All my new seedlings go into 4" unglazed pots. I don't have a good reason for doing this. I just don't want my potting soil to retain moisture long-term. I have a feeling my using clay is not necessary, since it appears that most just go right to plastic. Just be sure your media drains well and that there are good drainage holes. I probably leave my seedlings in clay for a couple of months. I will then use a knife blade to go between the clay and media so that the root ball comes out easily. If there are lots of roots, I up-pot to a 1 gal. plastic pot. I use Osmocote in my beginning clay pot media but nothing else. When I up-pot, I will still have Osmacote in the media but will begin to supplement that with a general purpose, water-soluble fertilizer. I dilute this fertilizer by 1/2 the recommended strength and fertilize every 2-4 weeks. It just depends on how much time I have.
