You’re missing out if you haven’t caught on to the dahlia craze yet. These gorgeous garden beauties stand out in the landscape, and their impressive blooms make wonderful cut flowers to bring indoors or share with a friend.
Chances are that you’ve found your way here because you have some dahlias and need to know how to handle overwintering them. And that is precisely what we are going to discuss.
Dahlias are native to Mexico and are hardy, meaning they can be left in the ground over the winter, only in zones 8-12. Our winters here in zone 8 can be unpredictable. However, we had a cold streak last year that would have killed my tubers, so I opted to store them for the winter and re-plant them in the spring.
If you live in zone 8 or higher, you should be able to leave them in the ground over the winter, but every couple of years, you should dig them up and divide them to prevent them from getting over-crowded and to keep the newer tubers healthy by removing dead weight.
If you garden north of zone 8, your tubers are unlikely to survive the winter in the ground. However, the nature of the dahlia root system makes it easy to store them for the winter without taking up much space. Here are some tips on properly preparing and storing your dahlia tubers for the winter.
Harvest at the Right Time
Timing is crucial to ensure successful dahlia tuber storage and regrowth in spring.
The first consideration when digging up your dahlia tubers is waiting until the right time. Much of the multiplying of tubers occurs early in the year, but these new tubers will not mature until much later. Waiting until the tubers are fully mature will give them the best chance of surviving storage and popping back up in the spring.
Dahlia tubers can handle some cold weather. They are cold hardy to zone 8, which can see some temperatures in the 20s come December and January. The best time to dig up your tubers is after the foliage has died back for the winter. If you live north of zone 7, don’t wait until a hard freeze hits, as this will kill off tubers.
Letting the foliage die back naturally is a good way to ensure you’re waiting long enough. You can also wait for the first frost. It all depends on what climate you garden in. In northern climates, you may find this time comes as early as October, while warmer climates may not see their dahlias die back until well into December.
Getting a head start on prepping plants for the cold can be tempting. However, waiting out your dahlias until the right time will give you the strongest tubers, which will get the best start in the spring. More mature tubers mean more dahlia plants and more gorgeous blooms.
Prep for Harvesting
Remember to use a clean and sharp cutting tool when working with plants to prevent disease transmission.
A few days before you plant to harvest your dahlia tubers, there are a couple of things that you can do to prep them. The first is to trim the stems. Trim the dead stalks to a few inches above the ground. This will force the eyes to come out, which makes them much easier to divide.
If there is any chance of rain between the time you cut your stalks and the day you plan to harvest the tubers, cover the tops of the cut stems with foil or plastic to protect them from filling with water.
Dahlia stems are hollow, which is great for transporting water to their flowers. Their flowers require a lot of water. However, you don’t want those hollow stems to fill with water in the days before you harvest the tubers, as this can lead to root rot.
Make sure to use a clean, sharp tool and to cut and clean your tools between plants. This helps prevent the transmission of diseases from one plant to another. You can dip your shears into a solution of 10 parts water to one part bleach between plants to keep them extra clean.
Tread Lightly with the Shovel
When digging up dahlia tubers, handle them delicately.
Dahlia tubers will be delicate at this stage, so it’s important to go easy when you’re digging them up to be careful and light-handed. Using a garden fork or small spade, loosen the soil in a one-foot radius around the stem. If you run into a tuber, expand your circle so that you don’t tear the cluster apart.
Use your garden fork or other tool to dig beneath the tubers and lift them up gently. The cluster should come away easily as long as the soil is not too compacted.
The neck will be quite fragile at this stage, so it is best to set them aside and allow the entire cluster to dry for a few hours. This helps to stiffen up that neck and make it easier to handle without breaking apart. You want to be able to make your own decisions about where to divide your tubers.
Clean Your Tubers
Make sure to gently remove as much soil as possible, paying close attention to the spaces between the tubers.
Soil contains microorganisms and, potentially, fungi and bacteria. You don’t want to store your tuber with the soil on them, as you might return to a box full of rotten tubers. This is the reason it is so important to clean before you store tubers.
Even if you store them in peat moss or another substrate, it should be a clean, fresh substrate. Gently brush off as much soil as possible, paying attention to the spaces between tubers.
Next, to ensure they are clean, use a gentle stream from the hose or a utility sink and rinse any leftover soil away. Examine your tubers for any damaged or rotting root tissue. This should be cut away to protect the rest of the tubers from rotting.
Locating and distinguishing the eyes, where fresh shoots will emerge, is crucial.
This is the point where you have to decide whether you want to leave the tubers intact or separate them. You can always separate them in the spring before planting, but it is an extra step you will probably want to take, as it means more dahlia plants.
When you separate your clumps of tubers, you want to look for and identify the eyes. There are the places where new sprouts will form. It can be more difficult to identify the eyes in the fall, so for this reason, you may decide to wait until spring when they are more pronounced and obvious.
When you separate, ensure each section has at least one eye, or you’re not likely to get any growth. Identify the mother tuber, the one that grew last season’s dahlias. This is going to be the darkest brown tuber. Remove this one from the new tubers and discard it.
If dirt is left on your newly divided tubers, rinse them off again. Always use a clean tool when separating, or you risk introducing pathogens. Newly cut tissue is more vulnerable. Think of this as an open cut. It needs to stay clean until it heals over.
Prep for Storage
Consider laying tubers on a screen for improved air circulation and faster drying.
Before storing, tubers must dry out to prevent mold or fungus from growing over the winter. If you have a screen you can lay them on, they will get better air circulation this way and require less time to dry.
You want to make sure that they are thoroughly dried before storing them. This can take anywhere from a few days to a few weeks. Set them in a spot that won’t experience freezing temperatures that’s in indirect sunlight, and let them dry until the skin begins to wrinkle.
Choose the Right Storage Method
Gardeners have a range of container choices when it comes to storing tubers.
A variety of different containers work well for storing. I like shallow boxes with vermiculite because I like to lay my tubers flat and not on top of each other. Some gardeners use plastic wrap, which prevents them from drying out.
You don’t want your tubers to get any more dried out than they already are at this stage, or the eyes will dry out and not sprout. You can use paper bags, milk crates, or boxes filled with vermiculite. Some gardeners like to wrap them in newspapers, although print newspapers are not quite as prevalent as they used to be.
Labeling your dahlias is optional, of course. If you have many different varieties, it can be nice to know which ones are which. Not all dahlias grow to the same height, so you want to avoid planting shorter plants behind taller ones, or the shorter ones won’t get enough light. I’ve tried this and had few to no flowers on the smaller plants.
Store Them in the Right Place
Your storage location choice should depend on your area’s prevailing climate conditions.
Store your tubers in their containers in a cool, dry, dark place. You want those tubers to take a nice long nap, staying as close to their present state as possible. If the eyes sprout a tiny bit, it will be okay, but you don’t want them growing in storage without water or sunlight.
The ideal temperature to store your dahlia tubers is in the range of 40°-45°F. This will keep them dormant for months in solitude. Don’t store them in a space that could freeze. Avoid exposing them to a lot of moisture, which can rot them.
Depending on your climate, your garage could be a great storage location. Store them up against the side of the house to avoid any unexpectedly cold weather that could bring the temperature to freezing.
Take a Peek from Time to Time
Look out for mold or fungus growth, as it can spread and potentially ruin all your tubers if left unattended.
Once your dahlias are properly stored, you can relax until spring. As long as the air stays cool and dry but not too cold, they will likely be in great condition in the spring.
With that being said, it is a good idea to check in on them from time to time just to make sure that things are staying as they should. Check for any mold or fungus growth, as this can spread, and you may end up with an entire box of rotten tubers if you don’t remove the source quickly.
Another factor to check on is moisture in general. You don’t want your tubers to dry out. There is a fine balance, which sounds counterintuitive, but if they are drying out too much, you’ll want to rehydrate them. You can rehydrate them by misting the packing material with some water. This is a great reason to use some vermiculite or peat moss when storing.
Don’t be afraid to remove tubers that look less than healthy. If you find any have become hollow, shriveled, or have fully dried out, cut them off. Check for signs of growth, and if the eyes look like they are growing, do not add any moisture, as you can end up with rotten eyes.
Storing your dahlias for the winter is an easy process that will save time and money in the long run, as you can keep those same tubers going for years. I hope your tubers survive the winter and you are graced with a bounty of beautiful blooms next season!