How to plant and care for dahlias
It’s easy to fall in love with dahlias. The huge flower heads are visual dynamite in a fall garden – and they look absolutely beautiful in a vase after being cut and arranged.
Dahlias are grown from tubers, which can put off some garden novices. However, planting and growing these beauties at harvest time is not a challenge; All you have to do is know when to put it in the ground (or in a container) and how to care for it as it grows.
To help, we enlisted the help of Kate Rowe, a horticulturist and former owner of Dahlia Farm in Petaluma, California. She learned the basics of growing these wonderful flowers 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 plant and care for dahlias in your own garden.
Start dahlias indoors
If you want to jump-start your dahlia plants’ growing season and encourage early flowering, consider starting new dahlia plants indoors as potted plants.
The best time to plant dahlias is in early spring, about six to eight weeks before you plan to move them outdoors. Of course, you can wait until the last expected frost and plant your dahlias directly in the ground or in your outdoor pot (more on that later!), but your blooming period will be shortened.
If your indoor space allows, you can also plant your tubers directly into the decorative containers you plan to take outdoors. Just be sure to keep the pots inside until the last expected frost has passed. “If you plan to grow your full-size dahlia in a container, make sure it is large. (It should be) 15 inches across the top and at least 12 inches deep so your dahlia has room 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-drained garden soil that is moist but not wet.
- Plant one tuber in each pot on its side, about 2 to 3 inches deep. “You can choose to leave the eye visible from the soil, but at least cover the body of the tuber,” says Rowe.
- Finally, place your pot in a warm, sunny location (at least 60 degrees) and do not water until a sprout appears above the soil.
When growing dahlias in pots, prioritize excellent drainage. “Make sure the container has good drainage holes in the bottom so water passes through the container and doesn’t pool,” Rowe says. Tubers will rot in standing water.
When to plant dahlias
As any gardener who has grown dahlias from a tuber can tell you, you may start to feel antsy before the growing season—you want to get the show on the road. But it’s important to resist the urge to put tubers in the ground too early, Rowe explains.
“Don’t transplant sprouted tubers you started indoors into your garden until after the last chance of frost,” she says. If you don’t give your plant a push inside, that’s okay; Simply plant your tubers after the last chance of frost as well.
How to plant dahlias
Plant your dahlia tuber in an area with full sun and well-drained 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 previously sprouted pot, try not to disturb the roots – in general, don’t move dahlias once they have grown.”
Fortunately, no special tools are needed when working with dahlias. All you need is your favorite garden shovel to dig a hole large enough to plant the tuber or transplant. Another tip to remember is to install sturdy stakes and string as your flowers grow; Tall dahlia varieties benefit from stacking to prevent the stems and large flowers from drooping.
How to care for dahlias
When the dahlia reaches about 12 inches tall or has three sets of leaves, Rowe recommends trimming the central bud to encourage side branching, which will create a stronger plant with more flowers.
Speaking of dahlia flowers: It’s important to cut them and enjoy them. If you choose to leave the flowers on the plant, remove them as soon as they begin to wilt and before seeds form. “The more you cut, the more it will bloom,” says Rowe.
Be selective about the shoots you do and don’t keep. Although it may seem difficult, you don’t have to save every bud. “Dahlias typically bloom in clusters of three, and the central bud will flower first,” Rowe says. “After the plant is about 2 feet tall, cut off the central flower when it is about 3/4 open. Cut the side shoots down to the next branching part of the plant, or the next ‘Y’ section on the stem.” She explains that the plant will then grow stronger at the bottom.
Fortunately, dahlias aren’t fussy, but Rowe recommends using a balanced fertilizer (10-10-10 or 15-15-15) and feeding the plants once a year. “If you use a less aggressive fertilizer, you’ll need to feed them twice if they seem to need it,” she says.
So, what does a hungry dahlia look like? The leaves usually appear yellow. Rowe recommends waiting until the plant is about 10 inches tall to fertilize.
As with most plants, watering amounts and frequency vary depending on soil, weather, and plant size. “In general, don’t water the tubers until they’ve sprouted above the ground, and then water them about twice a week,” Rowe says. “Allow the soil to dry and then give them a deep soak.”
Toward the end of the season, when the weather is hot and the plants are larger, you can increase the watering schedule with just a touch. “Let them grow and check in,” says Rowe. “They’ll tell you when they need something.”
How to avoid pests
To ward off pesky invaders trying to sabotage your dahlias, Rowe recommends removing the bottom 5 to 10 inches of leaf growth. “Plan to use a natural, bee-safe sterilization system specific to the pests in your area,” she says. And be sure to spray under leaves where critters can hide.