When to plant dahlias for the most beautiful blooms, according to gardening experts

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

Dahlias are true garden staples, and it’s easy to see why. Their unique petal arrangements come in a variety of colors, shapes and sizes, providing 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 flowers that are easy to grow are perennial in warmer climates and are considered hardy annuals in areas below USDA hardiness zone 8. Dahlias do well in full sunlight and well-drained soil with a nearly neutral pH of 6.6 to 7. If you’re planning on growing this flower in your garden, these expert-approved guidelines for when and how to plant dahlias will help you succeed.

Meet the Expert

Connected: How to grow dahlias – a stunning flower that blooms from summer to autumn

Finding the last frost date in your area

Dahlias are tender annuals, which means you’ll have to wait until the danger of frost has passed before you can start planting outdoors. “The last frost date is the average date of the last frost in the spring,” says Caitlin Meredith, owner of Quietside Flower Farm in Downeast Maine. “Light frosts typically reach temperatures between 29 and 32 degrees Fahrenheit, killing tender annuals such as dahlias.”

There are many resources to help you determine the last frost date in your area, including 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 the next expected frost date to ensure a safer start to the planting season.

When to plant dahlias with seeds

If you want to give your dahlia seeds a head start during the growing season, sow them indoors until spring. “Dahlias can be started indoors from seed six to ten 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 outdoors after the danger of frost has passed in the spring.

When to plant dahlia tubers

Dahlia tubers can be planted in the garden when the danger of frost has passed and the soil temperature is at least 55 to 60 degrees Fahrenheit. “Dahlia tubers will remain dormant until soil temperatures rise above 55 degrees Fahrenheit, and they have an increased risk of rotting if planted in soil that is too cool,” says Meredith. “Some gardeners prefer to pot the tubers indoors to give the dahlias a head start on flowering earlier.” If you do this, plant the tubers four weeks before you plan to plant them outdoors.

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If you are expecting a particularly wet period, hold off on planting the tubers. “Until they start to sprout, the tubers are prone to rotting due to too much moisture,” says Mary Turner, head gardener and owner of Salt Farm Flowers.

How to plant dahlias with seeds

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

1. Before planting, thoroughly moisten the potting soil or seedling potting mix.

2. Fill a large basket with soil. Leave the soil for a few minutes until the water is absorbed. Mix it with your hands and let it sit for a few more minutes.

3. Fill a six-pack container or plug tray with moistened soil. Make light indentations with your fingertips to create ¼-inch deep indentations.

4. Place one seed per hole in the tray by hand or using a seeder.

5. Cover the seeds by leveling the soil on top.

6. Water the seeds again very gently to settle the soil. (A jet that is too strong can dislodge or even wash away the seeds.)

7. Store the seeds in an area of ​​the house where the temperature is between 65 and 70 degrees Fahrenheit. The easiest way to do this is with a heat mat or grow light.

8. Water the seedlings once or twice a day until seedlings emerge.

9. Once the seeds have sprouted, move them from the heating mats to a sunny location. The frequency of watering depends on the location and climate of your seedlings. You will need to water at least once a day.

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

11. Once the seedlings have two or three sets of leaves and are at least two to three weeks past their last frost date, move them outside to acclimate to their environment for a few days and then transplant them into the ground.

Warning

Dahlias toxic to dogs and cats so keep this in mind when choosing a growing location.

How to plant dahlia tubers

Dahlia tubers have a bulb-shaped body at one end and a small crown with future growth points called buds at the other. “The body and eyes are connected by a thin neck, so it’s important not to separate them or your dahlia won’t grow,” says Sideris.

1. Dig the hole in which you want to grow your dahlia. Moisten the soil.

2. Before planting the tuber, place the stake you will use to support the dahlia so you don’t accidentally puncture the tuber.

3. Plant the tubers directly into the ground at a planting depth of about 4 inches. Place the tuber on its side so that the eye is closer to the place where you will secure the plant. (Placing the tuber at a 45-degree angle with the body down and the eye facing up works fine.)

4. Cover the tuber with soil and do not water it. Once sprouts emerge from the soil, begin watering the plants deeply once a week (or less frequently during periods of rain). Water until 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 initially do not have roots, so they cannot absorb water. “For this reason, it is important not to overwater, otherwise you risk rotting the tubers,” says Sideris. As your plant grows and develops roots, increase the amount and frequency of watering depending on your climate.

Frequently Asked Questions

Do dahlia tubers need to be soaked before planting?

Do not soak dahlias before planting. “Chances are they’ll turn to mush soon after you do this,” Turner says.

Is it too late to plant dahlia tubers in May?

“May is a great month to plant dahlias for anyone living in growing zones 3 to 6 because the soil is warmer at this time,” says Turner.

Do dahlias come back every year?

Dahlias will not return to growing zones 6 and below, which covers nearly half of the United States. “In these areas, the soil can freeze in the winter and the tubers turn to mush,” Turner says. – “They can’t stand freezing.” If you have a winter where the soil doesn’t freeze, you can overwinter them.