Dahlias are one of the most beloved flowers worldwide, only growing in popularity each year. They are also relatively easy to grow with the proper care and a bit of essential maintenance. This guide will cover everything you need to know when growing dahlia flowers, including their taxonomy, history, types, planting, care, growing tips, and storage over winter. Let’s go!
- Suitable USDA Growing Zones
- Dahlia Tubers Vs Dahlia Seeds
- Where To Buy Dahlia Bulbs
- How to Plant Dahlia Tubers
- Growing Dahlias
- How Long Do Dahlias Bloom?
- Growing Dahlias As Cut Flowers
- Do Dahlias Come Back Every Year?
- Digging Up and Storing Dahlia Tubers
- How To Divide Dahlia Tubers
- Types of Dahlias
- How Big Do Dahlias Grow?
- Popular Dahlia Societies to Join
Suitable USDA Growing Zones
Dahlias, used to the warmer climates of their native habitats, are hardy in USDA Zones 8 and above. This does differ slightly by species and variety. Some are hardier than others, potentially surviving in a growing zone as low as six if the cold is not too intense.
Those in Zones below eight don’t have to give up their Dahlia growing dreams. The tubers can be pulled from the ground before it gets too cold and overwintered and planted out again in early spring once the weather warms.
Dahlia Tubers Vs Dahlia Seeds
Dahlias are generally grown from tubers – long, starchy structures that hold the nutrients needed for the plant to pop up again in spring. However, Dahlias can also be grown from seed, as you will see if your blooms go to seed at the end of the season.
Unfortunately, this comes with a few caveats.
The Dahlias you grow from seed won’t be true to the original variety due to the influence of pollinators in the area. They also take a few years to mature and reach the prolific blooming stage. But, if you want to collect seeds and try them as an experiment, you may come up with a completely unique and interesting flower right in your backyard.
Tubers are the most reliable for planting and producing a plant true to type. When growing from seed, if you produce a flower you like, dig up those tubers to overwinter at the end of the season rather than planting from seed again, as the result will not be the same.
Where To Buy Dahlia Bulbs
You’ll easily find Dahlia tubers at your local nursery or general home and garden supply store. You can also purchase online from specialized growers. The tubers are easy to ship while dormant, so there is little risk in buying online.
If you are looking for a specific or rare type, it’s best to contact growers who specialize in Dahlia production in your area. Try these retailers across the USA for every Dahlia type you could ever want:
How to Plant Dahlia Tubers
Where to Plant
Dahlias must be planted in full sun positions to produce stunning blooms. Choose a south or west-facing site and ensure nearby plants do not shade shorter varieties. Consider the mature size of surrounding plants – not the current size – to avoid shading or overcrowding.
The plant tubers are prone to rotting. Avoid areas where water collects after rain and choose a spot with well-draining soil to ensure the plant’s tuberous root is not stagnant. To improve conditions, you can also amend clay soils with sand and compost before planting dahlia.
Finally, the site should be sheltered from strong winds or rain, especially for taller varieties. Flowering on long, thin stalks, Dahlias can quickly be knocked over with a strong gust of wind, ruining the blooms. Stalking will help strengthen the stems, but it’s better to plant them behind a wall or bed that softens any strong winds.
When to Plant
Plant Dahlias in spring when the soil has warmed and all signs of frost have passed. The exact planting time in the season will depend on your region.
Those in cooler seasons can still get a head start by planting dahlias in pots and transplanting them later in spring. To stop chilly nights and potential frost from ruining the tubers, bring the dahlias indoors overnight and move them back into the full sun in the morning.
How To Plant
When planting multiple Dahlias, space them around 10 inches apart to accommodate their mature growth. This can differ slightly depending on the variety – some can be planted closer together, while others require more space.
Bury the tuber just below the soil horizontally with the eye facing upwards. The eye is normally situated on the one end in the thinnest part of the tuber. Try to center this part, as this is where the stalk will grow.
As the stalk emerges, gently pack soil around the base to stabilize the plant and anchor it in the soil until the roots are better established.
Dahlias grow best in full sun positions with around 6 hours of direct light daily. In warmer zones with hot summers, they will benefit from shade when sunlight is highest in the afternoons.
They can also tolerate partial shade throughout the day in most regions, although they may not flower as prolifically. Choose varieties that are more tolerant of part shade for the best results. Avoid deep shade, which can stunt growth and prevent flowering.
Dahlias aren’t majorly fussy about soil but grow best when fertile and well-draining.
They will not tolerate heavy clay soils as the tuber is prone to rotting. Amend clay with compost, organic matter, and sand before planting, mixing it in several inches down to cover future root growth. Aim for a slightly acidic to neutral soil with a pH between 6.2 and 7.
Adding compost to the soil before planting will provide essential elements and improve nutrient levels and microorganism activity, aiding growth later on. While they store all the nutrients they need in their tubers for early growth, they will gather nutrients from the soil later for further development and flowering.
Tips for Growing Dahlias in Pots
With some growth and care adjustments, Dahlias are excellent container plants. These are also ideal for cooler zones as the pots can be planted inside and protected from harsh weather in the cooler months.
The first step to success is choosing a suitable variety. While you can grow taller dahlia varieties in pots, they need far more space than smaller types and require more attention and care. Instead, opt for dwarf varieties better suited to container growth, such as ‘Impression Festivo’ or ‘Pulp Fiction’.
The chosen pot should be large enough to accommodate the size of your selected variety – 8 to 12 inches in diameter is usually suitable. The plant’s mature height should not be greater than two times the depth of the plant to stop it from becoming top-heavy.
Ensure you use high-quality potting soil that drains well. If necessary, add a stake soon after planting, and water to encourage growth. Leave the soil to dry out completely before watering again to prevent rotting in the tuber. You can increase dahlia watering frequency once the plant has grown a few inches tall.
With some essential maintenance, Dahlias are not complex plants to grow. The correct watering, fertilizer, and upkeep will ensure your plant blooms prolifically across the seasons.
How Often To Water Dahlias
Dahlias are moisture lovers, requiring consistent watering every couple of days.
Immediately after planting, the soil can be left to dry out completely before watering again. As the tubers don’t have any roots to draw up moisture initially, any excess water will hang around in the soil, causing the tuber to rot.
Increase your watering once the stalk has emerged and the plant has grown a few inches tall. Established plants need watering once or twice weekly on average, but this will differ based on the environmental conditions and light levels.
They will require watering more often in summer when evaporation is higher, potentially as often as every two days. This will keep the plant flowering by preventing heat stress and the flowers from wilting too early. Adding mulch to the soil can help retain moisture by limiting evaporation.
Avoid overhead watering, which can leave water on the leaves, encouraging disease. Installing drip irrigation is the safest and most reliable way to water your plants, but you can also water with a hose, focusing on the soil at the base of the plant.
Water slowly and deeply to encourage strong root growth. Keep a close eye on the soil and water when the top half-inch to an inch dries out.
Do Dahlias Need Fertilizer?
To produce the best blooms, Dahlias benefit from a light fertilizer application during the growing season. They don’t require fertilizer at planting as the tubers contain all the nutrients needed to sprout, but added nutrients just before flowering will give them an extra boost.
Sprinkle a 5-10-10 or 10-20-20 fertilizer around the soil and mix it in gently. This is best done about a month after planting when the stalk has grown sufficiently. You can also apply again during flowering if the plant is not producing enough blooms.
Your chosen fertilizer will dictate the frequency of the application. Slow-release fertilizers are applied far less often than liquid fertilizers, for example. The concentration of nutrients will also impact how often you use them.
Overfertilization is a real risk. Excess fertilizer can cause yellowing leaves and wilting, potentially permanently damaging the tuber and killing the plants. Only apply fertilizer as recommended on the packaging – never more.
Compact dwarf Dahlias generally do not require staking. However, anything taller will generally benefit from some support. Any varieties over a few feet in height will often fall over under the weight of the large flowers or with wind, ruining the blooms you worked so hard for.
There are several material options for stakes, each with its own pros and cons. Wooden poles are affordable and sturdy but generally only last one or two seasons before they need to be replaced. Bamboo poles are also great options, best dug far into the ground for stability, but they also need replacement often.
Although more costly, metal stakes are the most durable and sturdy. Metal stakes can be removed at the end of the season, cleaned, and reused year after year throughout your garden. Like the ones used for tomato plants, metal cages are also suitable but don’t look as good as individual stakes.
How To Stake Dahlias
When planting one Dahlia, one stake is sufficient. Follow this process to install them:
- Install the stake next to the tuber while planting to avoid damaging it later on. Position it close to the eye, as this is where the first stalk will emerge.
- Choose a stake with at least one foot of extra height compared to the plant’s mature size. This will be buried below the ground for stability.
- Dig the stake into the ground or hammer it in next to the tuber. Stop when you’ve reached the plant’s potential mature height and when the stake is stable, not affected by wind or gentle movements.
- As the stalks develop, tie them to the stake with a stretchy material to avoid cutting into the stem. There are specially made staking ties for gardeners, but a piece of stretchy fabric also works well. Don’t tie too tightly to give them the necessary space to grow.
When planting multiple Dahlias in a row, the process is slightly different:
- In rows, stakes can be connected by string to support all plants in the row, limiting the need to stake each plant individually.
- Place stakes around 3 feet apart in the row, ensuring they are buried deep enough to remain stable with slight movement.
- Tie a durable twine to each of the posts horizontally, creating two or three rows depending on the height of the stakes.
- As the stalks grow, guide them through the twine. You can also create an additional row, circling the twine around the taller stems as you go.
How To Pinch Dahlias
Pinching is not a requirement for healthy growth, but it does improve flowering. By stimulating new growth and further branching, there will be more stalks on the plant to produce flowers. It also makes the overall growth denser.
Pinching is best done when the plants are around 8-12 inches tall with several sets of leaves. Pinching too early can make a recovery difficult, ultimately stunting growth. Only start this process when the plant begins to take off to ensure it recovers quickly.
Identify the central sprout on the main stem and pinch it off with your finger or a pair of trimmers. The cleaner the removal, the quicker the regrowth will be.
This wound produces a hormone at the site that triggers the plant to produce new growth. Two side shoots should develop from this point, leading to more stems and, ultimately, more flowers.
Pinching is suitable for any Dahlia type, regardless of species, flower shape, or size.
Weeds are the enemy of the Dahlia garden. These greedy plants compete for nutrients in the soil and crowd out your precious plants. The density of leaf growth is also a breeding ground for pests and diseases.
The first step to controlling weeds is to clear the planting site before starting. Weeds are much harder to manage and eradicate when working around existing plants. Controlling weeds around the rest of your garden will also stop the seeds from spreading to your Dahlias.
After planting, continue pulling any weeds as soon as they emerge while the roots are still easy to remove. The longer you wait, the more difficult it will be to pull the plant completely.
Once the Dahlia roots are established, apply a thick layer of mulch over the soil. This will inhibit germination in many seeds and make any weeds that do manage to sneak through the mulch easier to pull.
Herbicides are used in cut flower gardens when weeds cannot be controlled by pulling. However, these strong products can also harm your Dahlias, depending on the chemicals used, and impact the surrounding environment. It’s best to stick to natural methods for the health of your garden.
Diseases and Pests
Dahlias are prone to several pests and diseases that can ruin your blooms and potentially the tubers permanently.
When it comes to diseases, look out for these potential issues:
- Powdery mildew
- Stem Rot
- Botrytis blight
- Verticillium wilt
- Mosaic virus
- Necrotic spot virus
Prune away any affected foliage as soon as it is spotted, and keep an eye on the plant for further spread. Diseases are difficult to eradicate, so immediate control and prevention are key. Avoid overhead watering and prune dense growth to promote airflow.
These pests are also known to snack on Dahlia leaves and stems:
- Spider mites
- Slugs and snails
Again, the key to stopping these issues from killing your plants is to control them immediately. Pick any large bugs off your plant and drop them into a bucket of soapy water. Smaller bugs can be removed with insecticidal soap or neem oil. Repeat applications may be required to remove the problem entirely.
Do I Need To Deadhead Dahlias?
Deadheading is beneficial for the look of your garden and the health of your plants.
Removing spent flowers takes the energy that would have gone into seed production and directs it toward producing new flowers and keeping the plant vigorous. It also makes the plant look tidier, improving the overall appearance of your garden.
Once the flowers start to wilt, trim them off the stem right above the last set of leaves. Make a clean cut to encourage new growth. At the same time, remove any damaged or diseased foliage to improve overall plant health.
If you want to collect seeds from your Dahlia, leave some flowers on the plant at the end of the season.
How Long Do Dahlias Bloom?
Dahlias will typically begin blooming around two months after planting as long as the weather is warm enough. Some planted in early spring may take longer – up to midsummer – as they require warmer temperatures to begin flowering.
Some Dahlias start blooming later, while others bloom earlier in spring. The time largely depends on the variety, so check the specifics of your chosen cultivar to know what to expect.
These plants have a long blooming season – up to four months under the right conditions. With most blooming from early to midsummer, they will last until fall, when the cold weather causes them to die back.
Again, the flowering period is affected by type. Plant a variety of cultivars with different blooming periods to enjoy Dahlias for the longest possible time across the seasons.
Growing Dahlias As Cut Flowers
Dahlias make lovely, long-lasting cut flowers. They are one of the most sought-after flowers due to their vase life and range in color and flower shape. These factors combined make them great additions to a home-cut flower garden.
Choose flowers that have just begun to open, as cut buds will not open in a vase. Cut early in the morning before the day’s heat can impact the petals’ look. Use sharp shears and place the stems in warm water before arranging them in your vase.
To make the flowers last longer, cut the stems at an angle and trim the bottom half-inch to an inch off every few days to refresh the stem. Change the water every few days or when it gets cloudy. Keep the blooms in a cool area away from direct sunlight to prevent wilting and preserve their color.
Do Dahlias Come Back Every Year?
Depending on the variety, dahlias are perennials that return annually in USDA Zones 8 or higher. Those in lower Zones with cold winters can dig up the tubers and replant them the following year once the soil has warmed.
Digging Up and Storing Dahlia Tubers
When To Dig Up Dahlia Tubers
Once your Dahlia stops blooming, the tuber will begin to draw nutrients from the plant in preparation for dormancy over winter. This process allows the tuber to store enough nutrients to emerge again the following season.
Only dig up Dahlias when the plant dies completely to ensure it has drawn up all the nutrients. This is also why you should not cut back your Dahlias until the last minute, as this can stunt growth for the following season. If cut too early, the stems can also hold water that rots the tuber.
After the first frost, cut back the dead stems to the ground. Loosen the soil around the plant and gently lift out the tuber. Don’t damage the tuber in the process; this will impact storage and lead to rot.
How To Clean Dahlia Tubers For Storage
Microorganisms in the soil can lead to damage and rot after storage. The tubers must be cleaned before being put away to prevent this issue. Wash all the excess soil off with a hose or place it in a bucket and remove it by hand.
Once cleaned, place them in a warm and dry area for a few days to cure. Ensure the area is well-ventilated to prevent fungal growth. This will prevent rotting during storage, keeping the tubers viable for the next season.
How To Store Dahlia Tubers Over Winter
The cured tubers can be placed in a plastic bag, cardboard box, or another storage vessel for the winter. Space each tuber, so there is adequate airflow between each one. Some gardeners also store them in light, airy material like peat moss or sand.
Keep the box in a cool and dark place over winter. They need this period of cold and dormancy to trigger new growth in the spring.
How To Divide Dahlia Tubers
Dahlias are best divided in spring before planting. You can also separate them once they are pulled from the soil, but this exposes the tubers to potential problems with rot.
The process is simple. Identify the eyes – the pink or white spots usually on the thinnest part of the tuber. Using a sharp and disinfected knife, cut the tubers into sections with at least one eye on each, preferably two.
Most gardeners will take this opportunity to remove the central tuber, also called the mother. This primary growth does not store well or produce healthy plants and is best left out of the dividing process.
Replant immediately after dividing. If dividing in fall, dry the tubers out for a few days before storing.
Types of Dahlias
There are several ways to separate the different Dahlias, but most prefer to separate them according to their flower forms. The America Dahlia Society (ADS) lists 20 different flower forms, each with its own unique characteristics.
- Formal Decorative
- Informal Decorative
- Straight Cactus
- Incurved Cactus
- Miniature Ball
- Novelty Fully Double
- Novelty Open
- Mignon Single
You can find dahlia flowers in various colors within each type, including white, pink, red, yellow, green, purple, and black. Each color has a different meaning and significance, great to know when designing a bouquet or gifting.
With so many options to choose from, it can be hard to pick the perfect type for you. Here are a few of the most popular cultivars across the different types to get you started in the world of Dahlias:
- Café au Lait
- Kevin Floodlight
- Black Jack
- Bora Bora
- Myrtle’s Folly
- Franz Kafka
- Alloway Candy
- Totally Tangerine
- Mexican Star
- Pulp Fiction
- Apple Blossom
How Big Do Dahlias Grow?
With so many different species and cultivars, it’s understandable that there is such a range in sizes of these beloved plants.
Dwarf varieties remain compact, growing to around 15 inches tall. Other varieties can reach an impressive 5 feet tall in the right conditions, producing flowers on incredibly long stems that require staking. The entire plant spreads around 1-3 feet wide on average, depending on the variety.
There is also variety in flower sizes. The small pompoms stick to around 2 inches in size, while the larger dahlia blooms can grow over 10 inches in diameter. These are aptly named giant Dahlias or dinnerplate Dahlias.
Popular Dahlia Societies to Join
Dahlias have a dedicated fan base, spawning many societies around the world:
- American Dahlia Society
- National Dahlia Society – United Kingdom
- Dahlia Society of Australia
- Japan Dahlia Society