Table of Contents
- Introduction
- Choosing the Ideal Location
- When to Start Planting
- Preparing the Ground
- How to Plant Dahlia Bulbs in Ground Step-by-Step
- The "Wait to Water" Rule
- Supporting Your Dahlias
- Caring for Your Plants Through the Season
- Variety Spotlights: Choosing Your Favorites
- Troubleshooting Common Growth Issues
- Realistic Expectations for Your Garden
- Conclusion
- FAQ
Introduction
There is a unique kind of magic in watching the first dahlia of the season unfurl its petals. Whether it is a massive dinnerplate dahlia the size of a dinner plate or a perfectly symmetrical pompon, these flowers bring a sense of joy and accomplishment to any garden. At Longfield Gardens, we believe that everyone can grow these spectacular blooms with just a few simple steps.
This guide is designed for home gardeners who want to move beyond basic gardening and enjoy the rewarding experience of growing dahlias directly in their landscape. At Longfield Gardens, we believe that everyone can grow these spectacular blooms with just a few simple steps, and our dahlia collections make it easy to choose the right mix. We will cover everything from choosing the best spot and preparing your soil to the specific steps for putting your tubers in the ground. By focusing on the essential needs of the plant, you can ensure a season filled with vibrant color and endless bouquets. Successful dahlia gardening begins with understanding how to give these tubers the right start in their permanent summer home.
Choosing the Ideal Location
The first step in learning how to plant dahlia bulbs in ground is finding the right place for them to live. Dahlias are sun-loving plants that thrive when they have plenty of energy to produce those famous flowers. If you want strong stems and an abundance of buds, you must start with the right environment.
Sun Exposure Requirements
Dahlias need a minimum of six to eight hours of direct sunlight every day. In most parts of the United States, more sun generally leads to more flowers. Full sun helps the plants grow sturdy stalks that can support the weight of heavy blooms. If the plants are grown in too much shade, they often become "leggy," meaning they grow tall and thin as they stretch toward the light.
If you live in a region with extremely hot summer temperatures, such as the Deep South or the Southwest, your plants might appreciate a little bit of afternoon shade. This break from the intense heat can prevent the foliage from wilting and keep the colors of the petals from fading prematurely. However, for the majority of gardeners, the sunniest spot in the yard is the best choice.
Soil Drainage and Quality
The term "drainage" refers to how quickly water moves through your soil. This is perhaps the most important factor for dahlia health, and What do dahlias need to grow? explains why. Because dahlia tubers are fleshy and store a lot of moisture, they can rot if they sit in waterlogged soil for too long.
You can test your drainage by digging a small hole and filling it with water. If the water disappears within an hour, your drainage is excellent. If it sits for several hours or a day, you will need to improve the soil before planting. We maintain a trial garden where we test different soil conditions, and we have found that adding organic matter is the most effective way to improve any soil type.
Key Takeaway: For the best results, choose a location with at least six hours of direct sunlight and soil that does not hold standing water after a rainstorm.
When to Start Planting
Timing is more important than almost any other "trick" in gardening. Dahlias are tropical plants at heart, originating from the high plains of Mexico. They have no natural defense against freezing temperatures. If you put them in the ground too early, the cold, damp soil can cause the tubers to decay before they even have a chance to grow.
Checking Soil Temperature
The safest rule is to wait until all danger of frost has passed in your area. However, the air temperature is only half of the story. You should also wait until the soil temperature has reached at least 60°F.
You can use a simple soil thermometer to check this, or you can use a common gardening milestone: if it is warm enough to plant tomatoes and peppers outside without protection, it is usually warm enough for dahlias. In most regions, this happens in late May or early June. Planting in warm soil encourages the tubers to wake up quickly and start pushing out roots and sprouts.
Hardiness Zones and Shipping
We coordinate our shipping schedule based on your USDA hardiness zone, and our Shipping Information page explains the timing. This ensures your tubers arrive about two weeks before the ideal planting time for your specific climate. While it might be tempting to plant the moment your package arrives, waiting for the right conditions is the best way to ensure a healthy start. If your tubers arrive and the ground is still too cold, keep them in a cool, dark, and dry place until the weather settles.
Preparing the Ground
Before you dig your first hole, you should take a little time to prepare the soil. Dahlias are heavy feeders because they grow so much biomass in a single season. A single tuber can turn into a four-foot-tall bush in just a few months.
Amending the Soil
You do not need a complicated chemistry set to prepare your garden. Most soil can be improved by adding a two-to-three-inch layer of high-quality compost or well-rotted manure to the surface. Use a garden fork or spade to mix this into the top six to eight inches of soil.
Compost helps in two ways. In sandy soil, it acts like a sponge to hold onto moisture and nutrients. In heavy clay soil, it helps break up the tight particles so that water can move through more easily. If your soil is very heavy clay, you can also mix in some coarse sand or fine gravel to further improve the texture.
Using Simple Fertilizers
Dahlias appreciate a balanced start. You can mix a small amount of an all-purpose, low-nitrogen fertilizer into the soil at planting time. Look for a fertilizer where the three numbers on the bag (NPK) are relatively equal, or where the middle number (phosphorus) is slightly higher. Avoid high-nitrogen fertilizers early in the season, as these can encourage too much green leaf growth at the expense of flowers.
What to Do Next:
- Identify your local "last frost date."
- Check your soil for drainage and standing water.
- Source high-quality compost to mix into your planting area.
- Clear the area of weeds and large rocks.
How to Plant Dahlia Bulbs in Ground Step-by-Step
Once the soil is warm and the site is prepared, it is time to plant. For a refresher, see How to Plant Dahlias. Although many people call them "bulbs," dahlias grow from tubers, which look a bit like a bunch of carrots or sweet potatoes.
Digging the Hole
Dig a hole that is about four to six inches deep. If you are planting a large variety, like the stunning Kelvin Floodlight or the deep purple 'Thomas Edison', make sure the hole is wide enough to accommodate the entire tuber clump without crowding it.
Spacing Your Plants
Proper spacing is the "quiet winner" of dahlia gardening. It is tempting to crowd plants together for a full look, but dahlias need room for air to circulate around their leaves. Good airflow prevents many common fungal issues.
- Large varieties (Dinnerplate and Decorative): Space these 18 to 24 inches apart.
- Medium varieties (Border and Cactus): Space these 12 to 18 inches apart.
- Small varieties (Mignon and Gallery): Space these 10 to 12 inches apart.
Positioning the Tuber
Lay the tuber on its side in the hole, horizontally. Look for the "eye," which is a small bump or sprout near the neck where the tuber was attached to the old stem. This is where the new growth will come from. Try to position the eye so it is facing upward, but do not worry if you cannot find it. Dahlias are resilient and the sprouts will find their way to the surface regardless of which way the tuber is facing.
Covering with Soil
Fill the hole back up with soil and firm it down gently with your hands to remove any large air pockets. Do not pack the soil too tightly; you want the new sprouts to be able to push through easily.
"The secret to a great dahlia season is getting the depth and spacing right from day one. A horizontal placement at four to six inches deep gives the plant the stability it needs to grow tall."
The "Wait to Water" Rule
This is the part of dahlia planting that feels the most counter-intuitive to many gardeners. Most of the time, we are taught to water plants immediately after putting them in the ground. With dahlias, you should actually wait.
Why You Should Wait
Until the dahlia tuber has sent up green shoots and started to grow leaves, it does not have a way to process large amounts of water. If the soil is kept too wet during this dormant stage, the tuber is at a high risk of rotting.
There is usually enough natural moisture in the soil in the spring to sustain the tuber until it sprouts. You should only water at planting time if your soil is bone-dry, like dust. Otherwise, wait until you see the first green sprouts poking through the soil before you begin a regular watering schedule.
When to Start Regular Watering
Once the plants are about six inches tall, you can start watering deeply. Dahlias prefer a deep watering two or three times a week rather than a light sprinkling every day. This encourages the roots to grow deep into the ground, which makes the plant more drought-tolerant and stable. If you have sandy soil, you may need to water more frequently, as sandy soil loses moisture fast.
Supporting Your Dahlias
Because dahlias can grow quite large and produce heavy flowers, many varieties need a little bit of physical support. This is especially true for the tall decorative and dinnerplate types that we offer at Longfield Gardens, and How to Pinch and Stake Dahlias covers the basics.
Staking Early
The best time to put a stake in the ground is at the same time you plant the tuber. If you wait until the plant is large, you might accidentally drive the stake through the tuber underground.
- Use a sturdy wooden stake or a piece of rebar that is at least four to five feet tall.
- Drive the stake about a foot into the ground, a few inches away from the tuber.
- As the plant grows, use soft twine or garden ties to loosely secure the main stem to the stake.
Pinching for More Blooms
If you want a bushier plant with more flowers, you should "pinch" your dahlias. This sounds like a lot of work, but it is a very simple step. When the plant is about 12 to 16 inches tall and has four sets of leaves, snip off the very top of the center stem.
This tells the plant to stop growing only upward and start growing outward. It will produce more side branches, which means you will get more flowers throughout the summer. If you prefer one or two massive "show" flowers, you can skip this step, but most home gardeners find that pinching leads to a much better display.
Caring for Your Plants Through the Season
After the planting is done and the supports are in place, your main job is to keep the plants happy as they prepare to bloom.
Mulching
A thin layer of organic mulch, such as shredded bark or clean straw, can be very helpful once the plants are established. Mulch keeps the roots cool during the heat of July and August and helps the soil retain moisture. Keep the mulch a few inches away from the base of the stem to prevent any moisture-related rot on the main stalk.
Fertilizing for Flowers
Once your dahlias start blooming, they will benefit from a regular feeding every three to four weeks. Use a water-soluble fertilizer that is high in phosphorus (the middle number) to encourage continuous bud production. Avoid high-nitrogen fertilizers at this stage, as they can cause the plant to stop blooming and focus only on growing more leaves.
Monitoring for Pests
Dahlias are generally easy to grow, but they can occasionally attract slugs or snails, especially when the plants are young and tender. Slugs love the soft new growth that emerges from the ground. You can protect your young plants by using a pet-safe slug bait or simply by keeping the area around the base of the plants clear of debris where slugs like to hide.
Variety Spotlights: Choosing Your Favorites
When you are planning how to plant dahlia bulbs in ground, the variety you choose will determine the "personality" of your garden. We offer several categories of dahlias that each bring something different to the landscape.
Dinnerplate Dahlias
These are the giants of the dahlia world. Varieties like Fleurel (white) or 'Emery Paul' (bright pink) produce flowers that can reach 10 to 12 inches across. These require the most staking and the widest spacing, but the visual impact is unmatched. They are the stars of any late-summer garden.
Decorative Dahlias
These are the workhorses of the cutting garden. They have a classic flower shape with broad petals. Thomas Edison is a famous variety in this category, known for its deep, velvet-purple blooms and reliable performance. These typically grow to about three or four feet tall and produce dozens of flowers over the season.
Border Dahlias
If you have a smaller space or want to plant at the front of a flower bed, border dahlias are an excellent choice. They stay much shorter—usually under two feet—and do not require staking. They are perfect for adding a pop of color along a walkway or in the front of a perennial border.
What to Do Next:
- Order your favorite varieties early, as popular colors sell out.
- Purchase your stakes and garden twine before planting day.
- Set a reminder on your calendar to "pinch" the plants once they reach 12 inches.
- Check your garden tools to ensure your spade and clippers are clean.
Troubleshooting Common Growth Issues
Even with the best preparation, gardening involves some observation and adjustment. If your dahlias are not performing as expected, the cause is usually one of three simple factors.
Failure to Sprout
If it has been three or four weeks and you see no green shoots, check the soil temperature. If the soil is too cold, the tuber may just be sleeping. If the soil has been very wet, gently dig up one tuber to check for firmness. A healthy tuber should feel like a firm potato. If it is soft or mushy, it has likely succumbed to rot, usually caused by overwatering or poor drainage.
Yellowing Leaves
Yellow leaves at the bottom of the plant can be a sign of a few different things. Most commonly, it is a sign that the soil is staying too wet. Ensure you are letting the top inch of soil dry out between waterings. Yellowing can also indicate a lack of nutrients, which a balanced liquid fertilizer can usually fix within a week or two.
Few or No Blooms
If your plant is huge and green but has no flowers, you may be using a fertilizer with too much nitrogen. Nitrogen promotes leaf growth. Switch to a "bloom boost" style fertilizer with a higher middle number. Also, ensure your plants are getting enough sunlight; dahlias in the shade will often grow plenty of leaves but very few buds.
Realistic Expectations for Your Garden
Gardening is a partnership with nature. While we provide the highest quality tubers, your local weather, soil, and microclimate will all influence exactly when your dahlias bloom and how tall they grow. For a better sense of the timeline, see How Long Do Dahlias Take to Grow?.
In a typical year, most dahlias will begin to bloom about eight to ten weeks after planting. This means if you plant in late May, you can expect your first flowers in late July or early August. They will then continue to bloom with increasing intensity until the first hard frost of autumn. The colors often become even more vibrant as the nights get cooler in September.
Remember that every growing season is different. A very rainy spring might delay your planting, or a particularly hot summer might slow down bloom production for a few weeks in August. This is a natural part of the gardening cycle.
Conclusion
Planting dahlias in the ground is one of the most rewarding projects a gardener can undertake. These plants offer a spectacular return on investment, providing armloads of flowers for your home and a stunning display for your neighbors to enjoy. By focusing on the basics—sun, drainage, warm soil, and proper spacing—you are setting yourself up for a successful and enjoyable season.
- Wait for the soil to reach 60°F before planting.
- Plant tubers 4 to 6 inches deep and space them according to their variety size.
- Hold off on watering until you see green sprouts.
- Pinch the plants at 12 inches for a bushier, more floriferous habit.
We are here to support you throughout your gardening journey. Longfield Gardens is dedicated to providing you with the best plants and the most practical advice to help your yard look its best, backed by our 100% Quality Guarantee. If you follow these simple steps, you will be well on your way to a garden full of breathtaking dahlias.
Final Thought: Dahlias are not just flowers; they are a summer-long celebration of color. Start with healthy tubers and warm soil, and the rest will naturally follow.
FAQ
Can I plant dahlia tubers if they have already started to sprout in the bag?
Yes, you can absolutely plant tubers that have already begun to sprout. These "pre-sprouted" tubers often get a head start in the garden. Just be very careful not to snap off the delicate sprouts when you are placing them in the hole. If a sprout does break, do not worry—the tuber will usually send up a new one from a different eye.
Do I need to dig up my dahlia tubers every winter?
This depends on your USDA hardiness zone; the Hardiness Zone Map is the best place to check if you're not sure. Dahlias are only hardy in zones 8 through 11. If you live in zone 7 or colder, the tubers will likely freeze and die if left in the ground over winter. Most gardeners in northern climates dig them up after the first frost, store them in a cool, dry place, and replant them the following spring.
How deep should I plant dahlia tubers in the ground?
The ideal depth for most dahlia tubers is four to six inches. Planting them at this depth provides enough soil coverage to keep the tuber cool and protected, but it is shallow enough for the new sprouts to reach the surface quickly. If you plant them too shallowly, the plants may be unstable; if you plant them too deeply, they may struggle to sprout.
Why are my dahlia flowers smaller than they were supposed to be?
Flower size can be affected by several factors, including the amount of sunlight, water, and fertilizer the plant receives. For the largest blooms, ensure the plant is in full sun and receive regular water. Also, "deadheading"—the process of removing old, faded flowers—encourages the plant to put its energy into creating new, large buds rather than forming seeds.