If you saved dahlia tubers from last year, early spring is the time to see how your stored dahlias are coping and to throw away any tubers that show signs of rotting. When you’re ready to unpack and replant your tubers, here’s a refresher on how to do it!
Check Tubers in Early Spring
First, check your dahlias again in early spring to see if they are too wet or too dry or just right. It’s important to check if tubers are rotting and remove them so rotting doesn’t spread.
We have our tubers packed in plastic bags full of peat moss and stowed in a frost free spot in the greenhouse.
When You’ll Plant Dahlia Tubers
You’ll unpack your dahlia tubers well after your last spring frost date when there’s absolutely no chance of frost and the soil has warmed. See the Almanac Frost Date Calculator for your location in the U.S. or Canada. Wherever you live, remember that dahlia tubers absolutely will not stand cold soil! They are a warm-weather flower that is planted in late spring and blooms in late summer into fall. One good guideline is to plant in the same time frame as you would a tomato.
If you want blooms as early as possible, you can start the tubers indoors in good light about one month before planting time. You will then have a small plant ready at planting time. Dahlias can be planted as late as mid-June in most parts of the country.
Unpacking Dahlia Tubers
When you’re ready to unpack the tubers, some of the tubers are usually starting to sprout; this means it’s a good time to divide them. Each tuber must have at least one “eye” or a piece of the crown attached or it will not develop into a blooming plant.
The eyes are located at the base of the stem and look like little pink bumps; if the stem is split so that a piece of it goes with each tuber that should work as well. Since it might be a few more weeks until our soil has warmed up sufficiently to plant them outside, we may pot up a few in containers to get some early flowers.
Potting Up Dahlias
Dahlia tubers absolutely will not survive in cold soil. They will rot. If you’re still getting rainy, wet, and cold weather, wait until the soil is warmed up.
If you live in a colder climate, it helps to get a jump start on summer blooms by potting up your tubers about a month before planting. To put them up, you’ll need gallon-sized containers and a lot of potting mix. Pots are also increasingly popular way to grow dahlias.
If you have a warmer spring, it’s probably easiest to just plant the tubers in the ground. However, even in warmer climates, there can be benefits to potting up your dahlias if you have the time. The blooms will come later and it can be hard to store tubers that long.
If you are new to dahlias, there are about 60,000 named varieties and 18 official flower forms including cactus, peony, anemone, stellar, collarette, and waterlily. The American Dahlia Society recognizes 15 different colors and color combinations, and flower sizes range from tiny pompoms under 2 inches across to giants like the dinner-plate dahlia that measures over 10 inches in diameter.
Needless to say there are dahlias for every situation. The miniature and dwarf varieties stay small and bushy, grow 12 to 18 inches tall, and are perfect for containers or used as an edging. Taller varieties can reach 5 feet or more. They will look fabulous against a wall or fence or at the back of the border.
Tall plants and those with giant flowers will need some support to keep them from flopping or breaking in the wind and rain. Even some of the 2 to 3 foot tall plants will benefit from some support whether it is a stake, tomato cage, or grow-through support. If you plant them close enough, about 12 inches apart, they make a nice flowering hedge and will support each other.
Where to Plant Dahlias
Plant the dahlia tubers in fertile, well-drained soil in full sun and you will be rewarded with plenty of flowers for the garden and for cutting. Don’t overfeed your plants with high-nitrogen fertilizer or you’ll grow a leafy bush with no flowers. Do not bother mulching them. It harbors slugs and dahlias like the sun on their toes.
If you want to grow large flowers try disbudding—removing the 2 smaller buds next to the central one in the flower cluster. This allows the plant to put all of its energy into fewer but considerably larger flowers.
Dahlias are a great bouquet flower because the blossoms have a long vase life!
The best way to start a collection of dahlias is to swap with your dahlia-growing friends. If the tubers have survived winter storage we usually have more than we can replant and are happy to share.