The dahlia plant produces flowers in a range of colors, shapes and sizes.¹ The flowers are often loved by gardeners as they have one of the longest blooming periods compared to other plants.² Dahlias will start blooming in June and many continue to flower until the first frost. 

The dahlia plant is native to the high plains of Mexico. Some species have also been propagated in Guatemala, Honduras and Costa Rica.³ The dahlia has been grown in Europe since arriving at the botanical gardens of Madrid during the 18th century. The original flowers had an open center but it wasn’t long before gardeners found they could hybridize the plant and change both form and color. 

You can find dahlia plants in the form of water lilies, peonies, chrysanthemums and anemone.⁴ They’re grown as flat broad petals, rolled pointed petals or globular flowers. The flowers may be the size of a dinnerplate or a small pom pom.⁵ In other words, no matter your preference for shape and form, there’s likely a dahlia plant to suit your taste.

The plants are often grown as ornamental flowers and belong to the aster family,⁶ which also includes zinnias, safflower, ragweed and dandelions.⁷ The dahlia is the national flower of Mexico. 

Familiar with cultivating the plant, the Aztecs were the first to discover a dahlia tree known to grow approximately 20 feet high with a hollow interior.⁸ They were able to use the flowers for water. When the Spaniards conquered the Aztecs, they brought seeds back to Spain, where they were cultivated. 

Planting dahlias in your garden offers you some of the most spectacular views throughout the summer. According to The American Dahlia Society,⁹ there are now 42 recognizable species and several more subspecies. Growing dahlias is easy and they often yield beautiful blooms beginning in the middle of summer. This can go on well into the fall months.

The Fundamentals of Growing Dahlias

Learning how to grow dahlias requires a few steps before you plant. It’s important to choose the right type and size for your garden. Large plants can grow as high as 5 feet tall¹⁰ with flowers of up to 1 foot in diameter. Their height and blooms look best at the back of a perennial border. The larger plants require some staking to support the stems during wind and rain.¹¹

Medium dahlias grow up to 2 feet in height and can be grown in containers. The smaller ones reach 20 inches and remain fairly compact, which makes them a perfect addition for a window box, container or the edge of a border.¹²

Each dahlia grows from a tuber and can be found at most nurseries and garden centers.¹³ If you’re interested in a plant not commonly found in the garden center, nearly every local dahlia society has events where guests are welcome. The benefit to purchasing tubers or plants from a club is the ability to speak to experts who can answer your questions and help you through your first season.

The dahlia is a perennial plant in USDA Hardiness Zones 8 to 11. In cooler areas, gardeners may plant the tubers and either allow them to die at the end of the year or dig them up and store them for winter.¹⁴ When choosing your tubers, avoid those that look wrinkled and instead choose the ones that have a little bit of green growth or buds.¹⁵

Consider Soil, Water and Sun in Growing Dahlias

Dahlias appreciate well-drained, rich soil with a neutral pH near 6.5.¹⁶ If your soil is clay or heavier, consider enriching it with plenty of organic matter, even when planting in containers or window boxes. You may also add sand, aged manure or peat moss for better drainage and to keep the texture loose.¹⁷

Bone meal may be added as you plant the tuber, but if you have animals in the yard that are attracted to bone meal, they may dig up your tubers!¹⁸ In containers, use two parts garden soil with one part potting soil,¹⁹ which helps with moisture retention as potting soil dries quickly.²⁰ Dahlias grow from tubers that form at the base of the stem in the fall.²¹

In addition to rich soil, your growing dahlias will do best when regularly watered.²² Although the plants appreciate a drip irrigation system, if you’re hand watering, water at the base of the plants to keep the foliage dry and reduce the risk of fungal growth.

Select a site in full sun as your plants will produce more blooms when they have up to eight hours of direct sunlight.²³ In a less sunny location the plants will grow taller but have fewer blooms.²⁴ Look for a location protected from the wind as the larger plants may take a beating during inclement weather.²⁵