Can You Leave Dahlias In the Ground Over the Winter?
Have you gotten caught up in the Dahlia craze and want to know whether your pretty plants will pop back up in the spring? In this article, gardening expert Melissa Strauss discusses whether or not dahlias can be left outside in the winter and what you can do to keep them coming back year after year.
Dahlias have seen a recent rise in popularity as a garden favorite. And truly, it’s no wonder. These stately plants produce some of the largest and most stunningly varied blooms. However, the big question on the minds of gardeners everywhere is whether dahlias can survive if left in the ground for the winter.
As with most plants, the answer is not a straightforward yes or no. All plants have a native range and specific climate zones where they naturally grow. This is where they perform at their peak and are most likely to survive the winters and return in spring.
To determine whether or not your dahlias can survive the winter outdoors, we need to look at their native range and compare the climate with the one you live in. Let’s look and see if you can leave those tubers to overwinter outdoors or if they will need to be stored for the winter.
The Short Answer
The answer is yes and no. Dahlias can survive the winter outdoors in zones 8-10. While a frost will cause the foliage to die back, dahlia tubers can tolerate some cold weather if the soil doesn’t freeze. Adding a thick layer of mulch over your bulbs during winter is an excellent idea if you live in zone 8. If you live in an area with wet winters, you also risk rotted tubers due to overly moist conditions.
The Long Answer
Dahlias are native to Mexico and some parts of Central and northern South America. There are 42 listed species of dahlia, with about six or seven commonly seen in cultivation. As a result, thousands of varieties are available, and new variations become available regularly.
These popular garden flowers are known for their large, intricate, and highly varied blooms. Some dahlias produce flowers that are only two to four inches in diameter. These mini dahlias are often of the pompon flower formation and are just as adorable as can be.
The largest of the dahlias are often referred to as dinner plate dahlias. These giant blooms can reach diameters of 12”-24”. If you’re looking for impressively large flowers, dinner plate dahlias rank among the most spectacularly large and colorful.
So, can I leave my dahlias outdoors this winter or not?
That is the million-dollar question. It’s easiest to care for plants that naturally occur in your climate zone and specific region. Dahlias are considered hardy only in zones 8-10. That is not a very large range. Even here in zone 8, I don’t leave my tubers in the ground.
A surprise cold front that leaves the ground frozen could prove deadly to dahlias tubers. After four days of below-freezing temperatures last December, I’m not taking any chances with my precious dahlias. Wet winter weather, even if not particularly cold, could cause your dahlias to rot.
If your environment doesn’t usually experience a hard freeze and isn’t overly rainy, you can probably leave your tubers with a relatively high success rate. I recommend covering them with a thick layer of mulch in fall. This will help prevent damage in uncharacteristically cold weather.
When the weather begins to cool off, you may notice that your dahlias have a resurgence after struggling with the late summer heat. With the first frost, however, the foliage should begin to wilt, turn black, and die back. This does not indicate any problem, just that the tubers are preparing for dormancy.
After the dieback, cut your stems down to about two inches tall. You don’t need to leave that dead weight to rot with cold and warm weather fluctuations. After trimming off the stems, spread a thick layer of mulch or compost over the tops of the plants, covering the stems completely.
Can I still grow dahlias in cooler climates?
The good news is that dahlias grow perfectly well in cooler climates as long as they are adequately attended to during winter. My dahlias flourish in spring and fall while they slow down their blooming in winter as they try to conserve energy during the scorching north Florida summers.
Growing dahlias in a cooler climate is slightly more complicated. I won’t pretend they are low maintenance. But then, we don’t grow dahlias because they are easy; we grow them for the love of the flowers, knowing that most beautiful things require a bit of effort.
Growing dahlias in climate zones north of zone 8 means that you’ll be moving your tubers indoors during the winter months when the ground could potentially freeze. Let’s briefly go over the process of storing dahlia bulbs because, in some areas, now is probably the time to get started.
How should I store my dahlias for next year?
Dahlias grow from a special type of root called a tuber. These tubers are something between a bulb and a rhizome, as they have some characteristics of both. They have thin, papery skin, which can be fragile. From these reproducing tubers, they grow eyes, which turn into the next year’s new plants.
Tubers reproduce similarly to bulbs. When you dig them up, you will notice that there is a mother bulb, which is the bulb that produced this year’s plant. The young, new bulbs that will produce next year’s flowers are attached. These new bulbs form over the growing season, and they tend to mature close to the time the plant goes dormant for the winter. For this reason, leaving your tubers until after the first frost is a good idea.
A frost will generally cause the foliage to die back, but a hard freeze will kill the tubers. This makes the sweet spot fall directly after the first frost and before the first hard freeze. Once your dahlia foliage dies back, it is time to dig up your tubers and give them a cozy place to spend the colder months.
Storing dahlias is a similar process to storing other frost tender bulbs. Plants like cannas and gladiolus must be brought indoors for the winter, and their bulbs can be prepared and stored similarly. Here are some quick steps to preparing and storing your dahlia tubers and other frost-tender bulbs for the winter.
- After the foliage has died back and just before you dig them up, cut the stems to two or three inches above the ground. Avoid doing this right before rain. Dahlias have hollow stems that will fill up with water and can cause rotting issues in your tubers.
- Use a garden fork or small shovel to loosen the soil in a one-foot radius around your tubers. They are delicate, so a garden fork is a great tool. Once you know how large your tubers are, you can lift them lightly with a shovel from underneath to further loosen them from the soil.
- Use your hands to pull up the tubers, as you can feel them better this way and be gentle about keeping them in one piece.
Cure and Clean
- Set your tubers aside for several hours to allow them to dry out. Damp tubers are more vulnerable than dry ones, which can handle a bit more handling.
- Wash or brush as much of the soil from the tubers as possible. Soil can carry pathogens into storage; we don’t want to risk rotting tubers.
- Allow your tubers to cure, or dry out, which can take from a few days to several weeks, depending on the humidity and how damp they were to begin with. You want the skin to harden up and begin to wrinkle, but you don’t want them so dry that they die and crumble in storage.
Separate and Store
- At this stage, you decide whether to separate your tubers now or wait until spring. There are different schools of thought on this step. It is easier to divide tubers in fall but harder to locate the eyes, which will be more prominent in spring.
- Several types of storage solutions work well for storing bulbs and tubers. You can wrap them in paper and store them in nylon bags. You can also surround them with peat moss to protect them and help maintain a healthy moisture level. I like to store my tubers in shallow cardboard boxes with some peat moss or perlite surrounding them. Also consider coarse vermiculite. Tubers should not touch each other while in storage.
- Label your tuber storage containers and place them in a cool, dry space. A garage that stays above freezing temperatures is a good spot for storing tubers. But a cool, dark closet will work as well. Ideally, keep your tubers as close to 50°F as possible all winter.
- Check on your tubers monthly while they are in storage. Look for signs of rot or bulbs that have died and dried up, and remove these. If your bulbs are looking too dry when you check on them, you can lightly spray your peat moss or perlite with water before returning them to their storage space.
Storing tubers takes some foresight and preparation, but ultimately, it saves a lot of money you might otherwise spend on new tubers every spring. Your dahlias will multiply with the right care, and you will have even more beauties next season.
If you live in a relatively dry, warm climate that doesn’t experience a hard freeze, feel free to leave your dahlias in the ground for the winter. If you are on the fence, a thick layer of mulch on top of the soil will go a long way toward maintaining a more consistent and warmer soil temperature. In cooler climates, storing your dahlias during the colder months is always safer.