Can You Leave Dahlia Bulbs in the Ground Over Winter?
Dahlias are stunning summer bloomers, but their tropical origins mean they can’t withstand freezing winter temperatures in many climates. So can you leave dahlia bulbs in the ground over winter? The answer depends on where you live.
In USDA Hardiness Zones 8-10, dahlia bulbs can potentially survive the winter in the ground. However, even in these warmer zones, a thick layer of mulch is recommended to protect the tubers from cold and excess moisture Any areas that regularly experience sub-freezing temperatures for extended periods are too cold for dahlias to overwinter outdoors
Why Digging Up Dahlias is Advised
Dahlias are native to Mexico and Central America where winter temperatures rarely dip below freezing. Most gardening resources advise digging up dahlia tubers in any area where the ground freezes for winter storage. This prevents the hollow tubers from filling with water and rotting.
However, some experienced gardeners have successfully left dahlias in the ground in Zone 6 and even Zone 5 through winter with heavy mulch. But this is risky and you may lose some or all of your tubers.
Other factors like poorly drained soil or excessive winter rainfall also increase the chances of rot when left in the ground. Wet freezing soil is the worst condition for stored dahlia tubers.
How to Overwinter Dahlias Outdoors
If you want to experiment with leaving your dahlias in the ground, follow these tips to boost their survival rate:
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Wait until after the foliage has been damaged by frost, then cut all stems back to about 2 inches above soil level.
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Mound 6-12 inches of mulch such as leaves, straw, or compost over the tuber clumps. Avoid using plastic sheeting.
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Covering dahlias with an old bucket or pot adds an extra layer of protection.
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Check for rotted tubers in spring and scratch back some of the mulch if sprouts don’t emerge.
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Be prepared to lose some bulbs, especially in colder climates. You may need to replenish your stock periodically.
Overwintering Tubers Indoors
For gardeners in zones 7 and below, the safest way to save dahlia tubers is by digging them up in fall and storing them over winter. Here’s a quick overview of the process:
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Wait until after a light frost blackens the foliage before digging up the clumps.
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Allow clumps to dry out for a few days before separating the tubers.
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Remove excess soil but don’t wash or damage the tubers.
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Optionally divide the clumps but don’t damage the eyes.
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Pack tubers loosely in paper bags, sawdust, or vermiculite. Don’t store in plastic.
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Keep tubers between 45-55°F in a dark, dry spot like a basement or garage.
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Check periodically for rotting and dehydration.
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Start tubers indoors 6-8 weeks before your last expected spring frost.
With proper indoor winter storage, most healthy dahlia tubers will survive to bloom again the next summer. For cold climates, this method ensures you’ll have flowers without having to purchase new tubers annually.
How to Dig and Store the Tubers
1. LABEL. Start by labeling your plants with survey tape (plastic plant labels are too easily lost). Be sure to do this BEFORE you get a frost so you can still see the flowers and evaluate which plants you want to keep. Save only the plants that are strong and healthy, and that really impressed you. There are tons of great dahlias out there and no reason to grow underwhelming ones.
2. CUT BACK. After the first hard frost, try to leave the tubers in the ground for a week or two. While waiting isnt essential, it does help to toughen the skin of the tubers. Dont cut down the plants until right before you dig them. This way water wont accumulate in the hollow stems. When youre ready to dig, cut back all of the stems to within 3-4” of the ground. Re-tie the labels as needed, so they are securely attached. If your dahlias were grown in containers, skip down to the section on packing and storage.
3. DIG. Dig up each root ball, starting at least a foot away from the stem. Depending on the size of the plant, the root ball may be 12” to 18” across and equally deep. Go slowly and be gentle, as the tubers are extremely brittle. During storage, damaged tubers are more susceptible to decay.
4. DRY. If possible, let the clumps air dry for a day or two. But make sure they are protected from frost. Tubers may be divided at this point, or you can wait and do it during the winter or early next spring. If you plan to divide your tubers later, theres no need to wash soil off the clumps. Just store the entire root ball as it came out of the ground. The soil gives them some natural protection from damage and rot. If you want to divide the tubers now (which will save on space if thats an issue) skip ahead to the dividing instructions below.
Tips and Techniques for Storing Dahlia Tubers Indoors
Dahlias are at their best in late summer and fall, when the plants are mature and pumping out tons of blooms. But before the first frost, you have a decision to make. Will you treat your dahlias as annuals and plant a fresh batch of tubers next spring, or save the tubers from your favorite varieties and grow them again next year? If you want to try your hand at overwintering some tubers, read on for step-by-step instructions.
Can you leave dahlias in the ground over winter?
FAQ
What happens if you leave dahlia tubers in the ground over the winter?
I want to start with a disclaimer that overwintering dahlias is not possible in every climate. You need 2 important things to successfully leave tubers in the ground over the winter: (1) the ground cannot freeze because your tubers will also freeze and die and (2) you need excellent drainage so the tubers do not rot.
How do you winterize dahlias in the ground?
In late fall, simply cut the plants back to several inches above soil level. They will start growing again in spring. Dahlia tubers may survive a mild winter outdoors in zone 7 (as long as the soil is well drained and the area is thickly mulched).
What happens if you don’t separate dahlia tubers?
Each plant will produce a clump of new tubers which, undivided, will produce smaller plants with poorer quality blooms.
How to keep dahlia bulbs over winter?
Place the tubers in a cool, dry, dark space that won’t freeze. For many, this could be an unheated basement, attic, closet or utility room. If your space is prone to moisture or mold, it is not a good place to store your tubers.