Introduction
There is nothing quite like the feeling of watching a dahlia bud slowly unfurl into a massive, multi-layered masterpiece. Whether you are captivated by the dinnerplate varieties that grow as large as a serving platter or the perfectly symmetrical ball dahlias, these flowers bring a sense of wonder to any summer garden. At Longfield Gardens, we believe that every yard has room for these spectacular bloomers, provided you give them the right foundation to grow on.
This guide is designed to help you decide exactly where and what to plant your dahlias in for the best results. We will cover the specific types of soil they love, how to choose the right containers, and why raised beds are often a favorite choice for professional growers and home gardeners alike. By matching the right planting environment to your specific space, you can ensure a season full of vibrant, healthy flowers.
Success with dahlias is achievable for everyone, regardless of the size of your garden or your level of experience. The key is understanding that these plants have a few simple preferences for their "home." Once you get the soil and the container right, the plants will do the rest of the work for you.
The Ideal Soil for Dahlias
Before you decide on a pot or a garden bed, you must consider the soil itself. Dahlias are productive plants that require a steady supply of nutrients and, most importantly, excellent drainage. Drainage simply refers to how fast water leaves the soil. If water sits around the tubers for too long, they can become soft and fail to grow.
The most successful dahlia gardens start with loamy soil. Loam is a balanced mixture of sand, silt, and a little bit of clay. It feels crumbly in your hand and holds onto just enough moisture to keep the plant hydrated without becoming soggy. If your garden has heavy clay soil—which feels sticky and holds water like a sponge—you can improve it by mixing in organic matter like compost or well-rotted manure.
If you are planting in an area with very sandy soil, water might move through too quickly. In this case, adding compost helps the soil hold onto the moisture and nutrients the dahlias need to produce those heavy blooms. Aim for a soil pH that is slightly acidic to neutral, which is standard for most backyard gardens in the United States.
Key Takeaway: Dahlias need "fertile, well-drained soil." If your soil is too heavy or too sandy, adding a few inches of compost is the easiest way to create the perfect environment.
Amending Your Soil
If you are starting a new garden bed, it is helpful to prepare the area a few weeks before planting. You can follow these simple steps to get the ground ready:
- Clear the area of any weeds or grass.
- Spread a 2- to 3-inch layer of compost over the surface.
- Turn the soil to a depth of about 12 inches using a shovel or garden fork.
- Mix in a balanced, all-purpose granular fertilizer according to the package directions.
Growing Dahlias in Containers
Many gardeners wonder if they can grow dahlias in pots, and the answer is a resounding yes. In fact, planting in containers is a great way to bring color to patios, balconies, and porches. However, because dahlias can grow quite large, the type and size of the container you choose are very important.
For more planting guidance, see our container-growing guide.
Choosing the Right Pot Size
The most common mistake when planting dahlias in pots is using a container that is too small. A small pot dries out too quickly and does not provide enough room for the roots and tubers to expand.
- For Border Dahlias: These are shorter varieties that stay under 2 feet tall. They can thrive in a container that holds at least 2 to 3 gallons of soil (roughly 10 to 12 inches in diameter).
- For Full-Size Dahlias: Tall varieties and dinnerplate dahlias need a much larger home. A 5-gallon bucket or a large decorative pot that is at least 15 to 18 inches deep and wide is ideal. This provides enough weight to prevent the plant from tipping over when it is full of heavy flowers.
Pot Materials and Drainage
You can use plastic, ceramic, terracotta, or even fabric grow bags. Plastic and glazed ceramic pots hold moisture longer, which can be helpful during hot summer months. Terracotta is porous, meaning it "breathes" and dries out faster. If you use terracotta, you may need to water more frequently.
Regardless of the material, the pot must have drainage holes in the bottom. If the pot you love doesn't have holes, you can often drill them yourself. Without a way for excess water to escape, the soil will stay saturated, which is the primary cause of performance issues with container-grown dahlias.
The Best Potting Mix
Never use "garden soil" or "topsoil" in a container. These are too heavy and will pack down tightly, suffocating the roots. Instead, use a high-quality, lightweight potting mix. These mixes are usually made of peat moss, perlite, or coconut coir. They are designed to stay fluffy and provide the perfect balance of air and water for the tubers.
What to do next for containers:
- Select a pot with at least one large drainage hole.
- Fill the bottom two-thirds with a high-quality potting mix.
- Place the tuber on its side and cover with 1 to 2 inches of soil.
- Wait to water deeply until you see the first green shoots emerge.
Using Raised Beds for Dahlias
Raised beds are arguably the best way to grow dahlias, especially if you have difficult native soil. By building a bed above the ground, you have total control over the soil quality and drainage. This is often the preferred method for flower farmers who want the longest stems and the healthiest tubers.
If you are deciding between a traditional in-ground garden and a raised bed, our raised-bed guide is a helpful next step.
Benefits of Raised Beds
One major advantage of a raised bed is that the soil warms up faster in the spring than the ground does. Since dahlias are tropical plants that love warmth, this head start can lead to earlier blooms. Raised beds also prevent soil compaction because you never have to step on the soil where the plants are growing.
For the best results, use a bed that is at least 12 inches deep. This gives the tubers plenty of room to grow downward. Cedar is a popular choice for the frame because it is naturally resistant to rot, but you can also use stone, brick, or heat-treated lumber.
Filling Your Raised Bed
When filling a raised bed, a blend of 60% topsoil, 30% compost, and 10% potting mix or perlite creates an excellent environment. This mixture provides the structure of real soil with the drainage and nutrient boost of organic matter.
In-Ground Planting Locations
If you have plenty of space in your yard, planting dahlias directly in the ground is the most traditional and low-maintenance option. The key here is "site selection." You want to find a spot that matches the plant's natural needs.
For more placement tips, see where to plant dahlias in a garden.
Sun and Wind Requirements
Dahlias are sun-worshippers. To produce those famous flowers, they need at least 6 to 8 hours of direct sunlight every day. If they are planted in too much shade, the stems will become "leggy" (tall and weak) as they stretch toward the light, and you will see fewer blooms.
Wind is another factor to consider. Because dahlia stems are hollow and the flowers are heavy, a strong summer storm can easily snap them. If possible, plant your dahlias near a fence, a wall, or a hedge that can act as a windbreak. If your garden is very open, you will definitely want to use stakes or cages to support the plants as they grow.
Spacing Your Plants
Dahlias need room for air to circulate around their leaves. This helps keep the foliage dry and prevents common issues like powdery mildew.
- Small varieties: Space them 12 to 15 inches apart.
- Large varieties: Space them 18 to 24 inches apart.
It may look like a lot of empty space when you first plant the tubers, but within two months, the plants will fill that gap completely.
Companion Plants: What to Plant with Dahlias
While dahlias are the stars of the show, they often look even better when paired with "companion plants." These are other flowers or herbs that grow well in the same conditions and can help fill in gaps or provide a beautiful backdrop.
Best Flower Companions
Since dahlias don't usually start blooming until mid-to-late summer, it is smart to plant them with flowers that bloom earlier or provide a different texture.
- Sweet Alyssum: This low-growing flower acts as a "living mulch." It covers the ground around the base of the dahlia, keeping the roots cool and helping to retain moisture.
- Salvia and Snapdragons: These provide vertical interest and bloom earlier in the season, giving you color while you wait for the dahlias to mature.
- Cosmos: With their airy, feathery foliage, cosmos add a soft texture that contrasts beautifully with the bold, structured leaves of the dahlia.
Practical Companions
Some plants are chosen for more than just their looks. For example, planting herbs like lavender or marigolds nearby can help attract beneficial pollinators like bees and butterflies to your garden. Dahlias rely on these visitors to thrive, and having a diverse range of flowers ensures your garden remains a healthy ecosystem.
Key Takeaway: Choose companions that won't "bully" the dahlias. Dahlias are heavy feeders, so they prefer neighbors that aren't overly aggressive or invasive.
Managing the Growing Medium
Once you have decided what to plant your dahlias in, you need to maintain that environment throughout the season. Soil and potting mix change over time as the plant uses up nutrients and water moves through.
Watering Techniques
The way you water depends on what you planted in.
- In the ground: Soil holds onto moisture longer. You may only need to water deeply once or twice a week, depending on the rain.
- In containers: Pots dry out much faster, especially in plastic or terracotta. In the heat of July and August, you might need to water container dahlias every single day.
A simple trick is to stick your finger about an inch into the soil. If it feels dry, it is time to water. Always try to water the base of the plant rather than the leaves to keep the foliage healthy.
Fertilizing for Success
Dahlias are often compared to tomato plants because they are "heavy feeders." This means they use a lot of energy to grow and bloom. When you plant them in containers or raised beds, the nutrients in the potting mix are washed away every time you water.
To keep the soil rich, apply a low-nitrogen fertilizer every 3 to 4 weeks once the plant is about a foot tall. Look for a fertilizer where the middle and last numbers are higher than the first (such as 5-10-10). Nitrogen (the first number) encourages green leaves, while phosphorus and potassium (the middle and last numbers) encourage big, beautiful flowers and strong roots.
Preparing for the Next Season
Dahlias are perennial in warm climates, but in most of the United States, they are treated as annuals or dug up and stored for the winter. What you plant them in will affect how you handle them in the fall.
If you plant in containers, the process is very simple. Once the first frost turns the foliage black, you can cut the stems back, let the pot dry out, and move the entire container into a cool, frost-free basement or garage. If you plant in the ground or raised beds, you will likely need to "lift" the tubers—carefully digging them up to store them in a box of peat moss or wood shavings until spring.
We provide a wide variety of tubers at Longfield Gardens that are suited for all these different planting methods. Whether you want a compact variety for a window box or a towering dinnerplate for your back fence, starting with high-quality tubers is the first step toward a successful season. Browse our new dahlia collections or our spring collections to get started.
Summary of Planting Steps
Choosing what to plant your dahlias in doesn't have to be complicated. If you follow these simple steps, you will be well on your way to a garden full of blooms.
- Pick your spot: Ensure it gets at least 6 hours of sun.
- Check the drainage: If water puddles there for hours after a rain, choose a raised bed or a pot instead.
- Size matters: Use at least a 5-gallon container for large varieties.
- Use the right dirt: Use potting mix for pots and compost-enriched soil for the ground.
- Space them out: Give them 12 to 24 inches of elbow room to breathe.
- Support them: Have your stakes or cages ready at planting time so you don't damage the tubers later.
If you want an easy shopping shortcut, check out our 20% Off Dinnerplate Dahlias.
"The secret to beautiful dahlias isn't a magic trick; it's simply giving the tubers a warm, well-drained place to grow and enough food to fuel their spectacular show."
Conclusion
Dahlias are some of the most rewarding flowers you can grow, offering a massive variety of colors and shapes that last from mid-summer until the first frost. Whether you choose to plant them in large decorative pots on your patio, in a dedicated raised bed, or directly into your garden borders, the most important factor is providing a home with great drainage and plenty of sunlight. By taking the time to prepare your soil or choose the right potting mix, you are setting yourself up for a season of success.
At Longfield Gardens, we take pride in helping you find the perfect varieties for your specific garden needs. Our 100% quality guarantee ensures that your tubers arrive ready to plant and true to their variety. Gardening should be a source of joy and relaxation, and with a few simple preparations, your dahlia garden will be the highlight of your summer.
- Choose a sunny spot with excellent drainage.
- Use high-quality potting mix for containers and compost for garden beds.
- Space plants correctly to allow for healthy air circulation.
- Start with premium tubers from a trusted source like Longfield Gardens.
Ready to start your dahlia journey? The best time to plan is now, so you can be ready to plant as soon as the spring soil warms up!
FAQ
Can I use regular dirt from my yard in my dahlia pots?
It is best not to use yard soil in containers. Native soil is usually too heavy and dense, which can prevent water from draining and may suffocate the roots. For pots, always use a high-quality, "soilless" potting mix that is designed to stay light and airy.
How deep should I plant dahlia tubers in a raised bed?
In a raised bed or in the ground, you should plant the tubers about 4 to 6 inches deep. The "eye" or the sprout of the tuber should be facing up, and you should cover it with about 1 to 2 inches of soil initially. As the plant grows, you can fill in the rest of the hole. For a deeper dive, see our planting depth guide.
What is the best container for a dinnerplate dahlia?
Large dinnerplate dahlias need a heavy, sturdy container to keep them from tipping over. A pot that holds at least 5 gallons of soil and is 15 to 18 inches wide is the minimum size recommended. Using a heavy material like glazed ceramic or adding a few stones to the bottom of a plastic pot can provide extra stability.
Do I need to put rocks in the bottom of my dahlia pots for drainage?
Contrary to popular belief, putting rocks in the bottom of a pot does not actually improve drainage and can sometimes make it worse by raising the water table in the pot. The best way to ensure good drainage is to use a high-quality potting mix and ensure your container has large, open drainage holes at the very bottom.
For timing your order, see our shipping information and hardiness zone map.
