How to Plant and Care for Dahlias
These gorgeous blooms will brighten your garden—and your day.
Dahlias are the type of flowers that people often become smitten with. Take, for example, Kate Rowe, who left her job in software to buy Aztec Dahlias, a dahlia farm located in Petaluma, California. Together with co-owner Omar Duran, they grow approximately 7,500 gorgeous dahlias each year. Rowe and Duran learned the nuts and bolts of growing these stellar blooms both from their 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 these beautiful blooms at home.
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. The best time to do this 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, but your window of wonderful bloom time will be shortened. If you'll start your dahlias indoors, use a one-gallon pot to give the plant's roots plenty of room to grow, says Rowe. Just make sure the pot has bottom drain holes for proper drainage. Start by filling the pot with well-draining garden soil that is moist, but not wet. Then plant one tuber per pot on its side, about two to three 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.
Should your indoor space allow, you can also plant your tubers directly into the decorative containers you plan to display them in once outdoors. Just make sure to keep it inside until after the last expected frost. Rowe suggests, "If you plan to grow your dahlia to full-size in a container, ensure that it's a large one, at least 15 inches across the top and at least 12 inches deep so your dahlia has space to grow a large root ball." Another must-have according to the expert? Great drainage. "Make sure the container has good drainage holes in the bottom so the water passes through the pot and doesn't collect." 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 and want to get the show on the road. According to Rowe, it's important that you fight the urge to put them in the ground too soon. "Transplant the sprouted tuber plant you started indoors into your garden only after the last chance of frost," she urges. If you didn't give your plant a jump start, that's perfectly fine. You can plant your tuber after the last chance of frost, as well.
How to Plant Dahlias
Plant your dahlia tuber in 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 stresses. "And 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 needed 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 piece to remember is to install stakes and strong string because tall dahlia varieties benefit from staking to keep the stems and large flowers from drooping over.
How to Best Care for Dahlias
When your dahlia gets approximately twelve 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. And on the topic of those blooms, it's important to note that you really must cut and enjoy them. If you do 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," Rowe says. You'll also want to be choosey about what you do and don't keep. While it might seem hard, you shouldn't save every bud. Rowe says, "Dahlias typically bloom in sets of three, and the center bud will bloom first. After the plant is about two 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 steam. The plant will now grow stronger stems from lower on the plant."
Feeding Your Dahlias
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. What does a hungry dahlia look like? Typically the leaves look yellow. Rowe also recommends waiting until the plant is about 10 inches tall to fertilize.
Watering Your Dahlias
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 the hottest and the plants are larger, you can increase watering a bit. "Let them grown and just check-in," says Rowe. "They will tell you when they need something."
To ward off pesky invaders trying to sabotage your dahlias, Rowe advises removing the bottom five to ten 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.