Introduction
There is nothing quite like the feeling of walking into your garden on a sunny August morning and seeing the first massive, velvet-petaled dahlia bloom of the season. These plants are the undisputed stars of the late summer landscape, offering a range of colors and shapes that feel almost too beautiful to be real. Whether you are dreaming of dinnerplate-sized blossoms or neat, round pompons, dahlias provide an abundance of flowers that last until the first frost.
At Longfield Gardens, we believe that every gardener can find success with these dahlias. While they might look like they require expert-level skills, the truth is that dahlias are incredibly rewarding and straightforward to grow. If you can grow a tomato plant, you can grow a dahlia. This guide is designed to take the guesswork out of the process for home gardeners.
In the following sections, we will cover everything from selecting your tubers to the simple steps in 8 Tips for Growing Better Dahlias. We focus on the practical, high-impact actions that lead to healthy plants and more flowers. Growing dahlias is an achievable way to bring professional-quality blooms into your own backyard.
Understanding Your Dahlia Tubers
Before you get your hands in the dirt, it helps to understand what you are planting. Dahlias grow from tubers, which are thickened underground roots that store energy for the plant. They look a bit like a cluster of long, narrow potatoes.
When you receive your tubers from us, you might notice they come in different shapes and sizes. It is important to remember that the size of the tuber does not dictate the size of the flower. A small tuber can produce a massive six-foot plant, while a large clump might produce a compact border variety. As long as the tuber is firm and has a viable "eye," it has everything it needs to grow.
The Importance of the Eye
The "eye" is a small growth bud located at the neck of the tuber, where it connects to the old stem. This is where the new sprout will emerge. Sometimes eyes are easy to see as little pink or green bumps. Other times, they are dormant and harder to spot.
If you cannot see an eye right away, do not worry. Once the tuber is exposed to warmth and a tiny bit of moisture, the eye will naturally wake up and begin to sprout.
Common Dahlia Types
Choosing which dahlias to grow is the most exciting part of the process. We offer several categories that serve different purposes in the garden:
- Dinnerplate Dahlias: These produce the largest blooms, sometimes reaching 10 inches or more in diameter. Varieties like 'Cafe au Lait' or Thomas Edison are famous for their size and impact.
- Decorative Dahlias: These have broad, flat-tipped petals and are the classic dahlia shape. They are reliable, prolific, and come in every color imaginable.
- Cactus and Semi-Cactus: These have narrow, pointed petals that give the flowers a spiky, textural look.
- Ball Dahlias: These produce perfectly spherical flowers with tightly cupped petals. They are exceptionally hardy and have a very long vase life.
- Border Dahlias: These are shorter varieties that stay under two feet tall. They are perfect for the front of a garden bed or for growing in containers.
Key Takeaway: Focus on the health and firmness of the tuber rather than its size. Every viable tuber with an eye has the potential to become a beautiful, flowering plant.
Choosing the Right Spot
The "right plant, right place" rule is the foundation of dahlia success. These plants are native to Mexico and Central America, so they love sunshine and warmth.
Sun Requirements
For the best results, choose a location that receives at least six to eight hours of direct sunlight each day. While dahlias can grow in partial shade, they will produce fewer flowers and may become "leggy" as they stretch toward the light. Full sun ensures strong stems and the most vibrant colors.
Soil and Drainage
Dahlias are not overly picky about soil, but they do require excellent drainage. "Drainage" simply refers to how quickly water moves through the soil. If water sits in a puddle for hours after a rain, the tubers may rot before they have a chance to grow.
If you have heavy clay soil, you can improve the drainage by adding organic matter like compost or aged manure. This loosens the soil and provides a slow-release source of nutrients. Raised beds are also an excellent option for dahlias because they naturally drain better than the ground.
Timing Your Planting
Timing is perhaps the most important factor when learning how to grow dahlias. Because these are tropical plants, they are very sensitive to cold.
Wait for Warm Soil
The biggest mistake gardeners make is planting too early. Tuber growth stays dormant until the soil temperature reaches about 60°F. If you plant into cold, wet soil in early spring, the tuber may sit and rot.
A good rule of thumb is to plant your dahlias at the same time you would plant your tomatoes or peppers. In most parts of the United States, this is late May or early June. If you aren't sure, check your local frost dates and our Shipping Information. Wait until the danger of frost has passed and the soil feels warm to the touch.
Starting Early Indoors
If you live in a region with a short growing season, you can give your dahlias a head start. About four to six weeks before your last frost date, you can "pot up" your tubers. Place them in one-gallon pots with slightly damp potting soil and keep them in a warm, bright spot. By the time the weather warms up, you will have a small plant ready to go into the ground, which can lead to earlier blooms.
How to Plant Dahlia Tubers
Once the soil is warm and the site is ready, planting is a quick and simple process. Follow these steps for the best results:
- Dig a Hole: Dig a hole about 4 to 6 inches deep.
- Amend the Soil: If you haven't already, toss a handful of compost or a balanced, all-purpose fertilizer into the hole and mix it with the loose soil at the bottom.
- Place the Tuber: Lay the tuber horizontally in the hole. If you can see the eye or a sprout, point it upward.
- Space Them Out: Give your dahlias room to breathe. Large varieties should be spaced 18 to 24 inches apart. Smaller border dahlias can be spaced 12 to 15 inches apart.
- Backfill: Cover the tuber with soil. At this stage, the top of the tuber should be about 1 to 2 inches below the soil surface.
The Golden Rule of Watering at Planting
Here is a vital tip: Do not water your dahlias immediately after planting. This sounds counterintuitive, but the tuber has enough stored moisture to start growing. Adding water to the hole before the plant has roots can lead to rot. Wait until you see the first green sprouts poking through the soil before you start your regular watering routine.
What to Do Next:
- Check your local weather forecast for a stretch of warm nights.
- Clear the planting area of any weeds or debris.
- Dig your holes 4-6 inches deep and space them according to the variety size.
- Lay tubers horizontally and cover them with soil without watering.
Providing Support and Staking
Most dahlias grow quite tall and produce heavy flowers. Without support, a summer rain or a gust of wind can cause the stems to snap or the entire plant to topple.
When to Stake
It is best to put your stakes in the ground at the time of planting. This prevents you from accidentally driving a stake through the tuber later in the season. You can use wooden stakes, bamboo poles, or even sturdy metal T-posts.
How to Tie
As the plant grows, use soft twine or garden ties to secure the main stem to the stake. You should add a new tie every 12 to 18 inches of growth. Ensure the tie is loose enough to allow the stem to thicken but snug enough to hold the plant upright. For large groupings of dahlias, some gardeners use the "corralling" method, where they place stakes around the perimeter of the bed and wrap twine around the entire group.
Essential Care: Watering and Fertilizing
Once your dahlias have sprouted and are about six inches tall, they will need consistent care to thrive through the summer heat.
Water Correctly, Not Constantly
Dahlias love water, but they do not like to sit in "wet feet." The best approach is to water deeply once or twice a week rather than giving them a light sprinkle every day. Deep watering encourages the roots to grow further down into the soil, making the plant more resilient.
If you have sandy soil, you may need to water more often. If you have heavy soil, once a week is usually plenty unless the weather is exceptionally hot. Try to water at the base of the plant to keep the foliage dry, which helps prevent mildew.
Feeding Your Plants
Dahlias are "heavy feeders," meaning they use a lot of nutrients to produce those massive flowers. Start with a balanced fertilizer at planting time. Once the plants are well-established and starting to form buds, you can switch to a fertilizer that is lower in nitrogen and higher in phosphorus and potassium (similar to a tomato or "bloom booster" fertilizer).
Avoid high-nitrogen fertilizers late in the season. While nitrogen promotes lush green leaves, too much of it can lead to weak stems and fewer flowers.
The Secret Step: Pinching for More Blooms
If you want a bushier plant with twice as many flowers, you must "pinch" your dahlias. This is a simple technique that many beginners skip, but it makes a world of difference.
How to Pinch
When your dahlia plant is about 12 to 16 inches tall and has four sets of leaves, look at the very top of the center stem. Use your fingers or a clean pair of snips to remove the top 2 to 3 inches of that center shoot.
Why It Works
By removing the main growing tip, you signal the plant to stop growing upward and start growing outward. The plant will send out two new stems from the leaf axils below the cut. This results in a sturdier, more balanced plant that produces significantly more blooms throughout the season. It might feel strange to cut your plant, but the results are worth it.
Key Takeaway: Pinching your dahlias early in the season results in a stronger plant and a much higher flower count. It is the easiest way to improve your garden's performance.
Harvesting and Deadheading
The more you cut your dahlias, the more they will bloom. Harvesting flowers for bouquets is actually a form of pruning that keeps the plant productive.
How to Cut for Bouquets
Dahlias do not open much once they are cut, so wait until the flower is almost fully open before you harvest. The best time to cut is in the cool of the morning when the stems are full of moisture.
Use sharp, clean snips and cut the stem as long as you can. It is best to cut all the way back to a main branch. This encourages the plant to grow another long stem in its place. Immediately place the cut stems into a bucket of room-temperature water.
Deadheading
If you don't cut the flowers for bouquets, you must "deadhead" them. Deadheading is the process of removing faded or dying flowers. If you leave old flowers on the plant, it will start to produce seeds, which tells the plant its job is done. By removing the old blooms, you trick the plant into thinking it needs to keep producing more flowers.
When deadheading, don't just pop the head off. Cut the stem back to where it meets a larger branch or a set of leaves. This keeps the plant looking tidy and encourages new growth.
Managing Pests and Challenges
Gardening is a partnership with nature, and occasionally you might run into a few hurdles. Fortunately, most dahlia problems are easy to manage with simple, proactive steps.
Slugs and Snails
Young dahlia sprouts are a favorite snack for slugs. Keep an eye on your plants when they first emerge. You can protect them by using organic slug bait or by keeping the area around the base of the plant clear of debris where slugs like to hide. Once the plants are a foot tall, they are usually tough enough that slugs are no longer a major threat.
Earwigs and Japanese Beetles
Later in the summer, you might notice small holes in the petals. This is often caused by earwigs or Japanese beetles. For Japanese beetles, the simplest method is to hand-pick them and drop them into a bucket of soapy water. For earwigs, keeping the garden tidy and avoiding heavy mulch can reduce their hiding spots.
Powdery Mildew
In late summer, if the weather is humid, you might see a white, dusty coating on the leaves. This is powdery mildew. It usually doesn't kill the plant, but it isn't very pretty. You can prevent this by ensuring your plants have plenty of space for air to circulate and by watering only at the soil level rather than over the leaves.
What to Do After the First Frost
As autumn arrives, your dahlias will continue to bloom until a hard frost hits. A "hard frost" is when temperatures drop below freezing long enough to kill the foliage. When this happens, the plant will turn black and limp almost overnight.
Digging and Storing
In USDA zones 8 and warmer, dahlias can often stay in the ground all winter if the soil is well-drained and you apply a thick layer of mulch. However, in colder regions (zones 7 and lower), the tubers must be dug up and stored indoors if you want to grow them again next year.
- Cut Back: After the frost kills the foliage, cut the stems down to about 4 inches.
- Lift: Carefully use a garden fork to lift the tubers out of the ground. Be gentle, as the necks of the tubers are fragile.
- Clean: Shake off the excess soil and let them dry in a frost-free spot for a day or two.
- Store: Place the tubers in a box filled with slightly damp peat moss, vermiculite, or wood shavings. Store the box in a cool, dark, and dry place (like a basement or crawlspace) where temperatures stay between 40°F and 50°F.
If you don't want to go through the trouble of storing them, you can simply treat your dahlias as annuals and start fresh with new tubers from our facility in the spring.
Growing Dahlias in Containers
If you have limited space or poor soil, dahlias grow beautifully in pots. This is a fantastic way to brighten up a patio or balcony.
Container Selection
Choose a container that is large enough for the variety you are growing. Border dahlias can live in a 2-gallon pot, but full-sized dahlias need at least a 5-to-7-gallon container. Ensure the pot has plenty of drainage holes.
Potting Care
Use a high-quality potting mix rather than garden soil. Because pots dry out faster than the ground, you will need to water your container dahlias more frequently—sometimes daily during the height of summer. You will also need to fertilize every two weeks with a liquid bloom booster, as frequent watering washes nutrients out of the soil.
Conclusion
Growing dahlias is one of the most rewarding projects a gardener can undertake. These plants offer an incredible return on investment, providing months of spectacular color for just a little bit of care. By getting the basics right—planting in the sun, waiting for warm soil, and remembering to pinch the stems—you can enjoy a garden filled with professional-quality blooms.
At Longfield Gardens, our goal is to help you succeed. We provide high-quality tubers and the support you need to see them flourish. Whether you are planting your very first 'Cafe au Lait' or adding new varieties to a long-standing collection, the joy of dahlia season is something every gardener should experience.
- Wait for warmth: Only plant when the soil hits 60°F.
- Give them sun: Ensure at least 6-8 hours of direct light.
- Pinch for success: Snip the top of the plant at 12 inches for more flowers.
- Cut and enjoy: The more you harvest, the more the plant will produce.
We are here to support your gardening journey. If you have questions about your tubers or need advice on variety selection, don't hesitate to reach out to our team. Happy planting!
FAQ
How deep should I plant dahlia tubers?
Dahlia tubers should be planted approximately 4 to 6 inches deep. Place the tuber horizontally in the hole with any visible eyes or sprouts facing upward. After placing the tuber, cover it with soil so that the top is about 1 to 2 inches below the surface.
Do dahlias need to be watered every day?
No, dahlias usually do not need daily watering if they are planted in the ground. It is better to water them deeply once or twice a week to encourage deep root growth. However, if you are growing dahlias in containers, you may need to water them more frequently as pots dry out much faster than garden beds.
Can I grow dahlias from seed instead of tubers?
Yes, you can grow dahlias from seed, but there is a catch. Dahlias grown from seed will not be identical to the parent plant and often produce smaller, simpler flowers. If you want a specific variety with a certain color and shape, you must plant tubers, which are clones of the original plant.
Why are my dahlias not blooming?
The most common reasons for a lack of blooms are too much shade or too much nitrogen in the fertilizer. Ensure your plants get at least 6 hours of full sun. Also, avoid high-nitrogen fertilizers once the plant is established, as this promotes green leaves instead of flowers; switch to a bloom-boosting fertilizer instead.
