Table of Contents
- Introduction
- Understanding Dahlia Tubers
- Finding the Perfect Location
- Timing Your Planting
- Preparing the Soil
- Step-by-Step Planting Process
- The Most Important Rule: Watering
- Essential Early Care: Pinching
- Supporting Your Dahlias
- Managing Pests and Health
- Container Gardening with Dahlias
- Harvesting and Deadheading
- Preparing for Winter
- Conclusion
- FAQ
Introduction
Walking through a garden filled with blooming dahlias feels like entering a world of pure color and variety. From the massive, pillowy petals of dinnerplate varieties to the intricate, geometric patterns of pompon types, these flowers are the undeniable stars of the summer landscape. At Longfield Gardens, we believe that every gardener should experience the joy of harvesting their own dahlia bouquets.
Whether you are a seasoned pro or a beginner picking up your first set of tubers, the process is straightforward and incredibly rewarding. This guide is designed to help you understand the simple steps needed to get these spectacular plants into the ground and growing strong. We will cover everything from choosing the right spot to the correct planting depth and the essential early care that ensures a season full of blooms.
Understanding Dahlia Tubers
Before we dig into the soil, it is helpful to understand exactly what you are planting. While many people search for "how do you plant dahlias bulbs," dahlias actually grow from tubers. These are thickened, underground stems that store energy for the plant, much like a potato.
When you receive your order from us, your tubers may arrive as single units or in small clusters. Both are perfectly capable of producing a magnificent, full-sized plant. Each tuber needs at least one "eye" to grow. The eye is a small growth point located near the neck—the narrow part where the tuber connects to the old stem. It looks similar to the eye on a potato and is the spot where the new sprout will emerge.
Healthy tubers should feel firm to the touch, similar to a fresh vegetable. If you see a little bit of surface mold or a small shriveled end, there is no need to worry. As long as the body of the tuber is solid and the neck is intact, the plant has all the energy it needs to start the season.
Key Takeaway: Dahlias grow from tubers rather than traditional bulbs. A healthy tuber is firm and must have an "eye" near the neck to produce a sprout.
Finding the Perfect Location
The success of your dahlias starts with where you decide to put them. These plants are sun-lovers that thrive in the warmth of the summer months. To get the most flowers and the strongest stems, you need to match the plant's needs with the right spot in your yard.
Priority One: Sunlight
Dahlias need plenty of direct sunlight to fuel their rapid growth and heavy blooming. Aim for a location that receives at least six to eight hours of full sun every day. Morning sun is particularly beneficial as it helps dry any dew off the leaves, which keeps the plants healthy and vibrant. If you live in a very hot climate, a spot that offers a bit of light afternoon shade can help prevent the flowers from fading too quickly in the intense heat.
Priority Two: Soil Drainage
While dahlias appreciate consistent moisture, they do not like to sit in soggy soil. Good drainage is essential. If water tends to puddle in a certain area of your yard for hours after a rainstorm, that spot is likely too wet for dahlia tubers.
You can improve the drainage in your planting beds by mixing in some compost or well-rotted manure before you plant. This adds organic matter that helps the soil hold just the right amount of moisture while allowing the excess to drain away. If your native soil is very heavy clay, consider planting your dahlias in raised beds. For more on drainage and texture, see what soil dahlias grow best in. This is an easy way to ensure perfect drainage and gives you complete control over the soil quality.
Priority Three: Protection from Wind
Since many dahlia varieties can grow three to five feet tall, they can act a bit like sails in a high wind. If possible, choose a spot that is somewhat sheltered from strong gusts, perhaps near a fence or on the leeward side of a building. You will still need to support the plants as they grow, but a naturally protected location makes the job much easier.
Timing Your Planting
In gardening, timing often matters more than any secret tip or trick. Dahlias are tropical plants at heart, originating from the mountain regions of Mexico and Central America. This means they are very sensitive to cold temperatures and should only be moved outdoors when the environment is truly ready for them.
Wait for the Warmth
The most common mistake gardeners make is planting their tubers too early in the spring. If the soil is cold and wet, the tuber will sit dormant and may struggle. You want to wait until the soil temperature reaches about 60°F. A good rule of thumb for most US gardeners is to plant your dahlias at the same time you would plant your tomatoes or peppers.
Watch the Frost Dates
Make sure the danger of all spring frosts has passed before you put your tubers in the ground. If an unexpected late frost is predicted after your dahlias have sprouted, you can easily protect the tender green shoots by covering them with an overturned bucket or a heavy fabric frost blanket for the night.
A Note on Shipping
We time our shipments from Longfield Gardens based on your USDA hardiness zone. This ensures that your tubers arrive about two weeks before the ideal planting time for your specific area. This gives you plenty of time to prepare your garden beds while the tubers stay safe and dormant in their packaging.
Preparing the Soil
Dahlias are "heavy feeders," meaning they use a lot of nutrients to produce those massive flowers and lush green leaves. Preparing the soil properly before planting gives them a head start.
Start by loosening the soil in your planting area to a depth of about 12 inches. This makes it easy for the new roots to spread out and establish themselves. Mix in a 2-to-3-inch layer of compost or aged manure. This provides a slow-release source of nutrients and improves the texture of the soil.
If you want to add a bit of fertilizer at planting time, choose an all-purpose, balanced organic fertilizer. Follow the instructions on the label for the correct amount. Avoid using fertilizers that are very high in nitrogen, as this can lead to lots of green leaves but very few flowers.
What to Do Next:
- Check your local frost-free date.
- Clear the planting area of any weeds or debris.
- Work compost into the top 12 inches of soil.
- Have your stakes or support structures ready.
Step-by-Step Planting Process
Once your soil is prepped and the weather is warm, it is time to get your dahlias in the ground. Following a few simple steps for depth and orientation will set your plants up for success.
1. Dig the Hole
Dig a hole that is about 4 to 6 inches deep. If you are planting a large variety, like a dinnerplate dahlia, make the hole a bit wider to accommodate the tuber and give the roots plenty of room to expand.
2. Set the Support
If you are planting tall varieties, it is best to put your stake in the ground at the same time you plant the tuber. This prevents you from accidentally driving a stake through the tuber later in the season. For many decorative dahlias, place a sturdy bamboo pole, wooden stake, or metal T-post right into the hole before you place the tuber.
3. Position the Tuber
Lay the dahlia tuber horizontally in the bottom of the hole. If you can see the eye or a small sprout, point it toward the sky. If you cannot see the eye yet, do not worry—the plant will find its way up. Just lay it flat. For clumps of tubers, place them with the old stem pointing upward.
4. Spacing
Giving your plants enough room is vital for air circulation and easy harvesting.
- Large Dahlias (Dinnerplate and Decorative): Space these 18 to 24 inches apart.
- Medium Dahlias: Space these 12 to 18 inches apart.
- Border Dahlias (Low-growing): Space these 10 to 12 inches apart.
5. Cover and Label
Fill the hole back in with the amended soil. Do not pack it down too tightly; just a gentle firming with your hand is enough. This is also the perfect time to add a label so you remember which beautiful variety is growing in that spot.
The Most Important Rule: Watering
When it comes to planting dahlias, the most important rule is one of restraint: Do not water your tubers immediately after planting.
If the soil has a normal amount of spring moisture, the tuber has everything it needs to start growing. Adding extra water at this stage can lead to the tuber rotting before it has a chance to sprout. The tuber is currently a storage vessel, and until it develops roots and green leaves, it cannot "drink" the water you provide.
Wait until you see the first green shoots peeking through the soil surface. This is your signal that roots have formed and the plant is ready to be watered. Once the plants are about 6 to 12 inches tall, you can begin a regular watering schedule.
How to Water Established Dahlias
Dahlias like deep, consistent watering. It is much better to water them thoroughly once or twice a week than to give them a light sprinkle every day. This encourages the roots to grow deep into the soil. Aim the water at the base of the plant rather than over the leaves to help keep the foliage dry and healthy. In the heat of mid-summer, you may need to increase the frequency if the soil feels dry an inch below the surface.
Essential Early Care: Pinching
If you want the most flowers possible from each plant, there is one simple technique you should use: pinching. It might feel a little strange to cut back a healthy plant, but it is the best way to encourage a bushy, productive dahlia.
When your dahlia plant is between 12 and 18 inches tall and has about four sets of leaves, snip off the very top of the main center stem. You can use your fingers or a clean pair of garden snips. By removing the dominant center tip, you signal the plant to send its energy into the side branches.
Instead of one tall, lanky stalk, the plant will develop multiple stems. This results in a stronger plant that is less likely to blow over and produces significantly more blooms throughout the season.
Key Takeaway: Pinching the center stem when the plant is about a foot tall is an easy win for any gardener. It results in a bushier plant and way more flowers for your vases.
Supporting Your Dahlias
Because dahlias grow so quickly and produce such large, heavy flowers, they need a little help staying upright. Without support, a heavy rain or a summer breeze can cause the stems to lean or break.
The Single Stake Method
For most home gardens, tying the main stem to a single sturdy stake is the easiest method. For many cactus dahlias like Tahiti Sunrise, use soft garden twine or strips of fabric to gently secure the stem to the stake every 12 inches. Do not tie it too tightly; leave a little room for the stem to expand as it grows.
The Tomato Cage Method
For smaller or mid-sized dahlia varieties, a standard metal tomato cage works wonderfully. PomPon dahlias are a great fit for this approach. Place the cage over the plant early in the season so the branches can grow up through the wire supports. This provides 360-degree protection with very little effort.
The Corral Method
If you are planting a long row of dahlias, you can create a "corral." Drive heavy posts into the ground at the corners and every few feet along the row. Wrap sturdy twine around the posts at heights of 12 inches and 24 inches, essentially creating a fence that keeps the plants contained and upright.
Managing Pests and Health
Dahlias are generally robust plants, but like anything in the garden, they have a few visitors. Keeping your garden clean and the plants healthy is the best defense.
- Slugs and Snails: These are most common early in the season when the shoots are tender. You can protect your young plants by using organic slug bait or by keeping the area around the base of the plant clear of weeds and debris where they like to hide.
- Japanese Beetles: These can appear in mid-summer. The easiest way to manage them is to hand-pick them off the flowers and drop them into a bucket of soapy water.
- Powdery Mildew: This looks like a light dusting of flour on the leaves. It usually happens in late summer when the air is humid. You can help prevent it by ensuring your plants have plenty of space for air to circulate and by watering at the soil level rather than over the leaves.
Container Gardening with Dahlias
If you don't have a large garden plot, you can still enjoy these stunning flowers. Dahlias grow remarkably well in pots and containers. This is a great way to add color to a patio, deck, or balcony.
Choosing a Pot
For standard or dinnerplate dahlias, you will need a large container that holds at least 5 to 10 gallons of soil. The pot must have drainage holes in the bottom. For smaller border dahlias or gallery dahlias, a 2-gallon pot is usually sufficient.
Planting in Pots
Use a high-quality, well-draining potting mix rather than garden soil, which is too heavy for containers. Plant the tuber about 4 to 6 inches deep, just like you would in the ground. Because pots dry out faster than the ground, you will need to check the moisture level more frequently once the plant is established. During the peak of summer, container-grown dahlias may need water every day.
Harvesting and Deadheading
The more you cut your dahlias, the more they will bloom. This makes them the ultimate plant for anyone who loves fresh flowers in the house, and for more tips on growing dahlias for cut flowers, see our guide.
When to Cut
Unlike roses or lilies, dahlias do not open much once they are cut. Wait until the flower is almost fully open before you harvest it. For the longest vase life, cut your flowers in the cool of the early morning or late evening. Place the stems immediately into a bucket of clean, room-temperature water.
Deadheading
If you don't cut the flowers for bouquets, you must "deadhead" them. This simply means cutting off the faded flowers before they start to form seeds. This tells the plant to keep putting its energy into making new buds rather than focusing on seed production.
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 longer stems for the next round of blooms.
Preparing for Winter
As the season winds down and the first frost arrives, your dahlias will begin to go dormant. In warmer climates (USDA zones 8 and higher), dahlias can often stay in the ground year-round with a thick layer of mulch for protection.
In colder climates (zones 7 and lower), the tubers need to be dug up and stored indoors for the winter. Wait until the foliage has been blackened by a frost. This sends a signal to the plant to store its final bit of energy in the tubers. Cut the stems back to about 4 inches, carefully lift the tubers with a garden fork, and store them in a cool, dark, frost-free place like a basement or crawlspace until next spring.
At our farm, we take pride in the quality of the plants we send to your home. We stand behind our products with a 100% quality guarantee. If your tubers arrive damaged or do not perform as they should in their first growing season, we want to hear from you. Our goal is to make sure you are successful and happy with your garden.
Conclusion
Planting dahlias is one of the most satisfying projects a gardener can undertake. By focusing on the basics—waiting for warm soil, choosing a sunny spot with good drainage, and being patient with the watering can—you set the stage for a spectacular show. These plants are incredibly generous, offering a constant supply of blooms that only get better as the summer progresses.
- Wait for soil to reach 60°F before planting.
- Plant tubers 4 to 6 inches deep in a sunny, well-drained spot.
- Avoid watering until the first green shoots appear.
- Pinch the center stem at 12 inches to encourage more flowers.
We are here to help you every step of the way, from selecting the perfect varieties to seeing them bloom in your yard. For more detailed advice and to see our current selection of premium tubers, visit our website. Your journey to a garden full of color starts with that first simple step of putting a tuber into the warm spring earth.
Choosing to grow dahlias is an investment in beauty. With just a little bit of care in the spring, you are guaranteed a summer and autumn filled with the most vibrant flowers imaginable.
FAQ
Can I plant dahlia tubers in the shade?
Dahlias really need full sun to perform their best. If they are planted in a shady spot, they tend to grow very tall and "leggy" as they reach for the light. They will also produce far fewer flowers, and the stems will be much weaker. For the best results, ensure they get at least six hours of direct sunlight.
Should I soak my dahlia tubers before planting?
There is generally no need to soak dahlia tubers before you put them in the ground. Unlike some other bulbs or corms, dahlia tubers contain a large amount of stored moisture and energy. Soaking them can actually increase the risk of rot, especially if they are planted into cool or damp soil.
How long does it take for dahlias to sprout?
Dahlias are not the fastest starters in the garden. Depending on the soil temperature and the specific variety, it can take anywhere from two to four weeks for the first green shoots to appear above the ground. If the weather has been a bit cool, they may take even longer. As long as the tuber was firm when planted, have patience—they are busy growing roots underground!
Do I need to fertilize my dahlias all season?
While dahlias appreciate fertile soil, you don't need to overdo the fertilizer. Mixing compost into the soil at planting time is the most important step. If you choose to fertilize later in the season, use a low-nitrogen, high-potassium fertilizer once a month starting mid-summer to encourage more blooms rather than just more leaves. Stop fertilizing by early September to help the plant prepare for dormancy.
