Table of Contents
- Introduction
- Choosing the Right Dahlias for Your Garden
- Understanding Dahlia Tubers
- The Importance of Timing and Temperature
- Selecting and Preparing Your Planting Site
- How to Plant Dahlia Tubers Step-by-Step
- Staking and Supporting Your Plants
- The Secret to More Blooms: Pinching
- Water and Fertilizer for Peak Performance
- Harvesting and Deadheading
- Dealing with Common Challenges
- End of Season Care
- Conclusion
- FAQ
Introduction
There is nothing quite like the feeling of watching a dinnerplate-sized dahlia bloom slowly unfurl in late summer. These dinnerplate dahlias are the undisputed celebrities of the garden, offering a variety of colors, textures, and sizes that few other flowers can match. Whether you are looking for petite pompons or massive, ruffled blooms that command attention, dahlias provide an abundance of flowers from midsummer all the way until the first frost.
At Longfield Gardens, we believe that everyone can experience the joy of a flower-filled yard. Dahlias are often viewed as high-maintenance, but once you understand a few simple growing requirements, they are remarkably reliable. This guide is designed for the home gardener who wants to transition from admiring these beauties in bouquets to successfully harvesting them from their own backyard.
We will cover everything from selecting the right tubers to the critical steps of planting, pinching, and supporting your plants. By focusing on the basics of soil, timing, and water, you will be well on your way to a season of spectacular color. Growing dahlias is a rewarding journey that turns your garden into a source of endless floral inspiration.
Choosing the Right Dahlias for Your Garden
Before you get your hands in the dirt, the first step to success is choosing the right varieties for your specific space and goals. Dahlias come in a staggering array of shapes and sizes, usually classified by their flower form.
Popular Flower Forms
- Dinnerplate Dahlias: These are the giants of the dahlia world, with blooms that can reach 10 to 12 inches across. They are perfect as focal points in the garden or as a single-stem statement in a vase.
- Decorative Dahlias: This is the most common type, featuring broad, flat-tipped petals. They are excellent for cutting and come in both formal and informal styles.
- Cactus and Semi-Cactus: These have narrow, pointed petals that give them a spiky, starburst appearance. They add fantastic texture to both garden beds and arrangements.
- Ball and Pompon: These varieties produce perfectly spherical, honeycomb-like blooms. They are incredibly sturdy and have an exceptionally long vase life.
- Single Dahlias: These have open centers that are easily accessible to bees and butterflies. If you want to support local pollinators, collarette dahlias are also a wonderful choice.
Collarette dahlias are also a wonderful choice if you want to support local pollinators.
Considering Height and Space
Dahlias also vary significantly in height. Border dahlias are compact and typically grow 12 to 18 inches tall, making them perfect for containers or the front of a flower bed. Standard varieties usually reach 3 to 5 feet in height. When planning your garden, place taller varieties toward the back of a bed so they do not shade out smaller plants.
Key Takeaway: Choose varieties based on how you want to use them. If you love big bouquets, focus on decorative and dinnerplate types. For containers or small spaces, look for compact border varieties.
Understanding Dahlia Tubers
Unlike many spring-blooming flowers that grow from bulbs, dahlias grow from tubers. These look a bit like a cluster of small sweet potatoes. Understanding what makes a healthy tuber will ensure you start the season with a vigorous plant.
What to Look For
A viable dahlia tuber needs three specific parts: the tuber itself (the food storage), the neck (the narrow part connecting the tuber to the stem), and the "eye." The eye is a small bump or bud located on the crown (the area where the neck meets the old stem). This is where the new growth will emerge.
It is a common myth that larger tubers produce larger plants. In reality, a tuber the size of an AA battery is more than enough to grow a massive, healthy plant. As long as the eye is present and the neck is firm and not broken, the tuber has everything it needs to get started.
Storage and Arrival
When your order from Longfield Gardens arrives, it is a good idea to open the packaging immediately. If it is still too early to plant, store the tubers in a cool, dark, dry place—like a basement or a garage—where they won't freeze. If you need shipping details, see our Shipping Information page. If they look a little shriveled, don't worry. Once they hit the warm, moist soil, they will hydrate and begin to grow.
What to do next:
- Inspect your tubers for a visible eye or a small sprout at the crown.
- Check that the neck is firm and securely attached to the crown.
- Store in a frost-free, dark location until planting time.
- Avoid the temptation to pre-soak tubers; they prefer to hydrate naturally in the soil.
The Importance of Timing and Temperature
Timing is the most critical factor when learning how to plant and grow dahlias. Because these plants are native to Mexico and Central America, they have no tolerance for frost and do not like cold soil.
The Tomato Rule
A simple rule of thumb is to plant your dahlias at the same time you would plant your tomatoes. For more planting basics, see our 8 Tips for Growing Better Dahlias. This usually means waiting until all danger of frost has passed and the soil has warmed to about 60°F. If you plant too early into cold, wet soil, the tubers are likely to sit dormant and may even rot before they have a chance to grow.
Starting Indoors
If you live in a region with a short growing season, you can get a head start by potting up your tubers indoors about 4 to 6 weeks before the last frost. For a broader overview, see our All About Dahlias guide. Use a large pot with high-quality potting soil and place it in a sunny window or under grow lights. This gives the plant a "jump start," so you can enjoy blooms much earlier in the summer.
Selecting and Preparing Your Planting Site
Dahlias are sun-worshippers and heavy feeders. Giving them the right environment from day one will make the rest of the season much easier. For a deeper look at how they grow, see How Dahlias Grow.
Sun and Drainage
For the best results, choose a spot that receives at least 6 to 8 hours of direct sunlight. Morning sun is particularly beneficial as it helps dry the dew off the leaves, which keeps the plants healthy.
Drainage is equally important. Dahlias need consistent moisture, but their tubers will rot if they sit in standing water. "Drainage" simply refers to how fast water leaves the soil. If you have heavy clay soil that stays soggy after a rain, consider planting in raised beds or amending the area with compost to improve the soil structure.
Soil Preparation
Before planting, it is helpful to loosen the soil to a depth of about 12 inches. This makes it easier for the roots to expand and for the new tubers to form. You can mix in some well-rotted compost or a balanced, low-nitrogen organic fertilizer at this stage. Avoid high-nitrogen fertilizers, as these often encourage lush green leaves at the expense of flowers.
How to Plant Dahlia Tubers Step-by-Step
Once the weather is warm and your site is ready, it is time to plant. Following the correct depth and orientation is a simple win for any gardener.
Step 1: Dig the Hole
Dig a hole that is 4 to 6 inches deep. If you are planting several dahlias together, space the holes 12 to 18 inches apart. This might seem like a lot of space for a small tuber, but these plants grow quite large and need plenty of room for air to circulate between them.
Step 2: Placement
Place the tuber horizontally in the hole with the "eye" or the sprout facing up. If your tuber is part of a larger clump, just ensure the old stem base is pointing toward the surface.
Step 3: Add Support
If you are growing tall varieties, it is best to drive a sturdy stake into the ground now, before you cover the tuber. For more support tips, see How to Pinch and Stake Dahlias. This prevents you from accidentally piercing the tuber or damaging the roots later in the season. A 5-foot wooden stake or a heavy-duty tomato cage works well for most varieties.
Step 4: Cover and Wait
Fill the hole with soil until it is level with the ground. Now comes the hardest part: do not water yet.
Until the dahlia sprout emerges from the soil, it does not have a root system to take up water. Rainfall is usually enough to keep the soil slightly damp. Excess manual watering at this stage is the leading cause of tuber rot. Once you see green growth above the soil line, you can begin a regular watering schedule.
Key Takeaway: Plant your tubers 4–6 inches deep with the eye facing up. Resist the urge to water until you see the first green shoots emerge from the ground.
Staking and Supporting Your Plants
As dahlias grow, they become very top-heavy. A summer thunderstorm or a gust of wind can easily snap a stem loaded with heavy blooms. Supporting your plants is a simple step that protects your investment and keeps the garden looking tidy.
Individual Staking
For a few plants, individual stakes are the easiest method. As the plant grows, use soft twine or garden ties to secure the main stem to the stake every 12 inches. Be careful not to tie it too tightly; the stem will thicken as the season progresses.
The Corral Method
If you are growing a row of dahlias, the "corral" method is very efficient. Drive sturdy T-posts or wooden stakes into the ground at the four corners of your dahlia bed and every 5 to 6 feet along the sides. Wrap heavy-duty baling twine around the stakes at heights of 12 inches and 24 inches to create a "cage" that the plants can grow through.
Using Tomato Cages
For gardeners who want a low-effort solution, heavy-duty metal tomato cages are excellent for decorative and ball dahlias. Place the cage over the plant shortly after the first shoots appear. The foliage will quickly grow to cover the cage, providing invisible support all season.
The Secret to More Blooms: Pinching
If you want a bushier plant with significantly more flowers, you must "pinch" your dahlias. While it might feel counterintuitive to cut off a healthy part of a growing plant, it is one of the best things you can do for a dahlia.
When to Pinch
When your dahlia plant is between 12 and 16 inches tall and has at least four sets of leaves, it is time to pinch. Locate the center terminal bud (the very top sprout) and snip it off with clean garden shears or your fingers. You only need to remove the top 2 to 3 inches of the stem.
Why It Works
Pinching temporarily stops the upward growth and signals the plant to send its energy into the side buds. This results in a plant that has more branches, a sturdier base, and—most importantly—far more flowers. A pinched plant will be shorter and more compact than an unpinched one, which also makes it less likely to blow over in the wind.
What to do next:
- Wait for the plant to reach 12 inches in height.
- Identify the central growing tip.
- Snip off the top 2–3 inches of the center stalk.
- Observe the side shoots beginning to grow within the next week.
Water and Fertilizer for Peak Performance
Once your dahlias are established and growing vigorously, they will need regular care to maintain their high-energy lifestyle.
Watering Deeply
Dahlias love water, but they prefer a "deep soak then dry" approach. Rather than light daily sprinkling, aim for a deep watering 2 to 3 times a week, depending on your weather. The goal is to keep the soil moist about an inch below the surface. If you have sandy soil, you may need to water more frequently; for clay soil, less often.
Try to water at the base of the plant rather than over the leaves. Keeping the foliage dry helps prevent common issues like powdery mildew. Using a soaker hose or drip irrigation is a fantastic way to automate this and keep your plants happy.
Feeding Your Dahlias
Dahlias are "heavy feeders," meaning they require plenty of nutrients to produce those massive blooms. However, balance is key.
- Early Summer: Use a balanced organic fertilizer to help the plant build strong stems and leaves.
- Mid-to-Late Summer: Switch to a fertilizer that is lower in nitrogen and higher in phosphorus and potassium (look for a lower first number on the N-P-K label). This encourages the plant to focus on bloom production rather than just getting taller.
Harvesting and Deadheading
The more you cut your dahlias, the more they will bloom. Harvesting flowers for bouquets and removing old blooms (deadheading) prevents the plant from putting energy into seed production and keeps it focused on making new buds.
How to Cut for Bouquets
The best time to cut dahlias is in the cool of the early morning or late evening. Unlike roses or lilies, dahlias will not open much further once they are cut. Look for flowers that are about 75% to 90% open. If the back petals are starting to feel soft or look brown, the flower is past its prime.
Use sharp, clean shears and cut the stem long—even if it means cutting off some side buds. This encourages the plant to send up new, long-stemmed branches from lower down. Immediately place the stems into a bucket of clean, room-temperature water.
The Importance of Deadheading
If you aren't cutting flowers for the house, you should still remove them as they fade. A spent dahlia bloom can look very similar to a new bud. A bud is usually round and firm, while a spent bloom is more pointed or cone-shaped. Snipping off the old flowers keeps the plant looking fresh and ensures a continuous supply of color until the frost arrives.
Key Takeaway: Harvest flowers when they are almost fully open. Regular cutting and deadheading are the keys to a long, productive blooming season.
Dealing with Common Challenges
Even though dahlias are robust, they can occasionally face a few visitors in the garden. Dealing with these challenges is simple if you catch them early.
Slugs and Snails
Young dahlia shoots are a favorite snack for slugs. You can protect your new plants by using a non-toxic slug bait or by removing them manually in the early morning. Once the plants are about a foot tall, they are usually sturdy enough to withstand minor slug damage.
Aphids and Mites
Sometimes, you might notice tiny insects on the undersides of leaves or on the new buds. A strong blast of water from the garden hose is often enough to knock them off. If the problem persists, an insecticidal soap can be used—just be sure to follow the label instructions carefully and apply it in the evening to protect pollinators.
Powdery Mildew
This looks like a light dusting of white flour on the leaves and often appears in late summer when the air is humid. The best defense is prevention: space your plants correctly to allow for airflow and water at the soil level rather than over the foliage. If you see affected leaves, you can remove them to prevent the spread.
End of Season Care
When the first "killing frost" arrives, your dahlia plants will turn black and die back. This is a natural part of the cycle. At this point, you have two choices depending on your climate and preference. If you want to check your growing zone, use the Hardiness Zone Map.
Overwintering in the Ground
If you live in USDA hardiness zones 8 through 11, dahlias can often stay in the ground year-round. Cut the stalks down to about 3 or 4 inches and cover the area with a thick layer of mulch to protect the tubers from excessive winter moisture.
Digging and Storing
In colder zones (zones 3 through 7), the tubers must be lifted if you want to save them for next year.
- Wait: Let the plants sit for a few days after the frost to let the tubers "cure."
- Lift: Carefully dig around the clump with a pitchfork, being careful not to cut the tubers.
- Clean: Shake off the excess dirt.
- Dry: Let them dry in a frost-free area for a day or two.
- Store: Place them in a box filled with slightly damp peat moss, vermiculite, or wood shavings. Keep them in a cool (40-50°F), dark place until spring.
Conclusion
Growing dahlias is one of the most rewarding experiences a gardener can have. From the moment you plant those humble-looking tubers to the day you bring in an armload of vibrant, multi-colored blooms, the process is full of excitement. By focusing on the essentials—sun, well-draining soil, proper timing, and a bit of support—you can transform your garden into a late-summer masterpiece.
Dahlias remind us that the best things in the garden are worth a little patience and care. Whether you are a first-time grower or looking to expand your collection, we invite you to explore the Planning Guide for Dahlias. Start small with one or two varieties, and we are confident you’ll be hooked on dahlia gardening for years to come.
- Plant when the soil is warm (60°F) and the danger of frost has passed.
- Pinch the center stem when the plant is 12 inches tall for more blooms.
- Support tall varieties early to prevent storm damage.
- Enjoy the harvest—the more you cut, the more they grow!
Next Step: Browse our selection at Longfield Gardens and choose a variety that speaks to your style. Start small with one or two varieties, and we are confident you’ll be hooked on dahlia gardening for years to come.
FAQ
How long does it take for dahlias to bloom after planting?
Most dahlias will begin to bloom about 8 to 12 weeks after they are planted in the ground. The exact timing depends on the variety and your local weather conditions; warmer weather often leads to faster growth. Starting your tubers in pots indoors can help you see flowers even sooner.
Why are my dahlias growing lots of leaves but no flowers?
This is usually caused by too much nitrogen in the soil. High-nitrogen fertilizers encourage lush green foliage but can suppress flower production. Switch to a fertilizer with a higher middle and last number (phosphorus and potassium) to encourage the plant to set buds. Also, ensure your plants are getting at least 6 to 8 hours of full sun.
Do I need to water my dahlia tubers immediately after planting?
It is best to wait until you see the first green shoots emerge before you start a regular watering schedule. Because the tuber doesn't have roots yet, it cannot absorb water. Adding too much water to the soil before growth begins can cause the tuber to rot. Once the plant is a few inches tall, you can begin watering deeply 2 to 3 times a week.
Can I grow dahlias in containers?
Yes, many varieties thrive in pots! For the best results, choose border dahlias or dwarf varieties that naturally stay compact. Use a container that is at least 12 inches deep and wide with excellent drainage holes, and use a high-quality potting mix rather than garden soil. Remember that container-grown plants dry out faster and will need more frequent watering and feeding.