Dahlia flowers can be cut and displayed in a vase.
Dahlias are tuberous perennial plants that grow quickly in sunny areas and produce lots of brightly colored flowers. They grow well in containers or in the ground, and prefer moist, well-drained soil. Since they thrive in U.S. Department of Agriculture zones 7 through 11, they can be left outdoors in containers all year round. They're also easy to transplant into the ground and can provide an attractive display of flowers. March and April are ideal months for planting dahlia tubers in the ground.
Select a 12-inch-diameter pot with drainage holes in the bottom.
Fill the pot with two parts garden soil mixed with one part potting mix, leaving enough space to place the tuber 4 to 6 inches deep with the eyes facing upward. Cover the tuber with soil and pack it down lightly. Place the pot in a sunny location, such as a south-facing window or patio.
Water the dahlia just enough to keep the soil slightly cool and damp to the touch after it sprouts. Increase to deep watering two or three times a week after the plant reaches 1 foot tall. Water until it drains from the bottom of the pot.
Fertilize newly established dahlia tubers after they sprout within 30 days of planting. Use low-nitrogen, water-soluble fertilizer, such as 0-20-20, 5-20-20, 10-20-20 or 5-10-10, mixed according to the instruction label. Reapply fertilizer once about three or four weeks later.
Place a tomato cage in the pot when the dahlia starts growing taller to support its weight.
Remove flowers from the plants when they wilt. To encourage bushier growth, pinch off the top shoot above the third set of leaves.
Winterize dahlias by cutting down the stalk to a few inches above the soil when the foliage begins to die. The tubers can be left to over-winter in their containers by covering the soil with plastic or dry mulch. Alternatively, tubers can be dug up from the soil and stored about two weeks after cutting the plants down. Lift the tubers out gently and shake off the soil. Allow them to dry overnight and dust them with fungicide. Store the tubers in a plastic-lined box of slightly damp peat in a cool location, between 45 and 55 degrees F until the following spring when they can be replanted.
Select a location with plenty of full sunlight. Test the soil with a pH testing kit. The soil should have a pH between 6.5 and 7. If it's too acidic, add ground limestone and mix it into the soil at a rate of 10 lbs. per 100 square feet. If it's too alkaline, add about 1/2 lb. of aluminum sulfate per 10 square feet. Allow at least two months for the amendments to take effect and test the soil again.
Cover the planting area with 5-10-10 slow-release granulated fertilizer and mix it into the ground with a hoe or tiller to a depth of 1 foot. For heavier soil, mix in compost, manure, sand or peat moss until the soil feels lighter and aerated.
Dig a hole about 6 inches deep and place a handful of bone meal in the hole. Loosen the tuber from the pot and shake off the soil. Place the tuber into the hole and pack the soil around it. Transplants should take place when the plant is no more than 1 foot tall. If it is, trim it back.
Water the transplanted tuber deeply about twice a week or more often during hot, dry periods.
Fertilize the dahlia about three or four weeks after planting with low-nitrogen, water-soluble fertilizers such as 5-10-10, 10-20-20 or 0-20-20. Caging and winterizing tasks are the same as container plants.
Marie, Shelley. "How to Plant Potted Dahlias." Home Guides | SF Gate, http://homeguides.sfgate.com/plant-potted-dahlias-62922.html. Accessed 22 April 2019.