Introduction
Imagine walking into your garden on a sunny July morning and being greeted by a sea of vibrant, intricate blooms. Dahlias are some of the most rewarding flowers a home gardener can grow. They offer an incredible variety of shapes and sizes, from tiny, perfectly round pompons to massive dinnerplate varieties that can reach the size of a volleyball. The best part is that these plants keep blooming all the way through the first frost of autumn.
At Longfield Gardens, we want to help you experience the joy of a successful dahlia season. Whether you are a beginner or a seasoned gardener, the process of planting these tubers is simple and straightforward. Getting the basics right from the start ensures your plants grow strong and produce the maximum number of flowers for your bouquets and garden beds.
This guide will walk you through everything you need to know about starting your dahlia garden. We will cover selecting the right spot, preparing your soil, and the specific steps for planting your tubers correctly. By following these simple steps, you can transform your outdoor space into a blooming paradise.
What is a Dahlia?
Before learning how to grow dahlias, it helps to understand their botanical roots. The dahlia is a member of the Asteraceae family, which includes sunflowers, daisies, and zinnias. Native to the high plains of Mexico and Central America, these plants are tuberous perennials. They were named in honor of the 18th-century Swedish botanist Anders Dahl.
Because of their tropical origins, dahlias are not hardy in most northern climates. In USDA hardiness zones 8 and warmer, tubers may survive the winter in the ground if the soil stays dry and well-mulched. However, in zones 7 and colder, they are treated as tender perennials that must be planted in the spring and, optionally, lifted in the fall for winter storage.
Types of Dahlias and Choosing the Right Variety
With thousands of varieties available, choosing the right dahlia can feel overwhelming. The American Dahlia Society recognizes many different flower forms, and selecting the right one depends on your garden space and how you plan to use the flowers.
Match the Form to Your Space
- Border and Bedding Dahlias: These compact varieties reach only 12 to 24 inches in height. They are perfect for the front of a flower bed or for growing in containers because they rarely require staking.
- Decorative and Cactus Dahlias: These are the classic garden favorites. Decorative types have broad, flat petals, while cactus types have narrow, pointed petals that give them a spiky look. Most grow 3 to 4 feet tall and are excellent for cutting.
- Dinnerplate Dahlias: If you want a dramatic focal point, these are the way to go. Varieties like Cafe au Lait produce massive blooms. Because they grow tall and the flowers are heavy, they require sturdy support.
- Ball and Pompon Dahlias: These varieties produce small, spherical blooms with perfectly arranged petals. They are exceptionally long-lasting in a vase and add wonderful texture to floral arrangements.
Choosing the Perfect Location for Your Dahlias
Dahlias are sun-loving plants that thrive when they have the right environment. Selecting the best spot in your yard is the first step toward a healthy garden. You want a location that offers plenty of light and protection from harsh elements.
Prioritize Full Sun
For the best results, plant your dahlias in a spot that receives at least six to eight hours of direct sunlight every day. Sunlight is the primary energy source for these plants. The more sun they get, the more flowers they will produce. If you plant them in a shady area, the stems may become "leggy" or thin as they stretch toward the light, and you will see fewer blooms.
In very hot climates, such as the South or Southwest, dahlias may appreciate a little afternoon shade. This prevents the intense heat from wilting the foliage during the hottest part of the day. For most of the United States, however, the sunniest spot you have is usually the best choice.
Ensure Excellent Drainage
Dahlias have sensitive root systems that do not like to sit in water. Drainage refers to how fast water leaves the soil. If water puddles in a certain area after a rainstorm and stays there for hours, that spot is not ideal for dahlias.
If your soil is heavy clay, you can improve it by adding organic matter like compost or peat moss. This helps create air pockets and allows water to move through more freely. Another great option for areas with poor drainage is to use raised beds. This gives you total control over the soil quality and ensures the tubers stay at the right moisture level.
Protection from the Wind
Because many dahlia varieties grow quite tall and have hollow stems, they can be vulnerable to strong winds. If possible, choose a spot that has some protection, such as near a fence or the side of a building. Just make sure the structure doesn't block the sun they need. If your garden is in an open area, you will just need to be a bit more diligent about providing support as they grow.
What to do next:
- Walk your yard at different times of the day to identify the sunniest spots.
- Check the soil after a rain to see where water drains quickly.
- Clear away any weeds or old garden debris from your chosen planting area.
Understanding the Dahlia Tuber
Before you start digging, it helps to understand what you are planting. A dahlia grows from a tuber, which is a fleshy root that stores energy. While they may look like potatoes, they have a very specific anatomy that determines how they grow.
The Anatomy of a Tuber
A healthy dahlia tuber has three main parts: the tuberous root, the neck, and the crown. The "body" of the tuber holds the nutrients. The neck is the narrow part that connects the body to the crown. The crown is the most important part because it is where the "eyes" are located.
An eye is a small bump or growth point, similar to what you see on a potato. Every dahlia plant grows from one of these eyes. If a tuber is broken and doesn't have a piece of the crown with an eye, it will not grow. When you receive your tubers from us, we ensure they are high quality and ready to sprout.
Size Doesn't Always Matter
New gardeners are often surprised by the different sizes of tubers. Some varieties produce large, thick tubers, while others produce small, thin ones. The size of the tuber is determined by the variety of the dahlia, not the quality. A small, firm tuber with a healthy eye will grow into a plant just as large and beautiful as a big one.
When to Put Your Dahlias in the Ground
Timing is one of the most important factors in dahlia success. These are tropical plants by nature, and they are very sensitive to cold temperatures. Planting too early is a common mistake that is easy to avoid.
Wait for the Soil to Warm Up
The most important rule for planting dahlias is to wait until all danger of frost has passed. Even a light frost can damage or kill the new sprouts. Beyond the air temperature, you should also consider the soil temperature. Dahlias prefer soil that has warmed 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. In most parts of the country, this is usually between late April and early June. If the ground is still cold and wet, the tubers may sit dormant or, in some cases, rot before they have a chance to start growing.
Starting Early Indoors
If you live in a region with a short growing season and want to see flowers earlier, you can start your tubers in pots indoors. About four to six weeks before the last frost date, plant the tubers in containers with potting soil. Keep them in a warm, sunny spot or under grow lights. This gives the plants a head start, so they are already a few inches tall by the time the weather is warm enough to move them outside.
Preparing the Soil for Planting
Good soil is the foundation of a healthy garden. Dahlias are "heavy feeders," meaning they take a lot of nutrients from the ground to produce those spectacular blooms.
Amending the Soil
Before planting, loosen the soil to a depth of about 12 inches. This makes it easier for the roots to spread out. Mix in a few inches of compost or well-rotted manure. This adds essential nutrients and improves the soil structure.
Dahlias prefer a slightly acidic to neutral soil pH (around 6.5 to 7.0). If you aren't sure about your soil's health, your local agricultural extension office can provide a soil test. For most home gardens, simply adding organic compost each year is enough to keep the plants happy.
Using Fertilizer Correctly
When preparing the soil, you can add a small amount of balanced, all-purpose fertilizer. Look for a mix with equal parts nitrogen, phosphorus, and potassium (such as a 5-5-5 or 10-10-10). Avoid using a high-nitrogen fertilizer right at the start, as this can encourage too much leaf growth and not enough flowers.
Step-by-Step: How to Plant Your Dahlias
Now that your site is ready and the weather is warm, it is time to plant. The process is quick and easy if you follow these steps.
1. Dig the Hole
Dig a hole that is about 4 to 6 inches deep. If you are planting a single tuber, the hole should be about 8 inches wide. If you are planting a larger clump, make the hole a bit wider to accommodate it without crowding. For a step-by-step refresher on how deep to plant dahlia tubers, this is the right depth to remember.
2. Place the Tuber
Lay the tuber horizontally (flat) at the bottom of the hole. If you can see the "eye" or a small green sprout, try to point it upward. However, do not worry if you can't tell which side is up. Dahlias are very smart plants; the sprout will find its way to the surface regardless of how the tuber is positioned. A popular way to remember this is to "plant it like a hot dog in a bun."
3. Add Support Stakes
If you are planting tall varieties (anything over 3 feet), it is best to put your stakes in the ground now. Placing the stake at planting time ensures you won't accidentally drive it through the tuber later in the season. For more detailed support tips, see How to Pinch and Stake Dahlias. Use a sturdy wooden or bamboo stake and drive it into the ground right next to where you placed the tuber.
4. Cover with Soil
Fill the hole back up with the soil you removed. Press down gently with your hands to remove any large air pockets, but do not pack it too tightly. The top of the tuber should be about 4 inches below the surface.
Key Takeaway: Planting dahlias involves digging a 6-inch hole, laying the tuber flat, and covering it with loose soil. Always place your support stakes at the time of planting to protect the tuber from damage later.
Spacing Your Dahlias for Success
Giving your plants enough room to breathe is essential for preventing disease and ensuring they have enough sunlight. The amount of space needed depends on the variety you are growing.
- Border Dahlias: These are smaller, bushy varieties that usually stay under 2 feet tall. Space them about 12 to 18 inches apart.
- Standard and Decorative Dahlias: Most medium-sized dahlias need about 2 feet of space between plants.
- Dinnerplate Dahlias: These varieties, like the famous Cafe au Lait or Thomas Edison, grow very large. Give them at least 2 to 3 feet of space so they don't crowd each other.
Proper spacing allows air to circulate around the leaves. This is the best way to keep the plants healthy and free from mildew during the humid summer months.
A Seasonal Roadmap for Growing Dahlias
Understanding the lifecycle of your dahlias helps you know what to expect after your tubers are in the ground.
- Weeks 2–4 (Sprouting): The first green shoots should emerge. This is when you begin your regular watering and weeding routine.
- Weeks 6–8 (Pinching and Staking): Once the plant has four sets of leaves, pinch the center to encourage branching. As it grows, begin tying the stems to your stakes.
- Weeks 8–12 (Growth and Feeding): The plants will grow rapidly. Apply your mid-season fertilizer and keep the area free of weeds that compete for nutrients.
- July to Frost (Blooming): Most dahlias begin blooming in mid-to-late summer. Cutting flowers for bouquets actually encourages the plant to produce even more blooms.
The Most Important Rule: Watering Your New Dahlias
One of the most frequent questions we receive is, "How much should I water my dahlias right after planting?" The answer might surprise you: you usually shouldn't water them at all.
Wait for the Green
Unless your soil is bone-dry, there is enough natural moisture in the ground to get the tuber started. Watering too much before the sprout emerges can cause the tuber to rot. Since the tuber doesn't have a root system yet, it cannot drink the water you are giving it. For more detailed watering advice, see how often should I water my dahlia bulbs.
Wait until you see the first green shoots peeking through the soil before you start a regular watering schedule. This usually takes two to four weeks. Once the plant is established and growing, you can begin watering deeply once or twice a week.
Deep Watering Over Frequent Sprinkling
When you do start watering, focus on deep soakings rather than light daily mists. Deep watering encourages the roots to grow further down into the soil, which makes the plant more stable and drought-resistant. If you are growing dahlias in containers, they will dry out much faster and may need water every day during the heat of summer.
Supporting and Staking Your Plants
Dahlias have stems that are mostly hollow, which makes them very efficient at growing fast but also a bit fragile. As the plant grows and the flowers become heavy, they will need help staying upright.
Individual Staking
If you placed a stake at planting time, simply use soft garden twine or strips of cloth to tie the main stem to the stake every 12 inches as it grows. Do not tie it too tightly; leave some room for the stem to thicken.
Tomato Cages
For many home gardeners, a standard metal tomato cage is the easiest way to support dahlias. Place the cage over the planting spot shortly after you see the first sprouts. The plant will grow up through the center, and the side rings will keep the branches from flopping over.
The Corral Method
If you are planting a long row of dahlias, you can use the "corral" method. Drive sturdy posts into the ground at the four corners of your bed and every 5 feet along the sides. Wrap garden twine around the posts at a height of 12 inches, and then again at 24 inches. This creates a "fence" that keeps all the plants contained.
Pinching for a Bushier Plant
If you want the maximum number of flowers, you should "pinch" your dahlias. This might feel like you are hurting the plant, but it actually encourages it to grow stronger and more productive.
How to Pinch
When your dahlia plant is about 12 inches tall and has four sets of leaves, use your fingers or a clean pair of snips to remove the very top of the center stem. Cut it just above the highest set of leaves.
By removing the "terminal bud" (the top growth point), you signal the plant to send its energy to the side branches. This results in a shorter, bushier plant with many more stems. More stems mean more flowers! If you skip this step, the plant may grow as one tall, lanky stalk with only a few blooms at the very top.
Fertilizing for Long-Term Blooms
Dahlias are hungry plants, but they need the right kind of food at the right time. We recommend a balanced approach to feeding.
Mid-Season Feeding
Once your plants are about a foot tall and growing vigorously, you can begin a regular fertilization routine. An all-purpose liquid or granular fertilizer applied every three to four weeks is usually perfect.
As the season progresses toward late summer, some gardeners switch to a fertilizer with a higher phosphorus content (the middle number on the bag). Phosphorus helps the plant focus on flower production rather than leaf growth. Always follow the instructions on the product label to avoid over-fertilizing, which can stress the plant.
Growing Dahlias in Containers
You don't need a large backyard to enjoy these flowers. Dahlias grow beautifully in pots on a patio or deck. At Longfield Gardens, we offer many border varieties that are specifically bred for container life.
Choosing the Right Pot
The most important factor for container success is the size of the pot. Even a small dahlia needs plenty of room for its roots. Choose a container that holds at least 2 to 5 gallons of soil. For large dinnerplate varieties, you will need a 10-gallon pot or a large half-barrel.
Ensure the pot has drainage holes in the bottom. Use a high-quality potting mix rather than garden soil, as potting mix is lighter and drains better.
Container Care
Potted dahlias need more attention than those in the ground. They will dry out faster and use up the nutrients in the soil more quickly. Check the soil moisture daily. If the top inch of soil feels dry, give the plant a deep drink. You should also fertilize container dahlias every two weeks with a water-soluble fertilizer to keep them blooming.
Enjoying the Harvest: Cutting Your Flowers
One of the best ways to keep your dahlia plant blooming is to cut the flowers often. This is called "deadheading" if the flowers have faded, but most people prefer to cut them when they are fresh for bouquets.
When to Cut
Unlike roses or lilies, dahlias will not open much after they are cut. Wait until the flower is almost fully open before you snip it. The best time to cut is in the cool of the morning or late in the evening when the plant is fully hydrated.
How to Cut
Use sharp, clean shears and cut the stem long enough for your vase. Cut just above a set of leaves. This tells the plant to grow new stems from that point, which will lead to even more flowers in a few weeks. Place the cut stems immediately into a bucket of warm water.
Deadheading and Disbudding for Maximum Blooms
To keep your plants productive until the first frost, you must perform regular maintenance beyond simple cutting.
The Importance of Deadheading
Once a flower begins to fade, the plant starts putting its energy into producing seeds. To prevent this and keep the focus on new flowers, you must "deadhead" or remove spent blooms. Always cut the stem back to the next set of leaves or a side bud. If you leave a short, headless stem, it can look unsightly and potentially invite rot.
Disbudding for Larger Flowers
If you are growing dahlias for exhibition or want the largest possible blooms (especially with dinnerplate varieties), try "disbudding." Most dahlias produce a cluster of three buds at the end of each stem. The center bud is the largest. By carefully pinching off the two smaller side buds when they are about the size of a pea, the plant directs all its energy into that single center flower, resulting in a significantly larger bloom and a longer stem for cutting.
Common Dahlia Pests and Troubleshooting
Even with the best care, dahlias can sometimes face challenges. Knowing how to diagnose and treat common problems will keep your garden thriving.
Pests to Watch For
- Slugs and Snails: These are the biggest threat to young dahlia sprouts. They can eat an entire sprout overnight. Use organic slug bait or copper tape to protect your plants in the early spring.
- Japanese Beetles: These pests love to feast on dahlia blooms in mid-summer. The best defense is to hand-pick them and drop them into a bucket of soapy water.
- Aphids and Mites: If you notice curled or yellowing leaves, check the undersides for these tiny insects. A strong blast of water or insecticidal soap can usually keep them under control.
Disease and Growth Issues
- Powdery Mildew: This white, flour-like coating on leaves often appears in late summer when humidity is high. Improve air circulation by spacing plants correctly and watering at the base of the plant rather than overhead.
- Tuber Rot: If your sprouts fail to emerge and the soil has been very wet, the tuber may have rotted. This is why drainage and waiting to water are so critical.
- Viruses: If a plant shows stunted growth and mottled, yellow-patterned leaves that don't improve with fertilizer, it may have a virus. These cannot be cured, and the plant should be removed and disposed of (not composted) to prevent the virus from spreading to healthy dahlias.
End-of-Season Care: Lifting and Storing Tubers
Once the first frost hits, your dahlia foliage will turn black. At this point, you have two choices: treat them as annuals and buy new tubers next year, or "lift" and store them for the winter.
How to Lift Tubers
Wait a few days after the first frost for the tubers to go dormant. Cut the stalks down to about 4 inches. Carefully use a garden fork to lift the tuber clump from the soil, being careful not to nick or break the "necks" where the tubers connect to the crown.
Curing and Storage
Gently wash off the excess soil and let the tubers dry (cure) in a frost-free, shaded area for a few days. Once dry, store them in a breathable container, such as a cardboard box or burlap bag, filled with slightly damp vermiculite, peat moss, or wood shavings. Store the box in a cool, dark, and dry place (ideally between 40°F and 50°F), such as a basement or crawl space. Check on them once or twice during the winter to ensure they aren't shriveling or rotting.
Safety and Expectations in the Garden
While dahlias are a joy to grow, there are a few practical things to keep in mind for a safe and happy garden.
- Toxicity: It is important to note that dahlia tubers and foliage can be toxic to dogs, cats, and horses if eaten. If you have curious pets, consider planting your dahlias in a fenced area or in raised beds where they are harder to reach.
- Weather Variation: Gardening is always a partnership with nature. Your blooms may appear earlier or later depending on your local weather, soil quality, and how much sun your yard gets. If you are unsure about your garden conditions, check the Hardiness Zone Map.
- Patience is Key: Some varieties, especially the large dinnerplate types, take longer to reach maturity. You might see smaller varieties blooming in July while the larger ones wait until August. This wait is part of the excitement and makes the final display even more rewarding!
Conclusion
Planting dahlias is an easy and rewarding way to bring professional-quality flowers into your own backyard. By choosing a sunny spot, waiting for the soil to warm up, and providing just a bit of support, you can enjoy an abundance of color for months. These plants are incredibly resilient and eager to grow, making them a perfect choice for gardeners of all skill levels.
At Longfield Gardens, we take pride in providing high-quality tubers that are ready to thrive in your garden. We stand behind our products with a 100% quality guarantee, ensuring that you receive healthy, true-to-variety plants. If you ever have questions about your order or need extra advice, our team is here to help.
Your Next Steps:
- Order your favorite dahlia varieties early to ensure the best selection.
- Prepare your garden beds with compost so they are ready when the weather warms up.
- Start a garden journal to track when your different varieties begin to bloom.
Ready to start your dahlia journey? Visit us at Longfield Gardens to find the perfect colors and shapes for your summer garden.
FAQ
How deep should I plant my dahlia tubers?
You should plant dahlia tubers about 4 to 6 inches deep. Dig a hole to this depth, lay the tuber flat on its side, and cover it with loose soil. This depth provides enough insulation for the tuber while still allowing the new sprouts to reach the surface easily.
Which way is "up" when planting a dahlia tuber?
The best way to plant a dahlia tuber is horizontally, or flat on its side. If you can see a small bump or sprout (the "eye"), try to point it toward the sky. However, even if you plant it with the eye facing down, the sprout will naturally turn and grow toward the light at the surface.
When should I start watering my dahlias after planting?
Wait to water your dahlias until you see the first green sprouts appear above the soil. The tubers have enough stored energy and moisture to begin growing on their own. Watering too early can lead to the tuber rotting in the ground, so it is best to be patient and "wait for the green."
Can I grow large dinnerplate dahlias in pots?
Yes, you can grow dinnerplate dahlias in containers, but they require a very large pot to be successful. Choose a container that holds at least 7 to 10 gallons of soil and is very stable. Because these varieties grow tall and have very large flowers, you will also need to provide a sturdy stake to keep the pot from tipping over in the wind.
