How Big Do Dahlias Grow?

Updated November 21, 2016

Dahlia flowers come in a wide range of sizes, well suited for many types of gardens. There are more than 10 categories of dahlia blooms, all featuring different shapes and bloom sizes. As the bloom size varies, so does the average height of dahlia plants. Many dahlia nurseries use classification codes to provide gardeners with more information regarding the size and style of the dahlia bulb.

Average Height

With so many dahlia types available, it is difficult to determine the final height of a particular dahlia bulb. Most flowers reach a finished height around 4 feet tall, according to dahlia expert Barbara Jenke of the American Dahlia Society. Depending on the variety, dahlias may grow between 1 and 6 feet tall.

Size Codes

Due to the sheer volume of dahlia varieties, growers have assigned size codes to dahlias. These codes refer to the size of the dahlia blooms. There are six main dahlia size codes: AA, A, B, BB, M and P. AA classified dahlias are also known as giant dahlias with blooms exceeding 10 inches in diameter. A dahlia blooms range between 8 and 10 inches in diameter. The B classification features blooms between 6 and 8 inches across. The diameter of BB classified dahlias range between 4 and 6 inches. M and P dahlias are the smallest types. M dahlia blooms grow up to 4 inches wide while P classifications only reach 2 inches in diameter.

Single Dahlia Types

In addition to understanding the various size classifications, dahlia growers should understand the various blooming characteristics. There are several types of single bloom dahlias on the market including single, collarette and anemone dahlias. Single dahlias feature a single row of flat petals. Identify collarette dahlias by the single row of cupped petals and the petaloid forming a collar-like shape around the bloom. Anemone dahlias resemble their namesake with rows of petals surrounding a dense ring of disc florets.

Other Dahlias

In addition to single dahlias, there are several types of dahlias featuring multiple rows of petals. Orchid and peony dahlias feature open centres and irregular, overlapping petals. Decorative dahlias come in informal and formal varieties. Formal decoratives feature many rows of flat, even petals forming a multilayer bloom. Informal decoratives are similar to the formal variety, but feature irregularly shaped petals. Cactus types feature long, curving petals that closely resemble the spiny texture of a cactus flower. Pom-pom dahlias are among the smallest varieties with tiny blooms appearing as puffs of tightly packed petals.

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