Introduction
Imagine walking into your backyard and finding flowers the size of a dinner plate. These massive, colorful blooms are the undisputed stars of the late summer garden. They offer a level of drama and beauty that few other plants can match. Whether you want to grow flowers for stunning indoor bouquets or simply want to impress the neighbors, these oversized dahlias are the perfect choice.
At Longfield Gardens, we believe every gardener can find success with these spectacular plants. While their size might make them look intimidating, dinner plate dahlias are actually quite approachable. By following a few simple steps, you can transform a humble-looking tuber into a flowering machine that produces blooms from midsummer all the way until the first frost.
This guide will walk you through everything you need to know about how to plant dinner plate dahlia bulbs. We will cover site selection, proper planting techniques, and the simple maintenance required to support those heavy, magnificent flower heads. With the right start, you will be well on your way to a season filled with incredible color.
Growing giant dahlias is a rewarding journey that brings joy to any garden space.
What Makes a Dahlia a Dinner Plate?
Before we dig into the planting process, it is helpful to understand what exactly a "dinner plate" dahlia is. Interestingly, "dinner plate" is not an official botanical classification. It is a descriptive term used for any dahlia variety that produces flowers at least 8 to 10 inches in diameter. Some varieties can even reach a staggering 12 inches across.
These plants are impressive not just for their flower size, but for their overall stature. Most dinner plate varieties grow 4 to 5 feet tall and develop a bushy, shrub-like habit. This makes them excellent choices for the back of a flower border or as a focal point in a dedicated cutting garden.
We offer several popular varieties that fall into this category. You might recognize the soft, creamy tones of 'Café au Lait' or the deep, velvet purple of 'Thomas Edison.' Others, like the shaggy-petaled 'Penhill Dark Monarch' or the vibrant 'Emory Paul,' showcase the incredible diversity of shapes and colors available. No matter which variety you choose, the planting requirements remain largely the same.
Choosing the Best Time to Plant
Timing is one of the most important factors when learning how to plant dinner plate dahlia bulbs. Because dahlias are native to the warm climates of Mexico and Central America, they have no tolerance for frost. Planting too early in cold, wet soil is one of the few ways to encounter trouble, as the tubers may rot before they have a chance to grow.
Soil Temperature Matters
Wait to plant your dahlias until the danger of frost has completely passed. The soil should be warm to the touch, ideally around 60°F. A good rule of thumb for most US gardeners is to plant dahlias at the same time you would plant tomatoes or peppers. In many regions, this falls between late April and early June.
Starting Early Indoors
If you live in a northern climate 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 large pots filled with damp 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 often leads to earlier blooms in July. See our guide to starting dahlia tubers early for additional guidance.
Next Steps for Timing:
- Check your local frost-free date.
- Monitor soil temperature with a simple garden thermometer.
- Prepare pots if you choose to start your tubers indoors.
Selecting the Perfect Location
Dinner plate dahlias are high-energy plants. To produce those massive blooms, they need plenty of fuel from the sun and the soil. Choosing the right spot in your yard will do most of the work for you.
Sun Exposure
Dahlias need full sun to perform their best. This means a minimum of six to eight hours of direct sunlight each day. If they are planted in too much shade, the stems will become "leggy" as they stretch for light, and the flower production will be significantly lower. Morning sun is especially beneficial as it helps dry the dew off the leaves, which keeps the plants healthy.
Soil Quality and Drainage
The ideal soil for dahlias is rich, loamy, and well-drained. Drainage is the most critical element. "Drainage" simply refers to how quickly water moves through the soil. If water pools in your chosen spot after a rain, the soil may be too heavy for dahlias.
If you have heavy clay soil, you can improve it by mixing in organic matter like compost or aged manure. This creates a fluffier texture that allows roots to breathe. Dahlias also thrive in raised beds, which naturally provide the excellent drainage these tubers crave.
Preparing the Tubers for Planting
When your order from Longfield Gardens arrives, you will receive tubers that might look like a bunch of small potatoes. Each tuber must have an "eye" to grow. The eye is a small growth bud located on the "crown" or neck of the tuber, similar to the eyes on a kitchen potato. Learn more about dahlia tubers and their growth points.
Sometimes the eyes are easy to see, looking like tiny pink or green bumps. Other times, they are dormant and harder to spot. Do not worry if you cannot see them right away; they will wake up once they feel the warmth of the soil. When handling tubers, be gentle with the neck, as this is where the sprout will emerge. If the neck is snapped or broken, the tuber may not be able to grow. You can also review this visual guide to dahlia tubers.
How to Plant Dinner Plate Dahlia Bulbs: Step-by-Step
Once the soil is warm and your site is ready, it is time to get the tubers into the ground. Following these specific steps for depth and spacing will ensure your plants have the room they need to reach their full potential. For a broader overview, see All About Dahlias.
1. Dig the Hole
Dig a hole that is about 6 to 8 inches deep. If your soil is not already enriched, this is a great time to toss a handful of compost or a small amount of balanced, slow-release fertilizer into the bottom of the hole and mix it in.
2. Place the Tuber
Lay the tuber horizontally in the hole. If you can see the eye or a sprout, point it upward. If you cannot tell which end is which, laying it flat is perfectly fine; the plant will figure out which way is up.
3. Spacing
Dinner plate dahlias need plenty of elbow room. Because they grow so large, space the tubers 18 to 24 inches apart. This allows for good air circulation between the plants, which is vital for preventing common issues like powdery mildew later in the summer. Our guide to spacing dinnerplate dahlias covers this consideration in more detail.
4. Cover with Soil
Fill the hole back in with soil. At this stage, do not pack the soil down too hard; a gentle firming with your hands is enough.
5. The No-Water Rule
This is one of the most important tips for success: do not water your dahlias immediately after planting. There is usually enough natural moisture in the soil to kickstart growth. Watering too early can cause the dormant tuber to rot. Wait until you see the first green sprouts emerging from the soil before you begin a regular watering schedule.
Planting Summary Checklist:
- Dig a hole 6-8 inches deep.
- Lay the tuber flat with the eye facing up.
- Space plants at least 18 inches apart.
- Cover with soil but do not water until sprouts appear.
Providing Crucial Support
Because dinner plate dahlias produce such enormous flowers, the stems carry a lot of weight. A single heavy rain or a gust of wind can snap a beautiful stem or even pull the entire plant over. Providing support is not optional for these giants; it is a necessity.
Staking at Planting Time
The best time to install a stake is the day you plant the tuber. If you wait until the plant is large, you risk driving the stake through the tubers underground. Drive a sturdy wooden or metal stake (at least 5 feet tall) into the ground about 2 inches away from where you planted the tuber.
As the plant grows, use soft twine or garden ties to loosely secure the main stem to the stake every 12 to 18 inches. This keeps the plant upright and protects those heavy blooms.
Alternative Support Methods
If you are planting a large row of dahlias, you might prefer the "corral" method. Drive heavy-duty stakes at the corners of your bed and run sturdy twine around the perimeter at several heights. For individual plants in a mixed border, a heavy-duty tomato cage can also work well, provided it is tall enough to support a 5-foot plant.
Watering and Fertilizing for Maximum Growth
Once your dinner plate dahlias are about 6 inches tall and growing vigorously, they will need consistent care to fuel their fast growth.
Deep Watering
Dahlias prefer deep, infrequent watering over frequent light sprinkles. Aim to provide about an inch of water per week. When you water, try to target the base of the plant rather than spraying the leaves. Keeping the foliage dry helps prevent diseases and discourages pests like slugs. If you are growing in containers, you will need to water more often, as pots dry out much faster than the ground.
Feeding Your Dahlias
Dahlias are "heavy feeders," meaning they use a lot of nutrients from the soil. Start fertilizing once the plants are about 12 inches tall. Use a fertilizer that is low in nitrogen and higher in phosphorus and potassium (such as a 5-10-10 or 10-20-20 formula). High nitrogen can result in lots of green leaves but very few flowers. Apply fertilizer once a month through the peak of the blooming season.
The Secret Technique: Pinching
If you want the most flowers possible, you must "pinch" your dahlia plants. It feels a bit counterintuitive to cut a healthy plant, but it is the best thing you can do for a bushy, bloom-filled garden.
When your dahlia is about 12 to 16 inches tall and has four sets of leaves, use a clean pair of shears to snip off the very top of the center stem. This "pinch" signals the plant to stop growing upward and start growing outward. It encourages the plant to develop multiple side branches. Each of those new branches will eventually produce flowers, leading to a much more productive plant. The dahlia growing guide also covers pinching and plant support.
If you skip this step, the plant will often grow as one tall, lanky stalk with just a few flowers at the very top. Pinching creates a sturdier, more balanced plant that can better support its heavy dinner plate blooms.
How to Pinch Your Dahlias:
- Wait until the plant is 12-16 inches tall.
- Locate the center succulent stem.
- Cut the top 2-3 inches off, just above a set of leaves.
- Watch as new stems sprout from the leaf nodes below the cut.
Managing Pests and Diseases
Most gardeners find that dahlias are relatively easy to keep healthy, but a few common visitors might show up.
Common Pests
Slugs and snails love young dahlia sprouts. You can protect your plants by using organic slug bait or creating barriers around the base of the stems. Later in the season, you might see aphids or spider mites. A strong blast of water from the hose is often enough to knock these pests off.
Preventing Powdery Mildew
Powdery mildew looks like a dusty white coating on the leaves. It usually shows up in late summer when the air is humid. The best way to prevent it is to ensure your plants are spaced correctly and to avoid getting the leaves wet when you water. If it becomes a recurring issue, many gardeners find success with a simple spray of neem oil or a mixture of baking soda and water.
Harvesting and Deadheading
The more you cut your dahlias, the more they will bloom. This is one of the most rewarding parts of growing these giants!
Cutting for Bouquets
Dinner plate dahlias make breathtaking cut flowers. For the longest vase life, cut the flowers in the cool of the morning. Choose blooms that are almost fully open. Unlike roses or lilies, dahlias will not open much further once they are cut. Place the stems immediately into a bucket of clean, room-temperature water.
The Importance of Deadheading
"Deadheading" is the process of removing flowers that have finished blooming. If you leave the old flowers on the plant, it will stop producing new buds and put its energy into making seeds instead. By removing the spent blooms, you trick the plant into thinking it still needs to flower, which keeps the color coming until frost.
When deadheading, do not just snip off the flower head. Cut the stem back to where it meets a main branch. This keeps the plant looking tidy and encourages new, long-stemmed growth.
End of Season Care
When the first hard frost hits, your dahlia foliage will turn black and the growing season will come to an end. In warmer climates (USDA zones 8 and higher), you can often leave the tubers in the ground over the winter. Simply cut the stalks back to a few inches above the soil and cover the area with a thick layer of mulch.
In colder climates (zones 7 and lower), the tubers must be dug up and stored indoors. Wait a few days after the first frost, then carefully lift the tubers with a garden fork. Clean off the soil, let them dry in a protected area for a few days, and then store them in a cool, dark, frost-free place packed in peat moss or wood shavings. You can then replant these same tubers next spring, often with even more to share with friends! See the dahlia growing resources for additional seasonal guidance.
Summary of Success
Growing dinner plate dahlias is an achievable goal for any gardener. By focusing on the basics—warm soil, plenty of sun, and sturdy support—you can enjoy a summer filled with the largest flowers you’ve ever seen. We are proud to provide high-quality tubers that help you bring this touch of magic to your own yard.
- Wait for Warmth: Plant only after the soil reaches 60°F and frost is gone.
- Give Them Space: Space dinner plate varieties at least 18-24 inches apart.
- Support Early: Install stakes at the time of planting to protect heavy blooms.
- Pinch for More: Cut the center lead when the plant is 12 inches tall for a bushier habit.
- Water Wisely: Do not water until sprouts emerge; then water deeply once a week.
"Growing dinner plate dahlias is one of the most rewarding ways to add a 'wow' factor to your landscape. With just a little bit of patience in the spring and consistent support in the summer, these giant blooms will reward you with beauty that lasts for months."
Longfield Gardens is here to support you with quality plants and the practical advice you need to grow them well. Whether you are planting your first tuber or your fiftieth, the excitement of seeing that first giant bloom never fades.
FAQ
How deep should I plant dinner plate dahlia tubers?
You should plant dahlia tubers about 6 to 8 inches deep. Lay the tuber horizontally in the hole with the eye or sprout facing upward if visible. This depth provides the plant with a sturdy base and helps protect the tuber from temperature fluctuations as it begins to grow.
Do I need to water my dahlias right after planting?
No, it is best to avoid watering immediately after planting unless your soil is extremely dry. The tuber contains enough stored energy and moisture to begin growing on its own. Watering too early can lead to rot; wait until you see green sprouts appearing above the soil before starting a regular watering routine.
Can I grow dinner plate dahlias in containers?
Yes, you can grow these large dahlias in containers, but you must use a very large pot—at least 15 to 20 inches in diameter and depth. Ensure the container has excellent drainage holes and use a high-quality potting mix. Keep in mind that container-grown dahlias will need more frequent watering and a sturdy stake or cage to support their height. For more information, see this guide to planting dahlia bulbs in pots.
Why are my dahlia stems falling over?
Dinner plate dahlias have very large, heavy flower heads that can easily weigh down the stems, especially after rain. If your plants are falling over, they likely need more support. It is best to stake them at planting time and tie the stems to the stake every 12 inches as they grow to keep them upright and secure.
