I grow mine in quart sized zip-lock bags in standard greenhouse trays (16-18 baggies per tray). The trays are under shop lights on shelves in my work room. I have room for about 36 trays, but that space has to include all of my annuals and vegetables from seed too. As the weather warms up I shift everything out on to my screened in porch where they harden off before planting.
Last night I had to bring everything back inside due to temperature drops, I am just leaving them inside today since it will be even colder tonight, but then they can safely go back outside.
These pics don't have dahlias in them, but its my "system"
