FYI you might want to pick the bag, based on the plants you intend to grow, Luckily most hardware stores sell several different types of soil. Your going to want the squatter "brick" shaped bags for things like tomatoes, as well as longer root vegetables (carrots), the flat ones you find at Osh are fine for herbs though. You also might try not opening the top all the way, and simply creating individual openings for each plant, in some climates this can prevent excessive water loss, although you might find (in moister climates) that it turns the bag into a fungus farm.