Introduction
Imagine stepping into your backyard and finding flowers so large they rival the size of a dinner plate. Growing dinner plate dahlias is one of the most rewarding experiences a gardener can have, offering a massive splash of color just when the rest of the summer garden begins to fade. These impressive blooms are the undisputed celebrities of the floral world, and they are surprisingly easy to grow when you follow a few simple steps.
At Longfield Gardens, we want to help you fill your landscape with these spectacular, oversized blossoms. Whether you are a beginner or a seasoned pro, the "wow factor" of a dinner plate dahlia never gets old. We provide the high-quality tubers and practical advice you need to ensure your garden is the talk of the neighborhood.
This guide will walk you through everything you need to know about successfully growing these giants, from choosing the right spot to supporting those heavy flower heads. By focusing on the basics of sun, soil, and timing, you can enjoy a season full of incredible blooms. Success with dinner plate dahlias is achievable for everyone with a little bit of planning and care.
What Makes a Dahlia a Dinner Plate?
The term "dinner plate" is not actually an official botanical classification. Instead, it is a descriptive category used to group dahlia varieties that produce exceptionally large flowers. To earn this title, a dahlia must typically produce blooms that are at least 8 to 10 inches in diameter. Some varieties can even reach 12 inches across under the right conditions.
These plants are larger in every way. Beyond the massive flowers, the plants themselves often grow 4 to 5 feet tall and develop thick, sturdy stems to support the weight of the blossoms. The flower forms can vary widely. You might see the classic, orderly petals of a decorative dahlia like 'Café au Lait' or the wild, shaggy petals of a cactus-style dahlia.
Because they are such heavy producers, dinner plate dahlias are often treated as the centerpieces of the garden. They provide architectural height and a focal point that draws the eye from across the yard. Understanding that these are "hungry" and "thirsty" plants is the first step toward getting those famous, oversized results.
Finding the Right Place to Plant
The most important rule for growing dinner plate dahlias is "right plant, right place." Because these plants put so much energy into creating huge flowers, they have very specific needs regarding sun and soil. If you give them what they want from the start, the rest of the season will be much easier.
Sun Requirements
Dahlias are sun-loving plants. For the strongest stems and the largest flowers, they need at least six to eight hours of direct sunlight every day. In cooler northern climates, all-day sun is even better. If they are planted in too much shade, the plants will become "leggy," stretching toward the light and becoming weak. This makes them more likely to fall over once those heavy flowers start to bloom.
Soil and Drainage
"Drainage" refers to how fast water leaves the soil. This is critical for dahlias because their tubers can rot if they sit in cold, soggy ground. They prefer loose, loamy soil that is rich in organic matter. If you have heavy clay soil, consider planting your dahlias in raised beds or mounding the soil to improve drainage.
Before planting, it is a great idea to mix in some well-rotted compost or aged manure. This improves the soil structure and provides a slow-release source of nutrients. Think of your dahlias like a vegetable crop; if the soil is good enough for big beefsteak tomatoes, it is perfect for dinner plate dahlias.
Space to Breathe
Because these plants grow quite large, they need plenty of room for air to circulate. Crowding your plants can lead to issues with mildew or pests. Aim for a spacing of about 18 to 24 inches between each plant. This gives the foliage room to expand and ensures that every leaf gets the sunlight it needs to fuel those giant blooms.
Key Takeaway: Choose a spot with at least 8 hours of sun and soil that never stays soggy. Give each plant about two feet of space to ensure healthy growth.
Timing Your Planting
Timing is often more important than any gardening "trick." Dahlias are tropical plants at heart, and they have no tolerance for frost. Planting too early into cold, wet soil is one of the most common reasons tubers fail to sprout.
Soil Temperature Matters
Wait to plant your tubers until the danger of frost has completely passed and the soil has warmed up to about 60°F. In most parts of the US, this is around the same time you would plant tomatoes or peppers. If you aren't sure, a simple soil thermometer can take the guesswork out of the process.
Starting Early Indoors
If you live in a region with a short growing season, you can give your dinner plate dahlias a head start. About four to six weeks before the last frost date, plant the tubers in pots filled with slightly moist potting soil. Keep them in a warm, sunny spot indoors or in a greenhouse. By the time the weather warms up, you will have established plants ready to go into the ground, which can lead to earlier blooms in the summer.
Shipping and Zones
We ship our tubers at the appropriate time for your USDA hardiness zone. This ensures they arrive roughly two weeks before the ideal planting time for your area. While it is exciting to receive your order, keep the tubers in a cool, dark, dry place until the outdoor conditions are just right.
How to Plant Dinner Plate Dahlia Tubers
Once the soil is warm and the sun is shining, it is time to get your tubers in the ground. Planting at the correct depth and orientation sets the foundation for a successful season.
Digging the Hole
Dig a hole about 6 inches deep and about 12 inches wide. This gives you enough room to spread out the tuber clumps without crowding them. If you haven't already enriched the soil, you can toss a handful of compost into the bottom of the hole now.
Positioning the Tuber
Look for the "eye" of the tuber. This is a small bump or sprout located at the neck where the tubers meet the old stem. This eye is where the new growth will come from. Lay the tuber clump horizontally in the hole with the eye pointing upward. If you can't find the eye, don't worry—the plant will usually find its way up as long as it isn't planted upside down.
Filling and Covering
Backfill the hole with soil, gently firming it down with your hands to remove any large air pockets. You only need about 4 to 6 inches of soil covering the top of the tuber. For more guidance, see this guide to dahlia tuber planting depth.
What to Do Next:
- Mark the spot where you planted each tuber with a stake or label so you don't accidentally dig it up later.
- Do not water the tubers immediately after planting unless the soil is bone-dry. The tubers have enough stored moisture to start growing, and extra water at this stage can cause rot.
- Wait until you see the first green sprouts poking through the soil before you begin a regular watering schedule.
The Vital Step: Staking and Support
When you grow dinner plate dahlias, you are growing some of the heaviest flowers in the garden. A single bloom can weigh enough to snap a stem, especially after a summer rainstorm. Providing support is not optional—it is essential for protecting your hard work.
Stake Early
The best time to stake your dahlias is at the moment of planting. By driving a sturdy wooden or metal stake into the ground right next to the tuber, you avoid the risk of piercing the tuber later in the season. Use a stake that is at least 5 to 6 feet tall, as you will need to bury at least a foot of it in the ground for stability.
Tying the Plants
As the dahlia grows, use soft garden twine or fabric strips to loosely tie the main stem to the stake. Check the plants every week. As they get taller, add more ties every 12 to 18 inches. You want the plant to be secure but still have enough "wiggle room" so the tie doesn't cut into the fleshy stem.
Alternative Methods
If you are growing a large row of dahlias, you might prefer the "corralling" method. This involves placing heavy-duty stakes at the corners of your bed and running twine around the entire perimeter at different heights. This allows the plants to support each other while staying upright. Some gardeners also find success using extra-large tomato cages for dinner plate varieties.
Key Takeaway: Dinner plate dahlias are too heavy to stand on their own. Always install a sturdy stake at planting time and tie the stems every foot as they grow.
Watering for Maximum Growth
Watering correctly is a balance. Dahlias love moisture, but they hate "wet feet." The goal is to keep the soil consistently moist but never saturated.
Deep Watering
Instead of a light sprinkle every day, give your dahlias a deep soaking once or twice a week. This encourages the roots to grow deeper into the soil, making the plant more resilient during hot spells. If the weather is particularly hot or windy, you may need to increase the frequency.
Target the Roots
Always try to apply water at the base of the plant rather than spraying the leaves. Keeping the foliage dry helps prevent common issues like powdery mildew and reduces the hiding spots for pests like slugs. A soaker hose or a drip irrigation system is an excellent investment for a dahlia bed.
Mulching
In very hot climates, a thin layer of organic mulch—such as clean straw or shredded bark—can help retain soil moisture and keep the roots cool. However, avoid piling mulch directly against the stem of the plant, as this can encourage rot or provide a home for pests.
Feeding Your Dahlias
Because dinner plate dahlias produce so much biomass in a single season, they require a steady supply of nutrients. However, the type of fertilizer you use matters just as much as how often you apply it.
Choose the Right Fertilizer
Dahlias need a fertilizer that is low in nitrogen and high in phosphorus and potassium. In the gardening world, we look at the N-P-K numbers on the bag. A ratio like 5-10-10 or 10-20-20 is ideal.
- Nitrogen (N): Promotes green, leafy growth. Too much nitrogen will give you a giant bush with very few flowers.
- Phosphorus (P): Encourages strong root development and large blooms.
- Potassium (K): Helps with overall plant health and bloom quality.
Application Schedule
Wait until the plants are about 12 inches tall before you start your fertilizing routine. Apply a balanced, low-nitrogen fertilizer about once a month throughout the growing season. Follow the instructions on the product label for the correct amounts. Stop fertilizing by late August or early September to allow the plant to naturally wind down before the first frost.
Pinching for More Blooms
It might feel counterintuitive to cut off the top of a healthy young plant, but "pinching" is the secret to a bushier dahlia with more flowers. If you let a dahlia grow without pinching, it will often produce one main stem with a single giant flower at the very top.
When to Pinch
When your dahlia is about 12 to 16 inches tall and has at least four sets of leaves, use your fingers or a clean pair of shears to snip off the very top of the center stem. Aim to remove about 2 to 3 inches of growth.
Why It Works
This simple act signals the plant to stop putting all its energy into that one main stem. Instead, it will start growing several side branches from the leaf axils. This results in a sturdier, more balanced plant that produces many more flowers throughout the season. While the very first bloom might be delayed by a week, the total number of blooms you get will be significantly higher.
Cutting and Deadheading
The more you cut your dahlias, the more they will bloom. This is great news for anyone who loves fresh flower arrangements.
How to Cut for Bouquets
Unlike some flowers that continue to open after they are cut, dahlias should be harvested when they are nearly fully open. Look for flowers that are about 75% to 90% open. Avoid flowers that are starting to lose petals at the back.
Use sharp, clean scissors and cut the stem long—even if it means cutting off a few smaller side buds. This encourages the plant to produce longer stems for future flowers. Immediately place the cut stems into a bucket of room-temperature water.
The Importance of Deadheading
"Deadheading" means removing flowers that have finished blooming and are starting to fade. If you leave spent blooms on the plant, the dahlia will start to produce seeds. Once a plant thinks it has successfully made seeds, it will stop producing new flowers.
Check your plants every few days. If you see a flower where the petals are turning brown or falling off, follow the stem down to where it meets a main branch and snip it off. Keeping the plant "clean" ensures a continuous supply of color until the first frost.
What to Do Next:
- Carry a bucket of water with you when you go out to harvest.
- Cut stems in the cool of the morning for the longest vase life.
- Check the back of the flower head; if the petals are firm, it's ready to cut.
- Remove any leaves that will be below the water line in your vase to keep the water clean.
Troubleshooting Common Issues
Even with the best care, you might run into a few hurdles. Most dahlia problems are easy to fix if you catch them early.
Pests
Slugs and snails are the most common fans of young dahlia sprouts. They love the tender green growth. You can protect your plants by using iron phosphate granules or simple physical barriers. Once the plants get larger and the stems toughen up, slugs are less of a problem.
Earwigs can sometimes nibble on the petals of dinner plate dahlias, especially 'Café au Lait' and other light-colored varieties. If you notice small holes in the petals, you can try organic controls or simply encourage predatory insects like birds and ladybugs into your garden.
Diseases
Powdery mildew looks like a dusting of white flour on the leaves. It usually shows up in late summer when the air is humid and the nights get cooler. The best way to prevent it is to ensure good spacing between plants and to water only at the soil level. If it becomes a major problem, an organic neem oil spray can help manage the spread.
Preparing for Winter
In most parts of the United States, dahlia tubers must be dug up and stored indoors for the winter. Dahlias are only hardy in USDA zones 8 through 11. If you live in zone 7 or colder, the ground will freeze deep enough to kill the tubers.
When to Dig
Wait for a "killing frost" that turns the foliage black or brown. This signals the plant to go dormant and send its energy down into the tubers. After the frost, cut the stems down to about 4 inches above the ground and wait about a week before digging. This short wait helps the "eyes" become more visible.
How to Store
Carefully lift the tuber clumps with a garden fork, being careful not to nick or bruise them. Gently shake off the excess soil and let them air dry in a frost-free area for a day or two. For a detailed walkthrough, see this guide to overwintering dahlia bulbs.
Store the tubers in a cardboard box or plastic bin filled with slightly damp peat moss, vermiculite, or wood shavings. Keep the box in a cool, dark place that stays between 40°F and 50°F—an unheated basement or crawl space is often perfect. Check them once or twice during the winter to make sure they aren't shriveling or rotting.
Why We Love Dinner Plate Dahlias
Growing these giants is more than just a gardening task; it's a way to bring pure joy into the landscape. There is something truly magical about watching a tiny green sprout transform into a five-foot-tall plant topped with blooms the size of a dinner plate. They represent the peak of summer's beauty and the rewarding nature of a little bit of patience and care.
At Longfield Gardens, we take pride in seeing the success of our customers. Whether you are growing them for competition, for gorgeous indoor bouquets, or simply to enjoy the view from your porch, dinner plate dahlias never disappoint. With the right site, a sturdy stake, and regular watering, you can create a spectacular display that returns year after year.
As you plan your next garden, consider making room for a few of these oversized wonders. They are the perfect way to add drama, color, and a sense of accomplishment to your outdoor space.
Summary of Success:
- Plant in full sun and well-drained soil once the ground is warm.
- Install sturdy stakes at the time of planting.
- Pinch the center stem when the plant is a foot tall to encourage more blooms.
- Water deeply at the base and fertilize monthly with a low-nitrogen formula.
- Enjoy the massive blooms and cut them often to keep the plant producing!
Growing dinner plate dahlias is one of the easiest ways to add a "wow" factor to your yard. By getting the basics of sun, support, and soil right, you set yourself up for a season of spectacular, oversized color.
FAQ
When do dinner plate dahlias start blooming?
Most dinner plate dahlias begin blooming in mid-to-late summer, usually starting in July or August depending on your climate. They continue to produce flowers consistently until the first hard frost of autumn. Starting your tubers in pots indoors a few weeks early can help you see those first big blooms even sooner.
Can I grow dinner plate dahlias in containers?
Yes, you can grow them in pots, but you will need a very large, heavy container to prevent the plant from tipping over. A pot that holds at least 5 to 7 gallons of soil is recommended for one tuber. Make sure the container has excellent drainage and use a sturdy stake or a tomato cage to support the plant's height.
Why are my dahlia flowers smaller than expected?
Smaller flowers are often caused by too much nitrogen in the soil, which favors leaves over blooms. It can also happen if the plant is stressed by extreme heat or lack of water. To get the largest possible flowers, ensure you are using a phosphorus-rich fertilizer and consider "disbudding"—removing the two smaller side buds next to a central flower bud so the plant puts all its energy into one giant bloom.
Do I have to dig up my dahlia tubers every year?
If you live in USDA hardiness zone 8 or warmer, you can usually leave your tubers in the ground for the winter with a thick layer of mulch for protection. However, if you live in zone 7 or colder, the tubers will likely freeze and die if left outside. In those regions, digging them up and storing them in a cool, frost-free place is necessary to enjoy them again next year. For more winter-care details, read about storing dahlia bulbs during winter.
