Introduction
There is nothing quite like the moment a Dinnerplate dahlia fully unfurls in your garden. These flowers are the undisputed champions of the late-summer landscape, offering colors so vivid and shapes so intricate they almost look hand-painted. Whether you are looking for the soft, creamy petals of 'Café au Lait' or the bold, purple punch of 'Thomas Edison', dahlias provide a level of garden satisfaction that is hard to match. At Longfield Gardens, we believe that everyone can experience this joy by following a few straightforward steps to success.
If you have ever grown a tomato, you already have the skills needed to grow dahlias. These plants are vigorous, rewarding, and surprisingly resilient when given the right start. This guide will walk you through the entire process, from choosing the right spot to harvesting armloads of blooms for your kitchen table. We will focus on the practical, easy wins that ensure your tubers transition into healthy, flowering plants.
Growing dahlias is one of the most rewarding projects a gardener can undertake because the effort you put in during the spring pays off in a massive explosion of color by August. By understanding the simple needs of these unique plants, you can transform your yard into a professional-looking cutting garden.
Understanding the Dahlia Tuber
To grow a dahlia successfully, it helps to understand what you are planting. Unlike many spring flowers that grow from bulbs, dahlias grow from tubers. A dahlia tuber looks very similar to a small potato or a bunch of fingerlings. Inside that tuber is all the energy the plant needs to send up its first set of leaves and start its journey toward blooming.
When you receive your tubers, you might notice they come in different shapes and sizes. Some might be long and slender, while others are short and round. It is a common myth that a larger tuber produces a larger plant. In reality, the health of the "eye" and the "neck" of the tuber is what matters most. As long as the tuber is firm and has a viable growth point, it has everything it needs to thrive.
The eye is a small bump or sprout located on the crown of the tuber, where the tuber connects to the old stem. This is the point where the new plant will emerge. If you cannot see the eye right away, do not worry. Once the tuber is tucked into warm soil, that eye will quickly wake up and begin to grow.
Key Takeaway: Tuber size does not determine plant size. A firm tuber with an intact neck and at least one visible or potential "eye" is a healthy start for a beautiful plant.
Choosing the Right Spot
Success with dahlias starts with picking the right location. These plants are sun-worshippers and require a lot of light to produce those famous, heavy blooms. Think about the sunniest spot in your yard—the place where the sun lingers the longest during the afternoon.
Sunlight Requirements
For the best results, your dahlias should receive at least six to eight hours of direct sunlight every day. While they can grow in partial shade, they will often become "leggy," meaning they grow tall and thin as they reach for the light. More importantly, plants in the shade will produce fewer flowers. If you live in an exceptionally hot climate, such as the southern United States, your plants might appreciate a little bit of afternoon shade to protect the petals from the most intense heat.
Soil and Drainage
The single most important factor for tuber health is drainage. "Drainage" is simply a way of describing how quickly water moves through your soil. Dahlias love consistent moisture once they are growing, but the tubers are sensitive to sitting in soggy, wet ground before they have established roots.
If your soil is heavy clay and stays wet after a rain, consider planting in raised beds or containers. You can also improve your garden soil by mixing in a few inches of high-quality compost. This adds nutrients and improves the soil structure, allowing water to flow away from the tubers more easily.
Space to Breathe
Dahlias are not shy plants; they grow quite large and appreciate having their own space. Most varieties need about 12 to 24 inches of space between them. Giving them plenty of room ensures that air can circulate through the leaves, which helps keep the plants healthy and vibrant throughout the humid summer months.
When to Plant Your Tubers
Timing is everything when it comes to dahlias. Because they are native to the warm mountain regions of Mexico and Central America, they have no tolerance for frost. Planting too early into cold, wet soil is one of the few ways to slow down your progress.
The Soil Temperature Rule
A good rule of thumb is to plant your dahlia tubers at the same time you would plant your tomatoes or peppers. This usually happens in late spring, after the danger of frost has passed and the soil has warmed up to about 60°F. If the ground feels cold to the touch, it is better to wait a week or two.
Planning by Region
In northern states, this might mean waiting until mid-to-late May. In southern states, you might be planting as early as March or April. We time our shipping at Longfield Gardens to ensure your tubers arrive when it is nearly time to plant in your specific USDA hardiness zone. If your tubers arrive and it is still too cold outside, simply keep them in their original packaging in a cool, dark, and dry place until the weather warms up.
What to do next:
- Check your local frost dates to find the safest planting window.
- Use a soil thermometer or wait for a string of warm days to ensure the ground is ready.
- If you want a head start, you can "wake up" tubers in pots indoors 4 weeks before the last frost.
Step-by-Step Planting Guide
Once the weather is warm and your site is ready, How to Plant Dahlias is a quick and enjoyable task. You do not need any specialized tools—a simple garden trowel and some compost will do the trick.
Preparing the Hole
Dig a hole about 4 to 6 inches deep. If you are planting a variety that grows very tall, this is the perfect time to add a bit of compost to the bottom of the hole to give the plant a nutrient boost.
Placing the Tuber
Lay the tuber on its side, horizontally, at the bottom of the hole. Look for the "eye" or the piece of the old stem and make sure it is facing upward or toward the center of the hole. If you can't tell which end is which, don't worry—the plant will find its way to the surface. Refill the hole with soil, making sure not to pack it down too tightly. You want the soil to be firm but breathable.
The No-Water Rule
This is the most important "pro tip" for growing dahlias: Do not water your tubers immediately after planting. It sounds counterintuitive, but the tuber has all the moisture it needs to get started. Adding extra water to the soil before the plant has roots can lead to the tuber rotting. Wait until you see the first green shoots poking through the soil before you begin a regular watering schedule. If your soil is extremely dry or you live in a desert climate, a very light misting is okay, but generally, let nature do its thing until the plant emerges.
Spacing for Success
- Border Dahlias (Small): Space 12 inches apart.
- Decorative and Cactus Dahlias (Medium): Space 18 to 24 inches apart.
- Dinnerplate Dahlias (Large): Space at least 24 inches apart to allow for their massive leaf span.
Supporting Your Plants
Many dahlias can grow to be four or five feet tall. When those heavy blooms appear in late summer, the weight can cause the stems to lean or break, especially during a summer thunderstorm. Providing support early is much easier than trying to fix a leaning plant later.
Staking at Planting Time
The easiest way to support a dahlia is to drive a sturdy stake into the ground right when you plant the tuber. By doing it now, you avoid accidentally driving a stake through the tuber later in the season. You can use wooden stakes, bamboo, or even metal T-posts. As the plant grows, use soft garden twine to loosely tie the main stem to the stake every 12 to 18 inches. For more detail on support methods, see How to Pinch and Stake Dahlias.
The Corral Method
If you are planting a long row of dahlias, the "corral method" is a fantastic time-saver. Place sturdy stakes at the four corners of your dahlia bed and every few feet along the sides. Run twine around the outside of the stakes, creating a "fence" that keeps the plants from falling outward. You can even run a few lines of twine through the middle of the bed to create a grid for the plants to grow through.
Tomato Cages
For gardeners with just a few plants, a heavy-duty tomato cage is a simple and effective solution. Place the cage over the planting site shortly after the first shoots appear. The dahlia will grow up through the rings, and the side branches will be naturally supported as they fill out.
The Secret to More Flowers: Pinching
If you want a dahlia plant that is loaded with blooms rather than one single tall stem, you need to "pinch" your plant. This is a common practice used by professional flower farmers to create bushy, productive plants with long stems.
When your dahlia plant is about 12 to 18 inches tall and has four sets of leaves, snip off the very top of the center stem. You only need to remove about an inch or two. This tells the plant to stop putting all its energy into growing upward and instead start growing outward.
Within a week, you will see new branches emerging from the leaf nodes below where you made the cut. Instead of one main stem, you will now have four or more. This results in a much stronger plant and, most importantly, many more flowers for you to enjoy.
Key Takeaway: Pinching may feel like you are hurting the plant, but it is the best way to ensure a sturdy, multi-branched dahlia that produces a high volume of blooms all season long.
Summer Care and Maintenance
Once your dahlias are established and growing vigorously, they are relatively low-maintenance. A little bit of consistent care during the peak of summer will keep them looking their best.
Watering Deeply
Dahlias are thirsty plants, especially once they start blooming. Rather than a light sprinkle every day, it is better to water them deeply two or three times a week. This encourages the roots to grow deep into the soil, making the plant more drought-tolerant. If the weather is particularly hot, you might need to water more frequently. Aim the water at the base of the plant rather than the leaves to help prevent mildew.
Fertilizing for Blooms
Dahlias are heavy feeders. To keep them producing flowers, you can apply a balanced liquid fertilizer every two weeks. Look for a fertilizer where the middle and last numbers are higher than the first (such as a 5-10-10). The first number represents nitrogen, which promotes green leafy growth. While leaves are good, too much nitrogen can result in fewer flowers. The phosphorus (middle number) and potassium (last number) are what fuel the spectacular blooms.
Managing Pests
Dahlias are generally sturdy, but they can occasionally attract slugs or Japanese beetles.
- Slugs: These are most common when the plants are small. Use organic slug bait or hand-pick them in the early morning.
- Japanese Beetles: These can be found on the blooms in mid-summer. The easiest way to handle them is to flick them into a bucket of soapy water.
- Good Airflow: Keeping your plants spaced correctly and removing the bottom few inches of leaves as the plant grows can help prevent most fungal issues.
For more help identifying and managing common problems, see Common Dahlia Pests and Diseases.
Maximizing Your Bloom Season
The more you harvest dahlias, the more they bloom. This makes them the perfect plant for anyone who loves filling their home with fresh flowers.
Deadheading
If you aren't cutting flowers for bouquets, you must "deadhead" the plant. This means cutting off the spent blooms after they have faded. If you leave the old flowers on the plant, it will start to produce seeds, which tells the plant its job is done. By removing the old flowers, you signal to the dahlia that it needs to keep producing more buds.
When deadheading, don't just snip the flower head. Follow the stem down to the next set of leaves or a new bud and make your cut there. This keeps the plant looking tidy and encourages new growth.
Disbudding for Giant Blooms
If you are growing Dinnerplate varieties and want the absolute largest flowers possible, you can try "disbudding." At the end of each branch, dahlias usually produce a cluster of three buds. The center bud is the largest. By gently pinching off the two smaller side buds, all the plant’s energy goes into that single center flower, resulting in a truly massive bloom.
Harvesting and Flower Care
Cutting dahlias for a vase is the ultimate reward for your hard work. Unlike roses or lilies, dahlias do not open much after they are cut. This means you should wait to harvest them until they are almost fully open.
When to Cut
The best time to cut flowers is in the cool of the morning or late in the evening when the plant is fully hydrated. Look at the back of the flower head; if the petals on the back are starting to look papery or wilted, the flower is past its prime. Choose blooms that look fresh and firm. For more bouquet advice, see Expert Tips for Cutting and Arranging Dahlias.
Post-Harvest Tips
Use clean snips and place the stems immediately into a bucket of room-temperature water. To help the flowers last longer, you can remove any leaves that would be below the water line in your vase. Change the water every two days to keep it fresh. With proper care, most dahlias will last five to seven days in a vase.
What to do next:
- Harvest flowers regularly to keep the plant productive.
- Use clean, sharp snips to avoid crushing the stems.
- Experiment with different varieties to see which ones hold up best in your home arrangements.
Dahlias in Containers
If you don't have a large garden plot, you can still grow dahlia tubers in pots. This is a great way to add color to a patio, deck, or even a sunny balcony.
Choosing the Right Pot
For standard dahlias, you need a large container—at least 12 to 15 inches in diameter and depth. Ensure the pot has plenty of drainage holes. For smaller "border" or Gallery Art Nouveau & Gallery Bellini dahlias, a slightly smaller pot will work.
Potting Mix
Use a high-quality potting soil rather than garden soil. Potting soil is lighter and designed to drain well in a container environment. You can mix in a little bit of slow-release fertilizer at planting time to provide a steady supply of nutrients.
Container Maintenance
Plants in pots dry out much faster than those in the ground. During the height of summer, you may need to water your container dahlias every day. Because you are watering frequently, the nutrients also wash out faster, so regular liquid feeding is essential for container success.
End of Season: What to Do After Frost
In most parts of the United States, dahlias are treated as "tender perennials." This means they will grow back every year, but only if the tubers are protected from freezing temperatures.
The First Frost
In autumn, your dahlias will continue to bloom until the first hard frost. This frost will turn the leaves and stems black. When this happens, do not panic—it is a natural part of the cycle. Many gardeners like to wait about a week after the first frost before digging the tubers, as this helps the tubers prepare for dormancy.
Digging and Storing
If you live in USDA zones 8 to 11, you can often leave your tubers in the ground over the winter, provided the soil stays relatively dry. However, in zones 7 and colder, you must dig them up. How to Overwinter Dahlias walks you through the process.
- Cut the stems down to about 4 inches.
- Gently lift the tuber clump with a garden fork, being careful not to bruise them.
- Shake off the excess soil and let them dry in a protected area for a day or two.
- Store them in a cool (40–50°F), dark place inside a box filled with peat moss, vermiculite, or wood shavings.
The Reward of Next Year
The best part about growing dahlias is that they multiply. When you dig up your "tuber" in the fall, you will find it has grown into a large clump. Next spring, you can divide that clump into several new tubers, allowing you to grow even more plants or share them with friends.
Conclusion
Growing dahlias is a journey that starts with a simple tuber and ends with a garden full of breathtaking color. By focusing on warm soil, excellent drainage, and a little bit of support, you can enjoy these spectacular blooms from July all the way until the first frost. We are proud to provide the high-quality tubers and practical advice you need to make your garden a success.
Remember, gardening is meant to be a rewarding experience. Don't worry about perfection; instead, enjoy the process of watching your tubers wake up and transform into the stars of your summer landscape.
- Wait for Warmth: Ensure your soil is at least 60°F before planting.
- Drainage is Key: Avoid rot by using well-draining soil and waiting for sprouts before watering.
- Pinch for More: Cut the center stem when the plant is 12-18 inches tall to encourage more flowers.
- Support the Weight: Stake your dahlias early to protect the heavy blooms.
Growing dahlias is one of the most fulfilling ways to spend a season in the garden. Each tuber holds the potential for a summer filled with beauty and armloads of fresh-cut flowers.
For your next step, browse our Dahlia Assorted Sunlit Jewel Collection at Longfield Gardens and pick out a few colors that inspire you. Whether you start small or go big with a full cutting garden, we are here to support your success every step of the way.
FAQ
Do I need to soak dahlia tubers before planting?
No, you do not need to soak dahlia tubers. Unlike some other bulbs or corms, dahlia tubers are naturally hydrated and ready to go. Soaking them can actually increase the risk of rot, so it is best to plant them directly into warm, damp soil.
Why are my dahlia tubers not sprouting?
The most common reason is soil temperature. If the ground is too cold, the tuber will stay dormant. Give them a few weeks of consistent warm weather. Another possibility is deep planting; while 4–6 inches is standard, if the soil is heavy, it may take a bit longer for the shoots to reach the surface.
Can I grow dahlias in the shade?
Dahlias really need at least six hours of direct sun to bloom well. If they are in too much shade, they will spend all their energy growing tall and thin while searching for light, which often results in very few or no flowers. For the best floral show, prioritize your sunniest spot.
How often should I fertilize my dahlias?
Once your dahlias are about a foot tall, you can begin fertilizing them every two weeks with a water-soluble, bloom-boosting fertilizer. This ensures the plant has the nutrients it needs to produce large, healthy flowers continuously through the end of the season.
