Introduction
There is nothing quite like the sight of a dahlia in full bloom during the late summer months. From the massive, pillowy petals of dinnerplate varieties to the intricate, geometric patterns of pompons, these plants are the undisputed stars of the garden. At Longfield Gardens, we believe that every gardener should experience the joy of harvesting a fresh bouquet of dahlias from their own backyard. These stunning flowers offer a color palette and diversity of form that few other plants can match, and they continue to bloom right up until the first frost.
In this guide, we will show you how to care for dahlia plant varieties from the moment you put the tubers in the ground until the end of the season. Whether you are growing them in a dedicated cutting garden or tucking them into your flower borders, the steps to success are straightforward and rewarding. We will cover site selection, watering techniques, and the simple maintenance tasks that keep your plants healthy and productive.
With a little bit of sunshine and some basic attention, your dahlias will provide months of spectacular color. Growing these summer favorites is an achievable goal for gardeners of all skill levels, and the results are always worth the effort.
Selecting Healthy Tubers for Planting
Before learning how to care for dahlias in the ground, success begins with a quality tuber. When your tubers arrive or when you pull them out of storage, give them a quick inspection. A healthy tuber should feel firm to the touch, similar to a fresh potato. Avoid planting any tubers that feel mushy, shriveled, or show clear signs of decay, as these are unlikely to grow and can introduce pathogens into your soil.
The most important part of the tuber is the "eye"—a small, slightly raised bump located on the neck where the tuber meets the old stem. This is where the new growth will emerge. While some eyes are easy to spot, others may be dormant until they hit warm soil. If you see a sprout already beginning, handle it gently so it doesn't snap off during the planting process. Starting with a vigorous, healthy tuber is the best way to ensure a productive season.
Choosing the Right Spot for Your Dahlias
Success with dahlias begins with finding the perfect location. Like most summer-blooming plants, they have specific preferences for light and soil that help them reach their full potential. When you match the plant’s needs to the right spot in your yard, half the work is already done.
Sunlight Requirements
Dahlias are sun-loving plants. To produce the strong stems and abundant flowers they are known for, they need at least six to eight hours of direct sunlight each day. Morning sun is particularly beneficial as it helps dry the dew off the foliage, which keeps the plants healthy. If you live in an exceptionally hot climate, a spot that provides a little bit of filtered shade during the most intense part of the afternoon can help prevent the blooms from fading too quickly.
Soil and Drainage
The quality of your soil plays a major role in how well your dahlias grow. These plants prefer rich, loose soil that is high in organic matter with a slightly acidic to neutral pH (ideally between 6.0 and 7.0). If you are unsure about your soil's nutrient levels, a soil test is a valuable tool to help you understand what your garden needs before the season begins. Before planting, it is a great idea to mix in some well-rotted manure or compost to improve the soil structure.
The most important factor for the soil is drainage, which is the speed at which water moves through the ground. Dahlia tubers are sensitive to standing water and can rot if the ground stays too wet. If you have heavy clay soil that holds onto moisture, consider planting your dahlias in raised beds. This simple adjustment ensures the tubers stay at the right moisture level throughout the season.
Wind Protection
Because many dahlia varieties grow quite tall—sometimes reaching four or five feet—they can act like sails in a high wind. If possible, choose a planting site that offers some protection from strong gusts, such as near a fence or on the sheltered side of a building. If your only sunny spot is a windy one, don't worry; we will cover how to provide extra support for your plants in the sections below.
Starting Tubers Indoors for an Early Start
If you live in a region with a short growing season, or if you simply want flowers as early as possible, you can start your dahlias indoors about 4 to 6 weeks before the last expected frost. Plant individual tubers in pots filled with loose, damp potting mix and place them in a warm, bright location.
Because indoor-grown plants are accustomed to a stable environment, they need a transition period before moving permanently to the garden. This process, known as hardening off, involves gradually exposing the young plants to outdoor conditions. Start by placing them in a sheltered, shady spot for an hour or two each day, slowly increasing their time in the sun and wind over the course of a week. This prevents transplant shock and ensures they are strong enough to thrive once they are in the ground.
Planting Your Dahlia Tubers
Timing is everything when it comes to planting. Dahlias are tropical plants at heart and do not enjoy the cold. Waiting for the right conditions ensures your tubers get off to a fast, healthy start.
When to Plant
The best time to plant dahlia tubers is when the soil has warmed up to about 60°F and all danger of frost has passed. If you are ordering new tubers, our shipping information page explains shipment timing by zone. A good rule of thumb for many gardeners is to plant their dahlias around the same time they plant their tomatoes. If the ground is still cold and clammy, the tubers will simply sit there and may struggle. Patience pays off here; a tuber planted in warm soil will often outgrow one planted weeks earlier in cold ground.
Depth and Spacing
Proper spacing allows for good air circulation, which is key to keeping the foliage healthy.
- Large Varieties: Space these 24 to 36 inches apart.
- Medium Varieties: Space these 18 to 24 inches apart.
- Small/Border Varieties: Space these 12 to 18 inches apart.
To plant, dig a hole about 6 to 8 inches deep. If you are adding a handful of compost or bone meal, mix it into the bottom of the hole. Lay the tuber horizontally with the "eye"—the small bump where the sprout emerges—pointing upward. Cover the tuber with only an inch or two of soil to start. As the stem grows, you can gradually fill in the rest of the hole until it is level with the surrounding ground.
Key Takeaway: Always wait for warm soil before planting. Pushing the season too early can lead to slow growth or tuber rot.
The "No Water" Rule
One of the most common mistakes is watering dahlia tubers immediately after planting. Unless your soil is bone-dry, you should avoid watering until you see the first green sprouts emerging from the ground. The tuber contains all the moisture and energy the plant needs to get started. Adding extra water to the soil before there are roots to drink it up can lead to problems like tuber rot. Once the plant is established and growing, you can begin a regular watering schedule.
Watering and Fertilizing for Success
Once your dahlias have sprouted and are actively growing, their needs change. They become thirsty and hungry plants as they work to produce those famous blooms.
Establishing a Water Routine
Dahlias love consistent moisture, but they don't like to be soggy. Once the plants are about a foot tall, they will appreciate a deep watering two or three times a week. In very hot or dry weather, you may need to water more frequently.
The best way to water is at the base of the plant using a soaker hose or drip irrigation. This keeps the water at the roots and the leaves dry. If you are hand-watering, try to do it in the morning so any splashes on the leaves can dry in the sun. Deep, infrequent watering is always better than a light daily sprinkle, as it encourages the roots to grow deep into the soil.
Feeding Your Plants
Because dahlias grow so much in a single season, they benefit from a bit of extra nutrition. However, the type of fertilizer you use matters. If a soil test has indicated a specific deficiency, you can tailor your feeding accordingly, but general rules apply:
- Early Season: You can use a balanced fertilizer to help the plant grow its green structure.
- Blooming Season: Once the plants start to flower, switch to a fertilizer that is lower in nitrogen and higher in phosphorus and potassium (such as a 5-10-10 or 10-20-20 formula).
Too much nitrogen will give you a giant green bush with very few flowers. By using a "bloom booster" style fertilizer every 3 to 4 weeks, you encourage the plant to put its energy into making buds. Stop fertilizing by early September to allow the tubers to begin their natural transition toward dormancy.
Essential Maintenance: Pinching and Staking
If you want a dahlia plant that is sturdy, bushy, and covered in flowers, there are two simple tasks you shouldn't skip: pinching and staking.
Why You Should Pinch Your Dahlias
"Pinching" sounds like it might hurt the plant, but it is actually one of the kindest things you can do for it. When your dahlia is about 12 to 16 inches tall and has four sets of leaves, snip off the very top of the main center stem.
This tells the plant to stop growing into one tall, lanky stalk and instead start growing side branches. The result is a much fuller, stronger plant with many more stems for cutting. It may feel strange to cut off the top of a healthy plant, but the explosion of blooms you get later in the summer will prove it was the right move.
Providing Support (Staking)
Most dahlias, especially the decorative and dinnerplate types, need help staying upright. Their stems are hollow and can be brittle, making them susceptible to breaking under the weight of heavy, water-soaked blooms or strong winds.
It is best to put your stakes in the ground at the time of planting so you don't accidentally drive a stake through the tuber later. You can use wooden stakes, bamboo poles, or even sturdy tomato cages.
- Individual Stakes: Tie the main stem to the stake every 12 inches using soft twine or garden ties.
- Tomato Cages: These are great for medium-sized dahlias. Simply place the cage over the plant while it is small and let it grow through the rings.
- The "Corral" Method: If you are growing a row of dahlias, place heavy stakes at the corners and run twine around the entire perimeter at different heights to keep the plants contained.
What to Do Next:
- Check your plants weekly as they grow.
- Add new ties to the stakes every foot of growth.
- Remove any weeds growing at the base to prevent competition for water.
Boosting Bloom Production
The more you interact with your dahlias, the better they will perform. There are two simple ways to keep the flowers coming until the very end of the season.
The Magic of Cutting and Conditioning
Dahlias are unique because the more you harvest them, the more flowers the plant produces. When you cut a flower for a vase, the plant interprets that as a signal to send out more buds. If you leave the flowers on the plant until they wither, the plant starts to put its energy into making seeds, which slows down the blooming process.
For the best vase life, harvest flowers in the cool of the morning when they are about three-quarters of the way open. Immediately place the stems into a bucket of warm water. Once inside, you can condition the stems by recutting them at an angle under water and stripping any leaves that would sit below the water line. This simple step keeps your bouquets fresh and vibrant for much longer.
Troubleshooting Bloom Issues and Disbudding
If your plant is lush and green but producing very few flowers, it is usually a sign of too much nitrogen or not enough sunlight. Ensure your plants aren't being crowded by taller neighbors and that you have switched to a bloom-focused fertilizer.
For those who want truly spectacular, exhibition-sized flowers, you might try disbudding. This involves removing the two smaller side buds that form next to the central flower bud on a stem. By removing these competitors, the plant directs all its energy into that single central bloom, resulting in a much larger and more dramatic flower.
Deadheading
If you can't bring yourself to cut every bloom, or if you simply have too many to use, you must "deadhead" the plants. Deadheading is the process of removing faded or spent flowers.
Be careful when deadheading dahlias, as the new buds can look very similar to the old, spent flowers. A spent flower head will usually be pointed or cone-shaped and feel soft or mushy. A new bud is usually rounder and firmer. Follow the stem of the old flower back to the next set of leaves and make your cut there to keep the plant looking tidy.
Troubleshooting Common Diseases
While dahlias are generally robust, keeping an eye out for a few common diseases will help you maintain a healthy garden.
Powdery Mildew
This is a fungal disease that appears as a white, flour-like dusting on the leaves, usually in late summer when the air is humid. While it rarely kills the plant, it can weaken it. To prevent powdery mildew, ensure proper spacing for air circulation and try to keep water off the foliage. If it appears, you can treat it with an organic neem oil spray or a mixture of baking soda and water.
Preventing Tuber Rot
Rot is often the result of poor drainage or overwatering before the plant is established. If a sprout suddenly wilts or turns black at the base, it may be a sign of infection. The best defense is prevention: plant in well-draining soil, follow the "no water" rule at planting, and always inspect tubers for firmness before they go into the ground.
Managing Common Pests Positively
A healthy dahlia plant is quite resilient, but you might occasionally see a few visitors in your garden. Dealing with pests is simply a part of the gardening journey, and catching them early makes management easy.
Slugs and Snails
These are the most common issues for young dahlia plants. They love the tender green sprouts that emerge in late spring. To protect your plants, you can use organic slug bait or even simple physical barriers. Once the plants get a bit taller and the stems toughen up, slugs are much less of a concern.
Aphids and Mites
In the heat of summer, you might notice tiny insects on the undersides of leaves. A strong blast of water from the garden hose is often enough to knock them off and solve the problem. Encouraging beneficial insects like ladybugs into your garden is also a great way to keep pest populations in check naturally.
Earwigs
Earwigs sometimes like to hide inside the petals of dahlia blooms. While they don't usually hurt the plant, they can be a surprise when you bring flowers indoors. Simply shaking the flowers gently upside down before bringing them inside is a quick and easy fix.
Growing Dahlias in Containers
If you don't have a large garden space, you can still enjoy these beautiful flowers. Many smaller or border dahlia varieties are perfectly suited for life in pots.
To grow dahlias in containers, choose a pot that is at least 12 to 15 inches deep and has plenty of drainage holes. Use a high-quality potting mix rather than garden soil, as potting mix is designed to drain better and stay light.
Container-grown dahlias will dry out faster than those in the ground, so you may need to water them more frequently—sometimes daily in the height of summer. They also appreciate a regular liquid feeding since the nutrients wash out of the pots with every watering. A pot of brightly colored dahlias on a sunny porch or patio is a wonderful way to welcome guests to your home.
Late Season Care and Overwintering
In most parts of the United States, dahlias are treated as tender perennials. This means they cannot survive the freezing temperatures of winter in the ground (generally in USDA zones 7 and colder). To check your zone, see our Hardiness Zone Map. However, one of the best parts of dahlia care is that you can save the tubers and plant them again next year.
Waiting for Frost
In the fall, your dahlias will continue to bloom until a hard frost hits. A light frost might singe the leaves, but a hard frost will turn the entire plant black. This is the signal that the growing season is over. Many gardeners like to wait a few days after the frost before digging, as this helps the tubers "cure" and prepares them for storage.
Digging and Cleaning
Cut the stalks down to about 4 to 6 inches above the ground. Use a garden fork to gently lift the tuber clumps from the soil. Be careful to start your digging at least a foot away from the stem to avoid slicing through the tubers. Shake off the excess dirt and rinse them gently with a hose.
Storing for Winter
Before storing, let the tubers air dry in a frost-free, shady spot for a day or two. For a step-by-step guide, see How to Overwinter Dahlias. At Longfield Gardens, we recommend storing tubers in a cool, dark, and dry place where temperatures stay between 40°F and 50°F—an unheated basement or a crawl space is often ideal.
Place the tubers in a box or crate and cover them with a slightly damp material like peat moss, vermiculite, or wood shavings. This keeps them from drying out completely without making them wet enough to rot. Check on them once or twice during the winter; if they look shriveled, give them a tiny mist of water. If any look soft or rotten, remove them immediately to keep the rest of the batch healthy.
Conclusion
Learning how to care for dahlia plant varieties is a rewarding journey that pays off in a spectacular display of color and form. These plants are generous, providing an endless supply of cut flowers for your home and a vibrant backdrop for your outdoor living spaces. By focusing on the basics—sun, drainage, and a little bit of support—you can grow professional-quality flowers in your own backyard.
Remember that gardening is a practice of observation and enjoyment. As your dahlias grow, take the time to appreciate the small changes, from the first sprout to the opening of a giant dinnerplate bloom. Each season offers a new opportunity to learn more about your soil, your local climate, and the unique personalities of the different varieties you choose to grow.
Final Takeaway: Dahlias are a long-term investment in beauty. With simple winter storage, the tubers you plant today can return to your garden for many years to come.
We invite you to explore the wide world of dahlias and find the varieties that speak to your style. Whether you love the soft pastels of a cottage garden or the bold, fiery tones of a tropical border, there is a dahlia waiting for you. For more tips and to find the perfect additions to your garden, we encourage you to browse our collection at Longfield Gardens. You can shop with confidence thanks to our 100% Quality Guarantee. Happy gardening!
FAQ
How far apart should I plant my dahlias?
Spacing depends on the variety's mature size. Large dinnerplate dahlias need about 2 to 3 feet of space, while medium varieties do well with 18 to 24 inches. Smaller border dahlias can be planted closer together, around 12 to 15 inches apart, to create a dense, flowery look.
When will my dahlias start blooming?
Most dahlias begin blooming about 8 to 12 weeks after planting. In most regions, this means you can expect your first flowers in mid-to-late July. Once they start, they will continue to produce new blooms consistently until the first hard frost of autumn.
Can I grow dahlias in pots or containers?
Yes, dahlias grow very well in containers as long as the pots are large enough. Choose a pot that is at least 12 inches deep and use a well-draining potting mix. Keep in mind that container plants need more frequent watering and fertilizing than those planted in the ground.
Do I have to dig up my dahlia tubers every year?
If you live in USDA zones 8 or warmer, you can often leave your dahlias in the ground with a thick layer of mulch for protection. However, in colder climates (zone 7 and below), the tubers will freeze and die if left outdoors. In these areas, digging and storing them in a cool, frost-free place is necessary to save them for next year.
Why is my dahlia plant growing leaves but no flowers?
This is often caused by too much nitrogen in the soil, which promotes foliage growth over bloom production. It can also happen if the plant is not receiving the required 6-8 hours of direct sunlight. Switch to a fertilizer high in phosphorus and ensure the plant isn't shaded.
How do I prevent my dahlia tubers from rotting?
Prevention is key: ensure your soil has excellent drainage, never water at the time of planting until you see green sprouts, and always inspect tubers to ensure they are firm and healthy before they go into the ground.
