Even beyond the cheery summer garden beds and wedding bouquets many of us are used to, the dahlia is a flower of many faces — and many lives. Today, there are over 50,000 named cultivars of garden dahlia with radically different forms and colors. They’re grown all over the world, even in climates where their underground tubers have to be dug up by hand and stored every year in order to survive the winter. So, what’s so special about dahlias?
The Origins of the Garden Dahlia
In the Sierra Madre highlands of Mexico and central America, the ancestors of today’s dahlias have captured people’s attention for millennia. These wildflowers resembled today’s sweet, single-flowered varieties over the ornate, densely clustered decorative forms. Early Spanish accounts even describe dahlias growing in the grand botanical gardens of the Aztecs. Ornamental value is only part of the picture, though: every part of the dahlia is edible, from the petals and foliage to the starchy tubers. As a staple of Mesoamerican diets, dahlias were so widely cultivated that they were already hybridized as a food crop long before European botanists first recorded them in the 16th century.
Today’s garden dahlia is considered a ‘cultigen’ — a true hybrid, created through intensive human intervention. Generations of people (from highland farmers and Aztec elites to Victorian horticulturalists and modern plant nerds) have pushed these plants to their genetic frontiers. Dahlias have a uniquely diverse range of appearances, both in color and form.
You can see this variation first hand when you grow dahlias from seed. While most seed-grown dahlias err in the direction of pink-to-red single-flowered forms, there’s a great degree of randomness and there’s no way of predicting how the flowers will look. The only way to faithfully replicate a unique variety is to grow it from cuttings and tubers, so particularly attractive varieties can gain an avid following.
Growing Dahlias in the PNW
- Lighting — Dahlias grow best in full sun (6 - 8 hours per day)
- Water — While those tubers can make dahlias a bit more forgiving, ample summer irrigation helps support the growth of those generous blooms
- Soil — Loose soil with good drainage is essential for healthy root systems and tubers
- Deadheading — When the blooms begin to fade, clip the stem just above the next pair of leaves
Overwintering Dahlias in Portland
So, can you leave dahlias in the ground in Portland? Dahlias are right on the edge of our 8b growing zone, so they are susceptible to our coldest winters. Northwest gardeners report mixed success with overwintering tubers in place and, in certain microclimates, they may be able to return as perennials. One of the biggest issues with our climate is that the rainy season leaves the dormant tubers vulnerable to rot, so ensure good drainage or dig them up to store at the end of the season.
Dahlias at Cornell Farm
If you're looking for summer color, we grow hundreds of dahlias in our greenhouses each year. From massive dinnerplates like 'Thomas Edison' and 'Cafe au Lait' to the neon sunset hues of the 'Mystic' Series,' there's a dahlia for everyone — and our team is here to help you find yours!
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