But there have been other differences between the two types of tomatoes. True determinate tomato plants have one large harvest and then stop producing for the rest of the season, Upham says, while indeterminates spread their harvest over the season. But modern determinate varieties are more semi-determinate in that they produce tomatoes through the season unless disease or hot weather interferes. Research by Tom Fowler, horticulture specialist at the University of Missouri Extension Service, shows that there is a decrease of production over time with modern determinate tomato plants, but the plants continue to produce well over the season. It doesn’t appear that there is a need to grow indeterminates just to have tomatoes later in the season, Upham says.