Def a soil moister prob but the time that seedling grows into the three gallon and transplant to a 5 the seedling is gonna be pretty big for indoor grow! But you can easly put your seedling into a 4 inch pot even after you placed into a three gallon. And once your four inch or what ever your choose is nicly rooted, stick right into a three! U prob will want to say into a three gallon. I mean, you get some big nice plants in a three gallon, and can also get a lovely 4 oz a plant

Thats good on a seedling