Introduction
Imagine walking into your summer garden and being greeted by flowers the size of dinner plates. There is a unique thrill in seeing a dahlia bud slowly unfurl into a massive, multi-layered masterpiece that barely fits in both of your hands. These show-stopping blooms are the crown jewels of the late-summer border, offering a level of drama and color that few other plants can match. At Longfield Gardens, we believe that every gardener should experience the joy of growing these giants, regardless of their experience level.
Growing impressive, oversized flowers is a rewarding pursuit that is much simpler than it looks. While dahlias are generous plants by nature, achieving truly massive blooms requires a few specific techniques and a bit of focused care. This guide is for home gardeners who want to go beyond the basics and learn the art of cultivating the largest possible flowers. We will cover everything from selecting the right varieties to the professional secrets of pinching and disbudding.
By matching the right plant to the right location and following a few simple timing rules, you can transform your backyard into a gallery of floral giants. Growing large dahlias is a journey of patience and observation that leads to a spectacular payoff in the height of the season.
Start with the Right Varieties
The most important step in learning how to grow large dahlias happens before you even pick up a trowel. Not all dahlias are genetically programmed to produce massive flowers. If you want blooms that reach 8, 10, or even 12 inches across, you must start with "Dinnerplate" varieties. These cultivars have been specifically bred for their immense size and high petal count.
While a small pompon dahlia is charming, it will never produce a giant flower, no matter how much you fertilize it. When browsing our selection at Longfield Gardens, look for categories labeled as Dinnerplate or Decorative dahlias with a size rating of "A" or "AA." These ratings indicate the potential for the largest possible flower heads.
Some iconic large-flowered varieties include:
- Cafe au Lait: A world-famous variety known for its creamy, blush-pink petals and impressive 8-to-10-inch blooms.
- Emory Paul: One of the largest dahlias in existence, capable of producing shocking pink flowers that can exceed 12 inches in diameter.
- Thomas Edison: A classic deep purple decorative dahlia that provides reliable size and vibrant color.
- Spartacus: A magnificent dark red variety with velvety petals and a commanding presence in the garden.
Starting with high-quality, firm tubers ensures the plant has the energy reserves needed to establish a strong root system. A healthy start is the foundation for a plant that can eventually support heavy, oversized blooms.
Key Takeaway: You cannot force a small variety to become large. Success starts with selecting Dinnerplate or "AA" rated varieties that are genetically predisposed to produce giant flowers.
Right Plant, Right Place: Site Selection
Large dahlias are heavy feeders and sun worshippers. To produce those massive flower heads, the plant needs to photosynthesize efficiently. This means your dahlias need a minimum of six to eight hours of direct sunlight every day. In cooler northern climates, full-day sun is ideal. If you live in a very hot southern region, a spot that provides morning sun and a little bit of dappled afternoon shade can help prevent the petals from scorching.
Soil quality is the next piece of the puzzle. Large dahlias need soil that is rich in organic matter but, most importantly, provides excellent drainage. "Drainage" is simply a measure of how quickly water moves through the soil. Dahlias are susceptible to rot if they sit in soggy, waterlogged ground.
If your garden has heavy clay soil, the water may stay trapped around the tuber. You can improve this by adding compost or well-rotted manure to the planting area, which helps create air pockets and allows water to flow. Alternatively, growing in raised beds is an excellent solution for large dahlias, as it gives you total control over the soil mix and ensures the tubers stay at the perfect moisture level.
What to Do Next:
- Observe your garden for a full day to identify the spot with the most direct sunlight.
- Dig a small hole and fill it with water to see how fast it drains; it should be empty within an hour.
- Clear away any competing weeds or grass from a three-foot diameter area for each plant.
- Incorporate a few shovelfuls of compost into the soil a week before planting.
Timing and Planting Depth
Timing is a quiet winner when it comes to dahlia success. It is tempting to plant as soon as the first warm day of spring arrives, but dahlias are tropical plants at heart. They will not grow in cold soil, and they are extremely sensitive to frost.
Wait to plant your tubers until the soil temperature has reached about 60°F. A good rule of thumb is to plant your dahlias at the same time you would set out your tomato starts. In most of the US, this is usually mid-to-late May. If you plant too early, the tuber may sit dormant in cold, damp soil and rot before it ever has a chance to sprout.
When you are ready to plant, dig a hole about 4 to 6 inches deep. Place the tuber horizontally at the bottom of the hole. If you can see the "eye"—the small bump or sprout where the new growth begins—position it so it is facing upward.
One of the most important rules for dahlia planting is to avoid watering the tuber immediately after planting. The tuber contains all the moisture and energy it needs to send up its first shoot. Unless your soil is bone-dry, wait until you see the green sprout emerge above the soil line before you begin a regular watering schedule. This simple step is the best way to prevent rot during the early stages of growth.
The Secret to Size: Disbudding
If you want to know how to grow large dahlias that truly stand out, you must master the art of disbudding. This is the professional secret that separates "big" dahlias from "giant" dahlias.
Dahlias naturally grow flowers in clusters of three. There is one central bud (the terminal bud) and two side buds. If you leave all three buds to grow, the plant divides its energy between them. This results in three medium-sized flowers.
To get one massive bloom, you should remove the two side buds as soon as they are small enough to pinch with your fingers. This forces the plant to send 100% of its nutrients and energy into that single, central flower. The result is a significantly larger, more symmetrical, and more impressive bloom.
Additionally, you can practice "disbranching." This involves removing some of the side shoots that grow from the leaf axils (the point where the leaf meets the stem) further down the plant. By limiting the number of total stems on a plant to just 3 or 4 main branches, you focus the plant's resources into a few high-quality, giant flowers rather than dozens of smaller ones.
Key Takeaway: Disbudding is the most effective way to increase bloom size. Removing the two side buds in a cluster directs all the plant's energy into the central "king" bloom.
Structure and Support
Large dahlias are victims of their own success. A Dinnerplate dahlia in full bloom is incredibly heavy, especially after a rain shower when the petals hold onto water. Without proper support, the weight of the flower will cause the stem to snap or the entire plant to topple over.
The best time to provide support is at the moment of planting. By driving a sturdy stake into the ground before you cover the tuber, you avoid accidentally piercing the tuber later in the season. Use a strong material like a heavy-duty bamboo pole, a wooden stake, or even a metal T-post for the largest varieties.
As the plant grows, use soft garden twine to tie the main stem to the stake every 12 inches. Do not tie it too tightly; leave a little room for the stem to thicken as it matures. For very large varieties, you may even want to support individual flower stems if they look like they are struggling under the weight of a 10-inch bloom.
Support Steps:
- Install a 5-to-6-foot stake at planting time.
- Start tying the plant when it reaches 12 inches tall.
- Continue tying as the plant grows, creating a "figure-eight" loop with the twine to cushion the stem.
- Check ties after heavy winds or rain to ensure they are still secure.
For additional guidance, see this guide to planting dahlia tubers.
The Power of Pinching
While it might seem counterintuitive to cut off part of a healthy plant, pinching dahlias is essential for a strong, productive dahlia. When your plant is about 12 to 18 inches tall and has four sets of true leaves, use a clean pair of shears to snip off the very top of the center stalk.
This action breaks the plant's apical dominance, which is a fancy way of saying it stops the plant from just growing one tall, skinny stem. Instead, the plant will branch out from the base, creating a bushier, sturdier structure. A pinched plant has more stems to support flowers and is much less likely to blow over in a storm.
For those focusing purely on bloom size, pinching provides the necessary "scaffolding" to hold up those heavy heads. Once the plant has branched out, you can then select the strongest stems to keep and disbud them for those maximum-sized results.
Watering and Fertilizing for Maximum Growth
To grow a massive flower, a dahlia needs a steady, consistent supply of water and the right nutrients. We suggest a "deep but infrequent" approach to watering. Rather than a light sprinkle every day, give your dahlias a deep soaking once or twice a week. This encourages the roots to grow deep into the soil, making the plant more stable and drought-resistant.
Avoid getting water on the foliage or the flower heads, as this can lead to powdery mildew or cause the heavy blooms to rot. Drip irrigation or a simple soaker hose at the base of the plant is the best way to keep your dahlias hydrated.
When it comes to fertilizer, dahlias have different needs at different stages of their life.
- Early Season: Use a balanced fertilizer (like a 10-10-10) to help the plant grow healthy green leaves and strong stems.
- Mid-to-Late Season: Once the plant begins to set buds, switch to a fertilizer that is lower in nitrogen and higher in phosphorus and potassium (the second and third numbers on the bag).
Too much nitrogen late in the season will give you a giant green bush with very few flowers. Potassium is the key ingredient for vibrant, large, and healthy blooms. Always follow the instructions on the fertilizer label, and remember that more is not always better—consistent, moderate feeding is the way to go.
Protecting Your Prize Blooms
Once your giant buds begin to show color, you are in the home stretch. Large dahlias are attractive to several common garden visitors, including slugs, earwigs, and Japanese beetles. These pests are particularly fond of the tender petals of a developing Dinnerplate dahlia.
The best defense is a clean garden. Remove any fallen leaves or debris from the base of the plants where pests like to hide during the day. If you notice small holes in the petals, you can use organic solutions like neem oil or insecticidal soap, following the label instructions carefully.
In some cases, gardeners who grow for competition will even place organza bags over the developing buds to keep insects out. While this might be more effort than the average home gardener wants to put in, it is a highly effective way to ensure a "perfect" bloom.
Mid-Season Success List:
- Water at the base of the plant to keep leaves dry.
- Apply a low-nitrogen "bloom booster" fertilizer every 3-4 weeks once buds appear.
- Monitor daily for pests and remove them by hand or with a gentle spray of water.
- Deadhead (remove) any spent flowers immediately to keep the plant's energy focused on new buds.
Harvesting and Enjoying Your Large Dahlias
The best part of learning how to grow large dahlias is finally bringing them indoors. Unlike many other flowers, dahlias will not continue to open much once they are cut. This means you should wait to harvest them until they are almost fully open.
The best time to cut your dahlias is in the cool of the early morning when the plant is most hydrated. Use a sharp, clean pair of bypass pruners and cut the stem at an angle. To ensure a long vase life, immediately place the stems into a bucket of warm water.
For more detail, see this guide to cutting dahlia flowers for long-lasting blooms.
Large dahlias have heavy heads, so choose a sturdy, tall vase that can support their weight without tipping over. Change the water every day and trim a tiny bit off the bottom of the stem to keep the water flowing into the flower. Even a single 10-inch dahlia in a simple vase can be a breathtaking centerpiece.
Encouraging a Long Bloom Season
The more you cut your dahlias, the more they will bloom. If you aren't cutting them for bouquets, be sure to "deadhead" the plant. This means cutting off any flowers that are starting to fade. If you leave the old flowers on the plant, it will start to produce seeds, which signals the plant to stop making new flowers.
By keeping the plant clean and removing old blooms, you can enjoy these floral giants from mid-July all the way until the first hard frost of autumn. In many regions, the dahlias actually look their best in the late summer and early fall when the nights begin to cool down and the colors become even more intense.
Conclusion
Growing massive dahlias is one of the most rewarding projects a home gardener can undertake. It is a process that rewards patience and attention to detail, but the basics remain simple: start with the right Dinnerplate varieties, provide plenty of sun and drainage, and master the art of disbudding. At Longfield Gardens, we love helping gardeners achieve these "wow" moments in their own yards.
There is a deep satisfaction in watching a tiny tuber transform into a towering plant topped with flowers that defy belief. Whether you are growing them to impress the neighbors, to fill your home with incredible bouquets, or simply for the personal joy of the challenge, large dahlias never fail to deliver.
Key Takeaway: Success with giant dahlias comes from focusing the plant's energy. By selecting the right genetics and using techniques like disbudding, you can grow blooms that are truly spectacular.
Ready to start your own dahlia journey? The best time to plan is now. Select your favorite Dinnerplate varieties, prepare your sunniest garden spot, and get ready for a summer filled with the biggest, brightest blooms you've ever grown. Explore the Summer Spritz Dinnerplate Dahlia Collection for a coordinated selection of large-flowered varieties.
FAQ
Why are my dahlia flowers smaller than they should be?
The most common reason for smaller-than-expected blooms is skipping the disbudding process. If the plant is allowed to grow all its side buds, the energy is split between too many flowers. Additionally, ensure the plant is receiving at least 6-8 hours of sun and that you aren't over-applying nitrogen fertilizer, which promotes leaves over large flowers.
Do I need to fertilize my dahlias to get them large?
While dahlias can grow in good soil without extra help, a regular feeding schedule with a "bloom booster" (low nitrogen, high phosphorus/potassium) fertilizer will significantly increase the size and quality of the flowers. Start feeding once the plants are about a foot tall and continue every few weeks until the end of summer. For a broader overview, read how to care for dahlia plants.
Can I grow large Dinnerplate dahlias in containers?
Yes, but you need a very large, heavy pot—at least 12 to 15 inches in diameter and depth. Large dahlias are top-heavy and grow quite tall, so a small pot will tip over easily. You will also need to be more diligent with watering and staking when growing these giants in containers. The Dinnerplate Dahlia collection includes varieties suited to growing for large blooms.
Should I water my dahlia tubers as soon as I plant them?
It is best to wait until you see green growth emerging from the soil before you start a regular watering schedule. The tuber itself holds enough moisture to start the growing process. Watering too early, especially in heavy or cool soil, is the leading cause of tuber rot. For additional planting guidance, read How to Plant Dahlia Tubers in the Ground.
