If You Grow Dahlias, Don’t Wait Too Long to Do These 5 October Jobs – It’s Time to Get Them Ready for Winter
Frost is just around the corner – here's how to help your dahlias through the seasonal shift
Dahlias are some of the final late-summer blooms we get to enjoy into fall, and by October they're past looking their best. Before the dreaded frost arrives, it's important to prepare your dahlias for cold temps – though you may also be able to get one last flush of flowers over the next couple of weeks.
Growing dahlias requires lots of particular care and overwintering dahlias can initially sound complicated. However, when you break it down, lifting, drying, and storing tubers is pretty straightforward. Doing these things now will keep these tender perennials safe over winter and ensure they can be planted again next year for another summer of showstopping blooms.
You'll need a few things to hand to tackle the list of what to do with dahlias in October, including these Felco F2 pruning shears from Amazon. Here, a garden pro talks through five dahlia jobs for the coming weeks.
1. Encourage a Final Flush of Blooms
Dahlias tend to bloom up until the first hard frost in October. This means you can deadhead dahlias this month to encourage one last flush of blooms.
Many types of dahlias will bloom through October, so removing spent flowers can encourage the plant's energy to go towards opening the last buds.
You'll know if your dahlia has more blooms to offer by looking for emerging closed buds. If you don't see these and the foliage is looking paler and wilting, your dahlia is likely done for the season.
To deadhead, look for dahlia spent blooms and seed heads (they're similar to buds but elongated). Follow the stem down to where it joins the main stem and make a clean cut (these Fiskars pruning snips from Amazon can be useful to have to hand).
2. Reduce Watering
Dahlia tubers can rot easily, so it's important to pull back on watering in October. This is especially true as the plants slow down and prepare for dormancy, no longer needing so much water.
'Reduce your watering and stop fertilizing. This encourages the plants to begin directing their energy toward their roots – and, more specifically, their tubers – instead of producing new leaves and flowers,' says garden designer Kate Schneider.
A soil moisture meter (like this from Amazon) can help you keep track of your dahlia's moisture level. The soil should be allowed to dry out and you generally won't need to provide supplementary water alongside rainfall this month.
Kate is a former attorney whose passion for gardening caused her to leave her 9-5 in order to start Ibis Coastal Landscapes. Her vision for a gardening service that focuses on retaining historic Southern design and native species sets her apart immediately, with each project growing more beautiful and resilient over time.
3. Label Your Dahlias
Once your dahlias finish flowering and you're left with just the tubers, it can be really hard to identify the different varieties, especially if you have a sweeping cut flower garden of different types of dahlias.
'Label your dahlias while they're still blooming. This step is easy to overlook, but you'll be glad you did. There is nothing worse than cutting a gorgeous bouquet at the end of the season only to be left with a few leaves and no idea which dahlia was planted where,' Kate says.
You can use plant labels to do this, like these slate and chalk plant labels from Amazon, or repurpose popsicle sticks and pieces of wood from the garden.
4. Prepare and Lift the Tubers
You don't necessarily have to lift dahlia tubers to get them through winter – mulching can be enough frost protection in milder climes.
'If you're in Zone 7 or warmer, you may be able to leave your dahlias in the ground. Once the weather cools, apply a thick layer of mulch around the plants to provide additional insulation through winter,' Kate advises.
There are plenty of fall mulching materials you can gather from the garden for free, or you can pick up this bag of brown mulch from Lowe's.
'For gardeners in Zone 7 and below who routinely experience frost, wait for the first frost or until the plants have stopped growing. About two weeks after the first frost, cut the stalks back to approximately six inches and carefully dig up the tubers,' Kate says.
You can lift dahlia tubers using a long towel or a hori hori knife (like this from Amazon). Take care to dig a few inches away from the tuber to avoid damage.
5. Dry the Tubers for Storage
Before storing dahlia tubers, Kate says it's important to dry them out.
'Once you've dug up your dahlia clumps, let them dry before putting them into storage. A wet tuber can rot, potentially ruining it for next year's garden,' she explains.
Mushy dahlia tubers are caused by excess moisture and poor ventilation, making the tubers unviable for next year.
'Place the dug clumps somewhere cool, dry, shaded, and frost-free. A garage, covered porch, or barn works well. Let them sit for a few days to a week so the skins can dry and any cuts or damaged areas can callus over. Don't put your tubers in direct, hot sunlight to dry. The intense heat can cause them to shrivel,' Kate advises.
If any tubers have shriveled up, they're dehydrated and need a light misting to regain moisture (you can use this Amazon plant mister). If any have become brittle, discard them.
'Once they're thoroughly dry, you can safely store them in a cool, dark place for the winter. Check on them every few weeks to make sure they haven't become wet or begun to rot,' Kate continues.
You can store dahlia tubers in these wooden crates from Amazon. Use a dry medium to cover them, such as this vermiculite from Walmart, wood shavings, or newspaper. Ensure your storage container isn't airtight, as you want the tubers to have good airflow.
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'You can also divide your dahlia clumps once you've dug them up. Dahlia tubers can be divided either in the fall after they've cured or in the spring just before planting,' Kate adds.
'Fall division gives you smaller, easier-to-store pieces, while spring division can be easier because the eyes are beginning to swell and are much more obvious. Both approaches work, so it really comes down to whether you'd rather tackle the job now or save it for spring,' she explains.
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