Introduction
There is nothing quite like the feeling of watching your first dahlia of the season unfurl its petals. Whether you are dreaming of massive dinnerplate dahlias or petite, perfectly round pompons, dahlias are a rewarding choice for any gardener.
At Longfield Gardens, we want to help you fill your yard with these high-performance bloomers. These dahlias are surprisingly easy to grow once you understand a few basic principles. While they look exotic and intricate, dahlias are surprisingly easy to grow once you understand a few basic principles. This guide will walk you through everything you need to know about planting your dahlia tubers in the ground for a season full of color.
We will cover how to select the right spot, how deep to plant your tubers, and the essential steps to take during those first few weeks of growth. By focusing on simple, proven techniques, you can enjoy a professional-looking flower garden right in your own backyard. Success begins with waiting for the right weather and giving your plants the foundation they need to thrive.
What to Do When Your Tubers Arrive
It is a common scenario: your carefully chosen tubers arrive on your doorstep, but the ground is still cold or a late-season snowstorm is in the forecast. If your shipment arrives before the soil is ready, it is important to handle the tubers correctly to prevent rot or dehydration.
Keep your tubers in their original packaging or a paper bag and store them in a cool, dark, and dry location. A basement, root cellar, or an unheated garage that stays above freezing is ideal. Aim for a temperature between 40°F and 50°F. Ensure there is adequate ventilation so moisture does not collect, which could lead to mold. As long as the tubers stay firm—much like a fresh potato—they will remain healthy until planting time.
Choosing the Right Time to Plant
Timing is the most important factor when it comes to dahlia success. Many gardeners feel a rush to get their plants in the ground as soon as the first warm day of spring arrives. However, dahlias are tropical plants at heart, originally hailing from Mexico. They love warmth and are very sensitive to cold temperatures.
You should wait to plant your dahlia tubers until all danger of frost has passed. A late spring frost can damage or even kill the tender new shoots. A good rule of thumb is to plant your dahlias around the same time you would plant your tomatoes or peppers. If the weather is warm enough for those summer vegetables, it is likely warm enough for your dahlias.
Soil temperature is just as important as air temperature. Dahlias prefer to start their growth in soil that has reached at least 60°F. If you plant a tuber in cold, wet soil, it may sit dormant or even begin to rot before it has a chance to sprout. You can use a simple soil thermometer to check the temperature, or simply wait until the ground feels warm to the touch.
Your USDA hardiness zone can help you estimate your ideal planting window. At Longfield Gardens, our Shipping Information explains how we time shipments based on your specific zone to ensure your tubers arrive about two weeks before it is time to plant. This gives you a little bit of time to prepare your garden beds while the weather settles.
Starting Dahlias Indoors for Earlier Blooms
If you live in a region with a short growing season or simply want to see flowers sooner, you can "pot up" your tubers indoors about 4 to 6 weeks before the last frost date. Plant each tuber in a gallon-sized pot filled with damp potting soil, keeping the "eye" just below the surface. Place the pots in a warm, sunny window or under grow lights. By the time the outdoor soil reaches 60°F, you will have established plants ready to be transplanted, giving you a significant head start on the blooming season.
Key Takeaway: Patience pays off with dahlias. Wait until the soil is 60°F and the threat of frost is gone before putting your tubers in the ground.
Selecting the Best Planting Site
To get the most blooms from your plants, you need to find a spot that meets their two primary needs: plenty of sun and excellent drainage. "Drainage" is simply a term for how quickly water moves through the soil. Dahlias like to stay hydrated, but they cannot stand having "wet feet," which means sitting in stagnant water.
Sun Exposure Requirements
Dahlias are sun-worshippers. To produce those large, vibrant flowers 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." This means they grow tall and thin as they stretch toward the light, which makes them more likely to flop over.
If you live in a very hot climate, such as the southern United States, your dahlias might appreciate a little bit of filtered afternoon shade. This can help prevent the flowers from fading or wilting in the intense midday heat. However, for most northern gardeners, more sun always equals more flowers.
Soil and Drainage Basics
The ideal soil for dahlias is loose, crumbly, and rich in organic matter. If you have heavy clay soil, the water may not drain away fast enough, which can lead to tuber rot. If you have very sandy soil, the water might drain too quickly, leaving the plants thirsty.
You can improve almost any soil type by adding a few inches of compost or well-rotted manure before you plant. This adds nutrients and improves the soil's texture. If your yard has a spot where puddles linger for hours after a rainstorm, avoid planting your dahlias there. Instead, consider using a raised bed. Raised beds are a fantastic option for dahlias because they naturally provide the superior drainage these plants love.
Understanding the Dahlia Tuber
When you receive your order, you might notice that dahlias do not look like traditional round flower bulbs. Instead, they look like a cluster of small potatoes. These are called tubers. While many people search for "dahlia bulbs," the technical term is "tuberous roots." For more background, see Are Dahlias Tubers or Bulbs? Expert Growing Guide.
The American Dahlia Society notes that a healthy dahlia tuber needs three specific parts to grow:
- The Tuber: This is the fat part of the root that stores energy and nutrients for the plant.
- The Neck: This is the thin part that connects the tuber to the main stem. It is very important that this neck is not broken or cracked.
- The Eye: This is the small bump where the new growth will emerge. It is located on the "crown" of the plant, right where the neck meets the old stem.
It is a common myth that a bigger tuber will produce a bigger plant. In reality, the size of the tuber does not dictate the size of the flower. A small tuber with a healthy eye will grow into a magnificent plant just as well as a large one. As long as the tuber feels firm—similar to a fresh potato—it is ready to grow.
If you cannot see the "eye" yet, do not worry. Some varieties take a little longer to "wake up" than others. You can encourage them by keeping the tubers in a warm, dry place for a few days before planting. Once you see a small green or pink bump starting to swell, you will know exactly where the new growth is coming from.
Preparing the Ground for Planting
Once you have chosen your site and the weather is right, it is time to prep the ground. Taking a little extra time to prepare the soil now will result in much healthier plants later in the summer.
Start by clearing the area of any weeds or grass. Turn the soil to a depth of about 12 inches using a garden fork or a shovel. This loosens the earth so the new roots can spread out easily. If your soil is particularly poor, you can mix in a balanced, slow-release fertilizer at this stage. We recommend a low-nitrogen formula, such as a 5-10-10 fertilizer, to support root development and future blooms rather than just excessive leaf growth.
Spacing Your Dahlias
Dahlias need plenty of elbow room. Good air circulation is key to preventing powdery mildew, a common fungus that can make the leaves look dusty. The amount of space you need depends on the variety of dahlia you are planting; for a fuller spacing guide, see How Far Apart to Plant Dahlia Bulbs for Success.
- Large Varieties (Dinnerplate and cactus dahlias): Space these 2 to 3 feet apart. These plants can grow 4 to 5 feet tall and 3 feet wide.
- Border and border decorative dahlias: Space these 12 to 18 inches apart.
- Dwarf or Mignon Varieties: Space these 10 to 12 inches apart.
It might feel like you are leaving too much empty space when you first plant those small tubers, but they will fill in that gap quickly once the summer heat arrives.
How to Plant the Tubers: Step-by-Step
Now it is time for the main event. Planting dahlia tubers correctly ensures they have the best start. Follow these simple steps for success:
- Dig a Hole: Dig a hole that is about 4 to 6 inches deep. For more detail, see How Deep Should You Plant Dahlia Bulbs? Expert Planting Guide. This depth protects the tuber from temperature swings and provides a stable base for the tall stems.
- Add Support: If you are planting tall varieties, place a stake in the ground now, before you put the tuber in. If you wait until the plant is tall to add a stake, you might accidentally poke a hole through the tuber underground. A sturdy bamboo pole or a wooden stake works perfectly.
- Position the Tuber: Lay the tuber in the hole horizontally. Many beginners try to plant them vertically, like a carrot, but laying them on their side is the preferred method. Ensure the "eye" or the sprout is pointing toward the sky.
- Cover with Soil: Gently fill the hole back in with soil. You do not need to pack it down hard; just a light pat will do.
- Label Your Plants: It is easy to forget which color is which once they are underground. Use a waterproof marker and a garden tag to label each spot.
How to Plant Dahlia Mignon Bulbs
If you are specifically looking for how to plant dahlia mignon bulbs, the process is very straightforward. Because Mignon dahlias are naturally compact and dwarf-sized, they do not require the deep support stakes that larger varieties need. Plant these smaller tubers 4 inches deep and space them 10 to 12 inches apart. Their petite size makes them excellent for the front edge of a garden bed or for brightening up patio containers. Despite their small stature, they are prolific bloomers that will provide a carpet of color all summer.
Key Takeaway: Plant tubers 4–6 inches deep and lay them horizontally with the eye facing up. Install your stakes at the time of planting to protect the roots.
The Critical First Watering Rule
This is the one step where many gardeners get a little too eager. For most plants, you want to water them immediately after planting. Dahlias are different.
Because the tuber is currently dormant and has no roots, it cannot "drink" water yet. If you drench the soil immediately after planting, the tuber may rot before it ever sends out a sprout. Unless your soil is bone-dry and dusty, you should not water your dahlias until you see the first green shoots poking through the surface of the soil.
Once those green leaves appear, the plant has started to grow its root system and is ready to be watered regularly. This simple delay is one of the best ways to ensure your tubers stay healthy and productive.
Caring for Your Dahlias as They Grow
Once your dahlias are a few inches tall, the fun really begins. These plants are fast growers, and you will see visible changes almost every week.
Expected Sprouting Timeline
After planting, many gardeners watch the soil daily for signs of life. Typically, you can expect to see green shoots emerging within 2 to 4 weeks. However, don't worry if it takes a bit longer; depending on the variety and the soil temperature, some tubers can take up to 6 weeks to "wake up." If the soil remains warm and you followed the "no water" rule until sprouting, your patience will eventually be rewarded.
Watering and Mulching
After the sprouts appear, dahlias like consistent moisture. Aim to give them about an inch of water per week. If the weather is very hot and dry, you may need to water more frequently. It is best to water at the base of the plant rather than over the leaves. This keeps the foliage dry and helps prevent disease.
A thin layer of mulch, such as shredded bark or clean straw, can be very helpful. Mulch helps the soil retain moisture and keeps the roots cool during the heat of July and August. Just be sure to keep the mulch a few inches away from the main stem to prevent any moisture from sitting against the stalk.
Fertilizer and Feeding
Once the plants are established and about 6 to 12 inches tall, you can begin a regular feeding schedule. Use a 5-10-10 fertilizer every 3 to 4 weeks throughout the growing season. This ensures the plant has enough phosphorus to produce those stunning blooms without overdoing the nitrogen, which can lead to weak stems and fewer flowers.
The Secret to More Blooms: Pinching
If you want a bushier plant with twice as many flowers, you should "pinch" your dahlias. This sounds a little scary to beginners, but it is one of the best things you can do for the plant. For a step-by-step refresher, see How to Pinch and Stake Dahlias.
When your dahlia is about 12 to 16 inches tall and has about four sets of leaves, snip off the very top of the center stem. You can use your fingers or a clean pair of garden snips. This tells the plant to stop growing straight up and instead start growing side branches. More branches mean more stems, and more stems mean more flowers for you to enjoy.
Supporting and Staking
As your dahlias grow, they will become heavy with foliage and large flower heads. If you placed a stake at planting time, you can now begin to tie the plant to the stake. Use soft garden twine or even strips of old t-shirts. Tie the stem loosely to the stake every 12 inches as it grows. This prevents the plant from snapping during a summer thunderstorm or high winds.
Simple Troubleshooting
Gardening always comes with a few surprises, but most dahlia issues are easy to solve with a little observation.
- No Sprouts: If it has been three or four weeks and you see nothing, the soil might be too cold. Be patient; some varieties are "late sleepers."
- Holes in Leaves: Slugs and snails love young dahlia shoots. If you see damage, you can use organic slug bait or even a copper barrier around the base of the plant.
- Yellow Leaves: This is often a sign of overwatering or poor drainage. Check the soil moisture; if it feels soggy, let it dry out for a few days.
- Powdery Mildew: If you see a white, dusty coating on the leaves in late summer, it is likely mildew. This is common when the air is humid. Ensure your plants have enough space for air to flow between them.
At Longfield Gardens, we stand behind the quality of our tubers with a 100% Quality Guarantee. If your items arrive damaged or do not perform as they should during their first growing season, our customer service team is here to help with a replacement or credit. We want your first experience with dahlias to be a total success.
End-of-Season Care
Dahlias will continue to bloom beautifully until the first hard frost kills the top growth. In colder climates (USDA zones 7 and lower), the tubers must be dug up and stored indoors for the winter. Wait until the foliage has turned black from frost, then cut the stems to about 4 inches. Carefully dig up the tuber clusters, wash off the soil, and let them dry in a frost-free area for a few days. Store them in crates filled with peat moss or vermiculite in a cool, dark spot until next spring.
Enjoying the Harvest
One of the best things about dahlias is that the more you cut them, the more they bloom. They are the ultimate "cut and come again" flower. When you bring a bouquet of fresh dahlias into your home, you are rewarding the plant and encouraging it to produce even more buds.
To get the longest vase life, cut your dahlias in the cool of the morning. Unlike roses or lilies, dahlia buds will not open much after they are cut. Choose flowers that are already about 75% to 100% open. Place them immediately into a bucket of room-temperature water. With a little floral preservative, a fresh dahlia bouquet can last five to seven days.
Conclusion
Planting dahlias in the ground is a simple process that yields incredible rewards. By waiting for warm soil, choosing a sunny spot with good drainage, and being patient with your watering, you can create a stunning display that lasts from midsummer until the first frost of autumn. These flowers bring a sense of joy and abundance to any garden.
- Wait for the warmth: Ensure soil is 60°F and frost has passed.
- Plant with care: 4 to 6 inches deep, horizontal, with the eye up.
- Be patient with water: Wait for green shoots before soaking the ground.
- Pinch for progress: Cut the top of the stem at 12 inches for more blooms.
If you are ready to start your dahlia journey, we invite you to explore our Dahlia Assorted Sangria Collection. We take pride in providing high-quality tubers that are true to variety and ready to grow.
Growing dahlias is a rewarding hobby that transforms your yard into a colorful sanctuary. With just a few simple steps, you can enjoy these magnificent blooms all season long.
FAQ
Do I need to soak my dahlia tubers before planting?
No, it is not necessary to soak dahlia tubers before putting them in the ground. Unlike some other bulbs or corms, dahlia tubers contain plenty of moisture and stored energy to begin growing on their own. In fact, soaking them can sometimes increase the risk of rot if the soil is also damp.
Can I plant dahlias in large pots instead of the ground?
Yes, dahlias grow very well in containers. Ensure you use a pot that is at least 12 to 15 inches in diameter and has plenty of drainage holes. Use a high-quality potting mix and follow the same rules for sun exposure and watering as you would for plants in the ground. For a colorful container option, try the Dahlia Assorted Sunlit Jewel Collection.
What should I do if a frost is predicted after I have planted?
If you have already planted your tubers and a surprise frost is in the forecast, do not worry. If the shoots have not emerged yet, the soil will protect the tuber. If you already have green leaves above the ground, cover the plants with an upside-down bucket, a frost blanket, or a heavy layer of mulch overnight to protect the tender growth.
Why are my dahlias growing slowly?
The most common reason for slow growth in the early season is cool temperatures. Dahlias really hit their stride when the nights are warm and the days are long. If your plants seem to be sitting still, they are likely waiting for the summer heat to arrive. Once the temperature stays consistently high, you will see them grow several inches in a single week.
What fertilizer should I use for dahlias?
We recommend using a low-nitrogen, high-phosphorus fertilizer such as a 5-10-10 formula. Start applying it once the plants are about 6 to 12 inches tall and continue every few weeks until the end of the season. Avoid high-nitrogen fertilizers, as they result in lots of green growth but fewer flowers.
How long does it take for dahlia tubers to sprout?
Sprouting typically takes between 2 to 4 weeks after planting in warm soil. However, it is normal for some varieties or tubers planted in slightly cooler soil to take up to 6 weeks. As long as the tuber is firm and not sitting in soggy soil, it is likely just waiting for more consistent warmth.
