How to grow dahlias:
There are two ways to grow dahlias: from flower seeds and dahlia tubers. Some gardeners harvest seeds from dahlias at the end of each season, dry them, and replant next year. However, seed-grown dahlias can take a few seasons to flower. Our dahlias come as bare-root tubers, can be planted in the spring, and are winter hardy in zones 8 to 11. In more temperate zones, they will need to be lifted and stored for the winter.
You can start your dahlias indoors, four to six weeks before planting them, by placing the tubers in a 4-4.5" pot in a high-quality potting blend. Water moderately and be sure to let them get fairly dry between waterings. When you are ready to transfer your dahlias to an outdoor location, gently remove from their pots and clip off the bottom one or two sets of leaves, making sure those nodes are below the surface when placed in the garden.
You can also plant dahlias outdoors once the threat of frost has passed. Dahlias are best grown in warm, well-drained soil: don't plant them too early, and don't place them in a location where they'll get "wet feet." Choose a spot with lots of sun -- dahlias need at least six hours of light every day. The correct depth for your dahlia tubers is listed on their packaging -- bigger varieties require deeper planting than smaller dahlias!
Larger varieties of dahlias, like dinnerplate dahlias or any varieties that grow to heights of several feet, need staking. You should install your stakes when you plant your dahlia tubers: getting stakes into the ground early will help your dahlias be supported as they grow, and can prevent accidental damage that can occur if they're staked later. Place one or two stakes beside each dahlia tuber. As your dahlias grow, use twine to hold your dahlias to their stakes -- just be sure to give them plenty of room to breathe and expand.
Water your dahlias regularly, but don't overwater them. Because they grow from soft tubers, dahlias are susceptible to rot and fungus. Try watering them less frequently, but more deeply, than your other garden plants. Always water them at the base instead of on the foliage -- wet leaves can invite pests and rot. Don't pile mulch or compost around the base of your dahlias, as too much material can lead to water retention and overly wet conditions. Fertilize your dahlia plants with any balanced, flower-friendly fertilizer when you water them.
Dahlias are grown for their beautiful blooms, so feel free to clip some of these spectacular flowers for your kitchen table, floral arranging, or even an entry at the county fair! Just be careful not to pull too many flowers off of a single side of the plant, or your dahlia may begin to grow in a crooked direction.
Once the end of the season comes, your dahlias will likely cease flowering and begin to die back -- this time usually coincides with the first frost. If you're in Zone 8 or higher, you can simply leave your dahlias to enjoy next year. However, if you're in a temperate climate, you'll need to overwinter the flowers if you'd like to enjoy them for another season.
When do dahlias bloom:
Dahlias bloom about eight weeks after being planted, beginning in mid-July. One of the many features that makes a dahlia delightful is its bloom time -- just after your springtime blooms have ended, but with plenty of time to enjoy over the summer months. Many of our dahlia varieties will bloom right through the end of the season, up until the first frost date. Once they are done blooming, you can leave them in the ground if you are in a warm growing zone and they will return the next summer. Or, if your growing zone is more temperate, lift and store them for the next season.
How to plant dahlia tubers:
Read up on your style of dahlias when deciding where to locate them. The small, shorter "flowerbed" dahlias can be planted about ten inches apart, while multi-stem button varieties and other smaller flowering dahlias may need two or more feet. Giant dahlias, like dinnerplate varieties or Santa Claus dahlias, will need significantly more space -- think three or four feet.
Inspect your dahlia bulbs before planting, and discard any tubers that look rotten or that don't have a healthy eye. To plant your dahlias, dig a hole slightly wider than the tuber, and six to eight inches deep. Set the tuber into the hole with the "eyes'' facing up, so that the dahlia is ready to grow in the right direction. Backfill with a mix of soil and a loamy amendment like peat moss or light compost. Don't overfill the hole, and don't pile mulch around the base of your dahlia plant: dahlias actually like some sun around their roots, and too much piled-up, wet material can encourage rot and pests.
If you're planting a variety that will grow to over three feet, consider setting up stakes to support your dahlias' eventual height: those huge blooms make dahlias a little top-heavy! Place stakes in the ground when you plant, to avoid spearing the roots later in the season, and adjust the plants' ties to the stake as they grow.
When to plant dahlias:
Dahlias don't like the early spring chill, so wait to plant until the ground temperature is over 60 degrees Fahrenheit. Wait until after the last frost before planting. Even if you live in a colder zone, dahlias will catch up by growing quickly in the summer -- but won't survive being burnt by frost.
If you'd like to get ahead on your dahlia plants, you can give them an early start by planting dahlias in pots or other containers -- see How to Grow Dahlias. We recommend doing this for the smaller varieties -- dinnerplate varieties will quickly outgrow their containers!
How to store dahlia tubers:
How should you winterize dahlia tubers? In most temperate zones you'll need to lift and store your dahlias to enjoy them for another year. Even in warmer climates, dahlias can be susceptible to rainy-season rot. To overwinter your dahlias, they must be lifted before the first hard frost hits -- they will not bounce back from being frozen! In order to lift your dahlia bulbs, pull them up by the stems, wipe or rinse soil off the bulbs, and cut the stems a few inches above the tuber. Lay them out to dry for a few days in an area protected from moisture, then store the tubers in paper bags in a cool, dry place.
It's likely that your dahlia tubers will have grown significantly since the spring, but you shouldn't divide them in the fall. Instead, wait until spring to see which tubers have developed viable eyes. If you can't find the eyes on your dahlias, set them in a moist, warm place for about a week before planting: the eyes will begin to sprout, and you can cut then cut them apart, dividing into one or two eye tubers.