Introduction
There is nothing quite like the excitement of seeing your first dinnerplate dahlia unfurl its massive, intricate petals in the middle of summer. These garden stars offer an incredible variety of colors, shapes, and sizes, making them a favorite for both backyard enthusiasts and professional floral designers. Whether you are looking to create a vibrant cutting garden or simply want to add a splash of late-season color to your landscape, learning the right way to start your journey is the first step toward a season of abundance.
At Longfield Gardens, we believe that every gardener can find success with these stunning dahlias by following a few straightforward steps. Growing dahlias is an incredibly rewarding experience that allows you to enjoy fresh bouquets from midsummer all the way until the first frost of autumn. This guide is designed for home gardeners who want to understand the best practices for site selection, soil preparation, and the specific physical steps required to get tubers off to a great start.
We will walk through everything you need to know about the planting process, from identifying a healthy tuber to providing the right support as the plants grow tall. By focusing on a few simple rules regarding timing, depth, and water, you can ensure your garden is filled with beautiful blooms for months to come.
Choosing the Best Location
The secret to a flourishing dahlia garden begins long before the first shovel hits the dirt. These plants are sun-worshippers, and their performance is directly tied to the amount of light they receive. For the most robust stems and the highest number of flowers, choose a spot that receives at least six to eight hours of direct sunlight each day. While they can grow in partial shade, you will find that the plants tend to become "leggy" as they stretch for the light, often resulting in fewer blooms and weaker stems.
In addition to sunlight, consider the movement of air and the protection provided by nearby structures. While dahlias love the sun, they also appreciate a bit of shelter from strong, buffeting winds, which can snap heavy, bloom-laden stalks. Planting near a fence, a sturdy hedge, or the side of a building can provide a helpful windbreak. Just ensure that these structures do not cast too much shade during the peak hours of the day.
Soil drainage is the other non-negotiable factor for success. Dahlias are grown from tubers, which are fleshy underground storage organs. If these tubers sit in heavy, waterlogged soil, they may struggle to thrive. A simple way to check your drainage is to observe your garden after a heavy rain. If puddles remain for several hours, you may want to consider amending the area with organic matter or choosing a slightly higher spot in the yard.
Key Takeaway for Site Selection:
- Prioritize 6–8 hours of direct, unfiltered sunlight.
- Select a location with excellent drainage to keep tubers healthy.
- Look for a spot that offers some protection from high winds.
- Ensure the area has enough room for the plants to reach their full width, usually 18 to 24 inches.
Understanding Dahlia Tubers
When you first receive your dahlia tubers, they might remind you of a clump of slender potatoes. Each tuber is a powerhouse of energy, containing all the nutrients the plant needs to send up its first set of leaves. To be successful, a tuber must have three specific parts: the body (the fleshy part), the neck (the thin part connecting the body to the stem), and the "eye."
The eye is the most critical part to identify. It is a small, sometimes slightly raised bump located on the "crown" or the shoulder of the tuber, right where the neck meets the old stem. This is where the new growth will emerge. Sometimes the eyes are very easy to see, looking like tiny pink or green sprouts. Other times, they are dormant and harder to spot. If you are having trouble finding the eye, don't worry; as the weather warms, the eye will naturally become more prominent.
It is also important to handle tubers with care. The neck is the most fragile part of the plant. If the neck is snapped or severely creased, the energy in the tuber cannot reach the eye to support growth. When we ship tubers from our facility, we take great care to ensure they arrive in prime condition, but it is always a good idea to handle them gently as you move them from their packaging to the garden bed.
When to Start Planting
In the world of gardening, timing is often more important than any "secret" tip or trick. Dahlias are native to the high plains of Mexico, which means they love warmth and are very sensitive to the cold. Planting too early into cold, wet soil is one of the few ways to slow down your progress. The best rule of thumb is to wait until all danger of spring frost has passed and the soil has warmed up to about 60°F.
A great way to gauge the right time is to look at your vegetable garden. If it is time to plant tomatoes and peppers outside, it is usually safe to plant your dahlias. In most parts of the United States, this window opens up between mid-April and early June, depending on your local climate and USDA hardiness zone.
If you live in a region with a very short growing season, you can give your plants a head start by "waking them up" indoors. About four weeks before your last frost date, you can place tubers in pots filled with slightly damp potting soil. Keep them in a warm, bright spot, and by the time the garden soil is ready, you will have established plants to transplant. For most gardeners, however, planting directly into the ground is the simplest and most effective method.
Preparing the Soil
While dahlias are robust growers, they appreciate a little bit of preparation to help them reach their full potential. Before you dig your first hole, take some time to clear the area of weeds and large rocks. Loosening the soil to a depth of about 12 inches will make it much easier for the new root system to expand quickly once the plant starts growing.
Adding organic matter is one of the best things you can do for your soil health. Mixing in a two-inch layer of high-quality compost or well-rotted manure provides a gentle, slow-release source of nutrients. It also improves the soil's texture, helping sandy soil hold onto moisture and helping clay soil drain more effectively.
If you want to provide an extra boost, you can incorporate a small amount of bone meal or a balanced, low-nitrogen fertilizer into the planting area. However, it is important to be mindful of your local environment and follow the instructions on the product label. High-nitrogen fertilizers should be used sparingly early in the season, as too much nitrogen can lead to a lot of green leaves but very few flowers.
How to Plant Dahlias in Ground: A Step-by-Step Guide
Once your soil is prepared and the weather is warm, it is time for the physical act of planting. Following these steps ensures that the tubers are at the right depth and have the space they need to flourish.
Step 1: Digging the Hole
Dig a hole that is approximately 4 to 6 inches deep. For a fuller explanation of planting depth, see How Deep Should I Plant Dahlia Tubers?.
Step 2: Placing the Tuber
Unlike many bulbs that are planted vertically (pointy side up), dahlia tubers should be laid horizontally on their side at the bottom of the hole. Positioning them this way allows the new sprouts to grow upward toward the surface while the root system develops from the same point. If you can clearly see the eye or a sprout, point that end slightly upward, but the tuber itself should remain horizontal.
Step 3: Spacing Your Plants
Dahlias need plenty of elbow room. A mature plant can reach 3 to 5 feet in height and 2 feet in width. To ensure good air circulation—which helps keep the foliage healthy—space your tubers 12 to 24 inches apart. Smaller "border" varieties can be spaced closer together, while giant dinnerplate dahlias benefit from the full 24-inch gap.
Step 4: Filling the Hole
Cover the tuber with soil, gently firming it down with your hands to remove any large air pockets. You do not need to pack the soil down hard; just a light touch is enough to ensure the tuber has good contact with the earth.
What to Do Next:
- Clear the area of weeds and debris.
- Dig holes 4–6 inches deep and 18–24 inches apart.
- Lay tubers horizontally with the eye facing up.
- Cover with soil and level the surface.
The Golden Rule of Early Season Watering
One of the most common questions we receive is how much to water dahlias immediately after planting. This is where dahlias differ from many other garden plants. For tubers planted directly in the ground, the "Golden Rule" is to wait until you see green growth before you start a regular watering schedule.
Unless your soil is extremely dry or you live in a very hot, arid climate, the tuber contains enough moisture to get the plant started. Watering too heavily before the sprout emerges can lead to the tuber becoming overly saturated. Once you see those first green leaves poking through the soil, you can begin to water deeply once or twice a week, depending on your weather.
When you do start watering, aim for the base of the plant rather than the leaves. Keeping the foliage dry helps maintain the health of the plant throughout the humid summer months. Using a soaker hose or drip irrigation is an excellent way to provide deep, consistent moisture exactly where the roots need it most.
Staking and Providing Support
Most dahlias, especially the tall, large-flowered varieties, require some form of support to prevent them from tipping over during a summer storm. For more detailed support tips, see How to Support Your Dahlias.
For individual plants, a sturdy wooden or metal stake (about 5 to 6 feet tall) driven 12 inches into the ground is ideal. Place the stake just a few inches away from where you buried the tuber. As the plant grows, you can use soft garden twine to loosely tie the main stem to the stake every 12 to 18 inches.
If you are planting a long row of dahlias, you might prefer the "corral" method. This involves placing sturdy posts at the corners and every few feet along the row, then running twine around the perimeter of the plants to keep them contained. Some gardeners also find that heavy-duty tomato cages work well for medium-sized varieties, providing a simple and effective support system without the need for constant tying.
Enhancing Growth Through Pinching
If you want a dahlia plant that is full, bushy, and covered in flowers, there is one simple technique you should use: pinching. For a closer look at the technique, read 8 Tips for Growing Better Dahlias.
When your dahlia plant is about 12 to 16 inches tall and has at least four sets of leaves, use a clean pair of garden snips to cut off the very top of the center stem. You only need to remove an inch or two of growth, just above the highest set of leaves.
This temporary pause in vertical growth encourages the plant to send out two new stems from the leaf joints below the cut. Instead of one tall, lanky stalk, you will end up with a sturdy, multi-branched plant that produces many more flowers over the course of the season. It might feel strange to cut off the top of a healthy plant, but the results in August and September are well worth the effort.
Caring for Your Plants Throughout the Summer
As the summer progresses, your dahlias will begin to grow rapidly. During this time, consistent care will keep them looking their best.
- Mulching: Once the plants are about a foot tall and the soil is thoroughly warm, you can apply a layer of mulch around the base. Straw, shredded leaves, or wood chips help to retain moisture and keep the roots cool during the heat of July and August.
- Feeding: Dahlias are heavy feeders. They benefit from a monthly application of a balanced fertilizer. Look for something with a lower nitrogen number and higher phosphorus and potassium numbers (the second and third numbers on the bag) to encourage bloom production rather than just leaf growth.
- Deadheading: To keep the flowers coming, you must remove the old, faded blooms. This process, called deadheading, prevents the plant from putting energy into producing seeds and encourages it to keep making new buds. When cutting off an old flower, follow the stem back to where it meets a main branch and make your cut there.
- Pest Management: Keep an eye out for slugs and snails, especially when the plants are small and the weather is damp. These visitors enjoy the tender new growth. Using organic slug bait or simply hand-picking them in the early morning can protect your young plants.
Harvesting Flowers for Bouquets
One of the greatest joys of learning how to plant dahlias in ground is the ability to bring the beauty of the garden indoors. Dahlias make excellent cut flowers, but they have a few specific needs when it comes to harvesting.
Unlike roses or lilies, dahlias will not continue to open much once they are cut. This means you should wait until the flower is almost fully open before you harvest it. Check the back of the flower head; the petals should be firm and fresh. If the petals on the back are starting to look papery or wilted, the flower is past its prime.
The best time to cut your flowers is in the cool of the early morning or late evening when the plant is fully hydrated. Use sharp, clean shears and immediately place the stems into a bucket of clean, room-temperature water. To help your blooms last as long as possible in the vase, change the water every day or two and keep the bouquet out of direct sunlight and away from ripening fruit.
Protecting Your Investment
Because dahlias are tropical in origin, they will not survive the winter in the ground in most parts of the United States (typically zones 7 and colder). After the first hard frost in the fall kills the foliage, you have a choice to make. You can treat them as annuals and start fresh with new varieties from us next spring, or you can dig up the tubers and store them in a cool, frost-free place for the winter.
If you choose to save them, wait until the foliage has turned black from the frost. Cut the stems down to about 4 inches, gently lift the tubers with a garden fork, and wash off the excess soil. Once they are dry, you can store them in a box with slightly damp peat moss or vermiculite in a basement or crawl space where temperatures stay between 40°F and 50°F.
If you are planning an order, our shipping information page explains timing and delivery.
Conclusion
Planting dahlias is a wonderful way to bring vibrant color and a sense of accomplishment to your gardening season. By choosing a sunny spot, waiting for warm soil, and providing a little bit of support, you can transform a handful of tubers into a spectacular display of blooms. Whether you are growing a single plant in a sunny corner or an entire row for cutting, the process is straightforward and deeply rewarding.
At Longfield Gardens, we take pride in helping you find the perfect varieties to suit your style, from the delicate beauty of Cafe au Lait.
And the bold presence of Thomas Edison. Remember that gardening is an ongoing journey of discovery, and every season offers a new chance to see something beautiful grow.
Final Checklist for Success:
- Wait for soil to reach 60°F before planting.
- Plant tubers 4–6 inches deep and lay them horizontally.
- Don't water until you see green shoots.
- Pinch the center stem at 12 inches for a bushier plant.
- Enjoy the incredible transformation from tuber to bloom!
We invite you to explore our Dahlia Collections and start planning your most colorful summer yet. With a little bit of patience and these simple steps, your garden will soon be the talk of the neighborhood.
FAQ
How deep should I plant dahlia tubers in the ground?
Dahlia tubers should be planted approximately 4 to 6 inches deep in well-draining soil. This depth provides enough protection for the tuber while still allowing the new sprouts to reach the surface easily. If your soil is particularly heavy or clay-like, sticking closer to the 4-inch mark can help the sprouts emerge more quickly.
Can I plant dahlias before the last frost?
It is best to wait until all danger of frost has passed and the soil has warmed to about 60°F before planting dahlias in the ground. Because they are tropical plants, the tubers can rot in cold, soggy soil, and the young sprouts are very sensitive to freezing temperatures. If you want an earlier start, consider starting them indoors in pots a few weeks before the outdoor planting date.
Do I need to water my dahlias right after I plant them?
Unless your soil is extremely dry, you should avoid watering your dahlias until you see the first green sprouts appear above the ground. The tubers contain enough stored moisture to begin their growth, and excess water in the early stages can cause them to rot. Once the plant is established with several sets of leaves, you can begin a regular watering schedule of about one inch of water per week.
How far apart should I space my dahlias?
Proper spacing is important for air circulation and to give each plant enough room to grow to its full size. For most standard and large-flowered dahlias, space them 18 to 24 inches apart. Smaller, low-growing border varieties can be planted slightly closer together, around 12 inches apart, to create a fuller look in the front of your garden beds.
