Introduction
There is nothing quite like the excitement of seeing the first dinnerplate dahlia unfurl in your garden. These spectacular flowers are the crown jewels of the summer landscape, offering a range of colors and shapes that feel almost too beautiful to be real. Whether you are looking for soft, romantic pastels or bold, vibrant hues that command attention, dahlias provide an abundance of blooms from midsummer right up until the first frost.
At Longfield Gardens, we want to help you experience the joy of a garden filled with these impressive flowers. While their intricate petals and large sizes might make them look high-maintenance, they are actually very approachable for gardeners of any skill level. By following a few simple steps during the planting process, you can set your dahlias up for a season of vigorous growth and heavy flowering.
This guide will walk you through everything you need to know about how to plant dahlia flowers. We will cover how to identify healthy tubers, the best time to get them in the ground, and the simple techniques for depth and spacing that lead to success. Our goal is to make the process clear and rewarding so you can focus on the fun part: enjoying the flowers.
With the right preparation and a bit of patience, your garden will soon be a source of endless bouquets and beautiful views.
Understanding Dahlia Tubers
Before you dig your first hole, it is helpful to understand what you are planting. Dahlias grow from tubers, which are thickened, underground energy storage organs. These tubers provide the fuel the plant needs to send up its first shoots and establish a strong root system.
When you receive your order, you might see a single tuber or a small clump of several tubers attached to a central stem. Both are perfectly capable of producing a healthy, productive plant. The most important part of the tuber is the "eye." This is a small growth bud located at the crown, which is the point where the tuber meets the old stem.
What to Look For in a Healthy Tuber
A healthy dahlia tuber should feel firm and heavy for its size, much like a fresh potato. It is normal for tubers to have some shriveling or surface blemishes, and these usually do not affect the plant's performance. The key is ensuring the tuber is solid and has a visible or soon-to-emerge eye.
If you have trouble finding the eye on your tuber, don’t worry. Sometimes the eyes are "blind" or dormant until they feel the warmth of the soil. You can encourage them to wake up by placing the tubers in a warm, bright room for a week or two before planting. Once you see a small pink or green nub appearing at the crown, you know exactly where the new growth will start.
Handling Different Tuber Sizes
Dahlia tubers come in many different shapes and sizes. Some varieties produce long, finger-like tubers, while others produce round, chunky ones. The size of the tuber does not determine the size of the flower. A small tuber can produce a massive six-foot plant with dinnerplate-sized blooms just as well as a large one. We work with experienced growers to ensure that every tuber we ship has the energy reserves and the necessary growth point to thrive in your garden.
Key Takeaway: Focus on the health of the crown and the presence of an eye rather than the overall size of the tuber clump. A firm tuber with at least one eye is all you need for a beautiful plant.
Choosing the Best Location
Dahlias are sun-loving plants that thrive when they have plenty of energy from the sky and a comfortable place for their roots to grow. Choosing the right spot is the first step toward a successful season.
Sunlight Requirements
For the best results, place your dahlias in a spot that receives at least six to eight hours of direct sunlight every day. Sunlight is the engine that drives flower production. While dahlias can grow in partial shade, they often become "leggy" as they stretch toward the light, and they will produce fewer flowers. If you live in an exceptionally hot climate where afternoon temperatures regularly soar, a spot with morning sun and some light afternoon dappled shade can help prevent the flowers from fading too quickly.
Soil and Drainage
Good drainage is essential for dahlia success. "Drainage" simply refers to how quickly water moves through the soil. Dahlias like to stay hydrated, but they do not like to sit in soggy soil, which can cause the tubers to soften and struggle.
If you have heavy clay soil that stays wet for a long time after rain, consider planting your dahlias in raised beds or amending the area with compost. Compost improves the soil structure, allowing air and water to move more freely. A simple way to test your drainage is to dig a small hole and fill it with water. If the water disappears within an hour, your drainage is excellent.
Space to Breathe
Dahlias need room to grow. Depending on the variety, a single plant can grow three to five feet tall and two to three feet wide. Providing enough space between plants ensures that air can circulate freely around the foliage. Good airflow is a simple way to keep the leaves healthy and vibrant throughout the humid summer months.
When to Plant Dahlias
Timing is more important than almost any other factor when it comes to planting dahlias. Because they are tropical plants by nature, they are very sensitive to cold temperatures.
Wait for the Soil to Warm Up
The biggest mistake a gardener can make is planting dahlias too early in cold, wet spring soil. Tuber growth begins only when the soil temperature reaches about 60°F. If they are tucked into the ground while the soil is still chilly and damp, they will simply sit dormant, which increases the risk of the tuber failing before it even starts.
A good rule of thumb is to plant your dahlias at the same time you would plant tomatoes or peppers. In most regions, this is about two weeks after the last expected frost date. If you want to be precise, you can use a basic soil thermometer to check the temperature a few inches below the surface.
Considering Your Climate
In the southern United States, you may be able to plant as early as late March or April. In northern states, you might need to wait until late May or even early June. Do not feel rushed; dahlias grow incredibly fast once the weather warms up. A dahlia planted in warm soil in June will often catch up to and even outperform one planted in cold soil in May.
Starting Early Indoors
If you have a short growing season and want to get a head start on blooms, you can start your tubers indoors about four to six weeks before the last frost.
- Plant the tubers in pots filled with slightly damp potting mix.
- Keep them in a warm spot with plenty of light, such as a sunny window or under grow lights.
- Once the danger of frost has passed and the soil is warm, you can gently transplant these started plants into the garden.
What to do next:
- Check your local frost dates to determine your planting window.
- Monitor soil temperatures with a thermometer or wait until the weather consistently stays warm at night.
- Prepare your planting site by clearing weeds and adding a layer of compost.
How to Plant Dahlias: Step-by-Step
Once the soil is warm and your site is ready, it is time to get your dahlias in the ground. Following these specific steps for depth and orientation will help your plants emerge quickly and strongly.
Step 1: Prepare the Hole
Dig a hole about 6 to 8 inches deep. This gives you enough room to loosen the soil at the bottom so the new roots can spread out easily. If you haven't already amended your soil, you can mix a handful of compost or a well-balanced, slow-release fertilizer into the soil at the bottom of the hole. This provides a gentle source of nutrients as the plant begins to grow.
Step 2: Orient the Tuber
Lay the tuber horizontally at the bottom of the hole. While it might seem natural to plant it vertically like a bulb, laying it on its side is the preferred method. Ensure the "eye" or the sprout is pointing upward toward the sky. If you are planting a clump of tubers, lay the entire clump in the hole with the old stem base facing up.
Step 3: Proper Spacing
Give each plant enough room to reach its full potential.
- Large varieties (Dinnerplate and Decorative): Space these 18 to 24 inches apart.
- Medium varieties (Cactus and PomPon dahlias): Space these 12 to 18 inches apart.
- Small varieties (Border dahlias): Space these 10 to 12 inches apart.
Proper spacing makes it easier to navigate the garden for harvesting and ensures that each plant gets its fair share of sunlight and nutrients.
Step 4: Cover with Soil
Fill the hole back in with soil, covering the tuber so it is about 4 to 6 inches below the surface. Gently firm the soil with your hands to remove any large air pockets, but do not pack it down too tightly. The soil should feel snug but breathable.
Step 5: Install Supports Early
Tall dahlia varieties need support to keep their heavy blooms from toppling over in the wind or rain. It is much easier to install your stakes or cages at the time of planting rather than trying to hammer them in later when the roots are established.
Sturdy wooden stakes, bamboo poles, or even heavy-duty tomato cages work well. Drive the stake into the ground a few inches away from the tuber so you don't accidentally poke through it. As the plant grows, you can loosely tie the main stem to the stake using soft garden twine.
Initial Watering and Care
One of the most important rules for planting dahlias is to hold back on the watering immediately after planting. This is often counterintuitive for gardeners who are used to watering everything in right away.
The "Wait for Green" Rule
Because the tuber is currently dormant and has no roots, it cannot absorb water. Excess moisture in the soil at this stage can lead to problems. In most cases, the natural moisture already present in the spring soil is more than enough to trigger the tuber to wake up.
Wait until you see the first green shoots poking through the soil surface before you start a regular watering schedule. Once the plant has leaves, it will begin to transpire and grow a root system that can effectively use the water you provide.
Deep Watering for Established Plants
Once your dahlias are about 6 to 12 inches tall, they will appreciate consistent moisture. Rather than a light sprinkle every day, aim for a deep soaking two or three times a week. This encourages the roots to grow deeper into the soil, making the plant more resilient during hot, dry spells.
If the weather is particularly hot, you can check the soil by sticking your finger an inch or two deep. If it feels dry, it is time to water. Using a soaker hose or drip irrigation is an excellent way to deliver water directly to the roots while keeping the foliage dry, which helps maintain the health of the leaves.
Pinching for More Flowers
If you want a bushier plant with a massive amount of flowers, there is one simple trick you should use: pinching. While it might feel strange to snip off the top of a healthy young plant, it is one of the best things you can do for your dahlias.
How to Pinch
When your dahlia plant is about 12 inches tall and has at least four sets of leaves, use a clean pair of garden shears or your fingers to snip off the very top of the center stem. Aim to remove about 3 to 4 inches of the main stalk, cutting just above a set of leaves.
Why It Works
By removing the "apical dominance" of the main stem, you signal the plant to send its energy into the side buds. This results in a plant that is shorter, sturdier, and much more branched. Instead of one main stalk with a few flowers at the top, you will have a lush, multi-stemmed bush covered in blooms. This simple step can easily double the number of flowers you get from a single plant.
Key Takeaway: Pinching your dahlias when they are 12 inches tall creates a stronger, bushier plant with significantly more flowers for your bouquets.
Managing Growth and Support
As your dahlias grow, they will become quite heavy, especially the varieties with large, "dinnerplate" sized flowers. Keeping them upright ensures the stems stay straight and the flowers remain clean and visible.
Staking Techniques
If you are using a single stake, continue to tie the main stem to the support every 12 inches or so. Use a "figure-eight" tie, where the twine crosses between the stake and the stem. This provides a cushion that prevents the twine from rubbing against the plant's skin.
For large plantings, some gardeners use a method called "corralling." You place sturdy T-posts at the corners of your dahlia bed and run several rows of twine around the entire perimeter. This creates a supportive "cage" for a whole group of plants at once.
Our Trial Garden Experience
At Longfield Gardens, we maintain a trial garden where we grow and evaluate hundreds of dahlias each year. We have found that providing support early is the most effective way to prevent storm damage. A sudden summer downpour can add a lot of weight to a blooming dahlia; having that stake already in place makes all the difference. We use these trials to ensure the varieties we offer are not only beautiful but also have the stem strength required for a successful home garden display.
Encouraging Continuous Blooms
Dahlias are "cut-and-come-again" flowers. The more you harvest them, the more they will bloom. This makes them one of the most rewarding plants for anyone who loves making fresh floral arrangements.
Harvesting for Bouquets
The best time to cut dahlias is in the cool of the morning when the plants are fully hydrated. Unlike roses or lilies, dahlias will not open much further once they are cut. Look for flowers that are about three-quarters of the way open. Check the back of the flower head; the petals should be firm and fresh, not papery or brown.
Use a sharp, clean knife or shears to cut the stem as long as possible. Immediately place the stems in a bucket of room-temperature water. Dahlias can last five to seven days in a vase if you change the water daily and keep them out of direct sunlight.
The Importance of Deadheading
If you choose not to cut your flowers for vases, you still need to remove them once they begin to fade. This process is called "deadheading." If the plant is allowed to produce seeds, it will slow down its flower production. By removing the spent blooms, you tell the plant to keep producing new buds.
When deadheading, don't just snip off the flower head. Follow the stem back down to where it meets a main branch or a set of leaves and make your cut there. This keeps the plant looking tidy and encourages new flowering stems to emerge from the leaf axils.
Simple Solutions for Success
Gardening should be an enjoyable experience, and dahlias are generally very resilient. However, keeping an eye on a few basics will ensure your plants stay in top shape.
Protecting Young Plants
When dahlia shoots first emerge, they are very tender. In some gardens, slugs or snails might find them attractive. A simple way to protect your young plants is to clear away any old leaves or debris from the base of the plant, which removes the hiding spots for these visitors. You can also use organic iron phosphate granules, which are widely available and effective for protecting new growth.
Fertilizing for Performance
Dahlias are hungry plants, but they prefer a balanced diet. A fertilizer that is too high in nitrogen may produce lots of green leaves but very few flowers. Look for a fertilizer where the three numbers on the bag (NPK) are relatively equal, or one where the middle number (phosphorus) is slightly higher. Applying a liquid fertilizer once every two to three weeks during the peak of summer can give your plants the boost they need to keep blooming through the fall.
Monitoring for Health
As the season progresses, you may notice the lower leaves of your dahlias starting to look a bit tired. This is natural. To improve airflow and keep the plant looking fresh, you can gently snip off the bottom 12 inches of foliage once the plant is at least three feet tall. This allows air to move freely through the base of the plant and makes it easier to see the soil when you are watering.
Preparing for the End of the Season
In most parts of the United States, dahlias are grown as annuals, or the tubers are lifted and stored indoors for the winter.
After the First Frost
Dahlias will continue to bloom until a hard frost hits. Once the foliage has turned black or brown from the cold, the growing season is over. If you live in USDA zones 8 through 11, you can often leave your tubers in the ground for the winter, provided the soil does not freeze and has excellent drainage. Covering the area with a thick layer of mulch can provide extra protection.
Lifting and Storing
For gardeners in zones 7 and colder, you will need to dig up your tubers if you want to grow them again next year.
- Cut the stems back to about 4 inches.
- Gently lift the tubers with a garden fork, being careful not to bruise them.
- Shake off the excess soil and let them dry in a protected spot for a day or two.
- Store them in a cool, dark, frost-free place (around 40-50°F) in a box filled with peat moss, vermiculite, or wood shavings.
We provide detailed guides on our website for those who want to master the art of winter storage, but even if you choose to start with fresh tubers each spring, the effort of planting is always worth the reward.
Conclusion
Planting dahlias is a rewarding investment that pays off in a spectacular display of color and texture. By waiting for warm soil, planting at the correct depth, and providing sturdy support, you create an environment where these plants can truly shine. Remember that gardening is a journey, and every season brings new opportunities to learn and enjoy the beauty of the natural world.
At Longfield Gardens, we take pride in providing the high-quality tubers you need to get started. Our 100% quality guarantee ensures that your items arrive in prime condition and are true to variety, giving you the confidence to grow the garden of your dreams. Whether you are planting a single dahlia in a sunny corner or an entire row for cutting, the results are sure to bring a smile to your face.
Your Next Steps for Success:
- Select a variety that fits your space, from towering dinnerplates to compact borders.
- Prepare your soil with compost to ensure excellent drainage.
- Wait for the soil to reach 60°F before tucking your tubers into the ground.
- Install your stakes at planting time to avoid damaging the roots later.
- Pinch the center stem when the plant reaches 12 inches for a bushier, bloom-heavy plant.
"Dahlias are the ultimate reward for the patient gardener. By getting the basics of timing and depth right, you unlock a season of unparalleled beauty."
FAQ
Do I need to soak dahlia tubers before planting?
No, it is not necessary to soak dahlia tubers. Unlike some other bulbs or corms, dahlia tubers contain a significant amount of moisture and stored energy. Soaking them can actually increase the risk of rot if the soil is also damp. It is best to plant them dry and let them wake up naturally as the soil warms.
How deep should I plant dahlia tubers?
Dahlia tubers should be planted about 4 to 6 inches deep. You want to ensure there is enough soil over the top of the tuber to protect it from temperature fluctuations and provide a stable base for the heavy stems. Lay the tuber horizontally in the hole with the eye or sprout pointing upward.
When is the best time to plant dahlias?
The best time to plant dahlias is in late spring, once the danger of frost has passed and the soil temperature has reached at least 60°F. In most regions, this coincides with the time you would plant warm-weather vegetables like tomatoes. Planting in warm soil ensures the tubers sprout quickly and stay healthy. For timing by region, check the Hardiness Zone Map.
Can I grow dahlias in containers?
Yes, many dahlia varieties thrive in containers. Choose a pot that is at least 12 to 15 inches in diameter and has excellent drainage holes. Use a high-quality potting mix and remember that container-grown dahlias will need more frequent watering and fertilizing than those planted in the ground. Smaller "border" or "gallery" varieties are particularly well-suited for life in a pot. For shipping details before you order, see Shipping Information, and if you need help choosing plants, visit About Us or Contact Us.
