All About Dahlias - Planning, Planting, and Aftercare

Start with a Better Plant

We sell grade #1 dahlia clumps, which are the largest size available. These photos show the difference between a large clump of grade #1 tubers on the right and a smaller clump of #3 tubers on the left. With a larger clump, you begin the season with more eyes (or growth points), so it take less time to get a large plant and lots of flowers.

Dahlias are incredibly easy to grow. Here are a few tips to help you get the best results. 

Sun and Shade:  Dahlias are sun-lovers and need a minimum of 6 hours of sunlight per day. The more sun they get, the better they'll bloom, so it's best to plant your dahlias in the sunniest location possible.

Zone:  Though dahlias are only winter hardy in zones 8-11, gardeners in zones 3-7 can grow dahlia as annuals. Plant the tubers in spring, and the plants will be blooming by mid to late summer. Don't know your hardiness zone? You'll find the USDA Hardiness zone map here.

Soil:  Most plants, including dahlias, grow best in loose, fertile, well drained soil. To improve the quality of your soil, add compost and an all purpose fertilizer at planting time. Avoid growing dahlias in areas where the soil is soggy or compacted.

When to Plant: Dahlias tubers should be planted in spring after all danger of frost has passed. If you live in a cold climate and want your dahlias to bloom as soon as possible, you can start the tubers indoors or in a greenhouse 4 to 6 weeks before the last frost date. Fill 1 or 2-gallon pots with growing mix and plant one clump of tubers per pot. Put the pots in a warm, sunny place and then transplant them into the garden when the weather outside is warm and settled. Newly-planted dahlia clumps should receive very little water until they have sprouted and are in active growth.

Where to Plant Dahlias

Flower Gardens: Dahlias bloom from late summer through fall and hit their stride and the end of the growing season as most other plants are starting to fade. When planting dahlias into your garden, be sure you know each variety's ultimate height. Place the tallest in back, mid-size dahlias in the middle and border dahlias up front. 

Entryways, Patios. and Decks: Decorate your home and welcome guests with a brilliant display of dahlias. Border dahlias are ideal for containers and edging walkways. The compact, bushy plants grow just 18-24" tall and cover themselves with flowers from midsummer to frost.

Along Fences or for Screening: Dahlias can be functional as well as decorative. Full-size varieties can be planted along a property line to add privacy. They can also be planted in pots to enclose a space or be positioned in the garden to screen an unwanted view.

Vegetable Gardens: Dahlias like the same growing conditions as vegetables -- rich, well drained soil with consistent moisture and plenty of sun. Plant dahlias at the same time as tomatoes and peppers. When harvesting your dinner, you can bring in an armload of fresh flowers for your table.

Cutting Gardens: Dahlias are fabulous cut flowers and just a few plants will give you months of blooms. Planting several different flower styles will give your bouquets a professional look.

How to Plant Dahlias

1. Dig a hole to 4-6” deep in well-drained soil.

2. Set the tubers in the hole with the stem facing up. The crown of the plant (where tubers connect to the stem) should be 1-2" deep.

3. Replace the soil and water only if the soil is very dry. Sprouts will appear in 2-4 weeks.

Tips for Success

Choose a sunny spot. Dahlias bloom best in full sun.

To give your dahlias the best possible start, prepare the soil by adding compost or rotted manure, and an all purpose (5-5-5) granular fertilizer.

Position the tubers in the hole so the stem, where the tubers are joined, is upright.

Sprouts will develop just above where the tubers join the stem. This junction should be planted no more than an inch below the soil surface.

Once your dahlias are 8-10" tall, begin fertilizing them with an all-purpose liquid fertilizer every 3 to 4 weeks.

Pinching dahlias when they are about 10" tall will give you bushier plants with more flowers. 

When the first flower buds appear, cutting back a couple of the tallest stems will help the plant fill out and produce more flowers.

How to Support Your Dahlias

Dahlias have hollow stems and this makes them susceptible to breaking in rain and wind. If you are growing full size dahlias with large flowers, you'll need to provide support to keep them from breaking. You can use stakes, cages or a corral method.

If you are using stakes, plan on at least one sturdy, 6-foot-tall stake per plant. Drive the stake into the ground 8 to 10" deep. As the stems grow, tie them to the stake every foot or two. Inserting the stakes at planting time means you won't damage the plant or tubers later in the season.

Another method is to surround each plant with a tomato cage or a custom cage made of reinforcing wire. This is a quick and easy solution and the cages can be used year after year. Put them in place shortly after planting.

Flower farmers often use a corral method to support rows of dahlias. Insert stakes every 3 to 4 feet down both sides of the row. Wrap twine from one stake to another, starting at a height of about 12", so the plants are contained within the corral. As the plants grow, you may need to add a second or even third row of twine. For beds that contain a double rows of plants, adding a center stake makes it possible to provide even more support.

Growing Dahlias in Containers

Dahlias grow well in pots and planters. They can be combined with other plants, but grow best when planted on their own. Full size decorative dahlias and dinnerplate dahlias require very large containers. The bigger the better. For a full size dahlia, the pot should be a minimum of 18" deep and 18" wide.

Border dahlias may be grown in smaller pots with a minimum of width and depth of 12". Fertilize your container-grown dahlias every few weeks (or use a slow-release fertilizer). Always water deeply to ensure all the soil in the pot gets wet. This may be a daily task from midsummer on. 

Caring For Dahlias After They Bloom

Many gardeners treat dahlias as annuals. When the season is over, you can simply dig up the tubers and add them to your compost pile. If you want to save your dahlia tubers for the next growing season, here’s how to do it:

• Make sure each plant is labeled so you know which tubers are which, because they all look alike. After the first frost, cut off the stems to within 4” of the ground. Wait about a week before digging so the tubers begin entering dormancy.

• Start digging carefully, 10-12" out from the stem. Gently lift the tubers from the ground, using caution as they are fragile. If weather permits, allow the entire clump to air dry for a few days (protected from rain and frost). This will encourage the tubers to toughen their skin for winter storage.

• Dahlia clumps are usually divided before they are replanted. You can divide them in the fall, or store the clumps and divide them in the spring. Both techniques work equally well. It really depends on your time and storage space. 

• Before storing clumps for the winter, trim back the stems to 1". Gently place the clumps into a bin filled with several inches of sand, sawdust or vermiculite. If you are putting multiple tubers into one container, layer the tubers so they don't touch each other. Store the containers in a cool (40-50°F), dark place and check monthly to make sure the tubers are not too wet (rotting) or too dry (getting wrinkly). Adjust humidity level accordingly.