It's the end of another growing season, but what do I do with my dahlias? Learn when to dig up dahlia tubers for winter storage!
Dahlias are one of my favorite flowers, and I grow over 50 varieties in the raised beds of my cut flower garden. Their huge blooms create a riot of color along the street that stops people in their tracks (I've actually seen people slam on the brakes or suddenly pull over to take photos!)
But when the days get shorter and the nights get colder, it's time to start thinking about when to dig up all those dahlia tubers. Dahlias can be taken out of the ground as early as 120 days after planting, or you can wait until the first frost.
While I could leave them in the ground all winter here in zone 8b, I prefer to dig and divide them every year. Those huge clumps would get too crowded in these 3'x3' raised beds pretty quickly!
In this article, I'll go over when to dig up dahlia tubers and how to prepare them for lifting. Then, you can head over to my step-by-step tutorials on how to dig up dahlias, how to divide the clumps, and how to store them over the winter!
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Why you need to dig up dahlia tubers
Dahlia tubers aren't frost-hardy, meaning they're susceptible to rot if left in the ground over winter in colder regions. If you live in a growing zone of 7 or lower, you'll need to dig them up and store them over the winter.
Some gardeners have been able to successfully overwinter dahlias in colder zones under layers of mulch, leaves and tarps. However, you could also be overwintering insects or providing rodents with a warm winter home and plenty of dahlia tubers to snack on!
Even in warmer climates, leaving the tubers in the ground can expose them to pests, diseases, and other issues. Even though our winters are mild here in Seattle (zone 8b), we get a LOT of rain. I dig up my dahlias to prevent them from rotting underground.
Digging up your dahlias also allows you to divide them. Each plant comes from a single tuber, which multiplies underground over the growing season. If you want more of your favorite varieties, just dig and divide them every year!
Timing varies by climate
Timing is everything when it comes to digging up dahlia tubers. Pull them up too early, and you risk immature tuber development that will affect future blooms. On the flip side, waiting too long could expose the tubers to rot or frost damage.
Where you live can significantly influence when you should dig up your dahlia tubers. Search for the first frost date in your zip code to get a good estimate. If your area doesn't get a frost, you can just leave them in the ground!
Visual cues that it's time to dig up your dahlias
Dahlias are pretty good at communicating when they're done for the season. Here's what to look for!
Plants stop blooming
Some of my plants stopped producing buds and blooms weeks before our first frost. If you notice this issue early in the season, check out this list of reasons why your dahlias aren't blooming before you start yanking them out of the ground!
But if it's been at least four months (120 days) since you planted your tubers, you can safely dig them up. They've had enough time to produce new tubers and store energy away for next year.
Since I have so many dahlia plants to process, I dig up the ones that have stopped blooming first, rather than waiting for a frost. I'll cut down the stems to six inches and let them sit for another 4-5 days in the ground. The plant will try to send up new shoots, which makes the eyes easier to see when dividing.
Frost is another important indicator, especially in colder climates. After the first light frost, the above-ground foliage will darken and wilt. The flowers will look like they're melting or just turn brown. So sad!
This is a clear sign that it's time to dig. Make sure not to wait too long after a heavy frost, as that could damage the tubers below the ground.
What to do before digging
Before you grab that spade and start digging, there are some preparatory steps you'll want to consider.
Label each plant
First off, mark your dahlia varieties if you're growing more than one type. Trust me, it's easy to mix them up once they're out of the ground, and labels will save you a lot of guesswork later.
When my dahlias start flowering, I verify that the blooms match the plant tag. I always find a few mix-ups! These plant labels wrap easily around the stem and give the plant plenty of room to grow.
However, once the stems are cut down, those plant labels come off too easily! At this point, I switch to flagging tape. Just write the variety name on one end and tie it securely around the stem.
Prepare your storage containers
Once your tubers are out of the ground, it's a race against time to get them into storage before they dry out! Make sure you have everything you need on hand and ready to go.
Whether you're using plastic wrap, boxes filled with peat moss or vermiculite, or another method, having the supplies ready will make the transition from ground to storage smoother. This also minimizes the time the tubers are exposed to air, reducing the risk of them drying out.
Check the weather forecast
As dig day approaches, you'll want to keep an eye on the weather. You'll want to avoid digging right after heavy rainfall, as wet soil can stick to the tubers, making them more difficult to clean. A dry day with mild temperatures is ideal for this kind of garden task!
Now that you know when to dig up dahlia tubers, stay tuned for my step-by-step tutorial on how to do it without damaging them!