Starting Dahlia Tubers Indoors for Planting Outdoors
Four to six weeks before last frost, choose flower pot wide enough to fit tuber horizontally.
Add just enough moistened potting mix to lay tuber in pot six inches deep (or at depth recommended on your plant tag).
Cover with moistened potting mix up to one inch below lip of pot.
Place in full sun or six-inches below grow lights.
Water sparingly but never allow to dry out.
After last frost, gradually transition dahlia to life outdoors over a two-week period.
Transplant into ground when soil temperature is consistently 60°F (16°C) minimum or continue growing in pot (best only for dwarf varieties) in sunny location.
Add support rod at transplant time if dahlia variety is known to be top-heavy.