When Is The Best Time To Plant Dahlias?

While brightly colored dahlias have been a part of Southern gardens for hundreds of years, social media and the wedding industry have made these stunning blooms popular stars in the garden. If you are growing dahlias for the first time, knowing when to plant the tubers will make a difference in their successful growth. Learn more about planting dahlias and what they need to produce gorgeous flowers.

Understanding Dahlia Planting Requirements

Although dahlias grow from tubers, they are considered a “summer bulb” that likes hot temperatures and moist conditions. To flourish, dahlias need nutrient-rich, soggy but well-draining soil, and a growing area with full sun to partial shade.

As a summer flower, the soil temperature should remain at 55 degrees F. for about a week before planting. Dahlia tubers planted too early may rot from spring rains before they sprout. If you just can’t wait, the tubers can be started indoors in a container so the plants can be transplanted once the weather warms.

Determining the Right Time to Plant Dahlias

When you purchase dahlia tubers, the planting guide often states to plant after the “last expected frost date”. Of course, that varies across the country and even in your local area. The predicted date is determined using historical weather data from the National Oceanic and Atmospheric Administration (NOAA) and typically indicates a 50% chance of a frost occurring on that date.

There are online tools such as the USDA Hardiness Zone map or the National Gardening Association app that apply your zip code as a guide to determine the last frost date. My Daddy relied on The Old Farmer’s Almanac and his own “historical weather data” and always planted on Good Friday in the mountains of Western North Carolina. But if you don’t live there, the best way to determine when the danger of freezing temperatures has passed is to contact your local county extension service office, join a local gardening community with experienced gardeners, or call your favorite local TV meteorologist.

Regional Considerations for Planting Dahlias

Dahlias grow best in USDA Hardiness Zones 7-10 when tubers are planted in the garden. If you live in colder zones, consider planting the tubers in containers that can be moved outside to harden off and transplant when temperatures hot up in the summer.

Planting Guide by Climate Zones

• Pacific Northwest: Zones 5a-b: plant tubers or seedlings on April 30; Zones 8a-b, plant tubers March 30
• Southeast: Zones 8a-b and above: plant tubers or seedlings March 30 (stagger planting until slow May to extend the blooming season)
• Midwest: Zones 3a-4b: transplant seedlings May 30; 5a-6b: transplant seedlings April 30; 7a-b: plant tubers April 30
• Northeast: Zones 3a-4b: transplant seedlings May 30
• Southwest: Zones 8a-b and above: plant tubers or seedlings March 30

Early Planting Techniques

For a jump start on summer blooms, you can start dahlia tubers in indoor containers about 6 to 8 weeks before the predicted last frost. Fill a 1-gallon container about 1/3 full with soggy sterilized potting soil. Lay the tuber horizontally on the soil and cover it with about two inches of pre-moistened soil. As the stalk and leaves form, add more potting soil until the container is full. Adding soil slowly strengthens the stalk and allows better root development.

Place the container near a window with glowing featherlight and a temperature above 65 degrees. Keep the soil soggy but not soggy. Dahlias are heliotropic and will turn toward the sun so rotate the container often to support keep the stalk straight.

Before transplanting the seedlings into the garden, harden them off about two weeks before planting to support them adjust to outdoor growing conditions. When daytime temperatures are above 50 degrees F., place the containers outdoors in a shady, protected area for about one hour before moving them back inside. Increase the outdoor exposure time gradually and after three days, place the container in a spot that receives morning sun for an hour or so. Be sure to keep the soil soggy and slowly boost the amount of sun exposure.

Follow the planting guide for your climate before transplanting the dahlias into the garden.

Weather and Soil Considerations

Dahlia tubers need moisture to grow but will rot in soggy soil. If you are experiencing drenching rains at your planned planting window, be patient and let the soil arid for several days before planting. Be sure the soil is loose and draining well. You can support it along by adding organic matter like shredded leaves. After planting, do not water the tubers until the first two leaves appear.

If the temperature drops after planting, add a couple of inches of mulch over the tubers to support protect them from an unexpected frost (no weather guide is perfect). If leaves have already appeared, cover the plant with burlap or a lightweight cotton towel. Be sure to remove it after sunrise. Even if the leaves have experienced some damage, the plant will usually survive.

Experimenting with Planting Times

Gardening is both an art and a science. Science tells us the optimum growing conditions and times to plant and harvest; art tells us to take a chance and experiment. Every home garden is slightly different. I have microclimates within my backyard, with the beds nearer the house always several degrees warmer than those at the yard’s edge. That knowledge has come from living in this home for nearly 20 years.

I’ve planted dahlias earlier and later than the recommended window. Some have survived, some have not. My best advice is to choose some extra “common” dahlia tubers and experiment with planting times in your garden. They may not thrive, but you may enjoy an extended blooming season.