If you ask a flower grower the secret to incredible dahlia displays year-after-year, many will tell you it’s lifting each and every tuber to store away carefully and replant in spring. But, this only works if proper storage is in place, otherwise you may find you’re left with mushy dahlia tubers.
The truth is overwintering dahlias requires careful preparation and specific storage requirements, much like storing bulbs. They turn mushy when the storage set-up has allowed excess moisture in. At the same time, you don’t want to let your tubers dry out, as this can dehydrate and shrivel them.
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What Causes Dahlia Tubers to Go Mushy?
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‘Mushy tubers are the result of moisture penetrating the tuber without benefit of any top growth that needs the moisture,’ summarizes gardening expert Lorraine Ballato.
Essentially, because tubers don’t have any growth and are dormant in winter, isn’t needed in the same way as when they’re planted in the ground and actively growing.
‘So, the moisture just stays there and eventually rots the tuber,’ Lorraine explains.
You’ll be able to tell if you have mushy dahlia tubers by simply picking them up and giving them a soft squeeze. They shouldn’t be easy to indent and shouldn’t appear wet, or have an unpleasant smell.
‘Tubers that weren’t allowed to dry and cure properly before storage can also retain excess moisture,’ says gardening expert Michael Clarke.
It isn’t just excessive moisture behind mushy dahlia tubers, however, as improper ventilation and the wrong temperature are also key factors.
‘Freezing temperatures can rupture cell walls, causing the tubers to collapse once they thaw. Overly warm temperatures can likewise encourage premature sprouting and decay,’ Michael says.
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‘If tubers touch when they’re stored or are sealed inside plastic, moisture and heat can get trapped leading to rot,’ he adds.
This can even cause rot to spread among tubers, resulting in your entire stock being wiped out.
For this reason, Lorraine advises the following for storing dahlia tubers:
‘Properly dry the tubers before they’re stored,’ she says. You can do this by brushing off dirt and letting them air-dry somewhere cool, dark, and well-ventilated.
‘Use vermiculite (available from Amazon), perlite, which you can find at Walmart), or slightly dampened peat moss, from Amazon to pack tubers into a ventilated storage, like a crate. You don’t want them to dry out entirely in storage, and these materials retain sufficient moisture,’ says Lorraine.
As for location, keep tubers somewhere cool and dark, like an unheated garage or shed, ideally maintaining a temperature between 50-60°F. You should also check on stored bulbs and tubers once a month during winter, removing any rotting plant material to prevent spreading.
You can use these wooden crates to safely store dahlia tubers. The slats allow for airflow, keeping the tubers well-ventilated, reducing the risk of rot.
Burlap makes a great material to store tubers as bulbs, thanks to the material being breathable.
Use vermiculite to pack tubers away for winter. It’s a natural mineral that retains sufficient moisture to ensure the tubers don’t dry out.
Lorraine Ballato
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Gardening Expert
Lorraine Ballato is a flower growing expert and the author of the international best-selling book ‘Success with Hydrangeas’, available at Amazon. She is also an in-demand speaker throughout the US and the resident hydrangea expert at the New York Botanical Garden.
Can You Save Mushy Dahlia Tubers?
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It is possible to save mushy dahlia tubers, depending on how far gone the problem is.
If only part of the tuber is rotting, you can carefully cut away the bad parts (with this sharp garden knife from Amazon), leaving just healthy, firm flesh.
You should allow the wounds to dry before placing them in storage again. The tubers will form a protective callous when drying.
However, if your tubers are entirely mushy and have a very unpleasant smell, it’s unlikely they’re viable and you should dispose of them immediately.
Michael Clarke
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Gardening Expert
Michael Clarke is the founder of Yardwork and Pulled, the online platforms for everything home and garden. He has a degree in landscape architecture and horticulture from the University of California Davis. He was previously the founder of a landscape development and maintenance company.
FAQsHow Can I Rehydrate Dahlia Tubers?
If your dahlia tubers have shrivelled from dehydration, soak them in room temperature water for just a couple of hours. Avoid soaking for much longer because it may cause rotting. You should then let them air-dry sufficiently (when the outer skin is tough) before returning them to proper storage.
In some regions, you don’t have to lift dahlia tubers at all. Those living in US hardiness zone 7 and above can generally get away with leaving dahlia tubers in the ground, simply covering them with a generous layer of mulch. However, if you live in the harshest climes, you can lift and wrap dahlia tubers in burlap over winter to keep them in viable condition before replanting.
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