First, make the paper. Tear up small pieces of paper, tissue paper, junk mail. Stay away from plastic-coated or glossy papers. If you use red paper it will turn the card pink. Allow paper to soak in warm water. The longer you allow it to soak up water the easier the process is. Place paper pieces in blender and mix until you have a thick pulp. Make sure you don't have pockets of unprocessed paper. Next add seeds: marigold, cosmos or whatever you've saved from your flowers. If you do not have saved seeds you can buy seeds. Sprinkle in the blender and mix. Mix it as little as possible, just until seeds are mixed in.
Prepare a flat surface. Place newspaper on table. Place a long piece of foil, plastic wrap or waxed paper. Foil tends to stick if pulp is sticky. Place pulp with seeds on waxed paper. Place a second piece on top and spread with rolling pin as thin as possible without leaving holes or empty places. Paper will not be thin like copier paper. It will feel like cardstock, but be lumpy. Remove top piece of waxed paper and leave it in a flat place to dry. Pulp may begin to curl, but that's okay. As it dries, remove the bottom waxed paper when possible. Place between two books or hard surfaces to flatten, but be careful not to leave moist pulpy paper too long or it will mold. Cut and mail. Be sure to explain to those you mail to the process of "planting" their xmas card in the spring! Suggestion: If you receive a seed card and don't have a place to plant it, plant it in a public park where you know it will get watered regularly by sprinklers or park personnel.
Great project for children, too.