Introduction
There is nothing quite like the feeling of walking into your garden on a sunny July morning and seeing the first dinnerplate-sized dahlia bloom unfurling its petals. These spectacular flowers are the crown jewels of the summer garden, offering an incredible variety of colors, shapes, and sizes that can brighten any landscape.
Whether you are looking for the soft, romantic hues of a Cafe au Lait, growing these flowers is a rewarding experience that brings joy from mid-summer all the way until the first frost.
At Longfield Gardens, we believe that everyone can find success with these stunning dahlia collections, regardless of their experience level. We will cover everything from selecting the right site and the perfect planting time to the simple maintenance steps that ensure your plants stay healthy and productive all season long.
The bold, sunny yellow of a Kelvin Floodlight makes a dramatic statement from mid-summer all the way until the first frost.
Growing dahlias is a straightforward process that rewards a little bit of patience with an abundance of beauty. By focusing on a few essential basics—like soil temperature, sunlight, and proper watering—you can enjoy a garden filled with vibrant blooms and have plenty left over to share with friends and family.
Understanding Your Dahlia Tubers
Before we get into the soil, it is helpful to understand exactly what you are planting; see our Dahlia Tubers: What You Need to Know. While many people refer to them as "dahlia bulbs," these plants actually grow from tubers. If you have ever looked at a sweet potato or a fingerling potato, you have a good idea of what a dahlia tuber looks like.
A healthy tuber consists of three main parts: the body, the neck, and the eye. The body is the thick, fleshy part that stores energy and nutrients for the plant. The neck is the narrow portion that connects the body to the crown of the previous year's stem. The most important part is the eye, which is a small, sometimes hard-to-see bump located on the crown. This eye is where the new sprout will emerge.
When you receive your order from Longfield Gardens, your tubers may arrive as single pieces or as a clump. Both forms are excellent for planting. A single tuber with one healthy eye has everything it needs to grow into a large, vigorous plant. It is a common misconception that a bigger tuber will produce a bigger plant; in reality, even a small tuber the size of a AA battery can grow into a five-foot-tall floral giant as long as it is healthy and has an intact eye.
Key Takeaway: Success starts with a healthy tuber. As long as the neck is firm and there is at least one visible eye or sprout, your dahlia has everything it needs to thrive.
Choosing the Perfect Spot
Dahlias are sun-loving plants that belong to the same family as sunflowers and daisies. To get the best results, you need to match the plant's needs to the conditions in your yard.
Sunlight Requirements
For the most robust stems and the greatest number of flowers, choose a location that receives at least six to eight hours of direct sunlight every day. While some varieties can tolerate a little bit of afternoon shade in very hot climates, full sun is the gold standard. Sunlight provides the energy the plant needs to produce those massive, intricate blooms. If your garden is a bit shadier, the plants may grow taller and lankier as they stretch toward the light, and they will likely produce fewer flowers.
Soil and Drainage
The next most important factor is drainage, which is simply how fast water moves through the soil. Dahlias love consistent moisture, but they do not like to have "wet feet." If a tuber sits in soggy, waterlogged soil for too long, it can rot before it even has a chance to sprout.
You can check your drainage easily. After a heavy rain, look at your chosen spot. If the water disappears within an hour or two, your drainage is excellent. If puddles linger for half a day, you might want to consider planting in a raised bed or improving the soil by mixing in some compost or aged manure to help loosen it up.
Space to Breathe
Dahlias need room to grow. Depending on the variety, they can reach anywhere from 12 inches to five feet in height. For standard decorative or dinnerplate varieties like Thomas Edison, plan to space your tubers about 18 to 24 inches apart.
This same spacing works well for a Labyrinth, and it helps keep the foliage healthy and green all summer.
When to Plant Your Dahlias
Timing is one of the most important factors in dahlia gardening. Because these plants are native to the warm climates of Mexico and Central America, they are very sensitive to cold temperatures.
The best rule of thumb is to treat your dahlias like you would tomato plants. Wait to plant your tubers outdoors until all danger of frost has passed and the soil has warmed up. If you are not sure about your growing area, check the Hardiness Zone Map. Ideally, you want the soil temperature to be consistently around 60°F. In most parts of the United States, this usually happens in late May or early June.
If you plant your tubers in cold, wet soil too early in the spring, they will simply sit dormant. At best, they will wait for the weather to warm up; at worst, the damp cold can cause the tuber to deteriorate. There is no need to rush. Dahlias grow very quickly once the weather turns warm, and a tuber planted in late May will often catch up to and even outperform one planted too early in April.
What to do next:
- Check your local "last frost date" online.
- Wait for the soil to feel warm to the touch before planting.
- If you live in a very cold region with a short growing season, you can start your tubers in pots indoors 4–6 weeks before the last frost to give them a head start.
How to Plant Dahlias Step-by-Step
Once the weather is warm and your site is ready, planting is a quick and enjoyable task. Follow these simple steps to give your tubers the best possible start.
- Prepare the soil: Use a shovel or garden fork to loosen the soil in your planting area to a depth of about 12 inches. This makes it easy for the new roots to spread out.
- Add nutrients: Mix in a few handfuls of compost or a small amount of all-purpose garden fertilizer into the bottom of the hole. This provides a slow-release food source for the growing plant.
- Dig the hole: For each dahlia, dig a hole that is about 4 to 6 inches deep.
- Place the tuber: Lay the tuber horizontally at the bottom of the hole. If you can see a sprout or an eye, make sure it is facing upward. If you aren't sure where the eye is, don't worry—the plant will find its way to the surface.
- Set your support: If you are planting tall varieties, it is a great idea to push a sturdy stake into the ground right next to the tuber now. Doing it at planting time prevents you from accidentally poking a hole through the tuber later in the season when the plant is larger.
- Cover with soil: Fill the hole back in with soil. The top of the tuber should be covered by about 1 to 2 inches of soil.
The Most Important Watering Rule
One of the most common questions we hear is how much to water dahlias right after planting. This is one of the few times in gardening where the best thing to do is actually nothing.
Unless your soil is extremely dry and dusty, you should not water your dahlias immediately after planting. The tuber contains all the moisture and energy needed to send up its first sprout. Adding extra water before the plant has roots to soak it up can lead to rot.
Wait until you see the first green shoots peeking through the soil. This is your signal that the plant has established roots and is ready for a drink. Once the plants are about 6 inches tall, you can begin a regular watering schedule.
For the rest of the summer, aim to water deeply once or twice a week. Deep watering encourages the roots to grow further down into the soil, which makes the plant more stable and drought-resistant. If you have sandy soil, you may need to water more frequently; if you have heavy clay soil, you may need to water less often.
Supporting Your Plants
As your dahlias grow, they will become quite heavy, especially those with large flowers like Spartacus. A summer thunderstorm or a gusty afternoon can easily tip over a top-heavy dahlia if it isn't supported.
Even a variety like Otto's Thrill benefits from a sturdy stake or cage once the blooms get large.
Staking
For individual plants, a sturdy wooden or metal stake is the most popular choice. As the plant grows, use soft garden twine to gently tie the main stem to the stake every 12 to 18 inches. You want the tie to be snug enough to provide support but loose enough that it doesn't cut into the fleshy stem as it expands.
Tomato Cages
If you prefer a lower-maintenance approach, a heavy-duty tomato cage works wonderfully for dahlias. Place the cage over the tuber at planting time. As the plant grows, it will fill out the cage, which provides support from all sides. This is a particularly good option for border dahlias or medium-height varieties.
Pinching for More Flowers
If you want a bushier plant with a lot more flowers, there is one simple trick you should use: pinching. While it might feel a little strange to cut back a healthy plant, it is one of the best things you can do for your garden.
When your dahlia plant is about 12 to 16 inches tall and has four sets of leaves, use a clean pair of garden shears or your fingers to snip off the very top of the center stem.
If you want a few more practical growing tips, see our 8 Tips for Growing Better Dahlias.
By removing this main growing tip, you signal the plant to stop putting all its energy into growing one tall stalk. Instead, the plant will begin to grow two new stems from each leaf node below the cut. This results in a much fuller, stronger plant that can produce twice as many blooms.
Key Takeaway: Pinching your dahlias early in the season leads to a sturdier plant and a significantly higher number of flowers for your vases later in the summer.
Summer Care and Maintenance
Once your dahlias are established and growing, they are relatively low-maintenance. A little bit of attention every week will keep them looking their best until the first frost.
Fertilizing
Dahlias are "heavy feeders," meaning they use a lot of nutrients to produce their foliage and flowers. If your soil is already very rich in compost, you may not need much extra fertilizer. However, most dahlias benefit from a monthly feeding. Look for a fertilizer that is lower in nitrogen and higher in phosphorus and potassium (the second and third numbers on the bag). High nitrogen can cause the plant to grow lots of green leaves but very few flowers.
Mulching
Applying a two-inch layer of mulch around the base of your plants is a great way to save time. Mulch helps keep the soil cool and moist, and it also prevents weeds from growing. Use organic materials like shredded bark, straw, or compost. Just be sure to keep the mulch a few inches away from the main stem to prevent any moisture buildup against the stalk.
Dealing with Pests
The two most common visitors to the dahlia garden are slugs and Japanese beetles. Slugs love the tender young shoots in the late spring. You can manage them by using an organic slug bait or by removing them by hand in the early morning.
Japanese beetles sometimes appear in mid-summer to snack on the blooms. The simplest and most effective way to handle them is to knock them into a bucket of soapy water. If you do this once a day for a week or two when they first appear, you can usually keep their numbers under control without needing any harsh chemicals.
Harvesting and Deadheading
The more you cut your dahlias, the more they will bloom. This is one of the most rewarding parts of growing these flowers—you can fill your house with bouquets and the plants will just keep producing.
Cutting 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, so you should wait to harvest them until the flower is nearly fully open.
Use a clean, sharp knife or shears and cut the stem long—even if you have to cut off some side buds. This encourages the plant to grow longer stems for the next round of flowers. Immediately place the cut stems into a bucket of warm water.
Deadheading
If you aren't cutting your flowers for bouquets, you should still remove the "spent" blooms—the ones that have started to fade. This process is called deadheading. When a flower stays on the plant and starts to form seeds, the plant thinks its job is done and will stop producing new buds. By snipping off the old flowers, you "trick" the plant into continuing to bloom.
Be sure to cut the old flower stem all the way back to where it meets a main branch. This keeps the plant looking tidy and encourages fresh growth.
A Note on Safety
While dahlias are a delight in the garden, it is important to know that they are considered mildly toxic to cats and dogs if ingested. If you have curious pets that like to nibble on garden plants, it is a good idea to plant your dahlias in a fenced area or in large pots that are out of their reach. If you suspect your pet has eaten part of a dahlia plant and they show signs of an upset stomach or skin irritation, contact your veterinarian for advice.
Simple Steps for Success
To summarize, growing dahlia bulbs (tubers) is a simple cycle that fits perfectly into the rhythm of the summer garden. By focusing on these core steps, you can achieve professional-looking results in your very first season.
- Wait for the warmth: Do not plant until the soil is 60°F and the threat of frost is gone.
- Pick a sunny spot: Ensure your dahlias get at least six hours of direct sunlight.
- Hold the water: Do not water your newly planted tubers until you see green sprouts.
- Support and pinch: Stake your tall varieties and pinch the tops when they hit 12 inches for a bushier plant.
- Cut and enjoy: The more flowers you harvest, the more the plant will grow.
"Dahlias are the ultimate reward for the summer gardener. They offer an unmatched variety of color and form, and with just a few simple steps, they will bloom tirelessly from mid-summer until the first frost."
FAQ
Do I need to soak dahlia tubers before planting?
No, there is no need to soak dahlia tubers before you put them in the ground. Unlike some other bulbs or corms, dahlia tubers contain plenty of stored moisture. Soaking them can actually increase the risk of rot, especially if they are left in water too long. Simply plant them directly into warm, well-draining soil.
How deep should I plant dahlia bulbs?
Dahlia tubers should be planted about 4 to 6 inches deep. When you fill the hole back in, the top of the tuber—where the eye or sprout is located—should be covered by about 1 to 2 inches of soil. Planting at this depth protects the tuber from temperature swings while making it easy for the new sprout to reach the surface.
When will my dahlias start blooming?
Most dahlias begin to bloom about 8 to 12 weeks after planting, depending on the variety and the weather. If you plant in late May, you can usually expect to see your first flowers in late July or early August. They will continue to produce new flowers consistently until the first hard frost of autumn.
Why are my dahlia tubers rotting?
The most common cause of tuber rot is too much moisture in the soil before the plant has established roots. This often happens if the tubers are watered immediately after planting or if the soil does not drain well. To prevent rot, wait until the first green shoots appear before you start regular watering, and always choose a planting site with good drainage.
Conclusion
Growing dahlias is a wonderful way to add high-impact color and drama to your outdoor space. These plants are remarkably generous, offering a continuous supply of stunning flowers for your garden and your home. By choosing the right location, waiting for the soil to warm up, and following a few simple maintenance steps like pinching and staking, you can enjoy a season filled with spectacular blooms.
At Longfield Gardens, we are dedicated to helping you find the perfect varieties for your unique garden style. From the first sprout to the final frost, we are here to support your gardening journey with high-quality tubers and practical advice, backed by our 100% guarantee. We hope this guide helps you feel confident and excited about starting your own dahlia garden this year.
Next Step: Browse our Spring Planted Bulbs by Color and choose a mix of colors and sizes to create your own backyard floral retreat.
