How to Grow Dahlias for Months of Gorgeous Blooms

From sunflowers to roses, there are so many gorgeous flowers you can grow in your garden. But few types are as exquisite as dahlias. “Dahlias have such beauty and variety, combined with a long bloom season of up to three months,” says grower Andrew Hunter, of Lynch Creek Farm Dahlias. “With the abundance of flowers and their magnificence in bouquets, they’re fantastic to grow.”

There are tens of thousands of varieties of dahlias, which grow from tubers, in every imaginable color and size. They thrive just about anywhere, except in very hot climates such as Southern Florida and Arizona. In USDA Hardiness zones 8 and warmer (find your zone here), you can leave the tubers in the ground over the winter. In colder climates, you’ll need to dig the tubers up after the first frost has killed the foliage if you want to save them for planting again next spring, says Hunter.

Andrew Hunter, owner and grower of Washington-based Lynch Creek Farm Dahlias, a family-owned business that’s been around since 1980.

Ahead, here’s how to grow your own dahlias to add beauty to your garden for months to come.

There are a few key types of dahlias to know. Small pom pom types have more flowers, while larger dinnerplate dahlias have fewer blooms and bloom later in the season because they require more energy to produce flowers. There are also large, lush blooms called ‘decorative’ dahlias and fun ball-shaped types, too. However, every type of dahlia is worth growing! It’s really just personal preference. Larger types will need to be staked because they can become quite tall and heavy as they grow, says Hunter, so they’ll need a little extra support to keep them upright.

Dahlias don’t like the cold, so plant the tubers, which resemble sweet potatoes, after all danger of frost has passed. You want soil temperatures around 60 degrees F (find soil temperatures in your area here) in late spring. “If you put them in the ground too early, they just sit there and may rot,” says Hunter.

1. Find the ideal location. Choose a spot in full sun, which is six or more hours of direct sunlight per day. In hot climates, dahlias benefit from a little afternoon shade because they tend to wilt in temperatures consistently above 90 degrees F. Dahlias love sandy soil, but they’ll grow in most conditions. In heavy clay, amend the soil with some compost before planting.
2. Dig a hole about 4 to 6 inches deep, and lay each tuber flat in the hole with the “eye” on top; that’s the little bump that looks like a potato eye, except dahlia eyes form only on the part of the tuber where the stem had previously emerged. If you aren’t sure where the eye is, just place the tuber in the hole. We promise the plant will know how to grow up! Plant the tubers at least 8 to 12 inches apart.
3. After covering with soil, sprinkle on an extended-release granular fertilizer that’s lower in nitrogen (the first number on the package) than other nutrients so that you get more energy to the roots and blooms. Something like 10-20-20 or 5-10-10, or 10-20-20 will keep the blooms coming. About six weeks after planting, feed again by “side dressing” with fertilizer, placing the granules about 10 inches away from the plant, says Hunter.
4. Don’t water dahlias after planting. Unlike everything else you grow, you shouldn’t water dahlias right after planting to prevent the risk of rotting in the hole, says Hunter. Don’t worry if it rains, but otherwise, don’t give them a drink until the first green shoots appear, about a month after planting. Then give them a good soaking about three times a week if there’s no rain.

Yes, but make sure the pots are at least a foot or more in height. Hunter recommends using a mixture of 60 percent potting soil and about 40 percent native soil from your garden because dahlias tend to need lots of water once they get going, and most types of potting soil dry out too quickly. Otherwise, follow the same planting and care instructions.

Dahlias start blooming about two and a half months after planting in June to July, depending on the variety. Some types bloom all the way until a hard frost. “Cut the flowers as much as you like,” says Hunter. “If you don’t, the flowers go to seed and the plant will stop producing blooms.” If you don’t cut your flowers for bouquets, at least deadhead the faded flowers on the plant so it will keep making flowers.

If you live in USDA Hardiness zones 8 or warmer, you can leave your tubers in the ground over the winter. After a frost, cut back the foliage almost to the ground, then cover with plastic, straw or other organic mulch to prevent water from going down inside the hollow stem and rotting the tuber, says Hunter. Remove the mulch in the spring.

In colder areas of the country if you’d like to save the tubers to replant next spring, let the foliage die back after a hard frost, cut it to the ground, then use a digging fork to lift the tubers up out of the soil. Brush off most of the dirt, and let the tubers sit out for 48 hours or more in a cool, covered location to dry. Once dry, wrap in newspaper, cedar shavings or cat litter to keep the tuber protected over the winter. Store in an unheated location that remains around 40 to 45 degrees.

Don’t be disappointed if your tubers look shriveled and funky next spring. “It’s not the easiest task to overwinter these tubers successfully, so don’t feel bad if you grow dahlias only as annuals,” says Hunter. If that’s the case, treat yourself to some new tubers next year.

Arricca Elin SanSone is a gardener with more than 15 years of experience. In addition to PureWow, she writes for Prevention, Country Living, Veranda, The Spruce and many other national publications. She also trials new plant cultivars and field tests garden products to evaluate practicality and durability.

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