Toilet Paper Tubes, Paper Towel Tubes, Crochet Thread Spools, and other cardboard tubes make good planting pot alternatives. There's nothing new in this idea, avid recyclers have been recommending it for decades. Cut TP tubes in half, cut Paper Towel tubes down to 2-3" lengths, leave Crochet Thread Spools whole (they are best for larger plants like tomatoes). Set them upright in a tray. Fill with potting soil, right up to the top (when you water it, it will sink anyway). They follow the same rules as Peat Pots, though some roots may grow through the cardboard, some may not. If they do not, you can tear off the cardboard before planting - there isn't a real need to do so though, because it will break down and help the soil if you leave it there.