Introduction
Imagine walking into your garden in late August and being greeted by a sea of vibrant color. From dinner-plate-sized blossoms in sunset orange to delicate pompons in soft pastel pink, dahlias are the undisputed stars of the late-summer landscape. These remarkable plants offer a diversity of shapes and sizes that few other flowers can match, and they continue to bloom long after other perennials have faded.
At Longfield Gardens, we believe that everyone can experience the joy of growing these spectacular flowers. While their intricate petals might make them look delicate, dahlias are actually quite robust and straightforward to grow once you understand a few simple basics. This guide is designed to help home gardeners—whether you are a beginner or a seasoned pro—successfully navigate the journey from planting a humble tuber to harvesting armloads of stunning bouquets.
We will cover everything from selecting the right site and timing your planting to the essential techniques of pinching and staking. By following these practical steps, you can transform your backyard into a floral destination. With a little sunshine and the right care, anyone can grow a professional-quality dahlia garden.
Understanding Dahlia Tubers
To grow a healthy dahlia, you first need to understand the tuber. Unlike many spring-flowering plants that grow from true bulbs, dahlias grow from tubers. A dahlia tuber looks a bit like a small, elongated potato. It serves as the storage organ for the plant, holding the energy needed to send up the first shoots of the season.
When you receive tubers from us, you might notice they come in various shapes and sizes. It is a common misconception that a bigger tuber leads to a bigger plant. In reality, a small tuber with a healthy "eye" will perform just as well as a large one. The eye is a small growth point located on the "crown" or neck of the tuber, where it connects to the old stem. This is where the sprout will emerge.
Before planting, it is a good idea to inspect your tubers. They should feel firm to the touch, not mushy or hollow. While some shriveling is normal and won't hurt the plant, a healthy tuber is the foundation of a successful season. If you cannot see the eye right away, don't worry. Once the tuber is tucked into warm soil, that eye will quickly wake up and begin to grow.
Key Takeaway: The most important part of a dahlia tuber is the eye. As long as the tuber is firm and has a viable growth point on the crown, it has everything it needs to produce a magnificent plant.
Selecting the Perfect Planting Site
Choosing the right location is the first step toward a productive dahlia season. Dahlias have three primary requirements: plenty of sunlight, excellent drainage, and enough space to breathe.
Sunlight Requirements
Dahlias are sun-loving plants. For the best flower production and strong stems, they need at least six to eight hours of direct sunlight every day. If they are planted in too much shade, the plants often become "leggy," stretching toward the light, and they will produce fewer flowers. In very hot climates, such as the southern United States, providing a bit of filtered afternoon shade can help prevent the blooms from scorching, but full morning sun is still essential. For more guidance, see this guide to choosing the perfect garden spot for dahlias.
Soil and Drainage
Dahlias do not like "wet feet." This means they need soil that drains water away quickly. If the soil stays soggy for too long, the tubers can rot before they ever have a chance to grow. If you have heavy clay soil, consider planting in raised beds or adding organic matter like compost to improve the soil structure.
A simple way to check your drainage is to observe your garden after a heavy rain. If puddles remain for several hours, that spot might be too wet for dahlias. Ideally, the soil should be loose, crumbly, and rich in nutrients.
Space to Grow
Air circulation is often overlooked but is vital for keeping dahlias healthy. When plants are crowded, they are more susceptible to mildew and other fungal issues. Most dahlia varieties should be spaced about 18 to 24 inches apart. This gives the foliage room to expand and ensures that sunlight can reach the lower parts of the plant.
- Choose a sunny spot: Aim for 6-8 hours of direct light.
- Check the drainage: Ensure water leaves the soil quickly.
- Give them room: Space tubers 18-24 inches apart.
- Prepare the soil: Mix in a little compost if your soil is poor.
When to Plant Your Dahlias
Timing is everything when it comes to planting dahlias. Because they are native to Mexico and Central America, they have no tolerance for frost. Planting too early in cold, wet soil is one of the most common reasons tubers fail to sprout.
The Tomato Rule
A helpful rule of thumb is to plant your dahlias at the same time you would plant your tomatoes. This usually means waiting until the danger of frost has completely passed and the soil has warmed up to at least 60°F. In most parts of the US, this falls between late April and early June.
Watching the Weather
While it may be tempting to get them in the ground during a warm spell in early April, a sudden cold snap or a week of heavy spring rain can be detrimental. Patience is rewarded with dahlias. A tuber planted in warm soil in late May will often grow faster and surpass a tuber planted in cold soil in late April.
If you live in a region with a short growing season and want to get a head start, you can "start" your tubers indoors in pots about four weeks before the last frost date. Place them in a warm, bright spot and transplant the young plants outside once the weather is consistently warm. This hardiness zone guide for dahlias can help you plan.
Step-by-Step Planting Instructions
Once the soil is warm and you’ve picked the perfect spot, it’s time to get your dahlias in the ground. Follow these simple steps for the best results.
1. Dig the Hole
Dig a hole about 4 to 6 inches deep. If you are planting a large number of dahlias in a row, you can dig a trench instead of individual holes.
2. Set the Tuber
Lay the tuber horizontally in the bottom of the hole. Some gardeners worry about which way is "up," but laying it flat is generally the best approach. If you can see the eye or a small sprout, make sure that part is pointing upward or toward the center of the hole.
3. Add Support Early
If you are growing tall varieties (which most dahlias are), it is much easier to put your stakes in the ground at the time of planting. Driving a stake into the ground later can accidentally damage the tuber or the root system. Place a sturdy wooden or metal stake about an inch or two away from the tuber.
4. Cover with Soil
Fill the hole back up with soil. Do not add heavy amounts of fertilizer directly into the hole, as this can burn the young roots. A light sprinkling of a balanced, slow-release fertilizer on the soil surface is usually sufficient.
5. Label Your Plants
It is easy to forget which variety is which once they are covered with soil. Use waterproof labels to mark the variety name and color next to each stake.
What to do next: After burying the tuber, resist the urge to water right away unless the soil is bone-dry. The tuber has enough moisture to get started, and excessive water at this stage can lead to rot.
Watering and Early Care
One of the most important "Simple Gardening Rules" for dahlias is to water correctly, not constantly. The watering needs of a dahlia change significantly as the plant grows.
The "No Water" Phase
From the moment you plant the tuber until you see the first green shoots poking through the soil, you should generally avoid watering. During this early stage, the tuber is dormant or just beginning to wake up. Without leaves to transpire moisture, the plant doesn't need much water. Natural rainfall is usually more than enough.
Establishing a Routine
Once the plant is about 6 inches tall and has several sets of leaves, you can begin a regular watering schedule. Dahlias are thirsty plants once they start growing rapidly. They prefer deep, infrequent watering rather than light daily sprinkles. This encourages the roots to grow deep into the soil.
Aim to give your dahlias about an inch of water per week, either through rain or irrigation. If you are gardening in sandy soil or during a heatwave, you may need to water more frequently. Using a soaker hose or drip irrigation is ideal because it keeps the foliage dry, which helps prevent diseases like powdery mildew.
Mulching
Once the plants are established, applying a layer of organic mulch—such as clean straw or shredded bark—can help keep the roots cool and retain soil moisture. Just be sure to keep the mulch a few inches away from the main stem to prevent rot.
Support and Staking Methods
Most dahlias grow to be between 3 and 5 feet tall. Because their stems are hollow and their flower heads can be very heavy (especially after a rainstorm), they need support to keep from toppling over or breaking.
Single Staking
For individual plants in a flower border, a single sturdy stake is the simplest method. As the plant grows, use soft garden twine or strips of fabric to tie the main stem to the stake every 12 to 18 inches. Avoid tying too tightly; the stem needs a little room to expand.
The Tomato Cage Method
For smaller or mid-sized dahlia varieties, a heavy-duty tomato cage works wonderfully. Place the cage over the plant shortly after planting. As the dahlia grows, the branches will naturally lean on the wire rings for support. This is a great "set it and forget it" option for home gardeners.
The Corral Method
If you are growing a long row of dahlias, the corral method is very efficient. Drive heavy stakes (like T-posts) into the ground every 5 to 8 feet along the edges of the row. Run two or three levels of strong twine around the outside of the posts, creating a "corral" that keeps the plants from falling into the pathways.
- Stake early: Put supports in at planting time.
- Tie as they grow: Check your plants every week to see if they need a new tie.
- Support the blooms: Large "dinnerplate dahlias" need extra-strong support.
- Check after rain: Rain adds weight to the blooms; ensure stakes are still secure.
The Secret to More Blooms: Pinching
If there is one "trick" that transforms a leggy dahlia into a lush, flower-filled bush, it is pinching. Pinching sounds intimidating to beginners, but it is actually a simple way to signal the plant to grow more stems.
How to Pinch
When your dahlia plant is between 12 and 16 inches tall and has at least four sets of leaves, look for the very top center sprout. Using your fingers or a clean pair of snips, remove that top growth point, cutting it back to just above the highest set of leaves.
Why It Works
By removing the "terminal bud" (the main upward-growing tip), you stop the plant's vertical dominance. In response, the plant will push its energy into the "axillary buds," which are the small growth points located where the leaves meet the stem. These buds will grow into new branches. Instead of one tall, lanky stalk, you will have a multi-branched plant with many more flower-producing stems.
When to Skip It
If you are growing low-growing "border" or "bedding" dahlias, they are often bred to be naturally bushy and may not require pinching. However, for almost all medium and tall varieties, pinching is the best way to double your flower count.
Key Takeaway: Pinching your dahlias when they are about a foot tall is the easiest win for a more beautiful garden. It leads to stronger plants and significantly more flowers throughout the season.
Fertilizing and Ongoing Maintenance
Dahlias are "heavy feeders," meaning they require plenty of nutrients to produce those spectacular blooms all summer long. However, the type of fertilizer you use matters.
Choosing a Fertilizer
In the early stages of growth, a balanced fertilizer is fine. However, once the plants start to bloom, you want to avoid fertilizers that are too high in nitrogen (the first number on the package). High nitrogen promotes lots of green leaves but can result in weak stems and fewer flowers.
Look for a fertilizer that is higher in phosphorus and potassium (the middle and last numbers). These nutrients support root development and flower production. Many gardeners find that a "bloom booster" or a fertilizer designed for roses or vegetables works well for dahlias.
Application Timing
Start fertilizing about a month after planting, once the plant is well-established. You can apply a granular fertilizer once a month or use a water-soluble fertilizer every two weeks. Always follow the instructions on the product label.
Weed Control
Keep the area around your dahlias free of weeds. Weeds compete with your flowers for water and nutrients. Because dahlia roots grow close to the surface, it is better to pull weeds by hand rather than using a hoe, which could accidentally slice into the tubers.
Harvesting and Deadheading
The more you cut your dahlias, the more they will bloom. This makes them one of the most rewarding flowers for a cutting garden.
Harvesting for Bouquets
The best time to cut dahlias is in the cool of the morning or late in the evening. Unlike roses or lilies, dahlias will not open much after they are cut. You should wait until the flower is about three-quarters of the way open before harvesting.
Use clean, sharp shears and cut the stems long—even if it means cutting off some side buds. Long stems are easier to arrange in a vase, and deep cuts encourage the plant to produce even more long-stemmed flowers. Place the stems immediately into a bucket of clean, room-temperature water.
The Importance of Deadheading
If you don't cut the flowers for bouquets, you must "deadhead" them. Deadheading is the process of removing faded or spent blooms. If you leave the old flowers on the plant, it will begin to produce seeds. Once a plant starts making seeds, it thinks its job is done and will stop producing new flowers.
To deadhead correctly, don't just pop off the flower head. Follow the stem down to where it meets a set of leaves and make your cut there. This keeps the plant looking tidy and encourages new growth.
- Cut often: Regular harvesting keeps the plant productive.
- Wait for the bloom: Only harvest flowers that are mostly open.
- Remove the old: Deadhead weekly to prevent seed production.
- Use clean tools: This prevents the spread of garden diseases.
Preparing for Winter
As autumn arrives and the first frost nears, your dahlias will likely be at their peak. Enjoy this late-season show, but keep an eye on the weather forecast.
The First Frost
A light frost will damage the flowers and foliage, turning them black or brown. Once a "killing frost" has hit and the foliage is dead, the plant's growing season is over. In USDA hardiness zones 8 and warmer, dahlias can often be left in the ground over winter if the soil is well-drained and you apply a thick layer of mulch. Check the USDA hardiness zone guide for regional guidance.
Digging and Storing
In zones 7 and colder, dahlia tubers must be dug up and stored indoors if you want to grow them again next year. After the frost kills the tops, cut the stems down to about 4 inches. Carefully lift the tuber clumps with a garden fork, being careful not to bruise them.
Clean off the excess soil and let the tubers dry in a protected, frost-free area for a day or two. Store them in a cool, dark place (between 40°F and 50°F) in a box filled with peat moss, vermiculite, or wood shavings. Check them occasionally throughout the winter to ensure they aren't rotting or drying out completely.
At Longfield Gardens, we see the end of the season as a time of reflection and planning. Whether you choose to dig your tubers or start fresh with new varieties next spring, the beauty of the dahlia is always worth the effort.
Conclusion
Growing dahlias is a rewarding journey that brings unmatched color and drama to the garden. By focusing on the basics—choosing a sunny spot, waiting for warm soil, and providing steady support—you can achieve professional-looking results in your own backyard. These plants are generous, providing an abundance of blooms from mid-summer until the first frost of autumn.
- Start with quality: Firm tubers with visible eyes are the foundation of success.
- Prioritize timing: Wait for warm soil and the end of frost threats before planting.
- Maintenance pays off: Pinching and staking create stronger, more productive plants.
- Enjoy the harvest: Regular cutting and deadheading ensure a continuous floral display.
Gardening is about learning and enjoying the process. Every season brings new lessons and beautiful surprises. We hope this guide helps you feel confident as you begin your dahlia adventure.
Next Step: Explore the available dahlia collections and choose a few that speak to your style. Your most beautiful garden season is just a few months away.
FAQ
Do dahlias come back every year?
Dahlias are tender perennials. In warm climates (Zones 8-11), they can stay in the ground and return each year. In colder climates (Zones 7 and below), the tubers will freeze and die if left in the ground, so they must be dug up and stored indoors for the winter.
Do I need to soak dahlia tubers before planting?
No, it is not necessary to soak dahlia tubers before planting. In fact, soaking can sometimes increase the risk of rot if the soil is also wet. As long as you plant your tubers in slightly moist, warm soil, they will have plenty of hydration to begin growing.
Why are my dahlias not blooming?
The most common reasons for a lack of blooms are too much shade, over-fertilizing with high-nitrogen plant food, or a lack of water during the heat of summer. Ensure your plants get at least six hours of sun and use a "bloom booster" fertilizer with higher phosphorus to encourage flower production.
Can I grow dahlias in containers?
Yes, many dahlias thrive in containers. Choose shorter "border dahlias" or "gallery" varieties for the best results. Ensure the pot is at least 12 inches deep and wide, has excellent drainage holes, and use a high-quality potting mix. Remember that container-grown dahlias will need more frequent watering and fertilizing than those in the ground.
