Table of Contents
- Introduction
- Understanding the Dahlia Tuber
- Selecting the Right Spot
- When to Plant Your Dahlias
- How to Plant: Step-by-Step
- The "No-Water" Rule for New Tubers
- Why You Should Pinch Your Dahlias
- Staking and Supporting Your Plants
- Feeding for Better Blooms
- Harvesting and Deadheading
- End of Season Care
- Troubleshooting Common Issues
- Creating a Cut Flower Garden
- FAQ
- Conclusion
Introduction
Imagine walking into your backyard in late August and being greeted by flowers the size of dinner plates in colors so vibrant they look hand-painted. This is the magic of growing dahlias, one of the most rewarding and visually stunning plants you can add to your garden. Whether you are looking for petite pompons or massive, shaggy blooms, these plants offer a spectacular return on a little bit of planning and care.
At Longfield Gardens, we believe that everyone can grow a successful dahlia garden regardless of their experience level. We ship high-quality tubers from our facility in New Jersey to gardeners across the country, ensuring you start with the best possible foundation. See our dahlia collections for the varieties featured in this guide.
By focusing on a few simple rules of care, you can transform your landscape into a blooming sanctuary. Learning how to best grow dahlias is an exciting journey that rewards patience with an abundance of flowers.
Understanding the Dahlia Tuber
To grow a healthy dahlia, you first need to understand how the plant begins its life. Dahlia Tubers: What You Need to Know explains why these thick, underground energy-storage organs are so important. If you have ever seen a sweet potato or a bunch of fingerling potatoes, you already have a good idea of what a dahlia tuber looks like.
The most important part of a tuber is the "eye." The eye is a small growth bud located on the "crown" of the tuber— the area where the tuber meets the old stem. Just like the eyes on a potato, this is where the new sprout will emerge. If a tuber is missing an eye, it will not grow a plant, even if the tuber itself looks plump and healthy.
When you receive your order from us, your tubers may already have visible sprouts, or they may still be dormant. Both are perfectly fine. Sometimes the eyes are very small and hard to see until the tuber is exposed to warmth and a little moisture. The size of the tuber does not dictate the size of the final flower; a small tuber with a healthy eye can produce a massive, five-foot-tall plant just as well as a large tuber can.
Key Takeaway: The Eye is Essential Always look for a small bud or "eye" at the top of the tuber near the stem. This is the life center of the plant. As long as there is an eye and the neck of the tuber is not broken, the plant has everything it needs to grow.
Selecting the Right Spot
Dahlias are sun-loving plants that thrive in warm conditions. For the best results, you must match the plant's needs to the right location in your yard.
Sunlight Requirements
Most varieties need at least six to eight hours of direct sunlight every day to produce strong stems and plenty of flowers. If they are planted in too much shade, the plants will become "leggy," meaning they grow tall and thin as they stretch toward the light. This weakness makes them more likely to fall over and results in fewer blooms. Morning sun is particularly beneficial as it helps dry the dew off the leaves, which keeps the foliage healthy.
Soil and Drainage
"Drainage" simply refers to how fast water leaves the soil after a rain or watering. Dahlias have a complicated relationship with water: they love to stay hydrated, but their tubers will rot if they sit in soggy, "wet feet" conditions. To test your drainage, watch your garden after a heavy rain. If puddles stay for hours, the soil is likely too heavy in clay.
You can improve your soil by adding organic matter like compost or well-rotted manure. This helps "lighten" the soil, allowing water to move through while still holding onto the nutrients the plants need. If your soil is very heavy clay, consider planting in raised beds. Raised beds provide excellent drainage and allow the soil to warm up faster in the spring, which dahlias love.
Wind Protection
Because many dahlias grow to be four or five feet tall, they can act like sails in a windstorm. If possible, choose a spot that has some protection from high winds, such as near a fence or a building. Just make sure the protection doesn't block the sunlight they need to bloom.
When to Plant Your Dahlias
Timing is the most important factor in dahlia success. Many gardeners make the mistake of planting too early when the ground is still cold and damp. Because dahlias are native to the warm climates of Mexico and Central America, they have no tolerance for frost or cold soil.
The 60-Degree Rule
The best time to plant is when the soil temperature has reached about 60°F. A good rule of thumb is to plant your dahlias at the same time you would plant tomatoes or peppers. In most parts of the United States, this happens in late May or early June.
If you plant into cold, wet soil, the tuber will sit dormant and may rot before it ever has a chance to sprout. Waiting for the soil to warm up ensures the plant can hit the ground running. We time our shipping at Longfield Gardens to match the planting window for your specific USDA hardiness zone, so your tubers should arrive when the timing is nearly right.
Starting Early Indoors
If you live in a region with a short growing season, you can give your dahlias a head start by "potting them up" indoors about four to six weeks before the last frost. Place the tubers in pots filled with slightly damp potting soil and keep them in a warm, sunny spot. By the time the weather is warm enough to move them outside, you will already have a small plant ready to go. This can result in flowers appearing several weeks earlier in the summer.
How to Plant: Step-by-Step
Once the soil is warm and the danger of frost has passed, it is time to get your dahlias in the ground. For a complete walkthrough, see How to Plant Dahlias. Getting the depth and spacing right is a quiet win that sets the stage for the entire season.
- Dig the Hole: Dig a hole about 6 to 8 inches deep. If you are planting a tall variety, this is the best time to drive a stake into the ground (more on that later) so you don't accidentally poke a hole through the tuber later in the season.
- Amend the Soil: Mix a handful of compost into the bottom of the hole to provide a slow-release source of nutrients.
- Position the Tuber: Lay the tuber horizontally in the hole with the eye or sprout facing upward. Do not stand it up vertically like a carrot.
- Cover with Soil: Fill the hole back in with soil. You only need to cover the top of the tuber with about 1 to 2 inches of soil initially. As the sprout grows taller, you can gradually pull more soil into the hole until it is level with the surrounding ground.
- Space them Out: Dahlias need room for air to circulate around their leaves. Space smaller "border" varieties about 12 to 18 inches apart. For the larger "dinnerplate" or decorative types, give them at least 2 feet of space.
Next Steps for Planting Success:
- Check your local frost dates before starting.
- Ensure your stakes are in place for tall varieties.
- Lay tubers flat, not upright.
- Resist the urge to water immediately after planting.
The "No-Water" Rule for New Tubers
One of the most common mistakes new dahlia growers make is watering the ground immediately after planting. 8 Tips for Growing Better Dahlias covers why patience matters here. Until the dahlia tuber has sent up a green sprout and developed a root system, it has no way to "drink" the water you are giving it.
The moisture already present in the spring soil is usually more than enough to wake up the tuber. Adding extra water during this dormant phase often leads to rot. Once you see the green leaves poking through the soil surface, you can begin a regular watering schedule.
As the plants grow larger, they become very thirsty. In the heat of mid-summer, dahlias should receive about an inch of water per week. When you water, aim for the base of the plant rather than the leaves. Keeping the foliage dry helps prevent common issues like powdery mildew.
Why You Should Pinch Your Dahlias
"Pinching" is a simple technique that feels a bit scary the first time you do it, but How to Pinch and Stake Dahlias shows why it's worth it. If left alone, a dahlia will naturally grow one tall, dominant center stem. This often results in a "top-heavy" plant that produces fewer blooms.
When your plant is about 12 to 16 inches tall and has at least four sets of leaves, take a pair of clean garden snips and cut off the very top of the center stem. You want to snip it just above the highest set of leaves.
This tells the plant to stop putting all its energy into growing upward and instead start growing outward. The plant will respond by sending out multiple side branches from the "axils" (the spots where the leaves meet the stem). More branches mean a sturdier plant and, most importantly, many more flowers for you to enjoy.
Staking and Supporting Your Plants
Dahlias are surprisingly heavy. Between the weight of the large blooms and the hollow nature of their stems, a heavy rain or a summer breeze can easily snap a beautiful plant in half. Providing support is not optional for most varieties—it is a necessity.
Individual Staking
For a few plants in a garden bed, a sturdy bamboo stake, wooden post, or metal T-post works perfectly. Drive the stake at least 12 inches into the ground at planting time. As the plant grows, use soft garden twine to loosely tie the main stem to the stake every 12 inches.
Tomato Cages
For medium-sized dahlias, a heavy-duty tomato cage is an easy win. Place the cage over the plant while it is still small. As it grows, the side branches will rest on the wire rings of the cage, providing support from all sides.
The Corral Method
If you are growing a long row of dahlias, you can use the "corral" method. Drive sturdy posts at the four corners of your dahlia bed and every few feet along the sides. Wrap strong twine around the perimeter of the posts at heights of 12 inches and 24 inches. The plants will grow up inside this "box" of twine and support each other.
Feeding for Better Blooms
Dahlias are often called "heavy feeders," which means they use a lot of nutrients to produce their massive flowers. However, you have to be careful with the type of fertilizer you use.
In the early stages of growth, a balanced, all-purpose fertilizer is fine. But once the plant starts blooming, avoid fertilizers that are very high in nitrogen. Nitrogen encourages green, leafy growth but can result in fewer flowers and weak tubers. Look for a fertilizer where the second and third numbers (phosphorus and potassium) are higher than the first (nitrogen), such as a 5-10-10 or 10-20-20 formula.
Applying a liquid fertilizer every three to four weeks from mid-summer through early autumn will keep the plants energized. Always follow the instructions on the product label, as more is not always better when it comes to plant food.
Harvesting and Deadheading
The more you cut your dahlias, the more they will bloom. This is one of the best parts of growing them—you are encouraged to fill your house with bouquets!
Cutting for Vases
The best time to cut dahlias is in the cool of the morning or the evening when the plants are most hydrated. Unlike roses or lilies, dahlias will not open much further once they are cut. You should wait until the flower is about three-quarters of the way open before snipping it.
Use sharp, clean bypass pruners and cut the stem long—even if it means cutting off a few side buds. This encourages the plant to produce more long-stemmed flowers. Immediately place the cut stems into a bucket of room-temperature water.
Deadheading
If you don't cut the flowers for bouquets, you must "deadhead" them. Deadheading is the practice of removing faded or spent blooms. If you leave the old flowers on the plant, it will begin to put its energy into producing seeds. By removing them, you signal to the plant that it should keep producing new flower buds.
When deadheading, don't just snip the flower head. Follow the stem back down to where it meets a main branch and make your cut there. This keeps the plant looking tidy and prevents "stubs" from rotting.
End of Season Care
Dahlias will continue to bloom spectacularly until the first hard frost. If you want a refresher on saving them for next year, How to Overwinter Dahlias is a helpful guide. A light frost might nip the top leaves, but a "killing frost" will turn the entire plant black overnight. While this looks sad, it is actually a natural part of the plant's life cycle.
To Dig or Not to Dig?
Dahlias are only winter-hardy in USDA zones 8 through 11. If you live in a colder zone (zones 3-7), the tubers will freeze and die if left in the ground over the winter. To save them for next year, you must "lift" them.
- Cut Back: After the first frost turns the foliage black, cut the stems down to about 4 inches above the ground.
- Wait: Many gardeners wait about a week after the frost to dig. This encourages the tubers to go into dormancy and toughens the skin.
- Dig Carefully: Use a garden fork to gently loosen the soil around the plant, starting about 12 inches away from the stem to avoid piercing the tubers. Lift the entire clump out of the ground.
- Clean and Dry: Shake off excess soil and let the tubers dry in a protected, frost-free area for a day or two.
- Storage: Store the clumps in a breathable container (like a cardboard box or a crate) filled with slightly damp peat moss, vermiculite, or wood shavings. Keep them in a cool, dark place that stays between 40°F and 50°F, such as an unheated basement or a crawlspace.
If you live in a warm climate or simply prefer to treat dahlias as annuals, you can skip this process and start fresh with new varieties from us next spring.
Troubleshooting Common Issues
Even though dahlias are generally easy to grow, you might run into a few common hurdles. Most can be solved with simple, proactive care, and our 100% Quality Guarantee is there if you need help.
Slugs and Snails
Young dahlia sprouts are like candy to slugs. They can eat a small plant down to the ground overnight. To prevent this, use a pet-safe slug bait around the base of your plants as soon as they emerge from the soil. Once the plants are about a foot tall, the stems become tougher and less appealing to these pests.
Powdery Mildew
This looks like a dusting of white flour on the leaves and usually appears in late summer when the air is humid. To prevent it, ensure your plants have plenty of space for air to circulate. You can also snip off the bottom 12 inches of leaves on mature plants to improve airflow near the ground. If it becomes a major issue, a simple spray of neem oil or a potassium bicarbonate solution can help manage the spread.
Earwigs and Beetles
Sometimes insects like earwigs or Japanese beetles like to snack on the petals of your flowers. The most effective "simple" fix is to hand-pick them and drop them into a bucket of soapy water. Keeping the area around your dahlias free of debris and fallen leaves also removes the hiding spots where these insects like to live.
Creating a Cut Flower Garden
If your goal is to grow dahlias specifically for bouquets, you might want to dedicate a specific area of your yard to a "cutting garden." In a cutting garden, you can plant in straight rows, which makes staking and harvesting much easier.
Consider choosing a mix of flower shapes and sizes. Dinnerplate dahlias are a great way to start with big, romantic blooms.
The famous Cafe Au Lait is a standout example.
Thomas Edison is another dinnerplate favorite.
Ball dahlias are incredibly productive and have very long vase lives.
PomPon dahlias are similarly productive.
Cactus dahlias add a unique, spiky texture that looks wonderful in arrangements.
At Longfield Gardens, we offer collections and mixes that take the guesswork out of color coordinating. By planting a variety of types, you ensure that you always have the perfect bloom for any occasion.
FAQ
When is the best time to plant dahlias?
Dahlias should be planted in the spring once the soil has warmed to 60°F and the danger of frost has passed. This usually aligns with the same time you would plant tomatoes in your garden.
Do I have to dig up my dahlia tubers every year?
This depends on your location. If you live in USDA zones 8 or warmer, you can often leave them in the ground with a thick layer of mulch for protection. In zones 7 and colder, the tubers must be dug up and stored indoors to survive the winter.
Why are my dahlias not blooming?
The most common causes for a lack of blooms are too much shade, too much nitrogen fertilizer, or a lack of water. Ensure your plants get 6-8 hours of sun and switch to a low-nitrogen fertilizer once the plants are established.
How much sun do dahlias actually need?
For the best flower production and strong stems, dahlias need full sun, which means at least 6 to 8 hours of direct sunlight every day. Plants in partial shade will produce fewer flowers and may become weak or floppy.
Conclusion
Growing dahlias is a journey that brings immense joy to any gardener. By focusing on the basics—waiting for warm soil, providing sturdy support, and pinching for more blooms—you can achieve professional-looking results in your very first season. These plants are incredibly generous, offering a constant supply of color from the middle of summer until the first frost of autumn.
We are here to help you every step of the way. From our trial gardens to your front door, our mission at Longfield Gardens is to provide you with the quality plants and practical knowledge you need to succeed. Gardening should be a rewarding and enjoyable experience, and few plants offer as much "wow factor" for your effort as the dahlia.
- Wait for the warmth: Don't rush the tubers into cold, wet soil.
- Give them support: Stake tall varieties early to prevent damage.
- Keep cutting: The more you harvest, the more the plant will produce.
- Stay positive: Gardening is a learning process, and every season brings new successes.
Success with dahlias doesn't require a green thumb; it just requires a little bit of patience and the right timing. Once you see that first massive bloom open in your garden, you will be hooked for life.
If you are ready to start your dahlia journey, we invite you to explore our collection of tubers and find the varieties that speak to you. For more inspiration, visit our All About Dahlias guide. Happy gardening!