All About Dahlias

all about dahliaall about dahlia

By Katie Elzer-Peters, gardening expert and writer.

There are some flowers that, when you see them blooming, you just have to stop and stare awhile. Maybe snap an Instagram picture or twelve. Dahlias are like that for me.

There are not enough superlatives to describe the way the flowers turn into glowing orbs of color when the sun shines through the petals. Or the sheer delight of taking a garden tour and happening upon a huge dinnerplate dahlia flower that’s as big as my head and blooming at eye level.

You know you’re at the home of a Gardener (with a capital G) when the borders and flowerbeds are filled with dahlias. The plants take a bit of effort to coax into bloom, but they’re worth it.

Dahlias are Tubers, not Bulbs

Dahlias grow from tubers, which are swollen underground stems. They have eyes, which are the stems that grow up and produce flower stalks. Potatoes are tubers, to give you a bit of visual reference. When you see potatoes sprouting in the refrigerator drawer, you’re seeing the eyes grow.

Dahlia tuber clusters look like a strange, upside-down bouquet of sweet potatoes. At the top is the old stalk from the previous year’s growth. Tubers (that look like small sweet potatoes, tapering to a point) hang down from the stalk. The eyes are usually located at the top of the tubers, closest to the old stalk.

dahlia tubersdahlia tubers

You can divide dahlia plants that are more than an year old by cutting apart the tuber clump. Each separated tuber needs to have an eye in order to sprout and grow when planted.

Dahlias are Delicate Flowers (Sort-of)

There are some plants that fall into the “not difficult to grow as long as you give them what they want” category. Consider dahlias firmly ensconced right there.

They are not difficult to grow, given the right conditions: warm weather, at least six hours of sun per day, well-drained soil, a diet low in Nitrogen, sturdy support (for larger types), and a winter hibernation period somewhere cool, dark, and dry. (Dahlias will sometimes overwinter in the garden in zones 8 and higher, but they intensely dislike wet feet, and are prone to rot. It’s better to lift and store during the cool season.)

Read about how to grow dahlias here.

pink dahliaspink dahlias

Types of Dahlias

Dahlias, as a group of plants, are subdivided into smaller categories based on their blooms—much like roses, camellias, daffodils, and tulips. The number of categories or types depends on whether you’re reading a list from the UK (14) or the United States (16).

Unless you decide to grow and show dahlias, memorizing every single classification isn’t necessary. Here are a few of the more common and popular types available for purchase:

Cactus: Flowers are between 4 and 10 inches wide. Petals are tubular with pointy ends. They look like cactus flowers.

Pompom: Small flowers less than 2 inches across. Petals have rounded ends which makes the flowers look like pompoms. There is another category called “ball dahlias” with similar-looking flowers.

Dinnerplate: This is not an official classification of any dahlia society, but it is frequently used to describe plants with huge blooms—the size of dinner plates (between 8-10 inches in diameter). Plants are usually equally large to support such huge flowers with some dinnerplate dahlias topping out at 5 feet.

Other classifications include waterlily, peony, and anemone dahlias, named for their flowers’ resemblance to other types of plants.

It is worth noting that the size of the flower and the eventual size of the plant are not always related. Make sure you have room for the variety you selected to plant.


6 Secrets and Short Cuts for Beautiful Dahlias

1. Stake at the time of planting.

It is a lot easier to establish a framework of stakes and/or a lattice of stakes and twine for the plants to grow through than to wrestle plants into a support structure.

2. Give plants a head start in containers.

You’ll plant dahlias outside around the same time you plant tomatoes. If that’s not until late May or early June where you live, start dahlias early by planting them in containers. If you plan to transplant into the garden, you can start several dahlia tubers in 3-4 inch deep trays. Just lay tubers on their sides with the eyes up and cover with 2 inches of soil. Wait until you see new growth breaking through to water. If you want to leave plants in the containers, choose a 12-16 inch diameter container to plant the tubers.

3. Disbud to get larger flowers.

This sounds jargony and difficult, but it isn’t. Flower buds will form in groups of three. Leave the center bud on each stalk and remove the two side buds.

pink dahliaspink dahlias
4. Seal cut flowers.

Dahlias make wonderful cut flowers. Snip stems in the morning when the water content of the plants is highest. When you bring flowers inside, re-cut the ends and place the stems in 2-3 inches of hot, but not quite boiling hot, water for an hour. After the hour is up, you can incorporate the stems into your flower arrangement.

5. Dig up after the first hard frost.

Trim off the year’s growth, leaving 2-3 inches of stem to dry. Wash off the soil and allow plants to dry for several days before packing in cardboard boxes between layers of newspaper.

6. Divide dahlia tubers in spring.

Before you’re ready to plant, you can use a sharp, clean knife to cut a tuber cluster into individual tubers. Look for an eye near the stem and make sure each tuber has an eye. Allow cut tubers to dry for a few days before planting.

About the Author: Katie is a writer, runner, and reader, living in southern coastal North Carolina. Her favorite garden is her "wild flower patch" where something new is always blooming (or taking over).

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