Introduction
There is nothing quite like the moment dinnerplate dahlias open their first massive bloom in late summer. These flowers are the undisputed stars of the garden, offering a variety of colors and shapes that few other plants can match. Whether you want to grow flowers for cutting or simply want to fill your landscape with vibrant color, dahlias are a rewarding choice for every gardener.
At Longfield Gardens, we want to help you enjoy the beauty of these spectacular plants in your own backyard. Growing dahlias is a straightforward process that anyone can master with a little bit of patience and the right information. For a broader overview, see our All About Dahlias. You do not need to be a professional farmer to produce high-quality blooms that will impress your neighbors and fill your vases.
This guide covers everything you need to know about starting your dahlia journey, from choosing the right spot to the simple steps of planting and care. We will walk you through the lifecycle of the dahlia tuber and show you how to set your plants up for a successful season. By following these basic principles, you can transform a few humble tubers into a garden full of stunning, multi-layered flowers.
Understanding the Dahlia Tuber
To grow a healthy plant, it helps to understand what you are putting into the ground. A dahlia tuber is an underground storage organ, much like a potato. It contains all the energy and nutrients the plant needs to start growing in the spring.
When you receive a tuber from us, you might notice it has a unique shape. A viable dahlia tuber consists of three main parts: the body, the neck, and the crown. The body is the thick, fleshy part that stores food. The neck is the narrow portion that connects the body to the crown. The crown is the most important part because this is where the "eye" is located.
The eye is a small bump or bud, similar to the eyes on a potato. This is the only place where a new sprout can grow. It is a common misconception that a bigger tuber produces a bigger plant. In reality, even a small tuber can grow into a five-foot-tall plant as long as it has a healthy eye and an intact neck. Once the plant develops its own root system, the original tuber’s size becomes less important.
Key Takeaway: Always handle tubers gently to protect the neck. A tuber with a broken neck cannot send nutrients to the crown, and it will not grow even if an eye is present.
Choosing the Perfect Planting Site
Successful gardening starts with the right location. Dahlias are sun-loving plants that thrive in warm, bright conditions. When you are looking for a spot in your yard, aim for an area that receives at least six to eight hours of direct sunlight each day. The morning sun is particularly beneficial because it helps dry off any dew on the leaves, which keeps the plants healthy.
Drainage is the next critical factor. Dahlias do not like to have "wet feet," which means their roots should never sit in standing water. If your soil is heavy clay and drains slowly, the tubers may struggle. You can improve drainage by adding organic matter like compost or by planting in raised beds. Raised beds are a fantastic option for dahlias because they allow the soil to warm up faster in the spring and provide excellent control over soil quality.
Space is also a consideration. Most dahlia varieties grow quite large and need room for air to circulate between the plants. Good airflow helps prevent common leaf issues and ensures each plant gets enough light. Plan to space your tubers about 18 to 24 inches apart. If you are growing smaller border varieties, you can tuck them a bit closer together, about 12 inches apart.
Timing Your Planting
One of the most important rules for growing dahlias is to wait for the right temperature. Because they are tropical plants originally from Mexico, they are very sensitive to cold. If you plant them in cold, wet soil, the tubers will simply sit dormant or may even rot before they have a chance to grow.
The best time to plant is when all 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. In most parts of the United States, this happens between late April and early June. Use our Hardiness Zone Map to help narrow your planting window.
If you live in a region with a short growing season, you can give your dahlias a head start. About four weeks before the last frost date, you can "pot up" your tubers indoors. Place them in pots with slightly damp potting soil and keep them in a warm, bright spot. By the time the weather is warm enough to move them outside, you will already have small plants ready to take off.
What to do next:
- Check your local frost dates to determine your planting window.
- Use a soil thermometer to ensure the ground is at least 60°F.
- Prepare your garden beds by clearing weeds and mixing in a little compost.
How to Plant Dahlia Tubers Step-by-Step
Once the soil is warm and your site is ready, it is time to get your tubers in the ground. For a step-by-step overview, see our How to Plant Dahlias.
Prepare the Hole
Dig a hole that is about 4 to 6 inches deep. If you are planting a large variety that will need a stake, it is a great idea to drive the stake into the ground now, before you put the tuber in. This prevents you from accidentally piercing the tuber later in the season.
Place the Tuber
Lay the tuber horizontally in the bottom of the hole. If you can see the eye or a small sprout, make sure it is pointing upward. Do not worry if you cannot find the eye yet; sometimes they are hard to see until the tuber warms up in the soil. As long as the tuber is lying flat, the sprout will find its way to the surface.
Cover and Label
Fill the hole with soil, gently firming it down with your hands. Avoid packing the soil too tightly with your feet, as this can damage the fragile neck of the tuber. Immediately place a label in the ground so you remember which variety is planted where. It is easy to lose track once the garden starts growing!
What to do next:
- Dig holes 4-6 inches deep.
- Install stakes for tall varieties at planting time.
- Lay tubers flat with eyes facing up.
- Cover with loose soil and label the variety.
The Golden Rule of Watering
One of the most common mistakes new dahlia growers make is watering too much right after planting. This is a case where "less is more." Until you see green growth poking through the soil, you should generally avoid watering your dahlia tubers.
The tuber contains all the moisture it needs to start its first roots and shoots. If the soil is kept too wet during this dormant phase, the tuber can rot. Once you see the first few inches of green growth above the ground, you can begin a regular watering schedule.
As the plants grow larger, they will need more water. During the heat of the summer, dahlias appreciate a deep soaking two or three times a week. Try to water at the base of the plant rather than over the leaves. This keeps the foliage dry and ensures the water reaches the root system where it is needed most. If you have sandy soil, you may need to water more frequently than if you have soil that holds moisture well.
Key Takeaway: Do not water your dahlias immediately after planting. Wait until the first green sprouts appear above the soil line.
Supporting Your Dahlias
Most dahlias are vigorous growers that can reach heights of four or five feet. Because their stems are hollow and their flower heads can be very heavy, they need a little extra support to stay upright. For a compact option, border dahlias are easy to manage.
For individual plants, a sturdy wooden or metal stake is the easiest solution. As the plant grows, use soft twine or garden ties to loosely secure the main stem to the stake every 12 to 18 inches. You want the tie to be firm enough to provide support but loose enough that it doesn't pinch the stem as it thickens.
If you are growing a large row of dahlias, you might prefer the "corral" method. Drive heavy stakes into the four corners of your garden bed and at intervals along the sides. Run several rows of twine around the perimeter of the stakes to create a cage that holds the plants together. This allows the dahlias to support each other as they grow.
Pinching for More Flowers
If you want a bushier plant with a higher number of blooms, there is one simple trick you should use: pinching. It might feel counterintuitive to cut off part of a healthy plant, but it is one of the best things you can do for your dahlias.
When your plant is about 12 to 16 inches tall and has four sets of leaves, snip off the very top of the center leader. This removes the "apical dominance" of the main stem and signals the plant to send its energy to the side buds.
The result is a plant that branches out instead of growing as one tall, lanky stalk. These extra branches mean more stems, and more stems mean more flowers for you to enjoy. If you prefer to have one single, massive "prize" bloom, you can skip this step, but for most home gardeners, pinching is the way to go.
Steps for Pinching:
- Wait until the plant is 12-16 inches tall.
- Identify the central growing tip.
- Use clean garden snips to cut the center stem just above the top set of leaves.
- Watch for new side branches to emerge within a week.
Feeding and Fertilizing
Dahlias are "heavy feeders," meaning they use a lot of nutrients to produce their lush foliage and constant supply of flowers. Starting with good soil is the first step, but a little extra fertilizer throughout the season will keep them performing at their peak.
When you first plant, you can mix a small amount of balanced fertilizer into the soil. Once the plants are established, you can apply a water-soluble fertilizer every two to three weeks.
In the early summer, a balanced fertilizer works well. As you move into late summer and the plants begin to bloom heavily, you may want to switch to a fertilizer that is lower in nitrogen and higher in phosphorus and potassium. Too much nitrogen late in the season can result in lots of green leaves but very few flowers. Always follow the instructions on the product label for application rates and safety.
Managing Common Garden Visitors
Dahlias are generally robust, but they can occasionally attract a few pests. The most common visitors are slugs and snails, especially when the plants are small and the weather is damp. You can protect your young sprouts by using organic slug bait or by removing them by hand in the early morning.
Japanese beetles sometimes enjoy snacking on the flower petals in mid-summer. The most effective way to handle them is to knock them into a bucket of soapy water. Because dahlias are visited by many pollinators like bees and butterflies, we recommend using the gentlest methods possible for pest control. If you need help identifying trouble, read our Common Dahlia Pests and Diseases.
You may also notice that deer are less interested in dahlias than they are in hostas or lilies. While no plant is 100% deer-proof, dahlias are generally considered a "low-preference" food for them. If deer are a major issue in your area, a simple fence or a scent-based repellent can provide extra protection.
Harvesting Your Flowers
One of the best things about growing dahlias is that the more you cut them, the more they bloom. If you love cut flowers, dahlias are especially rewarding. Harvesting flowers for bouquets actually helps the plant by preventing it from putting energy into seed production.
The best time to cut dahlia flowers is in the cool of the morning or the evening. Unlike roses or lilies, dahlias will not open much further once they are cut. This means you should wait to harvest them until they are almost fully open.
Use clean, sharp shears and cut the stems as long as possible. Immediately place the cut stems into a bucket of warm water. For the longest vase life, change the water every day and keep the bouquet out of direct sunlight. Most dahlia varieties will last five to seven days in a vase.
Key Takeaway: Cut your dahlias when they are 75% to 100% open for the best display.
End of Season Care
Your dahlias will continue to bloom beautifully until the first hard frost. When a frost hits, the foliage will turn black and the plant will stop growing. In warmer climates (USDA zones 8 and higher), you can often leave the tubers in the ground over the winter if you provide a thick layer of mulch.
In colder regions, you will need to lift the tubers if you want to save them for next year. After the frost kills the tops, cut the stems down to about 4 inches. Carefully dig up the tuber clumps, wash off the soil, and let them dry in a protected area for a day or two.
Store the tubers in a cool, dark place that stays between 40°F and 50°F. Many gardeners use crates filled with slightly damp peat moss or vermiculite to keep the tubers from drying out completely. If you don't want to store them, you can simply treat them as annuals and start fresh with new varieties from us next spring. For shipping timing and order details, see our Shipping Information.
Growing Dahlias in Containers
If you do not have a large garden space, you can still grow dahlia tubers in pots. This is a perfect solution for patios, balconies, or small entryways. When growing in containers, it is important to choose the right pot and variety.
Choose the Right Pot
Use a container that holds at least 2 to 5 gallons of soil. The pot must have drainage holes at the bottom. Since pots dry out faster than the ground, you will need to monitor the moisture levels more closely.
Select a Variety
While you can grow tall dahlias in large pots, they can become top-heavy and tip over. Shorter border varieties are excellent choices for containers because they stay compact and usually do not require extensive staking.
Potting Mix
Use a high-quality potting soil rather than garden soil. Potting soil is lighter, provides better drainage, and is free of weed seeds. You can mix in a slow-release fertilizer at planting time to provide a steady supply of nutrients.
Creating a Beautiful Display
Dahlias come in an incredible array of forms, from the tight, geometric petals of "pompon" types to the wild, spiky petals of cactus dahlias. To create a visually interesting garden, try mixing different shapes and sizes.
Planting in groups of three or five of the same variety creates a high-impact "drift" of color. Alternatively, you can mix complementary colors like deep purple and bright orange for a vibrant, energetic look. We offer many different collections that take the guesswork out of color coordination.
Whatever varieties you choose, remember that gardening is a journey. Every season offers a chance to learn something new about your soil, your climate, and the plants you love. Growing dahlias is a fun and rewarding way to connect with nature and bring a little more beauty into your world.
At Longfield Gardens, we are proud to be part of your gardening success. We work with experienced growers to ensure you receive the highest quality tubers that are true to variety and ready to thrive. If you have questions as you grow, our team is always here to help you get the most out of your garden. Learn more on our About Us page.
- Start with high-quality tubers from a trusted source.
- Wait for warm soil and plenty of sun.
- Give them support and plenty of room to breathe.
- Cut often and enjoy the endless supply of blooms.
Growing dahlias is one of the most satisfying experiences a gardener can have. With just a few simple steps, you can enjoy a season of spectacular color and beauty that lasts from mid-summer until the first frost.
FAQ
How deep should I plant my dahlia tubers?
You should plant dahlia tubers about 4 to 6 inches deep. Lay the tuber horizontally in the hole with the eye pointing up if it is visible. This depth protects the tuber from temperature fluctuations while allowing the sprout to reach the surface easily.
When will my dahlias start to bloom?
Most dahlias begin to bloom about 8 to 12 weeks after planting. Depending on your local weather and when you put them in the ground, you can usually expect to see flowers starting in mid-July. They will continue to produce new blooms until the first hard frost of autumn.
Do I need to water dahlia tubers as soon as I plant them?
No, it is usually best to wait until you see green growth above the soil before you start watering regularly. The tuber has enough stored moisture to get started. Watering too early can lead to rot if the soil stays too cold and wet.
Why are my dahlias growing tall and leggy without many flowers?
This often happens if the plants are not getting enough sunlight or if they have received too much nitrogen fertilizer. Dahlias need at least six hours of direct sun to stay sturdy and produce blooms. Also, remember to "pinch" the center stem when the plant is 12 inches tall to encourage branching and more flowers.
