Any potting medium will work. Mixes with soil for potting or "soilless mixes" both work fine.
Avoid soil bags that say "weed-free" because they can contain chemicals mixed into the soil to keep any weed seeds from germinating. Unfortunately, this keeps ALL seeds from germinating, including the seeds you sow in that soil.
What's MY favorite? I like the most economical one I can find. I do a LOT of Winter Sowing...it's fun and is very addictive. So I look for the biggest and largest bag of soil I can find. It's an economical choice to get the biggest bag because it costs less per pound or quart. Plus, with more soil, I can sow more flats!
Cornell University's AgNIC Alliance Website
Home and Garden InformationFactSheet HGIC-1456
Clemson University Extension
healthrecipes.com
