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I grow several types of dahlias every year, and dig up the tubers in late Fall to keep them for next year. I cover them in potting compost and put them in the back corner of my basement which is dark, cool and dry. I use fresh compost every year.

I often find that I'll lose some of the tubers (one year I lost them all!) by the following Spring: they'll be crumbly and dried out and fall to pieces as I take them out of the compost.

What can I do to prevent this from happening?

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2 Answers 2

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Your profile reports your location as Portland, Oregon, so I'll assume that's where the dahlias we want to overwinter are located.

Let Dahlia tubers remind you of Goldilocks and the Three Bears--we don't want things "too" anything, we want things just right.

  1. Don't dig too soon, don't dig too late. Dig them up ten days or so after the first freeze or, if no freeze, in about mid November.
  2. Dry-ish, not so dry as to dry them out. Regardless of whether you use composting medium, sand or sawdust, the natural humidity of the area where they will be stored will effect their condition. If they start to dry out, you'll need to supplement humidity by using a spray bottle to dust a little moisture on the medium.
  3. Cool, but not too cold. A temperature between 40 and 50 degrees fahrenheit is "just right."

Overwintering your tubers is not a "set it and forget it" business. If you check the tubers every few weeks, you'll catch a problem before you lose the crop. The tubers will tell you if they are too dry, as they will start to shrivel.

Dahlias are beautiful, so the little extra care and keeping of the tubers is well worth the effort.

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Fall weather just started in earnest here, so this is a very timely answer. I think my mistake was to let them dry out. I'll keep an eye out for that this year. Thanks. –  Niall C. Oct 16 '12 at 1:01

I did a similar thing with tiger lilies that were taking over my garden, although this is more accidental an anecdotal than it is scientific. I was digging up the tiger lilies and I threw them all into a black trash bag. I kept the trash bag in my tool shed, where it would certainly get very cold in the winter, and the next year I discovered them, so I replanted them in some corners of my yard. Most of them took the next year and are flowering this year.

Alternatively, I'd imagine you could apply a thick mulch (i.e. full unopened bags of leaves) to your dahlias, then divide them in the spring.

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Did you use mulch on the lilies, or just whatever dirt happened to be stuck to them? In my area (Portland, Oregon) the problem with leaving them in the ground is usually more rain causing them to rot, than cold; I actually leave some tubers in the ground under the overhang from my porch and they do just fine. –  Niall C. Jun 11 '11 at 13:59
    
@Niall, good point, I'd imagine my advice is more suited to completely buried plants and not hardy weeds like tiger lilies. I just put the bags right on top of them. If you can pack the bags tight enough you can at least limit moisture and cold. –  Peter Turner Jun 13 '11 at 17:42

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