How to Plant Dinnerplate Dahlias for Giant Blooms

Table of Contents

1. Introduction
2. What Are Dinnerplate Dahlias?
3. Choosing the Right Location
4. When to Plant Dinnerplate Dahlias
5. Preparing the Soil
6. How to Plant Dinnerplate Dahlias Step-by-Step
7. Essential Support: Staking Your Dahlias
8. The Secret to Giant Blooms: Pinching and Disbudding
9. Water and Fertilizer Needs
10. Maintenance and Troubleshooting
11. Harvesting Dahlias for Bouquets
12. A Note on Toxicity
13. Realistic Expectations for Your Garden
14. Conclusion
15. FAQ

Introduction

Imagine walking into your garden and finding a flower the size of a dinner plate, its petals perfectly arranged in a stunning display of color and texture. Dinnerplate dahlias are the undisputed stars of the summer garden, offering a "wow" factor that few other plants can match. At Longfield Gardens, we believe every gardener should experience the thrill of growing these impressive giants. Whether you are a beginner or a seasoned pro, the process is rewarding and straightforward when you follow a few simple steps.

This guide will walk you through everything you need to know about how to plant dinnerplate dahlias, from choosing the right spot to providing the support these heavy hitters require. We will cover soil preparation, planting depth, and the specific care techniques that result in the largest possible blooms. Our goal is to help you grow healthy, vibrant plants that produce spectacular flowers from midsummer all the way until the first frost. For a step-by-step refresher, see our How to Plant Dahlias.

Success with these garden giants comes down to matching the plant’s needs for sun and drainage with a little bit of patience as the soil warms.

What Are Dinnerplate Dahlias?

While "dinnerplate" isn't an official botanical classification, it is a term used by gardeners and nurseries to describe dahlia varieties that produce exceptionally large flowers. To earn this title, a dahlia typically needs to produce blooms that are at least 8 inches in diameter. Some varieties, such as the famous 'Emory Paul' or Kelvin Floodlight, can even reach a staggering 10 to 12 inches across.

These plants are native to the high-altitude regions of Mexico and Central America. Because of their origins, they thrive in sunny spots with warm days and cool nights. They are perennial in warmer climates (USDA zones 8–11) but are grown as annuals or dug up and stored for winter in colder regions. Because of their sheer size—often reaching 4 to 5 feet in height—they require more space and more intentional care than smaller bedding dahlias. For a broader overview of dahlia care, see All About Dahlias.

Growing a dinnerplate dahlia is very similar to growing a beefsteak tomato. Both plants are heavy feeders, need plenty of sun, and require sturdy support to keep their fruit (or flowers) from pulling the plant to the ground. If you have had success in a vegetable garden, you are already well on your way to mastering these flowers.

Choosing the Right Location

The first rule of successful dahlia gardening is "right plant, right place." Because dinnerplate dahlias put so much energy into creating massive blooms, they cannot be neglected when it comes to their environment.

Sunlight Requirements

Dahlias are sun worshippers. To produce those legendary 10-inch flowers, the plants need a minimum of six to eight hours of direct sunlight every day. Morning sun is particularly beneficial because it helps dry the dew off the foliage, which reduces the risk of fungal issues. If you plant them in too much shade, the stems will become "leggy" as they stretch toward the light, and the flower size will suffer significantly.

Soil and Drainage

Drainage is perhaps the most critical factor in dahlia health. In gardening terms, "drainage" simply refers to how quickly water moves through the soil. Dahlias grow from tuberous roots (tubers) that are prone to rotting if they sit in cold, soggy soil. For more detail on planting depth, see How Deep Should You Plant Dahlia Bulbs?.

You want soil that is rich in organic matter but loose enough that excess water can escape. If you have heavy clay soil that stays wet like a sponge after it rains, consider planting your dahlias in raised beds or creating small mounds (berms) to keep the tubers above the water line.

Protection from Wind

Because dinnerplate dahlias grow tall and carry heavy flower heads, they are susceptible to wind damage. A sudden summer thunderstorm can easily snap a brittle dahlia stem. Look for a spot that is sheltered from the strongest winds—perhaps near a fence, a hedge, or the side of a building—while still ensuring the plant gets plenty of sun and airflow.

Site Selection Checklist:

• At least 6–8 hours of full, direct sun.
• Loose, well-draining soil (no standing water).
• Shelter from high winds.
• Enough vertical space for 4–5 foot tall plants.

When to Plant Dinnerplate Dahlias

Timing is more important than almost any other "secret" tip. Because dahlia tubers are tender, they cannot tolerate freezing temperatures. More importantly, they will not start growing until the soil itself is warm.

We recommend waiting to plant your tubers until the danger of frost has passed and the soil temperature has reached about 60°F. A good rule of thumb is to plant your dahlias at the same time you would plant tomatoes or peppers. If the ground is still cold and clammy, the tubers will simply sit there and may even rot before they get the chance to sprout. If you are unsure of your climate, the Hardiness Zone Map can help you time things.

In most parts of the United States, this means planting in May or early June. If you live in a region with a short growing season, you can give your dinnerplate dahlias a "head start" by planting them in pots indoors about four to six weeks before the last frost date. This allows the plant to develop a root system so it can hit the ground running once the weather warms up.

Preparing the Soil

Before you dig your first hole, take a moment to prepare the "bed" for your dahlias. These plants are heavy feeders, meaning they consume a lot of nutrients from the soil to build their large stems and flowers.

Start by loosening the soil to a depth of about 12 inches. This makes it easier for the roots to expand. Mix in a healthy amount of compost or well-rotted manure. This adds nutrients and improves the soil structure, helping with that all-important drainage.

If you are using a commercial fertilizer at planting time, look for one that is low in nitrogen and high in phosphorus (the middle number on the fertilizer bag, such as 5-10-10). Nitrogen encourages leaf growth, but too much of it can lead to weak, spindly stems and very few flowers. Phosphorus and potassium are what the plant needs to build strong roots and large, vibrant blooms.

How to Plant Dinnerplate Dahlias Step-by-Step

Once your soil is prepared and the weather is warm, it’s time to get your tubers in the ground.

1. Dig the Hole

Dig a hole about 6 to 8 inches deep. If you are planting multiple dinnerplate dahlias, space the holes 18 to 24 inches apart. For more spacing guidance, see How Far Apart to Plant Dahlia Bulbs. These plants grow wide as well as tall, and they need plenty of room for air to circulate between them.

2. Set the Tuber

Place the tuber in the hole horizontally (laying on its side). Look for the "eye"—a small bump or sprout near the neck of the tuber where the previous year's stem was attached. This eye should be facing upward. Don't worry if you can't see an eye yet; just lay the tuber flat, and the plant will find its way up.

3. Add Support (Staking)

This is a vital step for dinnerplate varieties. Because the flowers are so heavy, you must provide support. It is best to drive a sturdy stake (like a 5-foot bamboo or wooden garden stake) into the ground before you cover the tuber with soil. This prevents you from accidentally poking a hole through the tuber later in the season.

4. Cover with Soil

Cover the tuber with about 2 to 3 inches of soil. As the plant grows and the stem emerges, you can gradually fill in the rest of the hole until it is level with the surrounding ground. This helps create a deep, stable root system.

5. The "No-Water" Rule

This is one of the most common mistakes new dahlia growers make. Do not water your dahlias immediately after planting unless the soil is bone-dry. The tuber has enough stored energy and moisture to start growing on its own. Adding extra water to a dormant tuber in cool soil is a recipe for rot. Wait until you see the first green sprouts poking through the soil before you start a regular watering routine.

Planting Summary:

• Depth: 6 inches deep.
• Orientation: Lay tuber flat, eyes facing up.
• Spacing: 18–24 inches between plants.
• Staking: Place your stake at the time of planting.
• Water: Wait for green sprouts before watering deeply.

Essential Support: Staking Your Dahlias

We cannot emphasize enough how important staking is for dinnerplate dahlias. A single Café au Lait bloom can be heavy, and a plant covered in several of these massive flowers carries a lot of weight.

As the plant grows, use soft garden twine or strips of fabric to loosely tie the main stem to the stake. We recommend adding a new tie every 12 to 18 inches of growth. You want the support to be firm but not so tight that it cuts into the succulent stems.

Some gardeners prefer using tomato cages, which can work well for shorter varieties, but for true dinnerplate types that reach 5 feet, a tall, heavy-duty stake or a professional "corralling" method is usually more effective.

The Secret to Giant Blooms: Pinching and Disbudding

If you want your dahlias to look like the photos in our catalog, you need to use two professional techniques: pinching and disbudding. For more season-long advice, read 8 Tips for Growing Better Dahlias.

Pinching for Bushiness

When your dahlia plant is about 12 inches tall, it’s time for "the pinch." Use your fingers or a pair of clean snips to remove the very top of the center stem, just above a set of leaves. This might feel like you are hurting the plant, but it actually encourages the dahlia to branch out. Instead of one tall, lanky stem, you will get a bushier plant with more flowering stems.

Disbudding for Size

This is the real "secret" to achieving 10-inch flowers. Dahlias typically produce flower buds in clusters of three: one large central bud and two smaller side buds. If you let all three bloom, the plant’s energy is split between them.

To get the largest possible flower, carefully pinch off the two side buds when they are about the size of a pea. This forces the plant to send all its energy, nutrients, and water into that single central bud. The result is a significantly larger, more impressive flower head.

Water and Fertilizer Needs

Once your dahlias are established and growing vigorously, they will become quite thirsty.

Deep Watering

Dahlias prefer deep, infrequent watering over light daily sprinkles. This encourages the roots to grow deep into the soil. Aim for about one inch of water per week, either from rain or irrigation. In very hot or dry weather, you may need to water two or three times a week. Always try to water at the base of the plant to keep the leaves dry, which helps prevent diseases like powdery mildew.

Feeding Your Plants

Dahlias are "hungry" plants. To keep them blooming at full capacity, we suggest fertilizing them every three to four weeks. Again, use a fertilizer with low nitrogen and higher phosphorus and potassium. A water-soluble fertilizer is easy to apply during your regular watering routine.

Stop fertilizing in late summer (usually by early September). This allows the plant to start slowing down and focusing on toughening up its tubers for the winter rather than producing new, tender green growth that will be killed by the first frost.

Maintenance and Troubleshooting

Gardening is a journey, and dinnerplate dahlias are generally very resilient, but they do have a few common preferences.

Deadheading

To keep the flowers coming all season, you must "deadhead" the plant. This simply means cutting off flowers as they begin to fade. If you leave the old flowers on the plant, it will stop producing new buds and start putting its energy into making seeds.

When you cut a flower (either for a vase or to deadhead), cut the stem long—right down to where it meets a main branch. This encourages the plant to produce more long, sturdy stems for future blooms.

Common Pests

Slugs and snails are the primary fans of young dahlia sprouts. You can protect your new plants by using a pet-safe slug bait or creating barriers around the base of the stems. Once the plants are a foot tall, they are usually tough enough to withstand minor nibbling.

Later in the season, keep an eye out for Japanese beetles or aphids. Usually, a strong blast of water from the hose is enough to knock these pests off. If you notice white, dusty spots on the leaves, that is likely powdery mildew. Improving the airflow around the plant and keeping the leaves dry during watering are the best ways to manage this.

Success Tips for Late Summer:

• Deadhead weekly to keep blooms coming.
• Check stakes and ties to ensure they are secure.
• Water deeply during late-summer heatwaves.
• Monitor for pests and treat them early with simple methods.

Harvesting Dahlias for Bouquets

One of the best reasons to grow dinnerplate dahlias is for the spectacular cut flowers. They make an incredible centerpiece for a dining table or a show-stopping gift for a friend.

Unlike many other flowers, dahlias do not open much after they are cut. Wait until the flower is almost fully open before you snip it. The best time to harvest is in the cool of the morning when the plant is most hydrated.

Use clean, sharp scissors and immediately place the stems in 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. Most dahlia blooms will last about 5 to 7 days in a vase if you change the water every day.

A Note on Toxicity

It is important to remember that dahlias are considered toxic to dogs, cats, and horses if eaten. They can also cause mild skin irritation for some people. If you have curious pets that like to nibble on garden plants, it is best to plant your dahlias in a fenced-off area or a spot where pets don't wander. Always wash your hands after handling the plants or tubers if you have sensitive skin.

Realistic Expectations for Your Garden

While we all dream of every flower being a perfect 12-inch specimen, nature has its own plans. The exact size and color of your dahlias can be influenced by your local climate, the quality of your soil, and the intensity of the summer sun.

In very hot climates, the colors might be slightly more muted, or the plants might take a "break" during the hottest part of July before roaring back to life in the cooler days of August and September. This is perfectly normal. Gardening is about enjoying the process and celebrating the unique beauty of each individual bloom.

Conclusion

Growing dinnerplate dahlias is a deeply rewarding experience that brings a sense of grand scale and vibrant color to your home landscape. By focusing on the basics—sun, drainage, warm soil, and sturdy support—you can transform your garden into a showcase of these spectacular blooms. At Longfield Gardens, we take pride in providing high-quality tubers, and our About Us page explains our quality guarantee.

The most important thing to remember is to have fun with it. There is nothing quite like the feeling of watching a tiny sprout turn into a five-foot giant topped with a blossom the size of a dinner plate. With a little care and a lot of sun, you will be well on your way to a summer filled with floral wonder.

Next Steps for Your Dahlia Garden:

• Order your favorite dinnerplate varieties early from our Shop All Spring Planted Bulbs page.
• Browse our Top-Rated Dahlias collection for more proven performers.
• Choose a palette with Spring Planted Bulbs By Color if you want to plan by bloom color.
• Check Shipping Information before your order ships.

FAQ

How deep should I plant dinnerplate dahlia tubers?

You should plant dinnerplate dahlia tubers about 6 inches deep in well-drained soil. It is often helpful to cover them with only 2 or 3 inches of soil initially, then gradually fill in the rest of the hole as the green stem grows toward the surface. This method helps the plant establish a deep, stable root system that can support its heavy flowers.

Do I need to water my dahlias right after planting?

No, we recommend waiting to water until you see the first green sprouts appear above the soil line. Because dahlia tubers are prone to rot in cool, wet conditions, they do best when they are allowed to wake up naturally using the moisture already stored in the tuber. Once the plant is growing, you can transition to a deep, regular watering schedule.

When is the best time to plant dinnerplate dahlias?

The best time to plant is in the spring, after all danger of frost has passed and the soil has warmed to about 60°F. For most regions in the United States, this occurs in May or early June. Planting too early in cold, wet soil can cause the tubers to rot, so it is always better to wait for a stretch of warm weather.

Why are my dinnerplate dahlia flowers smaller than expected?

Smaller flowers are often caused by either too much nitrogen in the fertilizer or a lack of disbudding. To get the largest blooms, use a fertilizer high in phosphorus and potassium, and pinch off the two smaller side buds next to the main central flower bud. This directs all of the plant’s energy into creating one massive, show-stopping blossom.