Introduction
Walking into a garden filled with dahlias is one of the most rewarding experiences a gardener can have. Whether you are captivated by the massive, swirling petals of a dinnerplate variety or the neat, geometric patterns of a pompon, these flowers offer a level of beauty that is hard to match. At Longfield Gardens, we want to help you bring that same color and excitement to your own backyard.
Many people starting their dahlia journey wonder if they should be looking for seeds or bulbs at the garden center. The answer is a bit more interesting than a simple "yes" or "no." While dahlias can be grown from both, most of the spectacular named varieties you see in magazines are grown from tubers, which are often mistakenly called bulbs.
This guide will explain the differences between growing from seeds and tubers, why you might choose one over the other, and what to expect during the growing season. This information is for any home gardener who wants to understand the best way to fill their summer landscape with these stunning blooms. While both methods lead to beautiful results, understanding the science behind the plant helps you choose the right path for your garden goals.
Tubers or Bulbs: Clearing Up the Terminology
When you browse for dahlia "bulbs," you are actually looking for tubers. In the gardening world, the word "bulb" is often used as a catch-all term for any plant that has a fleshy, underground storage organ. However, there are technical differences between a true bulb, like a tulip, and a tuber, like a dahlia.
A true bulb contains a miniature version of the plant inside it, protected by layers of scales. A dahlia tuber is more like a potato. It is a thickened, underground stem that stores energy for the plant. Each tuber needs at least one "eye"—a small growth bud located near the neck where the tuber connects to the main stem—to produce a new plant.
At Longfield Gardens, we focus on providing high-quality dahlia tubers because they are the most reliable way to get the exact flower you want. When you plant a tuber, you are essentially planting a clone of the parent plant. If you buy a 'Cafe au Lait' tuber, you are certain to get those famous creamy, blush-pink blooms.
Key Takeaway: While gardeners often use the terms interchangeably, dahlias grow from tubers, not true bulbs. Tubers ensure that the plant you grow is an exact match for the variety you purchased.
Growing Dahlias from Tubers
Growing from tubers is the most popular method for home gardeners, and for good reason. It provides a level of predictability and ease that makes it accessible for everyone.
Why Choose Tubers?
The primary advantage of tubers is consistency. Dahlias are genetically complex plants. When a breeder finds a dahlia with a perfect shape and color, they cannot rely on seeds to reproduce that exact look. Instead, they divide the tubers. Because every tuber from that plant is a piece of the original, it will produce the exact same flowers every single year.
If you have a specific color palette in mind for a wedding or a special garden bed, tubers are the way to go. You can select for height, bloom size, and petal shape with total confidence.
The Investment Value
Another reason to love tubers is that they are an investment that grows over time. A single dahlia plant will produce a whole clump of new tubers underground by the end of the summer. If you dig them up and store them over the winter, you can often divide that clump into three or four separate tubers the following spring.
This means that a single purchase can eventually fill an entire garden border. It is a simple and rewarding way to expand your flower collection without additional cost.
What to Look For
When you receive your tubers, they should feel firm, much like a fresh potato. They come in many shapes and sizes; some are long and skinny, while others are round and plump. The size of the tuber does not dictate the size of the flower. A tiny tuber can produce a massive plant as long as it has a healthy eye and an intact neck.
- Check your tubers for a visible eye or a small sprout near the top.
- Wait until the soil is warm (about 60°F) before planting.
- Plant the tuber about 4 to 6 inches deep with the eye pointing up.
- Avoid watering until you see the first green sprouts emerging from the soil.
Growing Dahlias from Seed
While tubers offer predictability, dahlia seeds offer the thrill of discovery. Growing from seed is an entirely different experience that appeals to gardeners who love surprises and enjoy the process of starting plants indoors.
The Genetic Surprise
The most important thing to understand about dahlia seeds is that they do not grow "true to type." If you save a seed from a 'Thomas Edison' dahlia, the plant that grows from it will not look like 'Thomas Edison.' It might have a different color, a different shape, or even a different height.
This happens because dahlias have eight sets of chromosomes, which is much more than most plants. This genetic diversity means that every single seed contains a brand-new combination of traits. When you grow from seed, you are growing a dahlia variety that has never existed before.
Why Gardeners Love Seeds
Many gardeners enjoy the "treasure hunt" aspect of seeds. You might discover a beautiful new flower that you get to name yourself. Additionally, seeds are much more affordable than tubers if you want to fill a large area with color and don't mind what the specific flowers look like.
Seed-grown dahlias also tend to have "open centers," meaning the middle of the flower is visible and full of pollen. These are a favorite for bees and butterflies. If your goal is to support local pollinators, a patch of seed-grown dahlias is an excellent addition to your yard.
The Process of Starting Seeds
Growing dahlias from seed requires more patience and equipment than tubers. Because dahlias have a long growing season, you usually need to start the seeds indoors about 6 to 8 weeks before the last frost.
What to do next with seeds:
- Sow seeds in a high-quality seed-starting mix.
- Use a heat mat to keep the soil between 65°F and 70°F for the best germination.
- Provide plenty of light once the sprouts appear to prevent them from getting "leggy" (tall and weak).
- Harden off the seedlings by gradually exposing them to outdoor conditions before transplanting.
From Seed to Tuber: The Life Cycle
One of the most fascinating parts of the dahlia life cycle is that every dahlia, regardless of how it started, eventually produces tubers.
When you plant a tiny dahlia seed in the spring, the plant will spend the summer growing leaves and flowers. At the same time, it is working hard underground to create a storage system. By the time the first frost hits in the fall, that seed-grown plant will have developed a small clump of tubers.
If you fall in love with a flower that grew from a seed, you can dig up those brand-new tubers, store them over the winter, and plant them again the next year. From that point on, you are growing that variety from a tuber, which means it will finally be a clone. This is exactly how every named variety we sell at Longfield Gardens was originally discovered. Someone, somewhere, grew a seed, loved the result, and began saving the tubers.
Comparing Seeds and Tubers
To help you decide which method is right for your current project, here is a quick comparison of the two approaches.
Predictability vs. Variety
- Tubers: You get exactly what is on the label. This is ideal for planned landscapes, cutting gardens, and specific color schemes.
- Seeds: You get a mix of colors and shapes. This is great for a whimsical cottage garden or for gardeners who like to experiment.
Cost and Scale
- Tubers: Higher initial cost per plant, but the plants are larger and more robust from the start. They multiply every year, providing long-term value.
- Seeds: Very low cost per plant. You can grow dozens of plants for the price of one packet. This is the most budget-friendly way to fill a large new garden bed.
Bloom Time
- Tubers: Usually bloom earlier in the season because the plant starts with a large energy reserve in the tuber.
- Seeds: Take longer to reach maturity. You may not see your first blooms until later in the summer or early fall.
Pollinator Support
- Tubers: Many popular varieties are "doubles" with so many petals that bees cannot reach the pollen.
- Seeds: Most seed-grown dahlias have single or semi-double blooms, making them much more accessible and attractive to pollinators.
Key Takeaway: Choose tubers if you want a specific look and early blooms. Choose seeds if you want a low-cost adventure and want to support your local bees.
Simple Success with Tuber Planting
If you decide to go the tuber route, success comes down to a few basic steps. Most issues with dahlias happen when gardeners try to "over-care" for them too early in the season.
Right Place, Right Time
Dahlias love the sun. They need at least six to eight hours of direct sunlight to produce strong stems and plenty of flowers. If they are planted in too much shade, they will grow tall and spindly as they reach for the light, and they won't bloom as well.
The timing of your planting is also critical. Dahlias are tropical plants and have no resistance to frost. They also don't like cold, wet soil, which can cause the tuber to rot before it even wakes up. We recommend waiting until the danger of frost has passed and the soil feels warm to the touch. In many parts of the US, this is the same time you would plant your tomatoes.
Depth and Spacing
Proper spacing gives your plants room to breathe. Airflow is important for preventing powdery mildew, a common fungus that can appear on dahlia leaves in late summer. Space your tubers about 12 to 18 inches apart.
When you plant, dig a hole about 6 inches deep. Place the tuber horizontally at the bottom of the hole. You don't need to be perfect with the orientation, but if you can see the eye or a sprout, point that upward. Cover it with soil and leave it alone.
Water Correctly, Not Constantly
The biggest mistake people make with tubers is watering them too much right after planting. A tuber is full of moisture and energy; it doesn't need extra water until it has developed roots and a sprout.
Once the plant is about 6 inches tall and growing actively, you can start a regular watering schedule. The goal is to water deeply a few times a week rather than giving them a light sprinkle every day. This encourages the roots to grow deep into the soil, making the plant more resilient during hot, dry spells.
Simple Success with Seed Starting
If you are excited by the idea of creating something new, starting seeds is a fun indoor project for the late winter months.
Managing Germination
Dahlia seeds are known for being a bit irregular. Some might sprout in three days, while others might take two weeks. Don't be discouraged if your seed tray looks patchy at first. Keeping the trays on a heat mat helps significantly, as the warmth signals to the seeds that it is time to grow.
Because the germination rate isn't always 100%, we recommend sowing a few more seeds than you think you need. This ensures you have plenty of healthy seedlings to choose from when it comes time to move them into the garden.
Handling Seedlings
Once your seedlings have two sets of "true leaves" (the leaves that look like miniature dahlia leaves, not the smooth initial sprout leaves), they are ready for a little bit of food. Use a gentle, water-soluble fertilizer at half-strength every two weeks to keep them growing strong.
Before you move them into the garden, you must "harden them off." This is a simple process of taking the trays outside for an hour the first day, two hours the second day, and so on. This prevents the tender plants from getting sunburned or shocked by the wind.
Caring for Your Plants During the Summer
Regardless of how your dahlias started, they will eventually need the same care once they are established in your garden.
The Power of Pinching
One of the best ways to get more flowers is a technique called pinching. When your plant is about 12 to 16 inches tall, use your fingers or a pair of clean snips to remove the very top of the center stem.
This might feel like you are hurting the plant, but it actually does the opposite. It tells the plant to stop growing one tall stalk and instead start growing multiple side branches. More branches mean a sturdier plant and, most importantly, many more flowers for you to enjoy.
Supporting Your Dahlias
Dahlia stems are hollow and can become very heavy when they are covered in large blooms. A summer rainstorm or a gust of wind can easily tip them over.
For the best results, provide some support early in the season. You can use individual wooden stakes for each plant or use tomato cages. For larger rows, many gardeners use the "corral" method, where stakes are placed at the corners of the bed and twine is wrapped around the entire group of plants.
Enjoying the Harvest
Dahlias are one of the best cutting flowers you can grow. The more you cut them, the more the plant will produce. When you bring them inside, they can last up to five or six days in a vase.
The best time to cut a dahlia is when it is nearly fully open but hasn't started to lose its back petals. Unlike roses or lilies, dahlias will not open much further once they are cut, so wait until they look the way you want them to look in the vase.
Troubleshooting Common Issues
Gardening is a learning process, and dahlias are no exception. If things don't go perfectly, the fix is usually quite simple.
Why Aren't They Blooming?
If your plants are huge and green but have no flowers, they might be getting too much nitrogen. Nitrogen promotes leaf growth, while phosphorus promotes blooms. Check your fertilizer and make sure it is a "balanced" one.
Another common reason is heat. In extremely hot weather, some dahlias will take a "break" from blooming to conserve energy. Once the nights start to cool down in late August and September, they usually burst back into life with more flowers than ever.
Dealing with Pests
Slugs and snails love the tender leaves of young dahlias, especially those grown from seed. If you see jagged holes in the leaves, a simple application of organic slug bait or even just keeping the area clear of debris can help.
As the weather gets hotter, you might see aphids or spider mites. A strong blast of water from the hose is often enough to knock these pests off the plant. At Longfield Gardens, we believe in simple, gentle solutions first.
Growing Dahlias for Every Level
One of the reasons we love dahlias so much is that they grow well for everyone, from the absolute beginner to the experienced flower farmer. They are incredibly forgiving plants. Even if you miss a watering or forget to pinch them, they will still try their best to give you beautiful flowers.
If you are feeling overwhelmed, start with just three to five tubers. Pick colors that make you happy and plant them in a sunny spot. Once you see that first bloom open, you will understand why so many gardeners become obsessed with these plants. Whether you choose the predictability of tubers or the excitement of seeds, you are in for a wonderful summer.
Conclusion
Dahlias are truly the queens of the late-summer garden. Whether you choose to grow them from tubers to ensure specific varieties or from seeds to enjoy a mix of surprises, you are adding incredible value to your landscape.
At Longfield Gardens, we believe that gardening should be a source of joy and relaxation. By focusing on the basics—sun, warmth, and proper spacing—you can achieve professional-looking results in your own backyard. Remember that every giant dinnerplate dahlia started as a simple tuber or a tiny seed.
Next steps for your dahlia garden:
- Decide if you want specific colors (order dahlia tubers) or a surprise mix (order seeds).
- Check your local frost dates to plan your planting or seed-starting schedule.
- Pick out a sunny spot in your yard with well-draining soil.
- Browse our dahlia collections to find the perfect varieties for your style.
Growing dahlias is a journey of discovery. Whether you are planting your first tuber or starting your hundredth seed, the excitement of seeing that first bud open never fades.
FAQ
Can I grow dahlias in pots instead of the ground?
Yes, dahlias grow very well in containers. Use a pot that is at least 12 inches deep and 12 inches wide for most varieties. Ensure the pot has drainage holes so the soil doesn't stay too wet, and remember that container plants need more frequent watering and fertilizing than those in the ground.
How long does it take for a dahlia seed to bloom?
Dahlia seeds typically take about 90 to 120 days to go from planting to blooming. Because they need a long season, it is best to start them indoors in early spring. This gives them enough time to grow a strong root system and produce flowers before the autumn frost.
Should I dig up my dahlias every winter?
This depends on your climate. Dahlias are only hardy in USDA zones 8 through 11. If you live in a colder zone (zone 7 or lower), the tubers will freeze and rot if left in the ground. In these areas, you should dig them up and store them after the first frost and store them in a cool, dry place until spring.
Do seed-grown dahlias come back every year?
Yes, but only if you save the tubers they create. While the original plant will die in the frost, it will have grown a clump of tubers underground by the end of its first summer. If you dig up and store those tubers, you can replant them the following year to get the exact same flowers again.
