Janette Marker chose outdoors for her hypertufa containers projects with cement dust but she shows steps that can be done with plastic bowls or dishpans as forms inside. Here she dug a space in soil and lined it with black plastic to lift the container out once it cured. See her projects steps and tips: http://www.yankton.net/river_city/article_c2b8676c-3771-11e3-845e-001a4bcf887a.html
Plant Exchange Blog 