially true for dinnerplate dahlias, which can have blooms as large as a dinner plate.
If you placed a stake at planting time, you can simply tie the main stem to the stake as the plant grows. Use a soft material like garden twine or strips of old fabric. Avoid using wire or thin string that might cut into the soft stems.
Another popular method for home gardens is using tomato cages. If you place a sturdy metal cage over the tuber shortly after it sprouts, the plant will grow up through the center, and the side rings will support the heavy branches. This is a very simple "set it and forget it" way to keep your garden looking tidy.
Enjoying the Reward
The wait for the first dahlia bloom is always worth it. Depending on the variety and your local weather, most dahlias will begin blooming in mid-to-late summer and will continue until the first frost of autumn.
The best way to keep the flowers coming is to pick them often. Dahlias are prolific bloomers, and the more you cut the flowers for bouquets, the more the plant will work to produce new ones. When you cut the flowers, try to cut the stems long, especially on ball dahlias. This encourages the plant to produce more long-stemmed flowers that are perfect for vases inside your home.
If you don't want to cut them for bouquets, make sure to "deadhead" the plant. This means snipping off the old, faded flowers before they start to form seeds. This keeps the plant's energy focused on creating new blooms rather than producing seeds for the next year.
Summary of Success
Planting dahlias is a rewarding experience that brings vibrant color to any backyard. By getting the basics right at the start, you set the stage for a season full of flowers. Remember that gardening is a journey, and every season is an opportunity to learn something new about your unique soil and climate.
At Longfield Gardens, we stand behind the quality of our tubers and want your garden to be a source of joy. Our tubers are guaranteed to be true to variety and arrive in prime condition for planting. If you need shipping details, see our Shipping Information.
Final Tips for Success:
- Plant horizontally with the eye facing up for the fastest growth.
- Wait for warm soil (at least 60°F) before putting tubers in the ground.
- Resist the urge to water until you see green shoots above the soil.
- Pinch the center stem when the plant is 12 inches tall to get more blooms.
"The secret to a stunning dahlia garden isn't complicated—it's simply a matter of providing good sun, well-drained soil, and the patience to let the tubers wake up in their own time."
We hope this season brings you a garden full of beauty and plenty of blooms to share with friends and neighbors. Happy planting!
FAQ
Does it matter if I plant my dahlia tuber vertically?
While you can plant them vertically with the eye pointing up, we recommend laying them horizontally. Horizontal planting allows for a more natural root distribution and ensures the sprout has an easy path to the surface. It also helps prevent the tuber from being planted too deeply, which can happen more easily with vertical placement.
What happens if I can't find the "eye" on my tuber?
If you can't see the eye, don't worry—it is likely just dormant. You can place the tuber in a warm, brightly lit room for a week or two to encourage it to "wake up" and sprout. If you still aren't sure, simply lay the tuber horizontally in the soil; the sprout will naturally grow toward the light once it begins to develop. If you want a refresher on flower styles, our mignon dahlias guide shows how small-flowered types differ from singles.
Should I water my dahlias right after I plant them?
No, it is best to wait until you see the first green shoots before you start a regular watering routine. Dahlia tubers are prone to rotting in cold, wet soil because they cannot absorb water until they have developed roots and leaves. Unless your soil is bone-dry, the moisture already present in the ground is usually enough to start the growth process.
How deep should I dig the hole for my dahlia tubers?
You should dig a hole that is 4 to 6 inches deep. When you place the tuber inside and cover it, the top of the tuber (the crown) should be covered by about 2 to 3 inches of soil. Planting at this depth provides enough stability for the mature plant while still allowing the young sprout to reach the surface easily.
