Growing Dahlias

Henry David Thoreau said, “Where the most beautiful wild flowers grow, there man’s spirit is fed and poets grow.” These words highlight the benefits of spending time in nature and inspired this post about dahlias.

Dahlias are one of my favorite flowers. They are super easy to grow. Moreover, the broad swath of dahlia varieties available make them collector’s items to fans. Dahlias are tuberous plants that produce flowers in a variety of shapes and colors throughout the summer. Long stems make them particularly great for cutting, displaying, and sharing with friends and family.

Dahlias can be grown from seed but are more commonly propagated from tubers. This is because dahlias grown from tubers are genetically like their mother plant, whereas flowers grown from seed are unpredictable and often look very different from the mother plant.

Dahlias are native to USDA plant hardiness zones 8-10 and when properly cared for will reward you with new flowers year after year. Growers outside zones 8-10 typically need to dig up the tubers in the fall and store them in a cool dry place until they can be replanted the following year. You can look up your plant hardiness zone using your zip code by visiting USDA’s website at https://planthardiness.ars.usda.gov.

Getting Started

Dahlia tuber’s have a craggy anatomy consisting of a neck and body. While it is difficult to see them in the winter months, an eye forms on the neck of the tuber where shoots will sprout with leaves and eventually stems and flowers. Each tuber can have multiple eyes and produce many flowers. It is important to carefully handle tubers to avoid damaging the neck or eyes, both of which are vital to the tuber’s health.

It generally takes three to five weeks for dahlia tubers to begin sprouting and eight weeks to flower. Because of this long ramp up time, many growers pre-sprout tubers inside to get a head start before planting outside. To start indoors, plant the tuber in a small pot of damp soil lengthwise with the neck just above the soil line. Because dahlias will not begin to grow until the soil temperature reaches at least 62 degrees, it is helpful to place the pot on a heat mat.

After planting, wait for the tuber to sprout before watering. Dahlias do not like wet feet, so monitoring soil moisture is a critical step to sustaining them. (The soil should feel damp but not wet). Sprouts should be trimmed once they reach ten inches by cutting off the top one to two inches. Cutting dahlias back may seem counterintuitive but is necessary for growing long heathy stems. Also, where you make the cut, two new stems will form and produce even more flowers.

Planting Dahlias Outside

Dahlia tubers can be planted in the ground after the last frost date, spaced ten inches apart and eight inches deep. Support large dahlias with a bamboo stake and secure with string. Dahlias planted in rows will support themselves. Dahlias should be planted in full sun and watered regularly. I use drip lines in my garden but if you use a hose aim the water at the base of the plant to avoid toppling it over.

Once your dahlias bloom, you can cut and display them in a vase. Be sure to cut the stems at the base where the stem connects to the center branch. Cutting regularly will encourage the plant to produce more flowers.