Table of Contents
- Introduction
- Finding the Perfect Spot for Your Dahlias
- The Importance of Timing and Temperature
- Preparing the Soil for Planting
- How to Plant Dahlia Tubers Step-by-Step
- The Golden Rule of Early Watering
- Providing Support with Staking
- The Magic of Pinching for More Flowers
- Feeding Your Dahlias Through the Season
- Managing Garden Pests and Health
- Harvesting Blooms and Deadheading
- Wrapping Up the Season
- Conclusion
- FAQ
Introduction
Imagine stepping into your backyard on a warm August morning to find a sea of vibrant, dinnerplate-sized blooms in every shade of the rainbow. Growing dinnerplate dahlias is one of the most rewarding experiences a gardener can have, offering a level of abundance and variety that few other plants can match. Whether you are looking for delicate pompons or massive, multi-colored petals, these plants are surprisingly straightforward to manage once you understand a few basics.
At Longfield Gardens, we love how dahlias transform from humble, potato-like roots into spectacular, towering plants in just one season. This guide is designed for home gardeners who want to master the art of planting and caring for these summer favorites. We will cover everything from choosing the perfect sunny spot to the simple maintenance tasks that ensure your plants remain healthy and productive until the first frost.
Learning how to plant and grow dahlia tubers is an exciting journey that brings professional-quality cut flowers right to your doorstep. If you want to browse more options as you read, our PomPon dahlias are a great place to start. By following a few time-tested steps, you can create a high-impact garden display that keeps getting better as the season progresses.
Finding the Perfect Spot for Your Dahlias
Success with dahlias begins before you even dig your first hole. These plants are sun-seekers that thrive on warmth and light. When you are looking for the right place in your yard, prioritize sunlight and soil drainage above all else.
Prioritize Sunlight
Dahlias need at least six to eight hours of direct sunlight every day to produce strong stems and plenty of flowers. In northern climates, the more sun they get, the better. If you live in a region with extremely hot summer afternoons, a spot that provides some light shade during the hottest part of the day can help prevent the flowers from fading too quickly. However, without enough total light, the plants will become "leggy," stretching toward the sun and producing fewer blooms.
Ensure Excellent Drainage
The term "drainage" simply refers to how fast water leaves the soil after a rain or watering session. Dahlia tubers are sensitive to standing water, which can cause them to rot before they even have a chance to sprout. To check your drainage, observe your garden after a heavy rain. If water forms puddles that stay for hours, that spot might be too wet. You can improve drainage by adding organic matter or by planting in raised beds, which naturally allow excess water to move away from the root zone.
Consider Wind Protection
Because many dahlia varieties grow quite tall—sometimes reaching four or five feet—they can act like sails in a heavy wind. Choosing a spot near a fence, a wall, or a line of sturdy shrubs can provide a natural windbreak. If your only sunny spot is in the middle of an open lawn, don't worry; we will discuss staking later to keep your plants upright and secure.
What to do next:
- Identify a garden bed that receives at least 6 hours of sun.
- Avoid low spots where water collects after a storm.
- Clear the area of any weeds or old garden debris to prepare for planting.
The Importance of Timing and Temperature
One of the most common mistakes in dahlia gardening is planting too early. While it is tempting to get your tubers in the ground as soon as the first warm spring day arrives, these plants are tropical in origin and have no tolerance for frost.
The Soil Temperature Rule
Wait to plant your dahlia tubers until the soil has warmed to about 60°F. A helpful way to remember this is the "tomato rule": if it is warm enough to plant your tomato starts outside, it is warm enough for your dahlias.
Watching the Frost Dates
Always check your local "last frost date." This is the average date when the final spring frost occurs in your area. If you need help finding your planting window, use the Hardiness Zone Map. You should wait until this date has safely passed before putting tubers in the ground. If an unexpected late frost is predicted after you have planted, you can protect emerging shoots by covering them with an overturned bucket or a frost blanket for the night.
A Head Start Indoors
If you live in a region with a very short growing season, you can start your tubers indoors about four to six weeks before the last frost. Our How to Plant Dahlias video shows the basics. Place them in pots with slightly damp potting soil and keep them in a warm, bright location. By the time the weather is warm enough to move them outside, you will have established plants ready to take off.
Preparing the Soil for Planting
Dahlias are "heavy feeders," meaning they use a lot of nutrients to produce those massive blooms and lush foliage. For a broader overview of varieties and planning, see the Planning Guide for Dahlias. Starting with high-quality soil makes the entire growing season much easier.
Enriching with Organic Matter
Before planting, mix several inches of compost or well-rotted manure into the top 10 to 12 inches of your soil. This does two things: it provides a slow-release source of nutrients and improves the soil structure. In sandy soil, organic matter helps hold onto moisture; in clay soil, it helps improve drainage.
Choosing the Right Fertilizer
While dahlias love to eat, they are picky about the type of food they receive. At the start of the season, avoid fertilizers that are very high in nitrogen. Nitrogen encourages green, leafy growth but can result in weak stems and fewer flowers. Look for a balanced fertilizer or one that is slightly higher in phosphorus and potassium (the second and third numbers on the package). This encourages strong root development and future flower production.
Loosening the Bed
Use a garden fork or spade to loosen the soil in the entire planting area. This makes it easier for the dahlia's fine feeder roots to spread out and establish themselves. A loose, crumbly soil texture allows the plant to access water and nutrients more efficiently than compacted soil.
How to Plant Dahlia Tubers Step-by-Step
Once the soil is warm and the site is prepared, it is time for the main event. Planting dahlia tubers correctly is simple if you follow a few basic guidelines regarding depth and orientation.
Understanding the Tuber
A dahlia tuber looks a bit like a sweet potato. It has a "neck" that connects to the old stem, and a "body" where energy is stored. The most important part is the "eye." This is a small bump or sprout located on the crown (the area where the neck meets the stem). This eye is where the new plant will grow from.
Depth and Spacing
Dig a hole about 4 to 6 inches deep. If you are planting several dahlias, space them according to their expected size.
- Large varieties (like Dinnerplates and cactus dahlias): Space them 18 to 24 inches apart.
- Medium varieties: Space them 12 to 18 inches apart.
- Border or dwarf varieties: Space them about 12 inches apart.
Giving them enough room ensures that air can circulate between the plants, which helps prevent diseases like powdery mildew later in the summer.
Positioning the Tuber
Lay the tuber on its side, horizontally, at the bottom of the hole. Try to position it so the "eye" or sprout is pointing upward. If you cannot find the eye, don't worry—the plant is smart enough to find its way to the surface as long as it isn't buried too deep. Cover the tuber with soil, tamping it down gently with your hands to remove any large air pockets.
Key Takeaway: Planting dahlias is a lot like planting potatoes. Give them enough room to breathe, bury them about 6 inches deep, and make sure the sprout has a clear path to the sun.
The Golden Rule of Early Watering
This is the part of dahlia growing that feels counterintuitive to many gardeners. Most plants want a big drink of water right after they are tucked into the ground. Dahlias are different.
Resist the Urge to Water
Unless your soil is bone-dry, do not water your dahlia tubers immediately after planting. The tuber contains all the moisture and energy it needs to send up its first sprout. Adding extra water to the soil before the plant has roots can lead to rot.
When to Start Watering
Wait until you see the first green shoots poking through the soil surface. This is your signal that the tuber has developed roots and is ready to start drinking. Once the plants are established, they will need consistent moisture, especially during the heat of mid-summer.
Deep and Infrequent
When you do start watering, aim for deep sessions once or twice a week rather than a light sprinkle every day. This encourages the roots to grow deep into the soil, making the plant more resilient during dry spells. If you use a mulch, like shredded bark or straw, it can help keep the soil cool and retain moisture, but wait until the plants are at least a foot tall to apply it so the soil stays warm during the early growth phase.
Providing Support with Staking
Dahlias are famous for their large, heavy blooms. Without support, a summer thunderstorm or a heavy wind can snap the stems or tip the entire plant over. Staking is an essential part of the growing process for all but the smallest dwarf varieties.
Stake Early
The best time to put a stake in the ground is at the moment of planting. If you want a quick refresher on support methods, see our How to Pinch and Stake Dahlias. If you wait until the plant is large, you risk driving the stake right through the tuber underground. Drive a sturdy wooden or metal stake about 8 to 12 inches into the ground right next to the spot where you planted the tuber.
Types of Support
- Individual Stakes: For a few plants, a single tall stake per plant works well. As the plant grows, use soft twine or garden tape to loosely tie the main stem to the stake every foot or so.
- Tomato Cages: For bushier, medium-sized dahlias, a sturdy tomato cage can provide excellent support without the need for constant tying.
- The Corral Method: If you are growing a long row of dahlias, you can drive heavy posts at the corners and run twine around the perimeter of the bed at different heights to "corral" the plants.
The Magic of Pinching for More Flowers
If you want a bushy plant with dozens of flowers instead of one tall, lanky plant with only a few, you need to pinch your dahlias. This is a simple technique that signals the plant to stop growing upward and start growing outward.
When to Pinch
Wait until your dahlia plant is about 12 to 16 inches tall and has four or five sets of leaves. At this stage, the plant is established enough to handle a quick trim.
How to Do It
Locate the main center stem. Using your fingers or a clean pair of garden snips, remove the very top of that center stem, just above the highest set of leaves. You only need to remove an inch or two of growth.
The Result
By removing that lead bud, you encourage the plant to send out side branches from the leaf nodes below. These branches will eventually produce their own flowers, effectively doubling or tripling your bloom count. It might feel a bit scary to cut off the top of a healthy plant, but the long-term results are well worth it.
Feeding Your Dahlias Through the Season
Once your dahlias are about a foot tall and growing vigorously, they will benefit from regular feeding. For more season-long advice, see 8 Tips for Growing Better Dahlias. Consistent nutrition keeps the foliage green and the flower production high.
Monthly Fertilizing
Apply a balanced, low-nitrogen fertilizer once a month. Many dahlia experts suggest formulas with N-P-K ratios like 5-10-10 or 10-20-20. This provides the phosphorus and potassium needed for strong stems and vibrant petals.
Avoiding Late-Season Nitrogen
As you move into late summer and early autumn, stop using high-nitrogen fertilizers altogether. Too much nitrogen late in the year can make the tubers difficult to store over the winter. At this stage, the plant should be focusing its energy on finishing its blooms and preparing the tubers for dormancy.
Natural Options
If you prefer an organic approach, top-dressing the soil with a layer of high-quality compost or using a liquid seaweed or fish emulsion fertilizer every few weeks is an excellent way to provide gentle, sustained nutrition.
Managing Garden Pests and Health
Dahlias are generally robust, but they do have a few visitors that might show up in your garden. The key is to catch any issues early and use simple, gentle solutions.
Slugs and Snails
Young dahlia shoots are a favorite snack for slugs. If you see jagged holes in the leaves of your new plants, slugs are the likely culprit. You can manage them by removing garden debris where they hide or by using organic slug bait. Applying these baits early in the season when the plants are most vulnerable is often enough to protect them.
Japanese Beetles
In mid-summer, you might see metallic-green Japanese beetles on your flowers. The simplest way to handle them is to knock them into a bucket of soapy water in the early morning when they are still sluggish. This prevents them from eating the petals without the need for harsh chemicals.
Powdery Mildew
This is a white, dusty-looking fungus that can appear on the leaves in late summer when the air is humid and the nights are cool. To prevent it, ensure your plants have plenty of space for airflow. If it appears, you can often keep it in check by removing the most affected lower leaves. This also helps the sun reach the base of the plant, which keeps the soil healthy.
Harvesting Blooms and Deadheading
The best part of growing dahlias is cutting them for bouquets. In fact, the more you cut your dahlias, the more they will bloom.
How to Cut for Bouquets
Unlike some flowers that continue to open after they are cut, dahlias should be harvested when they are nearly or fully open. Look at the back of the flower head; if the petals are firm and lush, it is ready. If the back petals are starting to look papery or brown, the flower is past its prime. Cut the stems long, making the snip just above a set of leaves.
The Importance of Deadheading
"Deadheading" is the process of removing flowers that have faded. If you leave old flowers on the plant, the dahlia will put its energy into producing seeds. By removing the spent blooms, you trick the plant into thinking it hasn't finished its job yet, so it keeps producing new buds. Always cut the spent flower stem back to a main branch to keep the plant looking tidy and encourage new growth.
What to do next:
- Check your plants every few days for faded flowers.
- Use clean, sharp bypass pruners for smooth cuts.
- Bring a bucket of water out to the garden so you can plunge cut stems into it immediately.
Wrapping Up the Season
As the days grow shorter and the first frost approaches, your dahlias will likely be at their peak of production. Enjoy this time, but keep an eye on the weather forecast.
The Signal of Frost
A light frost might blacken the foliage, but it usually won't hurt the tubers underground. In fact, a hard frost is the signal for the plant to go into "storage mode," sending all its remaining energy down into the tubers.
To Dig or Not to Dig
Dahlias are hardy in USDA zones 8 through 11, where they can often stay in the ground year-round with a thick layer of mulch. In colder zones (3 through 7), you have two choices. You can treat them as annuals and buy new tubers from us next spring, or you can dig up the tubers, store them in a cool, dry place over winter, and replant them next year. If you choose to lift them, our How to Lift and Store Dahlia Bulbs video walks through the process. Both options are perfectly valid; it simply depends on how much time you want to spend in the garden in late autumn.
Conclusion
Growing dahlias is a journey that starts with a single tuber and ends with a garden full of color and joy. By choosing a sunny spot, waiting for warm soil, and providing a little bit of support and water, you can achieve professional-looking results in your very first season. These plants are incredibly generous, rewarding your effort with a non-stop parade of blooms from July until the first frost. If you want to shop the easiest options first, browse our best-selling dahlias.
- Pick a sunny, well-drained spot.
- Wait for the soil to reach 60°F before planting.
- Don't water until you see green shoots.
- Pinch the center stem at 12 inches for a bushier plant.
- Cut flowers often to encourage more blooms.
At Longfield Gardens, we take pride in providing high-quality tubers that are true to variety and ready to thrive. When you're ready to pick your palette, start with our Spring Planted Bulbs By Color. If you follow these simple steps, you'll find that dahlias aren't just a flower—they are a season-long celebration of gardening success. The next step is to choose your favorite colors and get ready for a summer of spectacular growth.
"There is no such thing as having too many dahlias. Each one you plant is a promise of beauty that the summer is sure to keep."
FAQ
How deep should I plant my dahlia tubers?
You should plant dahlia tubers about 4 to 6 inches deep. Lay the tuber horizontally in the hole with the "eye" or sprout pointing upward if possible. Covering them with this amount of soil protects the tuber from temperature fluctuations and provides a stable base for the stems to grow.
When should I start watering my dahlias after planting?
You should wait to water your dahlias until you see the first green shoots emerging from the soil. The tubers contain enough moisture to get the plant started. Watering too early, especially in cold or heavy soil, can lead to the tuber rotting before it has developed a root system.
Do dahlias need full sun to bloom?
Yes, dahlias perform best in full sun, which means at least six to eight hours of direct sunlight every day. While they can grow in partial shade, the stems will likely be weaker, the foliage thinner, and you will see significantly fewer flowers throughout the season.
Why is it important to pinch dahlia plants?
Pinching involves removing the top inch or two of the main stem when the plant is about 12 to 16 inches tall. This encourages the plant to branch out rather than growing as one single tall stalk. This results in a sturdier, bushier plant and a much higher number of flowers over the course of the summer.