Table of Contents
- Introduction
- Start with the Right Foundation
- The Power of Pinching
- Water Correctly, Not Constantly
- Feeding for Flowers
- Deadheading: The Secret to Continuous Blooms
- Harvesting for Bouquets
- Managing Summer Heat Stress
- Staking for Success
- Encouraging a Strong Finish
- Conclusion
- FAQ
Introduction
There is a unique sense of wonder that comes with watching a dahlia bud slowly unfurl to reveal its intricate, perfectly arranged petals. Whether you are growing dinnerplate varieties the size of a dessert plate or tidy, ball-shaped blooms, these plants are the hardworking celebrities of the summer garden. At Longfield Gardens, we want every gardener to experience the thrill of a yard filled with these spectacular flowers from mid-summer until the first frost.
While their exotic appearance might suggest they are difficult to maintain, dahlias are actually quite generous. They are vigorous growers that are eager to produce a constant supply of big blooms if they receive the right support. This guide is designed for home gardeners who want to maximize their bloom count and keep their plants healthy and vibrant throughout the entire growing season.
Success with dahlias is not about luck; it is about mastering a few simple habits that align with the plant's natural rhythm. We will cover the essential techniques of pinching, deadheading, and proper feeding that ensure your garden remains a sea of color for months on end. By following these practical steps, you can help your dahlias reach their full potential and enjoy a rewarding gardening experience.
Start with the Right Foundation
To keep dahlias blooming all summer, you must start with healthy plants in a location that meets their needs. While we often think of "blooming" as something that happens late in the season, the groundwork is laid the moment the tubers go into the soil, and how deep should I plant dahlias can help you get the depth right.
Choosing a Sunny Spot
Dahlias are sun-worshippers. They require at least six to eight hours of direct sunlight every day to produce the energy needed for flower production. If they are planted in a spot that is too shady, the plants will become "leggy," which means they grow tall and thin as they stretch toward the light. These weak stems are less likely to support heavy flowers and will produce fewer buds overall.
Soil and Drainage
"Drainage" refers to how fast water leaves the soil. Dahlias need soil that stays moist but never soggy. If your garden has heavy clay soil that holds water like a sponge, consider planting in raised beds or adding compost to loosen the ground. Tubers planted in soil with poor drainage are more likely to struggle before they even get a chance to bloom.
Timing Your Planting
Patience is a gardener's best friend when it comes to dahlias. These plants are native to warm climates and have no tolerance for frost. Wait until the soil has warmed to at least 60°F before planting. A common rule of thumb is to plant your dahlias at the same time you would plant tomatoes or peppers.
Key Takeaway: The foundation of a long blooming season is a sunny, well-drained location and warm soil. Get these basics right, and your dahlias will have the energy they need to produce flowers all summer.
The Power of Pinching
If you want to significantly increase the number of flowers on your dahlia plants, there is one simple technique you should use: when to pinch dahlias. It might feel counterintuitive to cut a healthy plant, but this is the single most effective way to encourage a bushy, flower-filled dahlia.
When to Pinch
When your dahlia plant is between 12 and 16 inches tall and has about four or five sets of leaves, it is time to pinch. Look at the main center stem. You will see a small sprout at the very top, which is the terminal bud.
How to Pinch
Use your fingers or a clean pair of garden snips to remove the top 2 to 3 inches of the center stem, just above the highest set of leaves. By removing this main growing point, you signal to the plant that it should stop growing straight up and instead start growing out.
The plant will respond by sending out two new branches from the leaf nodes just below where you made the cut. Instead of one tall, lanky stem with one flower at the top, you will create a sturdy, branched plant with multiple stems. More stems mean more buds, and more buds mean a garden that stays in bloom much longer.
What to do next:
- Wait for the plant to reach 12 inches in height.
- Locate the central growing tip.
- Snip off the top 3 inches.
- Watch for new side branches to appear within a week.
Water Correctly, Not Constantly
Water is the fuel that keeps dahlia blooms hydrated and fresh. However, dahlias have specific preferences for how they receive that water.
Deep Watering vs. Shallow Sprinkling
Dahlias benefit from deep watering rather than frequent, light sprinkles. Deep watering means providing enough water so that it reaches 8 to 10 inches into the ground where the roots live. This encourages the roots to grow downward, making the plant more stable and better able to handle summer heat.
Aim to water your dahlias two to three times a week. If the weather is exceptionally hot and dry, you may need to increase this frequency. A soaker hose or a drip irrigation system is ideal because it delivers water directly to the soil without wetting the leaves. Keeping the foliage dry helps the plant stay healthy and focused on flower production.
Checking Soil Moisture
Before you water, do a simple finger test. Poke your finger about two inches into the soil near the base of the plant. If the soil feels damp, you can wait another day. If it feels dry, it is time for a deep soak. Remember that dahlias in containers will dry out much faster than those in the ground and may need water every day during the peak of summer.
Feeding for Flowers
Dahlias are "heavy feeders," meaning they use a lot of nutrients to build their large stems and vibrant petals. To keep them blooming all summer, you need to provide the right kind of food at the right time.
Understanding Fertilizer Labels
Most fertilizers have three numbers on the label, such as 5-10-10. These represent Nitrogen (N), Phosphorus (P), and Potassium (K).
- Nitrogen helps leaves grow green and lush.
- Phosphorus encourages root development and flower production.
- Potassium supports overall plant health and disease resistance.
The Low-Nitrogen Rule
To keep your dahlias blooming, you want a fertilizer that is low in nitrogen and high in phosphorus and potassium. If you give a dahlia too much nitrogen, you will end up with a giant green bush but very few flowers. At our trial garden at Longfield Gardens, we find that a "bloom booster" style fertilizer works best.
Fertilizing Schedule
Start feeding your dahlias about a month after planting, once they are well-established. Apply fertilizer every three to four weeks through mid-August. Avoid fertilizing late in the season, as the plant needs to begin winding down as fall approaches. Always follow the instructions on the product label to ensure you are applying the correct amount.
Key Takeaway: For a summer full of flowers, choose a fertilizer with a low first number and higher second and third numbers. This tells the plant to prioritize blooms over leaves.
Deadheading: The Secret to Continuous Blooms
If there is one task that determines how long your dahlias will bloom, it is how and why to deadhead flowers. Deadheading is the process of removing flowers that have finished blooming.
Why Deadheading Works
The goal of any plant is to produce seeds to ensure the next generation. When a dahlia flower fades and begins to form seeds, the plant shifts its energy away from making new buds and toward seed production. By removing the faded flower before it can make seeds, you "trick" the plant into thinking its job isn't done yet. It will respond by producing more and more buds in an effort to finally complete its life cycle.
How to Tell a Bud from a Spent Bloom
For beginners, it can sometimes be tricky to tell the difference between a new bud that hasn't opened yet and a flower that has already finished.
- New Buds: These are usually round and firm, like a little green marble.
- Spent Blooms: These tend to be more pointed or cone-shaped. If you touch them, they often feel soft or mushy, and you may see the back petals starting to turn brown or drop off.
Where to Cut
When you deadhead, don't just snip off the flower head. For the best results, follow the flower stem down to where it meets a larger main stem or a set of leaves and make your cut there. This keeps the plant looking tidy and encourages new growth from the leaf nodes. Aim to deadhead your plants at least once a week—the more you do it, the more flowers you will have.
Harvesting for Bouquets
One of the best ways to keep your dahlias blooming is actually to cut them and bring them inside! Much like deadheading, harvesting fresh cut flowers encourages the plant to keep producing new buds.
The Best Time to Cut
The best time to harvest dahlias is in the cool of the morning when the plants are fully hydrated. For long-stem techniques, bring a bucket of room-temperature water out to the garden with you so you can put the stems in water immediately after cutting.
Choosing the Right Stage
Unlike many other flowers, dahlias do not open much further once they are cut. You should wait to harvest them until the flower is about 1/2 to 2/3 of the way open. If you cut a dahlia while it is still a tight green bud, it likely won't open in the vase.
Cutting for Stem Length
When you cut a dahlia for a bouquet, don't be afraid to take a long stem. Cutting deep into the plant (back to a joint or leaf node) encourages the plant to produce longer, stronger stems for the next round of flowers. It might feel like you are taking away a lot of the plant, but dahlias are incredibly resilient and will grow back quickly.
Managing Summer Heat Stress
Dahlias love the sun, but extreme summer heat (regularly above 90°F) can sometimes cause them to take a short "nap." This is a natural survival mechanism where the plant slows down its flower production to conserve energy and moisture.
Recognizing Heat Stress
During a heatwave, you might notice that your dahlia blooms are smaller than usual, or the colors may look a bit faded. The plant may even stop producing new buds entirely for a week or two. Don't worry—this is usually temporary.
How to Help
- Mulching: Apply a 2-to-3-inch layer of mulch, such as shredded bark or clean straw, around the base of your plants. This helps keep the roots cool and prevents moisture from evaporating too quickly from the soil.
- Morning Hydration: If a very hot day is forecasted, give your dahlias a deep drink in the early morning. This ensures they have plenty of internal moisture to handle the midday sun.
- Shade Cloth: If you live in an area with intense afternoon heat, you can provide some temporary relief with a 30% shade cloth. This filters the harshest rays while still allowing the plant to get the light it needs.
Once the temperatures drop back into a more comfortable range, your dahlias will naturally resume their vigorous blooming schedule.
Staking for Success
As dahlia plants grow and begin to produce heavy flowers, they can become top-heavy. A summer thunderstorm or a gust of wind can easily topple a tall dahlia, which interrupts its blooming cycle.
When to Stake
It is best to put your stakes in the ground at the time of planting to avoid poking through the tubers later. However, if your plants are already growing, you can still add support. For staking dahlias, use a sturdy wooden stake, a bamboo pole, or a metal T-post.
How to Tie
As the plant grows, use soft garden twine or strips of fabric to loosely tie the main stem to the stake every 12 to 18 inches. You want the tie to be firm enough to hold the plant up but loose enough to allow the stem to thicken as the plant matures. Supporting the plant ensures that the stems don't break under the weight of the blooms, allowing every bud to reach its full potential.
Encouraging a Strong Finish
As the summer begins to fade into autumn, your dahlias will often have their most spectacular showing. The cooler nights and shorter days of late August and September are exactly what dahlias love most.
Winding Down
In late August, you can stop fertilizing your dahlias. This allows the plant to focus on its current blooms rather than starting a lot of new green growth that won't have time to mature before winter. Continue to water and deadhead right up until the first frost.
The First Frost
The dahlia season officially ends when a "killing frost" arrives. This will turn the foliage black and the stems limp. While it is the end of the blooms for the year, it is also a sign that the plant has successfully completed its season. In many USDA plant hardiness zones, this is the time to decide whether to dig up the tubers for winter storage or treat them as annuals and start fresh next year.
Key Takeaway: Dahlias are late-season stars. By keeping up with watering and deadheading in late summer, you will be rewarded with the most intense colors and largest flowers of the year just as other garden plants are starting to fade.
Conclusion
Keeping dahlias blooming all summer is a rewarding journey that relies on a few consistent actions. By starting with warm soil, pinching your plants early to encourage branching, and staying on top of deadheading, you create an environment where the flowers simply won't want to stop. Remember to water deeply and use a fertilizer that prioritizes blooms over foliage to ensure your garden remains a vibrant sanctuary.
- Plant in full sun and well-drained soil once the ground is 60°F.
- Pinch the center stem at 12 inches to create a bushier plant.
- Deadhead spent blooms weekly to trick the plant into making more buds.
- Water deeply at the base of the plant to keep roots hydrated and leaves dry.
Gardening is a practice of observation and partnership with nature. As you spend time with your dahlias each week, you will learn to recognize exactly what they need to thrive. We invite you to explore the wide variety of dahlia collections available at our Lakewood, New Jersey facility to find the perfect match for your garden.
With a little care and attention, you can enjoy a spectacular display of dahlias that lasts from the heat of July to the crisp days of October.
FAQ
How many times a week should I water my dahlias?
Most dahlias in the ground need a deep watering two to three times a week, providing about an inch of water total. If the weather is very hot or your soil is sandy, you may need to water more frequently. Dahlias grown in pots usually need water every day during the summer because the soil in containers dries out much faster than the ground.
Do I have to deadhead every single flower?
While you don't have to, deadheading is the most important thing you can do to keep the plant producing new flowers. If you leave the old flowers on the plant, it will stop making new buds and put all its energy into making seeds. For the best results, try to walk through your garden once a week and snip off any flowers that have started to fade.
My dahlias have lots of leaves but no flowers. What is wrong?
The most common cause of "all leaves and no flowers" is too much nitrogen in the fertilizer. Nitrogen helps plants grow big and green, but it can prevent them from blooming if there is too much of it. Switch to a fertilizer that is higher in phosphorus (the middle number) and make sure your plants are getting at least six to eight hours of direct sunlight every day.
Should I cut the flowers even if I want to see them in the garden?
Yes! Cutting flowers for bouquets actually helps the plant. It works just like deadheading—it tells the plant to produce even more buds. If you want plenty of flowers both in your house and in your garden, the trick is to plant a few extra tubers so you have plenty to share and plenty to enjoy outdoors.