Planting at the wrong time can cause the tubers to rot.

Dahlias are real showstoppers in the garden, and it’s easy to see why. The unique leaf arrangements are available in many colours, shapes and sizes and provide a spectacular display from summer until the first frost of autumn. Closely related to sunflowers, daisies, chrysanthemums and zinnias, the dahlia plant produces single-stemmed flowers ranging from 2 inches to 1 foot in diameter.

These easy flowers to grow It is a perennial in warmer climates and is considered a hardy annual in zones below USDA hardiness zone 8. Dahlias thrive in full sunlight and well-drained soil with a nearly neutral PH of 6.6 to 7. If you plan to grow this flower in your garden, these expert-approved guides on when and how to plant dahlias will set you up for success.

Meet the Expert

Relating to: How to Grow Dahlia, a Showy Flower that Blooms from Summer to Autumn?

Determining the Last Frost Date in Your Regions

Dahlias are tender annuals, which means you’ll need to wait until the threat of frost has passed before planting them outside. “The last frost date is the average date of the last light freeze in the spring,” says Caitlin Meredith, owner of Quietside Flower Farm in Downeast Maine. “A light freeze is generally temperatures ranging from 29 to 32 degrees Fahrenheit, which will kill tender annuals like dahlias.”

There are many resources available to help you determine the last frost date in your area; your local extension office, The Old Farmer’s AlmanacNOAA National Centers for Environmental InformationAnd Our helpful guide.

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Local gardeners know the microclimate well. Ask local growers about their next expected frost date to ensure a safer start to the planting season.

When to Plant Dahlia from Seeds?

If you want to get a head start on your Dahlia seeds growing season, plant them indoors before spring. “Dahlias can be started indoors from seed six to 10 weeks before your desired planting date,” says Marina Sideris, co-owner of Dooryard Farm, an organic farm in Camden, Maine. Alternatively, you can sow dahlia seeds directly outside in the spring after danger of frost has passed.

When to Plant Dahlia Tubers?

Dahlia tubers can be planted in your garden once all danger of frost has passed and the soil temperature is at least 55 to 60 degrees Fahrenheit. “Dahlia tubers will remain dormant until the soil temperature rises above 55 degrees Fahrenheit, and the risk of rot increases if planted in soil that is too cold,” says Meredith. “Some gardeners like to start the tubers in pots indoors to give their dahlias a head start on blooming earlier.” If you do this, start the tubers four weeks before you plan to plant them outside.

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Stay away from planting tubers, especially if you are expecting a rainy period. “Until they start to sprout, tubers are prone to rot from too much moisture,” says Mary Turner, master gardener and owner of Salt Farm Flowers.

How to Plant Dahlia from Seeds?

Growing dahlias from seed is a good way to get a head start on the growing season. But be aware that dahlias grown from seed are not true to their parent plants due to cross-pollination. “If you want to grow a clone of a particular variety, it needs to be grown from a tuber,” says Meredith.

1. Moisten your potting soil mix or seedling soil mix well before planting.

2. Fill a large box with soil. Let the soil sit for a few minutes until the water recedes. Mix it with your hands and let it sit for a few more minutes.

3. Fill the six-pack or plug tray with your moistened soil. Make slight depressions with your fingertips to create ¼-inch deep grooves.

4. Place one seed in each divot by hand or with a planter.

5. Cover the seeds by amending the soil again.

6. Water your seeds once more using a very light spray to allow the soil to settle. (A spray that is too harsh will dislodge or even wash the seeds.)

7. Store the seeds in an area of ​​your home where the temperature is between 65 and 70 degrees Fahrenheit. This can be most easily accomplished with a heat mat or grow light.

8. Water the seedlings once or twice a day until germination occurs.

9. Once the seeds have germinated, move them off the heat mats to a sunny location. How often you need to water depends on your seedlings’ location and climate. You will need to water at least once a day.

10. Once your seedlings have developed one or two sets of leaves and some roots, they can be transplanted into 4-inch pots.

11. Once the seedlings have two to three sets of leaves and it has been at least two to three weeks since your last frost date, move them outside for a few days to acclimate to the environment, then transplant them into soil.

Warning

Dahlias poisonous to dogs and cats so keep this in mind when choosing your growing location.

How to Plant Dahlia Tubers?

Dahlia tubers have a bulbous stem at one end and a small crown at the other end, where future growth points, called eyes, are located. “The body and eyes are connected by a thin neck, so it’s important not to disconnect the two or your dahlia won’t grow,” says Sideris.

1. Dig a hole where you want to grow your dahlia. Moisten the soil.

2. Insert the stake you will use to support your dahlia before planting the tuber to avoid accidentally puncturing the tuber.

3. Plant the tubers directly into the soil at a planting depth of about 4 inches. Lay the tuber on its side with the eye closest to where you will plant the plant. (Placing the tuber at a 45-degree angle with the stem facing down and the eye facing up works well.)

4. Cover your tuber with soil and do not water it. Once soil growth appears, begin watering your plants deeply once a week (or less during rainy periods). Water until the plants are at least 8 inches tall with 3 or 4 sets of leaves. If you live in a hot, dry climate, you may need to water more than once a week.

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Dahlia tubers don’t have roots to begin with, so they can’t take in water. “So it’s important not to overwater, otherwise you run the risk of the tubers rotting,” says Sideris. As your plant grows and develops roots, increase the amount and frequency of watering as your climate requires.

Frequently Asked Questions

Should I soak dahlia tubers before planting?

Do not soak dahlias before planting them. “They’ll probably turn to mush shortly after you do this,” says Turner.

Is it too late to plant May dahlia tubers?

Turner says May is a great month to grow dahlias because the soils in zones 3 through 6 are warmer.

Do dahlias come back every year?

Dahlias will not come back to growing zones 6 and below, which make up nearly half of the United States. “These areas can have soil that freezes in the winter, causing the tubers to turn to mush,” says Turner. “They can’t stand freezing.” If you have a winter where the soil does not freeze, you can overwinter it.