Table of Contents
- Introduction
- Understanding the "Black" Dahlia
- Choosing the Best Dark Varieties
- The Importance of Quality Tubers
- Finding the Perfect Spot
- Preparing the Soil
- When and How to Plant
- Water Correctly, Not Constantly
- Feeding for Better Blooms
- The Secret of Pinching
- Staking and Support
- Managing Pests and Common Issues
- Harvesting Your Black Dahlias
- End of Season Care: Lifting and Storing
- Summary of Success
- FAQ
Introduction
There is something truly magical about the first time a dark, moody dahlia unfurls its velvety petals in your garden. These "black" varieties are show-stoppers, offering a level of sophistication and drama that few other flowers can match. While they look like exotic treasures that might require expert-level skills, growing them is a rewarding and achievable project for any gardener.
At Longfield Gardens, we love how these deep hues transform a landscape, adding depth and contrast to summer borders, and a dark-hued dahlia collection can make that drama easy to achieve. Whether you are a beginner or a seasoned grower, the process is straightforward once you understand the basic needs of the plant. This guide will walk you through everything you need to know, from selecting the right varieties to ensuring your blooms stay vibrant and healthy all season long.
Our goal is to help you feel confident as you bring these striking flowers into your home garden. By focusing on simple steps like proper timing, drainage, and support, you can enjoy a massive harvest of dark, romantic blooms. Growing black dahlias is an exciting journey that rewards your effort with spectacular color from midsummer until the first frost.
Understanding the "Black" Dahlia
The first thing to know about black dahlias is a bit of a botanical secret: there is no such thing as a truly black flower. In the plant world, "black" is actually a very high concentration of deep red, purple, or maroon pigments called anthocyanins. When these pigments are densely packed into the petals, the flower appears black to the human eye, especially in the shadows or under the soft light of dawn and dusk.
These dark tones are highly sought after because they provide a visual "anchor" in the garden. While bright yellows and pinks pop forward, dark colors add a sense of mystery and make the surrounding colors look more vivid. When you look closely at a variety like Arabian Night, you will see flashes of burgundy and garnet that give the blooms their rich, multi-dimensional look.
The intensity of this dark color can actually change depending on your local conditions. Cooler night temperatures often help the plant produce more of those deep pigments, making the flowers look even darker as autumn approaches. This is why many gardeners find their dahlias look their absolute best in September.
Key Takeaway: Black dahlias are actually deep shades of burgundy and purple. Their color often intensifies and becomes more dramatic as the weather cools in late summer.
Choosing the Best Dark Varieties
When you start looking for tubers, you will find several different flower shapes and sizes, including a dinnerplate dahlia collection. Choosing the right one depends on how you want to use them in your garden or in floral arrangements. Here are some of the most reliable and beautiful dark varieties we often recommend.
Decorative and Dinnerplate Varieties
These are the classic dahlia shapes with broad, flat petals.
- 'Arabian Night': A beloved favorite that produces 4-inch wide, deep crimson-maroon blooms. It is known for being a very productive bloomer.
- Rip City: This variety features dark, velvety red centers that transition to slightly lighter edges. It has a high petal count and looks stunning in bouquets.
- 'Black Jack': A large-flowered variety with pointed petals that give it a slightly "spiky" and modern look.
Ball and Pompon Varieties
These flowers are perfectly spherical and hold up exceptionally well in rain and wind.
- Jowey Mirella: A beautiful ball-shaped dahlia with tightly packed petals in a rich, chocolate-burgundy shade.
- 'Natal': This is a smaller pompon type that produces dozens of dark red, almost-black spheres. It is a workhorse in the cutting garden.
Cactus and Orchid Types
If you like unique textures, these varieties offer narrow, pointed petals.
- 'Chat Noir': This is a famous "cactus" dahlia with long, pointed petals that create a starburst effect. Its name translates to "Black Cat," fitting for its dark and mysterious look.
- 'Honka Dark': An orchid-type dahlia with simple, single-layered petals that look like dark stars. These are fantastic for pollinators because the center of the flower is easy for bees to reach.
What to do next:
- Browse a mixed dahlia collection and choose 2–3 different shapes for visual interest.
- Check the mature height of your chosen varieties to plan your garden spacing.
- Order your tubers early in the winter or spring, as popular dark varieties often sell out fast.
The Importance of Quality Tubers
Your success starts with the health of the dahlia tuber. A dahlia tuber looks a bit like a small sweet potato, and its job is to store energy for the plant to grow. When you receive your order from us, you want to see tubers that feel firm and plump, not mushy or shriveled.
The most important part of the tuber is the "eye." The eye is a small growth bud located at the neck of the tuber, where it connects to the old stem. Just like the eyes on a potato, this is where the new sprout will emerge. Sometimes the eyes are hard to see when the tubers are dormant, but once they are exposed to warmth and a little moisture, they will begin to swell and turn pink or green.
Size does not necessarily indicate the quality of the bloom. A small tuber with a healthy eye will grow into a massive, productive plant just as well as a large one. We ensure our tubers are handled with care to protect that vital neck and eye area, giving you the best possible start.
Finding the Perfect Spot
Black dahlias have three main requirements: sun, drainage, and space. Getting these basics right is the easiest way to ensure a healthy season.
Sunlight is Key
Dahlias are sun-lovers. To get those deep, dark pigments and strong stems, they need at least 6 to 8 hours of direct sunlight every day. If they are planted in too much shade, the stems will become "leggy" (long and weak) as they stretch toward the light, and you will get fewer flowers.
However, there is one small trick for black dahlias. Because dark colors absorb more heat from the sun, the petals can sometimes "scorch" or fade in extremely hot climates. If you live in a region with intense afternoon heat, a spot that gets morning sun and a little bit of light shade during the hottest part of the day can help preserve the velvet texture of the petals.
Drainage Prevents Problems
"Drainage" is a fancy way of saying how fast water moves through your soil. Dahlias have a very low tolerance for "wet feet." If the tubers sit in soggy soil, they can rot before they even have a chance to sprout.
If your soil is heavy clay and holds onto water like a sponge, consider planting your dahlias in raised beds. This keeps the tubers safely above the water line. If you are planting in the ground, mixing in some compost or well-rotted manure can help improve the soil structure and allow water to move through more freely.
Giving Them Room to Breathe
A healthy dahlia plant can grow 3 to 4 feet tall and nearly as wide. Giving them enough space is vital for air circulation. When plants are crowded, moisture gets trapped between the leaves, which can lead to issues like powdery mildew. Space your tubers about 18 to 24 inches apart to give each plant the "elbow room" it needs to thrive.
Preparing the Soil
You don't need a lab-tested soil mix to grow beautiful dahlias, but a little preparation goes a long way. These plants are "heavy feeders," meaning they use a lot of nutrients to produce those massive leaves and constant flowers.
About a week or two before planting, work some organic matter into your garden bed. Compost is the gold standard here. It adds nutrients, improves drainage, and helps the soil hold just the right amount of moisture. If your soil is very acidic, you might add a small amount of garden lime, but dahlias are generally quite flexible with soil pH.
Avoid using high-nitrogen fertilizers right at the start. Nitrogen encourages lots of green leaves, but too much of it can actually result in fewer flowers and weak tubers. A balanced, all-purpose fertilizer is usually the best choice for the early season.
Key Takeaway: Start with loose, well-draining soil enriched with compost. Avoid heavy nitrogen early on to ensure the plant focuses on root and flower development rather than just leaves.
When and How to Plant
Timing is the most important part of the planting process, and our How to Plant Dahlias guide walks you through the basics. Because dahlias are tropical plants originally from Mexico, they have no resistance to frost. Planting them too early in cold, wet soil is the most common mistake beginners make.
The Right Time
Wait until all danger of spring frost has passed and the soil has warmed up to at least 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 tuber will just sit there and potentially rot. It is much better to wait an extra week for warm weather than to rush and lose the plant.
Step-by-Step Planting
- Dig a Hole: Dig a hole about 6 to 8 inches deep.
- Position the Tuber: Lay the tuber horizontally (flat) at the bottom of the hole. If you can see the "eye" or a small sprout, make sure it is pointing upward.
- Cover with Soil: Fill the hole with soil. You want the tuber to end up being covered by about 4 to 6 inches of soil.
- Do Not Water Yet: This is a key secret to success. Unless your soil is bone-dry, do not water your dahlias until you see the first green sprouts poking through the ground. The tuber has enough stored moisture to get started, and adding extra water to a dormant tuber in cool soil can lead to rot.
What to do next:
- Check your local "last frost date" online.
- Wait for a stretch of warm, sunny days before heading to the garden.
- Mark your planting spots with stakes so you don't accidentally dig them up before they sprout.
Water Correctly, Not Constantly
Once your dahlias have sprouted and are about 6 inches tall, they will start to get thirsty. The goal is to provide deep, consistent moisture.
Instead of a light daily sprinkle, give your dahlias a deep soaking once or twice a week, depending on the weather. This encourages the roots to grow deep into the ground, making the plant more resilient during hot spells. Using a soaker hose or drip irrigation is ideal because it keeps the water at the base of the plant. Keeping the leaves dry helps prevent leaf diseases.
During the peak of summer, you might need to water more frequently, especially if you see the leaves start to wilt slightly in the afternoon sun. If you are growing your black dahlias in containers, they will dry out much faster than those in the ground and may need water every day.
Feeding for Better Blooms
Dahlias are like athletes; they need a lot of fuel to perform. Once the plants are well-established (about a month after planting), you can start a regular feeding schedule.
A water-soluble fertilizer with a slightly higher phosphorus count (the middle number on the bag) is great for encouraging blooms. Many gardeners use a "bloom booster" style fertilizer every two to three weeks through the summer. Stop fertilizing by late August or early September. This tells the plant to stop putting energy into new growth and start storing energy in the tubers for the winter.
The Secret of Pinching
If you want a dahlia plant that is loaded with flowers rather than one single tall stem, you must follow our 8 Tips for Growing Better Dahlias.
When your plant is about 12 to 16 inches tall and has four sets of leaves, take a pair of clean garden snips and cut off the very top of the center stem. You only need to remove about an inch or two of growth.
By removing that top bud, you signal the plant to stop growing upward and start growing outward. The plant will send out new branches from the "armpits" of the remaining leaves. This results in a bushier, stronger plant with many more flower-producing stems. It’s an easy win that significantly increases your harvest.
Staking and Support
Dahlias grow fast and their stems are hollow, which makes them susceptible to snapping in heavy rain or wind. This is especially true for the "black" varieties that produce large, heavy flower heads. Supporting them is not optional—it is a necessity, and our All About Dahlias guide covers stakes, cages, and corrals.
The best time to stake a dahlia is the day you plant the tuber. If you wait until the plant is large, you might accidentally drive the stake through the tuber underground.
- Single Stakes: Drive a sturdy wooden or metal stake (at least 5 to 6 feet tall) into the ground next to the tuber. As the plant grows, use soft twine or garden tape to loosely tie the main stem to the stake every 12 inches.
- Tomato Cages: For smaller or mid-sized varieties, a heavy-duty tomato cage can work well.
- The "Corral" Method: If you are growing a long row of dahlias, you can place stakes at the corners and wrap twine around the entire perimeter to keep the plants from flopping over.
Key Takeaway: Support your dahlias early. Staking and pinching are the two most important tasks for creating a sturdy, productive plant that won't fall over in a summer storm.
Managing Pests and Common Issues
Gardening is a natural process, and occasionally you might run into a few uninvited guests. Because we want your experience to be enjoyable, we recommend a "simple first" approach to troubleshooting in our Common Dahlia Pests and Diseases guide.
Slugs and Snails
These are the most common issues for young dahlia sprouts. They love the tender green leaves of a new plant. You can protect your dahlias by using iron phosphate pellets (slug bait) or simply checking your plants in the early morning and removing them by hand.
Earwigs
Earwigs love to hide inside the petals of dahlia blooms and nibble on them. If you see tiny holes in your flowers, earwigs might be the culprit. A simple way to manage them is to place an upside-down pot filled with damp straw near the plants; the earwigs will hide there during the day, and you can empty it into a bucket of soapy water.
Powdery Mildew
This looks like a light dusting of white flour on the leaves. It usually happens late in the season when the air is humid. To prevent it, ensure your plants have plenty of space for air to move through. If it appears, you can use a simple organic neem oil spray or a mixture of baking soda and water to keep it under control.
Harvesting Your Black Dahlias
One of the best reasons to grow black dahlias is to bring them inside for stunning floral arrangements. The more you cut your dahlias, the more they will bloom!
When to Cut
Unlike roses or lilies, dahlias will not continue to open much after they are cut. You should wait until the flower is nearly fully open before you snip it. Look at the back of the flower; if the petals are starting to turn brown or feel papery, it might be slightly past its prime.
The best time to harvest is in the cool of the morning when the plant is most hydrated. Bring a bucket of clean, lukewarm water out to the garden with you and place the stems into the water immediately after cutting.
Deadheading
If you don't cut the flowers for bouquets, you must "deadhead" them. This simply means cutting off the spent blooms once they start to fade. If you leave the old flowers on the plant, it will start to produce seeds. Once a plant produces seeds, it thinks its job is done and will stop making new flowers. By removing the old ones, you trick the plant into blooming all the way until the first frost.
End of Season Care: Lifting and Storing
In most parts of the United States, dahlia tubers cannot survive the freezing temperatures of winter in the ground. Unless you live in a very warm climate, Know Your Growing Zone can help you decide whether they can stay in the soil.
Wait until the first frost has turned the foliage black; then follow How to Overwinter Dahlia Tubers for the rest of the storage process. After the frost, cut the stems down to about 4 inches above the ground. Leave them in the soil for about a week to let the tubers "cure" and toughen their skins.
Carefully dig up the tuber clumps using a garden fork, being careful not to nick the tubers. Shake off the excess dirt and let them dry in a shady, frost-free spot for a day or two. Store them in a cool, dark place (like a basement or garage that stays between 40°F and 50°F). Many gardeners pack them in cardboard boxes filled with slightly damp peat moss, vermiculite, or wood shavings to keep them from drying out completely.
Summary of Success
Growing black dahlias adds a touch of elegance and mystery to your summer garden. By following the simple rules of "right plant, right place," you can enjoy these dramatic blooms year after year.
- Plant in late spring once the soil is warm and the threat of frost is gone.
- Provide full sun and ensure the soil has excellent drainage.
- Pinch the stems when they are 12 inches tall to encourage a bushy, flower-filled plant.
- Stake early to protect the heavy blooms from wind and rain.
- Water deeply once a week rather than frequent light misting.
Longfield Gardens is proud to provide high-quality tubers that are true to variety and ready to thrive. We stand behind our quality with a 100% guarantee, so you can plant with confidence knowing we are here to support your gardening journey.
"A garden full of dark dahlias is more than just a collection of plants; it is a seasonal masterpiece that rewards a little bit of patience with a huge amount of beauty."
FAQ
Are black dahlias actually black?
No, black dahlias are not truly black. They are actually very deep, saturated shades of burgundy, maroon, or dark purple. Under certain lighting conditions, especially in the shade or at twilight, these high concentrations of pigment appear black to the eye.
Do black dahlias need more sun than other colors?
Like all dahlias, black varieties need at least 6 to 8 hours of direct sunlight to grow strong stems and produce plenty of flowers. However, in very hot climates, the dark petals can absorb significant heat, so providing some light afternoon shade can help prevent the petals from scorching or fading.
Why are my dahlia tubers rotting in the ground?
The most common cause of tuber rot is planting in cold, wet soil or overwatering before the plant has sprouted. It is vital to wait until the soil is warm (60°F) and to avoid watering until you see green growth above the soil line unless your conditions are extremely dry.
When will my black dahlias start to bloom?
Dahlias usually begin blooming about 8 to 12 weeks after planting. For most gardeners, this means the first flowers appear in mid-to-late July, with the most intense and prolific blooming happening in August and September as the weather begins to cool slightly.