How to Plant and Care for Dahlias, the Show-Stopping Fall Bloomers We Look Forward to Year After Year
Michelle Westling Photography
TABLE OF CONTENTS
On This Page
Starting Dahlias Indoors
When to Plant
Planting Tips
Care Tips
Pest Prevention
It's easy to fall in love with dahlias. Their massive flower heads are visual dynamite in a fall garden—and they look just as beautiful in a vase after you cut and arrange them.
Dahlias are grown from tubers, which can give some garden novices pause. Planting and growing these harvest-time beauties, however, isn't challenging; you simply need to know when to get them in the ground (or a container) and how to nurture them as they grow.
To help, we tapped Kate Rowe, a gardening expert and the former owner of a dahlia farm in Petaluma, Calif. She learned the nuts and bolts of growing these stellar blooms both from her own trial and error and from others who were generous enough to share their knowledge. In the spirit of passing on what she's learned, Rowe shares her best tips on how to grow and care for dahlias in your own garden.
Related: Dahlia Fields Forever: How Floret Flower Farm's Erin Benzakein Makes Her Garden Grow
Starting Dahlias Indoors
If you want to get a head start on your dahlia growing season and encourage earlier blooming, consider starting your new dahlias indoors as potted plants.
Potting
The best time to pot your dahlias is in early spring, about six to eight weeks before you plan to move them outside. Of course, you can wait until after the last expected frost and plant your dahlias directly in the ground or into your outdoor decorative pot (more on that later!), but your window of bloom time will be shortened.
Should your indoor space allow, you can also plant your tubers directly into the decorative containers you plan to move outdoors. Just make sure to keep the pots inside until the last expected frost has passed. "If you plan to grow your dahlia to full-size in a container, ensure that it's large. [It should be] 15 inches across the top and at least 12 inches deep so your dahlia has space to grow a large root ball," says Rowe.
If you decide to start your dahlias indoors, use a 1-gallon pot to give the plant's roots plenty of room to grow, says Rowe.
Start by filling the pot with well-draining garden soil that is moist, but not wet.
Plant one tuber per pot on its side, about 2 to 3 inches deep. "You can choose to leave the eye showing out of the soil, but at least cover the tuber body," says Rowe.
Lastly, place your pot in a warm, sunny spot (at least 60 degrees) and don't water until the sprout shows above the soil.
Drainage
When planting dahlias in pots, prioritize excellent drainage. "Make sure the container has good drainage holes in the bottom so the water passes through the pot and doesn't collect," says Rowe. The tubers will rot in standing water.
When to Plant Dahlias
As any gardener who's ever grown dahlias from a tuber can tell you, you may start to get antsy ahead of growing season—you want to get the show on the road. But it's important that you fight the urge to put tubers in the ground too soon, explains Rowe.
"Transplant the sprouted tuber plant you started indoors into your garden only after the last chance of frost," she says. If you didn't give your plant a jump start inside, that's perfectly fine; simply plant your tuber after the last chance of frost, as well.
How to Plant Dahlias
Plant your dahlia tuber in an area with full sun and well-draining soil. Rowe suggests adding good soil around the tuber or transplanted plant to improve drainage. "Dahlia tubers rot easily," she says. "When transplanting from a pre-sprouted pot, try not to disturb the roots—in general, don't move dahlias once they're growing."
Luckily, no special tools are required when working with dahlias. All you need is your favorite garden trowel to dig a big enough hole for your tuber or transplant. The other tip to remember is to install stakes and strong string as your flowers grow; tall dahlia varieties benefit from staking to prevent the stems and large flowers from drooping over.
LianeM / Getty Images
How to Care for Dahlias
When your dahlia reaches approximately 12 inches tall or has three sets of leaves, Rowe recommends pinching off the center shoot to encourage side branching, which will create a stronger plant with more blooms.
Speaking of dahlia blooms: It's important to cut and enjoy them. If you choose to leave the flowers on the plant, deadhead them as soon as they start to wilt and before seeds form. "The more you cut, the more they will bloom," says Rowe.
Cutting
Be choosey about the buds you do and don't keep. While it might seem difficult, you shouldn't save every bud. "Dahlias typically bloom in sets of three, and the center bud will bloom first," says Rowe. "After the plant is about 2 feet tall, cut the center flower when it's approximately 3/4 open. Cut past the two side buds down to the next branching part of the plant, or the next 'Y' in the stem." The plant will then grow stronger stems below, she explains.
Fertilizing
Luckily, dahlias are not demanding, but Rowe recommends using a balanced fertilizer (10-10-10 or 15-15-15) and feeding the plants once per year. "If you use a lower strength fertilizer, you'll want to feed them twice if they look like they need it," she says.
So, what does a hungry dahlia look like? Typically the leaves appear yellow. Rowe recommends waiting until the plant is about 10 inches tall to fertilize.
Watering
As with most plants, watering amounts and frequency vary depending on soil, weather, and plant size. "In general, don't water tubers until they sprout above the ground, then water about two times a week," says Rowe. "Allow the soil to dry out and then give them a deep soak."
Near the end of the season, when it's hottest and the plants are larger, you can increase the watering schedule a touch. "Let them grow and just check in," says Rowe. "They will tell you when they need something."
How to Avoid Pests
To ward off pesky invaders trying to sabotage your dahlias, Rowe advises removing the bottom 5 to 10 inches of leaf growth. "Plan on using an all-natural, bee-safe spaying regimen specific to the pests in your area," she says. And be sure to spray under the leaves, where the critters may hide.
