Introduction
There is nothing quite like the sight of a dahlia in full bloom. These garden stars offer a spectacular range of colors and shapes, from the massive, fluffy petals of "dinnerplate" varieties to the tight, geometric perfection of pompons. If you missed the traditional spring planting window, you might be wondering if it is too late to join in the fun. The good news is that with a little extra care, you can often enjoy these beautiful flowers even if you start a bit later in the season.
At Longfield Gardens, we want every gardener to feel confident in their backyard, regardless of when they get their hands in the dirt. Whether you found a forgotten bag of tubers or you are looking to fill a gap in your late-summer landscape, planting dahlias in the warmer months is a rewarding project. While the traditional advice focuses on spring, summer planting simply requires a slightly different approach to manage the heat and ensure your plants have time to shine.
This guide will walk you through everything you need to know about planting and caring for dahlias during the summer months. We will cover the best timing for late starts, how to protect young plants from the sun, and which varieties are most resilient when the temperatures rise. By following a few simple steps, you can look forward to a vibrant display of flowers that lasts until the first frost of autumn.
Gardening is all about working with nature and being flexible with your schedule. Even a late start can lead to a garden full of stunning blooms that make the wait well worth it.
Is It Too Late to Plant Dahlias?
The most common question gardeners ask as June rolls around is whether they have missed the window entirely. For most of the United States, the answer is a hopeful "no." Dahlias are remarkably fast growers once the soil is warm. While spring planting is ideal because it gives the plant a longer time to establish roots before the peak heat of July, you can still plant dahlia tubers as late as mid-June in many regions.
If you plant in June, your dahlias will likely begin blooming in late August or September. This timing is actually quite lovely, as many other garden favorites begin to fade just as the dahlias are reaching their peak. Because dahlias thrive when the nights start to cool down in late summer, a "late" crop often produces some of the most intense colors and strongest stems of the season.
If it is already July, planting dormant tubers directly into the ground becomes more of a gamble. In most zones, a July-planted tuber may not have enough time to reach its flowering stage before the first frost hits in October or November. However, there is a simple workaround: planting started plants. If you can find dahlias that are already growing in pots at a local nursery, you can transplant them into your garden throughout the summer with great success.
Key Takeaway: The Late-Season Strategy
- Tubers: Plant by mid-June for blooms by late summer.
- Started Plants: Can be transplanted in July or August for immediate impact.
- The Goal: Ensure the plant has at least 90 days of frost-free weather to complete its cycle.
For additional timing guidance, see this dahlia planting timing guide.
Managing the Heat for Summer Planting
The biggest challenge with planting dahlias in the summer is not the timing, but the temperature. Dahlias are native to the high altitudes of Mexico and Central America. In their ancestral home, the days are warm and sunny, but the nights stay quite cool. They generally prefer temperatures between 70°F and 80°F. When the thermometer climbs above 85°F, dahlias can begin to feel the stress.
If you are planting in the middle of a heatwave, your primary goal is to keep the "feet" of the plant cool and the "head" of the plant hydrated. Unlike spring-planted tubers, which we usually suggest leaving unwatered until they sprout, summer-planted tubers need a bit of moisture right away. The soil in June and July is much drier and hotter than it is in May.
Choosing the Right Spot
In the spring, we usually recommend the sunniest spot in the garden. However, if you are planting in the summer, especially in hotter climates like the South or the Southwest, a spot with dappled afternoon shade can be a lifesaver. Morning sun provides the energy the plant needs for blooms, while afternoon shade protects the foliage from the harshest, most dehydrating rays of the day.
For more help selecting a location, read where to plant dahlias.
Mulching for Root Protection
Mulch is a summer gardener’s best friend. Dahlias have a shallow root system that sits just an inch or two below the soil surface. In the summer heat, the sun can bake the soil, stressing those delicate roots. Applying a 2- to 3-inch layer of organic mulch, such as clean straw, shredded bark, or compost, acts like an insulated blanket. It keeps the soil temperature consistent and slows down the evaporation of water.
Step-by-Step Summer Planting Guide
If you are ready to get your dahlias in the ground this summer, the process is straightforward. Because the soil is already warm, you will often see sprouts much faster than you would in the chilly dampness of early spring.
1. Prepare the Soil
Dahlias love "well-drained soil," which simply means soil that doesn't stay soggy like a wet sponge after it rains. If your soil is heavy clay, mix in some compost or aged manure to help loosen it up. This creates a "humusy" environment that allows roots to spread easily.
2. Dig and Place
Dig a hole about 4 to 6 inches deep. Place the tuber horizontally at the bottom of the hole with the "eye" (the small bump where the sprout emerges) pointing upward. If you are planting multiple tubers, space them about 18 to 24 inches apart to ensure good airflow. Airflow is vital in the summer to prevent powdery mildew, a common fungus that looks like white dust on the leaves.
3. Add a Support Stake
It is always easiest to put a stake in the ground at the time of planting. Large dahlias, like the famous "Dinnerplate" varieties, can grow 4 or 5 feet tall and become very top-heavy once they are loaded with blooms. By placing the stake now, you avoid accidentally driving it through the tuber later in the season.
4. Water and Wait
Give the area a good drink of water immediately after planting to settle the soil. In the summer, you may need to water every few days until you see the first green sprouts peeking through the soil. Once the plant is about 6 inches tall, you can transition to a deeper, less frequent watering schedule.
What to Do Next:
- Clear the planting area of any weeds that might compete for water.
- Mix a handful of balanced, slow-release fertilizer into the soil.
- Set your stake firmly into the ground next to the tuber.
- Label your varieties so you remember which colors are where!
Success in Hot Climates
For gardeners in USDA hardiness zones 8, 9, and 10, "summer" is a season that requires a specific strategy. In places like Texas, Georgia, or Arizona, the peak of summer is often a time of "dormancy" for dahlias. They may stop blooming entirely when the nights stay above 70°F because the plant is focused solely on survival.
If you live in a very hot area, you can actually use summer planting to your advantage. Some southern gardeners wait until the end of June or early July to plant their tubers. This allows the plant to grow during the heat, but delays the blooming phase until the weather breaks in September and October. This ensures the flowers aren't scorched by the July sun and that the plant stays vibrant well into the late autumn.
For zone-specific advice, consult this USDA hardiness guide for dahlias.
Using Shade Structures
If your garden is in a spot with no natural shade, a temporary shade structure can work wonders. You can buy "shade cloth" at most garden centers. A cloth that filters out about 40% of the sunlight is perfect for dahlias. It lowers the air temperature around the leaves and prevents "sunscald," which is when the leaves turn brown and crispy from too much direct heat.
The Power of Misting
On the hottest days of the year, dahlias appreciate a little "spa treatment." Briefly misting the foliage with a garden hose in the late afternoon can help lower the temperature of the leaves. Just be sure to do this early enough that the leaves dry before nightfall, as wet leaves in the dark can encourage pests and disease.
Choosing Heat-Tolerant Varieties
Not all dahlias handle the summer sun the same way. Some varieties are naturally more "heat-tolerant" than others. These plants tend to have sturdier stems, thicker leaves, or a growth habit that stands up better to the humidity and sun.
When choosing dahlias for a summer start or a hot climate, look for these proven winners:
- Bishop of Llandaff: This is a classic "peony-flowered" dahlia with stunning dark, almost black foliage. The dark leaves are very resilient, and the bright red flowers are a favorite for pollinators.
- Cornel: A "ball" type dahlia with deep red petals. Ball dahlias have a very tight, organized structure that holds up exceptionally well in the heat and makes for an incredible cut flower.
- Thomas Edison: A famous "decorative" dahlia with large, deep purple blooms. This variety has been a garden favorite for decades because it is vigorous and reliable even in tough conditions.
- Arabian Night: Another dark-colored beauty, this dahlia produces velvety, deep maroon flowers. Darker flowers sometimes handle the sun better than pale whites or light pinks, which can show "scorch" marks more easily.
- Kelvin Floodlight: If you want a giant "dinnerplate" dahlia that can handle the heat, this bright yellow variety is a champion. It is known for its massive blooms and strong stems.
At Longfield Gardens, we select varieties that have been tested in trial gardens to ensure they perform well for home gardeners across the country. Focusing on these robust types gives you a head start on a successful summer garden.
Summer Care and Maintenance
Once your summer-planted dahlias are up and growing, a little routine maintenance will keep them happy and productive. Because the summer growing season is compressed, the plants are working overtime to produce leaves and flowers.
Watering Correctly
The rule of thumb for summer dahlias is "deep and infrequent." Instead of a light sprinkle every day, give your plants a heavy soak once or twice a week. You want the water to reach at least 6 inches into the ground. This encourages the roots to grow deep into the soil where it is cooler and more moist. If you are growing dahlias in containers, you will likely need to water every day, as pots dry out much faster than the ground.
Feeding Your Plants
Dahlias are "heavy feeders," meaning they need plenty of nutrients to create those big, beautiful blooms. Start fertilizing once the plant is about a foot tall. Use a fertilizer that is low in nitrogen (the first number on the package) and higher in phosphorus and potassium (the second and third numbers). Too much nitrogen will give you lots of green leaves but very few flowers. A fertilizer labeled for tomatoes or roses is usually a great choice.
The "Pinch" for More Blooms
When your dahlia is about 12 to 18 inches tall and has several sets of leaves, it’s time for a simple trick called "pinching." Use your fingers or a pair of clean garden shears to snip off the very top of the center stem. It might feel a bit mean, but this tells the plant to stop growing tall and start growing wide. It will send out side branches, resulting in a bushier plant with many more flower buds.
Deadheading
As your dahlias begin to bloom, you’ll want to practice "deadheading." This simply means cutting off the flowers as soon as they start to fade. If you leave the old flowers on the plant, it will put its energy into making seeds. If you remove them, the plant will keep pumping out new blossoms all the way until frost.
For more information about harvesting and deadheading, see how to cut dahlia flowers.
Key Takeaway: Summer Maintenance Checklist
- Water: Deeply 1–2 times a week (more for pots).
- Feed: Every 2 weeks with low-nitrogen fertilizer.
- Pinch: Once at 12–18 inches to encourage branching.
- Deadhead: Regularly to keep the blooms coming.
Troubleshooting Common Summer Issues
Even with the best care, summer gardening can bring a few challenges. The key is to catch things early and keep it simple.
Wilting Leaves
If you see your dahlias wilting in the middle of a 90-degree day, don't panic. This is often the plant's way of protecting itself from the sun by reducing the surface area of its leaves. Check the soil with your finger. If the soil is moist a few inches down, the plant is just resting and will perk back up when the sun goes down. If the soil is dry, give it a deep drink.
Yellowing Bottom Leaves
It is natural for the very oldest leaves at the bottom of the plant to turn yellow and die back as the plant grows. Simply snip them off to keep the garden looking tidy and to improve airflow around the base of the plant. However, if the whole plant is turning yellow, it might be a sign of poor drainage or a need for fertilizer.
Pests
Japanese beetles and grasshoppers sometimes find dahlias delicious in the mid-summer. For a few beetles, the easiest "win" is to simply flick them into a bucket of soapy water in the morning when they are sluggish. For smaller pests like aphids or spider mites, a strong blast of water from the hose is often enough to knock them off and keep the population under control.
Enjoying the Harvest: Cutting Dahlias
One of the best reasons to plant dahlias is for the incredible bouquets. Summer-planted dahlias will provide you with armloads of flowers for your kitchen table or to share with friends.
The best time to cut dahlias is in the cool of the morning when the plants are fully hydrated. Unlike roses or lilies, dahlias will not continue to open much once they are cut. Look for flowers that are about three-quarters of the way open. If the back of the flower feels firm and the petals are crisp, it is ready for the vase.
Place the stems immediately into a bucket of room-temperature water. To make them last as long as possible, change the water in your vase every day and snip a tiny bit off the bottom of the stems every few days. This keeps the "straws" of the plant open so they can keep drinking.
Key Takeaway: The Perfect Cut "Cutting flowers regularly actually helps the plant. The more you harvest, the more the plant is stimulated to produce new buds. It’s a win-win for you and your garden!"
Preparing for the End of the Season
As the summer winds down and the days grow shorter, your dahlias will likely put on their most impressive show. This is the "grand finale" of the garden. In many parts of the country, dahlias will continue to bloom through September and October, often looking better than ever as the nights cool down.
Once the first hard frost arrives, the foliage will turn black or brown. This is the signal that the growing season is over. In warmer zones (Zone 8 and above), you can often leave the tubers in the ground for the winter, provided the soil stays well-drained. In colder zones, you will need to dig up the tubers and store them in a cool, dry place like a basement or garage until next spring.
For more information about leaving tubers in the ground or lifting them for winter, read can dahlias grow in the ground.
Every garden is a learning experience. If you planted late this year and loved the results, you might decide to make "succession planting" a regular part of your routine—planting some in May for early color and some in June for a fresh burst of life in the fall.
Conclusion
Planting dahlias in the summer is an achievable and joyful project that can extend your garden's beauty well into the autumn months. While it requires a bit more attention to watering and heat management than spring planting, the reward of vibrant, late-season blooms is more than worth the effort. By choosing heat-tolerant varieties and providing plenty of mulch and water, you can transform a bare summer spot into a spectacular floral display.
We at Longfield Gardens are here to support your gardening journey every step of the way. Whether you are a beginner or a seasoned pro, there is always something new to discover in the world of flowers. Remember that gardening isn't about perfection; it's about the pleasure of watching something grow and the satisfaction of a job well done.
Final Thought for Success "The best time to plant a garden was twenty years ago; the second best time is today. Don't let a late start stop you from enjoying the magic of dahlias this year."
- Choose the right spot: Look for morning sun and afternoon shade in hot areas.
- Keep it cool: Use mulch to protect shallow roots from the sun.
- Water deeply: Focus on the roots, not the leaves, to prevent disease.
- Enjoy the wait: Late-summer blooms are often the most colorful and lasting.
We invite you to explore our selection of dahlia collections and gardening guides to help you create the beautiful backyard you've always imagined. Happy planting!
FAQ
Can I plant dahlia tubers in July?
While you can plant them in July, they may not have enough time to bloom before the first frost, as dahlias typically need 90 to 120 days to flower. If you live in a very warm climate with a late frost date, or if you are planting "started" plants in pots, July planting can still be successful.
How often should I water dahlias planted in the summer?
Summer-planted dahlias need more frequent watering than those planted in the spring because the soil is hotter and drier. Check the soil daily; if the top inch feels dry, give the plant a deep soak. Generally, two to three deep waterings per week are sufficient for plants in the ground, while container dahlias may need water every day.
Do dahlias need full sun in hot climates?
In the North, dahlias love 6 to 8 hours of full sun. However, in hot southern climates, they benefit from "filtered" sun or afternoon shade. Providing protection from the intense sun between 2:00 PM and 5:00 PM can prevent the plants from wilting and help the blooms last longer.
What is the best mulch for dahlias in the summer?
Organic mulches like straw, shredded leaves, or clean wood chips are excellent choices. These materials help regulate soil temperature and retain moisture. Aim for a layer about 2 to 3 inches thick, but keep the mulch a few inches away from the actual stem of the plant to prevent rot.
