Rita, if I use paper pots for peas I only plant one pea per pot. The paper pots are wrapped around a small soup can so they aren't big enough for more than one seed. That way you plant each seedling exactly where you want it. Yes, it takes a lot of paper pots, but you could be rolling them as you watch TV!
Rick, anything solid (no holes) is game, i.e. Styrofoam trays that come under meat and fruit, plastic tray lunchmeat comes in, etc. i had the opportunity to get some trays used (I think) for feeding chickens at an auction once. They're great except a little brittle so I have broken the edges on several. This year I am finally ordering some heavy plastic trays. Oh, I have also used old cookie sheets that have a lip, sheet cake pans, mud trays, anything I can set them in and water the bottom. You have to make sure not to let them dry out because the newspaper will wick the moisture away from the plants if you do.
Oh, my mother one time got some old cafeteria trays! They are perfect!
