Taller varieties will need staking, with stakes placed carefully so as not to injure the tuber or roots. How to Grow and Care for the Dahlia Flower in Containers. In cool climates, dahlias can be planted indoors, 4 to 6 weeks before the last frost date. They can be grown from tubers, bulbs, or seeds but in this post, I’ll be sharing with you a foolproof way to planting dahlias from seeds. Place pots in a sunny window or under grow lights, and then plant outside after danger of frost has passed. They also will need to be regularly fertilized during the growing season, and many will need to be staked so they don't fall over. In addition, all border dahlias can be grown in containers. These Mexico natives grow in U.S. Department of Agriculture plant hardiness zones 7 through 10, where the tuberous root systems overwinter well. Fill 1 or 2 gallon pots with moist growing mix. I was just going to give it a bit of bubble wrap around the whole pot and drag it back out next spring. About six weeks before the last expected frost in your area, plant each tuber in a 5-inch pot filled with all-purpose potting mix. Replace about half the soil, then place tubers flat and cover with remaining soil. You can do this with tubers you’ve overwintered yourself, or with new tubers purchased from your favorite garden center or mail order source. If started inside, place the containers under plant lights. How to Grow and Care for the Dahlia Flower in Containers. Pinch and disbud dahlias for later and larger flowers. Growing dahlias in containers saves some of this work as you can grow them indoors, or bring the containers in before the weather turns. Where to plant. Medium dahlias, also known as border dahlias, are compact 1- to 2-foot-tall plants.These dahlias look great in the front of a perennial bed mixed with other late-blooming perennials, such as phlox and asters. If you want to grow dahlias in pots, choose a pot that's at least 12 inches by 12 inches and fill it with a rich potting mix, like 2 parts compost to 1 part peat moss. Plant the tuber(s) with the stem or sprouts facing up and cover with 2” of soil. About six weeks before the last expected frost in your area, plant each tuber in a 5-inch pot filled with all-purpose potting mix. Dahlias will not grow in cold soil and their foliage is sensitive to frost. Dahlias are summer-flowering plants that grow from tuberous roots. Plants can bloom in any sun garden during the growing season, creating a 120-day long-term attraction. Pots are also increasingly popular way to grow dahlias. Orange dahlias to grow How to take basal cuttings from dahlias If you plant them out before all risk of frost has passed then they may die, so plant the tubers in large pots filled with peat-free multi-purpose potting compost in March or early April. (We plant them a little after the tomato plants go in.) Then, plant your dahlia tubers on their sides about 4-6 inches deep in the soil during spring. Some gardeners start tubers indoors in containers … How to Grow Dahlias. Mine were free since they were overwintered from plants grown in containers on my deck last year. If you want the best varieties though, be taking notice of the plants that are blooming in early fall, and take note of the variety. How to Grow Dahlias. When to Plant Dahlias. Where to plant. Dahlias are beautiful, full-blooming natives of Mexico that can be grown virtually anywhere in the summer. Dahlias are not frost hardy, so those grown outdoors must be dug and brought in to overwinter.