I'm growing Purple Prince tomatoes in a variety of locations, potted and in ground. These are supposed to have 10 oz tomatoes. The largest I have got may be 4 oz and most are smaller. I have fertilized three times during the season and generally kept them watered. Are the tomatoes small because of lack of fertilizer or some other condition? I am in zone 3a; however, most of the summer has been relatively (record for the last two weeks of August) warm. Normally evenings are in the 10C (50F) range.