Introduction
Few things match the sheer excitement of seeing the first deep violet petals unfurl in a summer garden. Purple dahlias are a favorite for home gardeners because they offer a regal, sophisticated look that stands out against green foliage. Whether you are looking for a soft lavender or a moody plum, these flowers are surprisingly easy to grow when you start with high-quality tubers.
At Longfield Gardens, we want to make sure you have the best experience possible from the moment your tubers arrive. Growing a garden full of vibrant blooms is an achievable goal for any skill level. All it takes is a little bit of planning and the right environmental conditions to see these stunning plants thrive.
This guide will walk you through everything you need to know about selecting, planting, and caring for purple dahlias. We will focus on the most reliable methods to ensure your garden is filled with these spectacular plants from midsummer through the first frost. By the end, you will have a clear path to a successful and colorful growing season.
Choosing the Best Purple Dahlia Varieties
The first step in learning how to get a purple dahlia to grow in your garden is selecting the right variety. "Purple" is a broad category in the dahlia world, ranging from delicate orchids to massive dinnerplate varieties. Choosing a variety that matches your space and your style is the best way to ensure you are happy with the results.
Some of our favorite purple varieties offer consistent performance and breathtaking color. If you want a classic, 'Thomas Edison' is a legendary decorative dahlia with deep, royal purple blooms. It is known for its sturdy stems and prolific flowering. For those who prefer something a bit more intricate, 'Purple Gem' is a cactus-style dahlia with pointed, narrow petals that give it a unique, spiky appearance.
If you are looking for a softer look, consider lavender shades. 'Lavender Perfection' produces massive, fluffy blooms that look like clouds of violet in the garden. For smaller spaces or the front of a border, border dahlias are a compact option that delivers plenty of purple blooms without needing as much room to spread out.
Key Takeaway: Choose Your Hue
- Deep Purple: 'Thomas Edison' or 'Royal Purple'
- Lavender/Lilac: 'Lavender Perfection' or 'Lilac Time'
- Unique Shapes: 'Purple Gem' (Cactus type)
- Compact Spaces: 'Bluesette' (Melody series)
Finding the Best Spot for Your Dahlias
Dahlias are sun-loving plants that need plenty of energy to produce those intricate purple flowers. Before you dig your first hole, take a day to observe the light patterns in your yard. The "right plant, right place" rule is essential here. Dahlias need at least six to eight hours of direct sunlight every day. If they are in too much shade, they may grow tall and "leggy" as they reach for the light, and they will produce fewer blooms. For more guidance, see where dahlias grow best.
Soil drainage is another critical factor. While dahlias appreciate moisture, they do not like to sit in soggy soil. If water tends to puddle in your chosen spot after a rainstorm, the tubers may struggle. You can improve the drainage in your garden beds by adding organic matter like compost. This helps create a loose, crumbly texture that allows water to move through the soil while still holding enough moisture for the roots.
Space is the final consideration for your site. Most dahlia varieties grow quite large, often reaching three to four feet in height and two feet in width. Make sure you give them enough room to breathe. Good airflow between plants helps keep the foliage dry and healthy throughout the humid summer months.
When to Plant Your Purple Dahlias
Timing is often more important than any gardening "trick." For dahlias, the biggest mistake is planting them too early in the spring. These are tropical plants that love warmth. If you put them in cold, wet soil, they may sit dormant or experience issues before they even have a chance to sprout.
The best time to plant is when the soil temperature has reached about 60°F. For most gardeners, this is about the same time you would plant tomatoes or peppers. A simple way to check is to wait until all danger of frost has passed and the outdoor air feels consistently warm. If you are eager to get a head start, you can start your tubers in pots indoors about four to six weeks before the last frost date, then move them outside once the weather settles. See this guide to dahlia planting temperatures.
We ship our tubers from Longfield Gardens based on your USDA hardiness zone. This ensures they arrive close to the ideal planting time for your specific region. When they arrive, keep them in a cool, dry, dark place until the soil in your garden is warm enough for planting.
Planting for Success: Depth and Spacing
Once your soil is warm and your site is ready, it is time to plant. Getting the depth and spacing right sets the foundation for the entire growing season. For most dahlias, you will want to dig a hole about 4 to 6 inches deep.
Place the dahlia tuber in the hole horizontally, with the "eye" or the sprout pointing upward. The eye is found on the neck of the tuber, where it connects to the old stem. If you don't see an eye yet, don't worry. Just lay the tuber flat, and the sprout will find its way to the surface.
Space your plants about 18 to 24 inches apart. This might seem like a lot of empty space when you are looking at a small tuber, but these plants grow quickly. Giving them enough room now prevents them from crowding each other out later. After placing the tuber, fill the hole with soil, but do not water it immediately unless the soil is exceptionally dry. The tuber has enough stored energy and moisture to start growing on its own, and waiting to water until you see the first green sprouts helps keep the tuber healthy. For additional guidance, review how late you can plant dahlias.
What to Do Next: Planting Steps
- Wait for soil to reach 60°F.
- Dig a hole 4 to 6 inches deep.
- Place the tuber horizontally with the eye facing up.
- Space multiple tubers 18 to 24 inches apart.
- Wait for sprouts before you start a regular watering schedule.
Supporting Your Growing Dahlias
As your purple dahlias begin to grow, they will eventually need a little extra support. Because these plants produce heavy, petal-packed blooms, the stems can sometimes lean or bend under the weight, especially after a heavy rain. Staking your dahlias early is the easiest way to keep them standing tall.
It is best to place your stake in the ground at the time of planting. This prevents you from accidentally poking a hole through the tuber later in the season. You can use sturdy bamboo stakes, wooden garden stakes, or even metal tomato cages. As the plant grows, use soft garden twine to loosely tie the main stem to the stake every 12 inches or so.
This simple step ensures that your purple flowers stay off the ground and remain the centerpiece of your garden. It also makes it much easier to see and harvest the blooms for indoor bouquets.
Water Correctly, Not Constantly
Dahlias have specific watering needs that change as they grow. As mentioned earlier, they don't need much water until they have sprouted and established a root system. Once the plant is about a foot tall and has several sets of leaves, you can begin a more regular watering routine.
The goal is to water deeply and then let the soil dry out slightly. This encourages the roots to grow deeper into the ground, making the plant more resilient. In most climates, a deep watering two or three times a week is sufficient. If you live in a very hot or sandy area, you may need to water more frequently.
When watering, try to apply the water at the base of the plant rather than over the leaves. Keeping the foliage dry helps maintain a healthy plant and prevents common summer leaf issues. If you notice the leaves wilting in the heat of a July afternoon, don't panic. They often do this to conserve moisture and will perk back up once the sun goes down.
Encouraging More Blooms
One of the most rewarding parts of growing purple dahlias is the "multi-harvest" nature of the plant. The more you cut the flowers, the more the plant will produce. This is because the plant's main goal is to produce seeds. By removing the flowers before they fade, you signal to the plant to keep trying by sending up new buds.
The Art of Pinching
When your dahlia is about 12 inches tall, you can perform a simple move called "pinching." Use your fingers or a clean pair of shears to snip off the very top of the main center stem. This might feel like you are setting the plant back, but it actually encourages the plant to branch out from the base. This results in a bushier plant with more stems and, ultimately, more purple flowers.
Deadheading for Continuous Color
Throughout the summer, keep an eye out for flowers that have started to fade. This process is called deadheading. When a flower begins to lose its petals or look "tired," follow the stem down to where it meets a set of leaves and make a clean cut. This keeps the garden looking tidy and ensures the plant's energy goes into making new buds rather than developing seeds.
Key Takeaway: More Cuts Equal More Blooms
- Pinch the center stem at 12 inches high.
- Cut flowers regularly for indoor arrangements.
- Remove faded blooms (deadhead) to trigger new growth.
- Always cut stems just above a leaf node.
Feeding Your Purple Dahlias
Dahlias are heavy feeders, meaning they require a good amount of nutrients to produce their large, colorful flowers. Starting with soil that has been enriched with compost is a great first step. However, a little extra help during the peak of the growing season can make a big difference in the size and intensity of your purple blooms.
A balanced, water-soluble fertilizer applied every two to four weeks is usually enough. Look for a fertilizer where the middle number (phosphorus) is equal to or slightly higher than the first number (nitrogen). Too much nitrogen can lead to a lot of green leaves but very few flowers. Always follow the instructions on the fertilizer label to ensure you are giving your plants the correct amount.
Stop fertilizing in late summer or early fall. This allows the plant to start winding down for the season and focus its energy back into the tuber for winter storage.
Designing a Garden Around Purple Dahlias
Purple is a versatile color that plays well with almost any other shade in the garden. When you are planning where to put your dahlias, think about the visual impact you want to create.
For a high-contrast, high-energy look, pair your purple dahlias with yellow or orange flowers. Since purple and yellow are opposites on the color wheel, they make each other pop. Imagine a deep violet 'Thomas Edison' next to a bright yellow 'Kelvin Floodlight'.
If you prefer a more serene and harmonious look, create a "cool" garden by mixing purple dahlias with blues, pinks, and whites. Planting various shades of purple together—from the pale lavender of 'Bluesette' to the dark plum of 'Arabian Night'—creates a sophisticated, monochromatic look that adds depth and texture to your borders.
Don't forget to consider the height of your plants. Place your tall purple dahlias at the back of the garden bed and use shorter perennials or annuals in the front to hide the base of the dahlia stems. This creates a full, lush look that lasts all summer long.
Harvesting Purple Dahlias for Bouquets
One of the greatest joys of growing these flowers is bringing them inside. Purple dahlias make excellent cut flowers and can last for five to seven days in a vase if handled correctly. Longfield Gardens also features dahlia collections selected for cut flowers.
The best time to cut your dahlias is in the cool of the early morning or late evening. Unlike roses or lilies, dahlias do not open much after they have been cut. You want to choose blooms that are almost fully open but still have firm, fresh petals at the back of the flower head.
Bring a bucket of room-temperature water out to the garden with you. Use a sharp, clean pair of shears to cut the stems at an angle, and immediately place them in the water. Once you are inside, remove any leaves that will be below the water line in your vase. This keeps the water clean and helps the flowers stay fresh longer.
Overwintering Your Dahlia Tubers
Dahlias are perennials in warm climates (Zones 8-11), but in colder regions, they are treated as annuals or "tender perennials." This means the tubers will not survive a freezing winter in the ground. However, you can easily save your tubers to plant again next year. Learn more about dahlia hardiness and winter care.
Wait until a light frost has turned the foliage black or brown. This signals the plant to go dormant. Cut the stems down to about 4 inches above the ground and wait a few days before carefully lifting the tubers with a shovel or garden fork. Shake off the excess soil and let them dry in a protected area for a day or two. This dahlia lifting guide provides additional winter-storage guidance.
Store your tubers in a cool, dark, frost-free place (like a basement or crawl space) in a box filled with slightly damp peat moss or vermiculite. Check on them once or twice during the winter to make sure they haven't dried out or become too wet. When spring returns and the soil warms up, you can start the whole process over again.
Success Is Just a Few Steps Away
Growing a garden full of purple dahlias is one of the most rewarding projects a gardener can take on. By focusing on the basics—sun, drainage, warmth, and consistent cutting—you can enjoy a spectacular display of color for months. Whether you are a seasoned pro or just starting your first garden bed, these flowers are designed to impress.
At Longfield Gardens, we take pride in providing high-quality tubers that are true to their variety and ready to grow. We stand behind the quality of our plants with a 100% guarantee, so you can plant with confidence. If you encounter any issues during your first growing season, our team is here to help you find a solution.
Gardening is a journey of discovery and beauty. With a few purple dahlia tubers and a sunny spot in your yard, you are well on your way to a stunning summer landscape.
Final Checklist for Purple Dahlias
- Choose a variety that fits your style and space.
- Plant in a sunny spot with good drainage.
- Wait for warm soil (60°F) before planting.
- Provide a stake for support early in the season.
- Cut blooms often to keep the plant producing.
FAQ
When is the best time to plant purple dahlias?
The best time to plant is in late spring after the danger of frost has passed and the soil has warmed to about 60°F. Planting in warm soil ensures the tubers sprout quickly and stay healthy throughout the early growing season.
How much sun do purple dahlias need?
For the best results and the most vibrant purple color, your dahlias should receive at least six to eight hours of direct sunlight every day. Plants grown in too much shade will produce fewer flowers and may have weaker stems.
Do I need to dig up my dahlias in the winter?
If you live in USDA zones 7 or colder, dahlia tubers will generally not survive the winter in the ground. You will need to dig them up after the first frost and store them in a cool, dry place until the following spring. See the dahlia winter-storage guide for more details.
What are the best purple dahlia varieties for beginners?
'Thomas Edison' is an excellent choice for beginners because it is very reliable and produces classic deep purple blooms. 'Purple Gem' and 'Lavender Perfection' are also great options that offer different shapes and shades of violet for a varied garden look.
