Hey Toronto416! For starting your seeds with Happy Frog, the ideal container size depends on whether you're growing autos or photoperiods. If they're autoflowers, I highly recommend planting them directly into their final 3 to 5-gallon (roughly 11-19 liters) fabric pots to avoid transplant shock, which can really stunt their short growth cycle. If they are photoperiods, starting them in a small solo cup or a 1-liter starter pot is perfect to help establish a solid root ball before moving them up to something larger. Happy Frog is a great choice it's nice and light for those delicate young roots!
Happy Growing Growmie🌱