Here’s exactly how to store dahlia bulbs for winter and tips for replanting them in spring.
Dahlias are some of the most striking flowers you can grow in your garden and landscape. They come in so many different sizes and colors that there’s sure to be an option for every gardener.
Dahlias shine equally well in garden landscapes and container gardens, catching your eye with their cheerful colors and large flowers.
The only drawback to dahlias is that in most growing zones they won’t last. Once frost sets in, these subtropical flowers are done for.
While you can grow dahlias as annuals, digging the bulbs up and storing them for the winter isn’t difficult and will save you money when the next growing season comes around. You simply replant the bulbs in the spring and enjoy their flower display all over again.
Why Store Dahlia Bulbs?
You may have heard of some gardeners growing dahlias as a perennial and are wondering what the point of digging them up each fall is.
Dahlias are native to Central America and enjoy tropical weather. While they can be grown as a perennial in USDA planting zones above 8 (and sometimes in zone 7 with heavy mulch over the winter), most northern gardeners are out of luck.
Dahlias are show-stopping plants that have beautiful, large blooms. You can grow them in your garden landscape or in pots and store the bulbs over the winter to plant again next year.
The underground bulbs, more accurately known as dahlia tubers, will die once hard frosts start freezing the ground.
However, rather than buying new dahlias every year, you can choose to dig up the dahlia tubers in the fall and store them somewhere warmer over the winter. You can then replant them as is or divide them to get more plants.
Even if you don’t have extremely cold winters, dahlia bulbs are also in danger of rotting in wet soil. So if your winters are wet, it’s safer to dig up and store your plants rather than risk losing them all.
When to Dig Up Dahlia Bulbs
Although dahlia tubers will die once hard frosts set it, you don’t need to be in a hurry to dig them up before the first frost.
The leaves above ground continue to feed the bulbs below ground until the first light frost hits and the leaves turn brown. Even after this happens, the bulbs continue to grow and mature beneath the ground.
Your best option is to dig up the dahlia tubers after a light frost turns the leaves black or brown but before a hard freeze comes to do major damage.
Wait until after the first light frost to dig up your dahlia bulbs. The dahlia tubers will continue to mature underneath the ground, storing up vital energy to make it through the winter.
How to Store Dahlia Bulbs
After the first frost has come through, you can start the process of storing your bulbs for winter. Follow these steps to make sure you do it the right way.
This first step is optional, but if you’re growing a lot of different varieties of dahlias, you’ll want to label them while you still know which variety is which.
Technically, this is best done before frost when you can still see what color the blooms are.
To label, you can do something like attach the name of each variety to a stake driven in next to each plant or write and tie the label directly around the stem. If you attach the label to the stem, be sure to put it at the very bottom, since you’ll be cutting most of the stem off.
Make sure to shield the labels with plastic covers or write with something that won’t fade. After you store the bulbs, you’ll want to transfer the label to the storage container.
Cut Back the Foliage
After the leaves have turned black or brown and you’re ready to start digging, the first step is to cut back the now dead foliage.
Use a pair of small garden pruners or clippers to cut back the foliage almost all the way, leaving only 2-4” of stem.
If you have more than one variety of dahlia, it’s a good idea to label each one while you can still see the blooms. Put the labels right next to each plant or attach them to the very bottom of the stems.
To avoid infecting your plants, it’s a good idea to clean your pruners before each use and dip them in a solution that’s one part bleach to ten parts water.
Dahlias can also get plant viruses that are deadly and will kill your plants. You won’t always know if one is infected or not, so to be completely safe you can disinfect your pruners in the bleach solution in between cutting back each plant.
Dig Up the Dahlia Tubers
After you cut back the foliage, it’s time to dig up the dahlia tubers.
For this job, you’ll need either a garden fork or shovel. The main goal is to dig up the dahlia bulbs without damaging any, so use the tool you feel most comfortable with.
Start by pushing your fork or shovel down into the dirt about a foot away from the plant itself. Keep doing this in a circle around the plant, lifting the dirt as you go so that you can pry the dahlia tubers out.
Once you’ve completed your circle, put your fork or shovel down under the plant and grab what’s left of the stem with one hand. Pull up on the stem while pushing up with the fork/shovel until the whole clump of tubers comes out at once.
Shake or brush off as much dirt as you can, and put the tubers in a safe spot while you finish digging up the rest. If you labeled your varieties, make sure each label is still with the plant it belongs to.
Your dahlia bulbs will vary in size depending on what variety they are and how old they are, but they should resemble thin sweet potatoes.
The tubers are easily damaged, and any punctures will invite bacteria and other pathogens in. Continue to be careful and gentle as you handle them.
Clean Off the Tubers
Your next goal is to get the freshly dug up tubers clean and dry before you store them. There are two main ways gardeners do this.
One way is to use a garden hose to thoroughly (but gently) wash off as much dirt as you can. Then, you’ll need to set them somewhere to dry. Put the washed tubers somewhere that temperatures will be above freezing and make sure there’s good air flow and no direct sunlight.
It can take anywhere from a few days to a few weeks to dry out depending on conditions. If you can, stand the tubers upside down because they dry more quickly this way.
Another way you can approach this is to first let the tubers dry without rinsing them off. Once the dirt is relatively dry, brush off as much of it as you can. Then, let them dry for a few more days, upside down if possible.
Rinse off the dahlia with a garden hose, or brush off as much dirt as you can with your hands. Whichever method you choose, be gentle and let the dahlia dry thoroughly before you store them.
This second method won’t get the dahlia as free of dirt as the first, but they will dry more quickly and thoroughly since you aren’t rinsing them with water.
Preparation for Storage
After your dahlia bulbs are dried, sort through them to see if any are damaged. If you find any rotten or damaged spots, cut them off with clean pruners to prevent the rot from spreading to the other bulbs.
You can also trim the stems all the way back, leaving only an inch or two.
At this point, you can divide the dahlia if the clumps are large enough to have more plants next spring. To do this, you’ll need to find tubers that have an “eye” on them (similar to potatoes) and pull them away from the “mother” tuber.
The eyes aren’t always visible in the fall. If you can’t find any, wait until spring to grow dahlias when the eyes start to sprout.
Many gardeners will also put some kind of fungicide powder on their dahlia bulbs before storing them away for winter to further prevent rotting. Sulfur dust is a popular choice because it’s suitable for organic gardening.
If you choose to do this, wear protective gear like a face mask, gloves, and eye covering while you work. Even natural powders and fungicides are dangerous to inhale or get in your eyes.
If you choose to use sulfur dust or another type of fungicide, be sure you wear protective gear like gloves and a face mask when you apply it. Breathing in the dust can be harmful to your lungs and may irritate your eyes as well.
Cover all the dahlia with a good layer of your chosen fungicide dust. Be sure to especially cover any sections that you had to cut.
You can also choose not to use a fungicide. You’ll just need to check the dahlia more often through the winter to make sure they remain healthy.
How to Store
Now that your tubers are prepped and ready, there are several options for how to store dahlia bulbs through the winter. Make sure you also move over your labels if you’re using them.
Each gardener has their preferred method but all can be equally effective.
First, you’ll need some kind of storage containers. You can use cardboard boxes, plastic bags, paper bags, storage bins, baskets, milk crates, and even planting pots.
You’ll also want a packing medium. Vermiculite, sand, peat moss, and wood chips are the most popular choices.
Once you have these, place your dahlia bulbs into your containers, spacing them so that there’s room for air circulation between each clump of dahlia. Pack around individual tubers with your packing medium.
If your packing medium is very dry (peat moss, for example, often is), slightly moisten it with a spray bottle. You don’t want rot setting into the dahlia, but you also don’t want them to dry out and shrivel.
You can use many different types of containers to store the tubers in, including garden pots like these ones. Just make sure the pots are big enough to hold the tubers without crowding.
Once your containers are filled, store them in a dark, cool, and dry spot like a garage or unheated basement. The ideal storage temperature is 40-45°F. Try not to store them anywhere the temperature goes above 55°F, and avoid freezing temperatures.
Monitor the Tubers
At this point, you’ve done all the hard work, but you still need to keep an eye on your dahlia bulbs through the winter.
Check on them periodically to make sure they aren’t either drying out too much or starting to rot.
If they start looking shriveled and dried, you can lightly spray them with water. If any tubers start getting rot, remove them immediately or trim off the rotted sections.
Replanting Dahlia Bulbs in Spring
Once you’ve successfully overwintered your dahlia tubers, here are a few tips for replanting them in spring:
- Replant your dahlias when all danger of frost has passed and the soil has warmed. You just kept them from frost all winter, so make yourself wait until the weather is really warm.
- If you didn’t divide the tubers in the fall, you can do so now if you wish, or plant them as is. The eyes should have started to sprout by this time, so it will be easier to see which tubers you can take off and plant.
- Dig a hole several inches deeper than your dahlia bulbs are tall. Mix some homemade compost in with your native soil to give your plants some food throughout the growing season.
After you store the bulbs through the winter, you’ll be able to replant and enjoy blooms all the way from midsummer to late fall.
- Plant the tubers so that their tops are about 2-4” below the soil surface. Cover them up gently with soil, and plant any others that you have at least 1-3’ apart.
- Throughout the summer, you can feed them occasionally with an organic fertilizer or homemade plant feed. Avoid nitrogen-rich fertilizers or you’ll end up with lots of foliage and few flowers.
- Mulch as needed to discourage weed growth, and water your dahlias during dry spells. Most varieties will start blooming in midsummer, and many will continue blooming into late fall.
Once you get to this point, you’ve successfully come full circle, and it will be time to store your dahlia bulbs for winter again. Each time you do it, you’ll learn more about which methods work best for you.