How To Grow Dahlias

When I was a kid, my dad often planted a row of dahlias along the edge of our vegetable garden. As the garden faded in late summer, the dahlias took over with big blooms, often measuring more than six inches across. These beautiful blooms are great for enhancing your garden or landscape design, and they come in a variety of sizes and colors. The best thing about Dahlias? They’re easy to care for, even if your thumb isn’t exactly green. Here’s everything you need to know about planting and growing dahlias.

What Are Dahlias?

Depending on who you ask, you’ll get a variety of answers. Dahlias are the national flower of Mexico, where native species grow high up in the mountains.

A forager may excitedly tell you dahlias are a food source. Although I’ve never eaten them, the tubers are edible. Dahlias bloom in late summer and early fall and make excellent cut flowers to spruce up your home in a vase or give as a gift.

Types of Dahlias

The American Dahlia Society classifies Dahlias based on flower size, form and color.

• Sizes vary from micros, up to two inches across, to giants, which can be more than 10 inches across. In between are large, medium, small and miniature blooms.
• Forms range from pom-poms to cactus-flowered, with many variations.
• Colors include almost all except blue. Some varieties feature bi-colored petals.

Where Can Dahlias Grow?

In United States Department of Agriculture (USDA) Plant Hardiness Zones 8 through 10, dahlias are considered perennials. They will survive in the ground over winter. “USDA hardiness zones are important so that you select plants that will thrive in your growing conditions,” says gardening expert Annette Hird.

In USDA Zones 6 and colder, dahlias are grown as annuals. In late fall, dig up dahlia tubers to overwinter out of the ground. In Zone 7, dahlias may survive winter in the ground. But to be safe, dig up the tubers in fall.

Dahlias prefer well-drained soil and at least six hours a day of full sun. They don’t do well in South Florida and similar hot climates.

When To Plant Dahlias

Plant dahlia tubers in spring once your garden is frost-free. Or you could start them in containers a few weeks before your last frost.

If you go the latter route, use small containers and a general potting mix. Four-to five-inch plastic pots with drainage holes work well. Keep the pots outside in a warm location and bring them in on nights with a risk of frost.

Dahlias started in containers are ready to plant once the shoots are a few inches tall and small roots come out of the drainage holes.

How To Plant Dahlias

Most dahlias are purchased as tubers. Here’s how to plant them:

• Lightly cultivate the soil.
• Dig a hole approximately six inches deep.
• Secure a sturdy stake next to the hole. This supports the dahlia, which can grow more than four feet tall.
• Place the tuber in the hole with the “eye” facing up. The “eye” is the little shoot on the end of the tuber where it was cut from the main stem.
• Cover the dahlia with the soil dug from the hole. Some gardeners fill in only two to three inches at first, then cover the rest of the hole once the shoot begins growing.
• Stick a plant label next to the stake with the variety name on it. This helps if you planted several varieties and want to remember which is which.
• Hold off watering until you see the shoots. Dahlias don’t like wet soil, which may cause the tubers to rot.

When Do Dahlias Bloom?

Dahlias begin flowering in mid-summer. If you cut off spent blooms, they’ll continue to flower into fall.

How To Care for Dahlias

Once planted, dahlias are easy to care for.

• Water them just enough so the soil is moist but not sopping wet.
• Watch for slugs and other pests. You’ll find them on the undersides of leaves early in the morning. There are many natural ways to control slugs.
• Fertilize your dahlias once a month with a product lower in nitrogen. They’re heavy feeders.
• As the plants grow, tie them to the stakes for support.
• Cut flowers to enjoy inside. This encourages more blooms.

What To Do With Dahlias in Fall

Dahlias can’t survive the cold weather; so in zones 7 and colder, you must dig up the tubers. “In colder areas, the tubers should be lifted, divided (if necessary) and then stored in a paper bag in a cool, dark spot. They can then be replanted once the danger of frost has passed,” says Hird.

There is an exception to this rule if you live in a warmer climate. “In areas where the ground doesn’t freeze, dahlias can actually be left in the ground, and the soil can be covered with a layer of mulch over winter,” says Hird.

FAQ

Do dahlias need to be staked?

Yes, most dahlias need to be staked because the weight of the large bloom can make the stem break. The American Dahlia Society recommends placing a sturdy stake in the soil before you plant the dahlia. If you put the stake into the ground after the plant is growing, you must be careful to not damage the tuber or the root system. Tie the plant to the stake several times as it grows.

Can dahlias survive winter outdoors?

No, in most parts of the country, dahlias cannot survive the winter. After the first frost, you should lift the tubers from the ground and store them in a dry, frost-free location until the spring when they can be replanted.

About the Expert

• Annette Hird is the owner and author of Easy Urban Gardens. Hird has an Associate Diploma in Horticulture and is an urban gardening expert. She has worked as a professional propagator and managed, maintained and improved many urban and rural gardens.