Table of Contents
- Introduction
- Understanding the Dahlia Tuber
- Choosing the Best Spot for In-Ground Dahlias
- Preparing Your Garden Soil
- When to Plant Dahlias in the Ground
- Step-by-Step Guide to Planting Dahlia Tubers
- Early Season Care: The No-Water Rule
- Supporting Your Plants: Staking and Pinching
- Watering and Feeding for Maximum Blooms
- Caring for Dahlias Through the Summer
- In-Ground vs. Containers: Which is Right for You?
- Lifting or Leaving: End-of-Season Care
- Conclusion
- FAQ
Introduction
There is nothing quite like the excitement of seeing the first dahlia bloom of the summer. These spectacular flowers are famous for their incredible variety of colors, shapes, and sizes.
They also come in a huge range of forms, from tiny pompons to massive dinnerplate varieties. Whether you are a beginner or an experienced gardener, adding these beauties to your yard is one of the most rewarding projects you can undertake. At Longfield Gardens, we want to help you succeed by making the process as straightforward and enjoyable as possible.
Many people wonder if they need a greenhouse or fancy containers to grow these stunning dahlias. The simple answer is that you can absolutely plant dahlias directly in the ground with fantastic results. In fact, planting in the garden soil often allows the plants to reach their full potential, producing stronger stems and more abundant flowers. This guide will walk you through everything you need to know to get your tubers into the earth successfully.
For a quick video walkthrough, see our How to Plant Dahlias.
We will cover how to choose the best spot, how to prepare your soil, and the most effective way to plant and care for your dahlias. By focusing on a few key basics like soil temperature and drainage, you can ensure your garden is filled with color from midsummer through the first frost. This article is designed for any home gardener looking to turn a sunny patch of dirt into a floral masterpiece.
Planting dahlias in the ground is a simple, effective way to create a breathtaking summer display that improves year after year.
Understanding the Dahlia Tuber
Before you start digging, it is helpful to understand what you are planting. Dahlias grow from tubers, which are thickened underground stems that store energy and moisture. While they might look like small sweet potatoes, they are actually powerhouses of growth.
A healthy dahlia tuber needs three specific parts to grow: the neck, the crown, and the eye. The neck is the narrow part that connects the tuber to the main stem. The crown is the area where the neck meets the stem, and this is where the "eye" or growth bud is located. The eye is a small bump that will eventually become the sprout.
When you receive your tubers from us, they may already show a small green or pink sprout at the eye. If they do not, don't worry. Sometimes the eyes are dormant and just need the warmth of the soil to wake up. As long as the tuber feels firm and is not shriveled or mushy, it is ready for the garden.
It is important to remember that dahlias are not frost-hardy in most of the United States. They are tropical plants by nature, originally from Mexico and Central America. This means they love warmth and will not survive a freeze. Because they are sensitive to cold, we treat them as annuals in northern climates or lift them for winter storage once the season ends.
Choosing the Best Spot for In-Ground Dahlias
Finding the right location is the first step toward a successful dahlia garden. Dahlias have specific needs when it comes to light and space, but once those needs are met, they are very low-maintenance plants.
Sun Exposure
Dahlias are sun-loving plants. For the best flower production and strong, upright stems, they need at least six to eight hours of direct sunlight every day. Sunlight provides the energy they need to create those massive, intricate blooms. If they are planted in too much shade, the plants may become "leggy," meaning they grow tall and thin as they stretch toward the light. Shaded plants also tend to produce fewer flowers.
If you live in a very hot climate, such as the southern United States, your dahlias might appreciate a little bit of afternoon shade. The intense heat of a July afternoon can be stressful for the plants, so a spot that gets morning sun and filtered light in the afternoon is often ideal in those regions.
Wind Protection
Because many dahlia varieties grow quite tall and produce heavy flower heads, they can be vulnerable to wind. A sudden summer thunderstorm with high winds can snap stems or tip over top-heavy plants. When choosing a spot in the ground, look for an area that has some protection from prevailing winds. Planting near a fence, a hedge, or the side of a building can provide a helpful windbreak. Just make sure the windbreak doesn't block the necessary sunlight.
Spacing for Success
One of the biggest advantages of planting in the ground is that you have more room to work with than you do in containers. However, it is still easy to crowd your plants. Dahlias need good air circulation to stay healthy and avoid common issues like powdery mildew, which is a white, dusty-looking fungus that can grow on leaves.
As a general rule, you should space your tubers 12 to 24 inches apart. If you are planting smaller, border dahlia varieties, 12 inches is usually enough.
For the large decorative types, give them at least 2 feet of space. This room allows the plants to bush out and ensures that air can move freely between them.
Preparing Your Garden Soil
The quality of your soil is one of the most important factors in dahlia success. While dahlias are adaptable, they perform best when the soil is rich, loose, and well-draining.
What is Drainage?
In gardening, "drainage" refers to how quickly water leaves the soil after rain or watering. Dahlias have a very low tolerance for "wet feet." If the soil stays soggy and saturated for too long, the tubers can easily rot.
You can check your soil's drainage by digging a hole about 12 inches deep and filling it with water. If the water drains away within an hour, your drainage is excellent. If it takes several hours or even a full day, your soil has a high clay content and may need some help before you plant.
Improving Soil Texture
If you have heavy clay soil, do not be discouraged. You can improve it by adding organic matter. Mixing in a generous amount of compost, well-rotted manure, or chopped leaves will help break up the clay and create "pore spaces" for air and water to move through.
If your soil is very sandy, organic matter is also the answer. In sandy soil, water often drains away too fast, taking nutrients with it. Compost helps sandy soil hold onto the moisture and food your dahlias need to thrive. We recommend spreading a 2- to 3-inch layer of compost over your planting area and tilling or digging it into the top 6 to 8 inches of soil.
Fertility and pH
Dahlias are "heavy feeders," meaning they use a lot of nutrients from the soil to grow their large stems and flowers. Most garden soils benefit from a balanced, slow-release fertilizer mixed in at planting time. Look for a fertilizer with a balanced ratio, such as 10-10-10.
Dahlias prefer a slightly acidic soil pH, ideally between 6.5 and 7.0. If you are unsure about your soil's pH, your local county extension office can provide a low-cost soil test. However, for most home gardeners, simply adding compost is enough to create a healthy environment for growth.
Key Takeaway: Success starts with the soil. Ensure your planting site has excellent drainage and is enriched with compost to give your dahlias the best possible start.
When to Plant Dahlias in the Ground
Timing is everything when it comes to planting dahlias. Because these plants are so sensitive to cold, rushing them into the ground too early can lead to disappointment.
The 60-Degree Rule
The most common mistake gardeners make is planting tubers in soil that is too cold and wet. For a dahlia tuber to wake up and start growing, the soil temperature needs to be at least 60°F. If you plant in cold, clammy soil, the tuber will sit idle and may eventually rot before it ever has a chance to sprout.
You can use a simple soil thermometer to check the temperature at a depth of 4 to 6 inches. If you don't have a thermometer, a good rule of thumb is to wait until you are ready to plant warm-weather vegetables like tomatoes or peppers.
Watching the Frost Dates
In addition to soil temperature, you must consider the risk of frost. A late spring frost can kill new green sprouts as soon as they emerge from the ground. Wait until all danger of frost has passed in your area. Depending on where you live in the United States, this could be anywhere from March in the South to late May or early June in the North.
Hardiness Zone Map can help you match your planting time to your region.
We time our shipments based on your USDA hardiness zone so that your tubers arrive at roughly the right time for planting. However, local weather varies every year. If your tubers arrive but the ground is still cold or a frost is predicted, you can keep them in their shipping material in a cool, dark place for a week or two until conditions improve. For shipping timing and zone-based estimates, see our Shipping Information.
The Benefit of Patience
It might be tempting to plant as early as possible to get a head start, but dahlias actually grow much faster when the ground is warm. A tuber planted in late May in warm soil will often catch up to and even outperform a tuber planted in early May in cold soil. The wait is worth it for a healthier, more vigorous plant.
Step-by-Step Guide to Planting Dahlia Tubers
Once your soil is prepared and the weather is warm, it is time to plant. Follow these simple steps to get your tubers in the ground correctly. For a deeper look at spacing, see our How Far Apart to Plant Dahlias.
- Dig the Hole: Dig a hole that is about 4 to 6 inches deep. For more detail on planting depth, see our How Deep Should You Plant Dahlia Bulbs?. If you are adding a handful of bone meal or a small amount of balanced fertilizer, mix it into the bottom of the hole and cover it with a thin layer of soil so it doesn't touch the tuber directly.
- Place the Tuber: Lay the tuber horizontally (flat) on its side in the bottom of the hole. If you can see the "eye" or a small sprout, point it toward the sky. If you can't tell where the eye is, don't worry—the sprout will find its way to the surface regardless of which way the tuber is facing.
- Space Your Plants: Ensure that your holes are spaced 12 to 24 inches apart, depending on the variety you are growing.
- Install Stakes Now: If you are growing tall varieties (those that reach 3 feet or more), it is best to drive your support stake into the ground now, before you cover the tuber. This prevents you from accidentally piercing the tuber with a stake later in the season.
- Fill the Hole: Gently fill the hole back in with soil. Do not pack the soil down too hard; a light touch allows for better air and water movement.
What to do next:
- Mark each spot with a plant label so you know which variety is where.
- Avoid the urge to water the area immediately unless your soil is bone-dry.
- Check the area every few days for the first signs of green sprouts.
Early Season Care: The No-Water Rule
This is the part of dahlia care that feels the most counter-intuitive to many gardeners. Most plants need a good drink immediately after being put in the ground, but dahlias are different.
Avoiding Tuber Rot
Unless your garden soil is extremely dry (like dust), you should not water your dahlia tubers until you see the first green shoots poking through the soil. The tuber contains all the moisture and energy it needs to start its first roots and sends up its first sprout. Adding extra water to the soil before the plant has roots to "drink" it up only creates a soggy environment that encourages rot.
When to Start Watering
Once the sprouts are a few inches tall and have their first set of leaves, you can begin a regular watering schedule. At this point, the plant has established a root system and is ready to start growing rapidly.
Dealing with Pests
Young dahlia sprouts are a favorite snack for slugs and snails. These pests can eat a new sprout down to the ground overnight. It is a good idea to apply an organic slug bait around the planting area as soon as you put the tubers in the ground. This protects the tender new growth as it emerges.
Supporting Your Plants: Staking and Pinching
As your dahlias grow, they will need a little bit of "tough love" and some physical support to look their best.
The Importance of Pinching
When your dahlia plant is about 12 to 18 inches tall and has three or four sets of leaves, it is time to "pinch" it. This sounds scary, but it is one of the best things you can do for your plant. Using a clean pair of garden snips or your fingers, remove the very top of the center stem, just above the top set of leaves.
Pinching stops the plant from putting all its energy into one single, tall stalk. Instead, it signals the plant to grow multiple side branches. This results in a much bushier plant with many more flowers. It also creates a sturdier plant that is less likely to flop over.
Staking Tall Varieties
Dahlias are famous for their heavy blooms, which can sometimes weigh down the stems, especially after a rain. If you installed your stakes at planting time, you can now begin to loosely tie the stems to the stake as they grow. Use soft garden twine or strips of old t-shirts to avoid cutting into the green stems.
If you are growing a large row of dahlias, you might prefer the "corral" method. This involves placing sturdy posts at the corners of your dahlia bed and running twine around the perimeter and through the plants to create a supportive grid. For a step-by-step refresher, see our How to Pinch and Stake Dahlias.
Watering and Feeding for Maximum Blooms
Once your dahlias are established and growing fast, they will need consistent care to keep those flowers coming.
Deep Watering
Dahlias prefer deep, infrequent watering over light daily sprinkles. You want to soak the soil so the water reaches the roots, which are several inches deep. A good rule of thumb is to give them about an inch of water per week, either from rain or your hose.
If you live in a hot, dry climate, you may need to water more often. To keep the foliage healthy, try to water at the base of the plant rather than over the top of the leaves. This helps prevent diseases like powdery mildew. Using a soaker hose or drip irrigation is an excellent way to keep your in-ground dahlias hydrated.
Fertilizer Schedule
Since we already added compost and a balanced fertilizer at planting time, your dahlias have a good head start. However, to keep them blooming until frost, you can provide a supplemental feeding every 3 to 4 weeks during the summer.
Avoid fertilizers that are very high in nitrogen. Nitrogen encourages lots of green leaves but can result in fewer flowers and weak tubers. Look for a fertilizer that is higher in phosphorus and potassium (the middle and last numbers on the bag), which support bloom production and tuber health.
Caring for Dahlias Through the Summer
The middle of summer is when the dahlia show really begins. To keep the display going, there are a few simple maintenance tasks to keep in mind.
Deadheading
"Deadheading" is the process of removing faded flowers. When a dahlia bloom starts to wilt and lose its petals, snip the stem back to the next set of leaves. This prevents the plant from spending energy on producing seeds and instead encourages it to produce more flower buds. The more you cut your dahlias—either for bouquets or by deadheading—the more they will bloom.
Mulching
Applying a layer of mulch around the base of your plants is very helpful in midsummer. A 2-inch layer of straw, shredded bark, or compost helps the soil stay cool and retain moisture. It also helps suppress weeds that might compete with your dahlias for nutrients. Just be sure to keep the mulch a few inches away from the main stem of the plant to maintain good air circulation.
In-Ground vs. Containers: Which is Right for You?
While this guide focuses on planting in the ground, you might be wondering if you should try containers instead. Both methods have their perks.
Planting in the ground is usually easier because the soil stays moist longer and provides a more stable temperature for the roots. In-ground plants also have more room for their roots to spread out, which often leads to larger plants and more flowers. It is the ideal choice if you have a sunny yard with decent soil.
Planting in containers is a great option if you have limited space, poor garden soil, or if you want to be able to move your plants around. However, container dahlias need much more frequent watering—often once or twice a day in the heat of summer. They also need more frequent fertilizing because nutrients leach out of the pots every time you water.
For most people, the ground is the simplest path to a high-yield garden. We work with trusted growers in Holland and around the world to ensure the tubers we provide are of the highest quality, whether you choose to plant them in a garden bed or a large pot.
Lifting or Leaving: End-of-Season Care
What happens to your dahlias when the summer ends? This depends largely on where you live and your personal preference.
The First Frost
Dahlias will continue to bloom beautifully until the first hard frost. When the temperature drops below freezing, the foliage will turn black and die back. This is the plant's natural signal that it is time to go dormant.
For Gardeners in Warm Climates
If you live in USDA zones 8 through 11, you may be able to leave your dahlia tubers in the ground year-round. In these areas, the ground does not freeze deep enough to damage the tubers. You can simply cut the dead stems back to about 2 to 3 inches above the soil and cover the area with a thick layer of mulch to protect them from winter rains.
For Gardeners in Cold Climates
If you live in zone 7 or colder, the ground will freeze, which will kill the tubers if they are left unprotected. Most gardeners in these regions "lift" their tubers for the winter.
- Cut Back: After the first frost turns the leaves black, wait a few days for the energy to move back into the tubers, then cut the stems down to about 4 inches.
- Dig Gently: Use a garden fork to carefully lift the tubers out of the ground. Be careful not to puncture them.
- Clean and Dry: Shake off the excess soil and let the tubers dry in a protected, frost-free area for a day or two.
- Store: Place the tubers in a box filled with slightly damp peat moss, vermiculite, or wood shavings. Store the box in a cool, dark, and dry place (around 40-50°F) until next spring.
Key Takeaway: Dahlias offer a rewarding cycle. Whether you leave them in the ground or store them away, they are a long-term investment in your garden's beauty.
Conclusion
Planting dahlias in the ground is one of the most fulfilling ways to spend time in the garden. From the quiet anticipation of the first sprout to the overwhelming beauty of a late-summer bouquet, these plants bring a unique joy to any outdoor space. By following the basics—waiting for warm soil, ensuring good drainage, and providing plenty of sun—you can achieve professional-looking results right in your own backyard.
Gardening is a journey of observation and small successes. If you get the timing and the planting depth right, the rest of the process is simply about enjoying the growth. Our team at Longfield Gardens is always here to provide the support and quality plants you need to make your garden dreams a reality.
- Wait for 60°F soil before planting.
- Choose a sunny spot with excellent drainage.
- Don't water until you see green sprouts.
- Pinch the plants at 12 inches for a bushier habit.
"Dahlias are the workhorses of the summer garden, providing endless color and beauty with just a little bit of care and the right start in the ground."
We encourage you to pick out your favorite varieties and get ready for a spectacular growing season. With a little patience and some sun, your garden will soon be the talk of the neighborhood.
FAQ
Can I plant dahlia tubers in the ground if they have already sprouted?
Yes, you can absolutely plant sprouted tubers. If the sprouts are very long (more than 3 inches), you can gently snip them back to about 1 inch long before planting. This encourages the plant to grow a stronger, sturdier main stem as it pushes through the soil.
How deep should I plant dahlias in the ground?
The ideal depth for planting dahlia tubers is 4 to 6 inches. Dig a hole to this depth, lay the tuber horizontally at the bottom, and cover it completely with soil. Planting at this depth protects the tuber from temperature swings and provides a stable base for the growing plant.
Do dahlias need a lot of water right after planting?
No, you should actually avoid watering dahlias immediately after planting in the ground unless the soil is exceptionally dry. The tuber holds enough moisture to start growing. Wait until you see green shoots appearing above the soil before you begin a regular watering routine to prevent the tubers from rotting.
What is the best soil for planting dahlias in the ground?
Dahlias thrive in loose, fertile soil that drains well. They do not like to sit in soggy earth. You can improve almost any garden soil by mixing in a few inches of compost or well-rotted manure, which helps with both drainage in clay soil and moisture retention in sandy soil.