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This is a relatively

This is a relatively complicated process (that is, relative to planting in ground) but apparently quite do able.

Gardeners in Alaska do it, as shown in pictures here (http://www.alaskamastergardeners.org/Dahlias.html); note that specific lighting details are not provided.

Gardeners in Nove Scotia do it: More info on lighting is here https://sites.google.com/site/novascotiadahliasociety/growing-advice/starting-tubers

And a gardener in Colorado does it and provides a lot of detail here: http://www.dahlias.net/seabox/lightem.htm

Hope this helps!