Once-ler had lots of truffula seeds. However when he planted them, they didn’t grow. So he planted more until he had only three left. He gave two of those to other people (Norma and Audrey’s mum) and kept one. He started growing his mustache out to resemble the Lorax’s in the hope that the Lorax would come and make the seeds sprout. The final seed he gave to Ted because Ted brought him marshmallows.