Determinate varieties are compact plants which are often smaller than the indeterminate varieties. Each shoot on a determinate plant ends in a flower cluster, and consequently a fruit cluster. Determinate tomato plants tend to produce fruit all at once.
Indeterminate cultivars are vining or sprawling in habit. The shoot tips continue to grow and flower clusters are borne in the leaf axils of the expanding shoot. Indeterminate tomato plants yield fruit over a long time.
Determinate tomatoes, which grow on the ends of branches, tend to ripen earlier than indeterminate tomatoes because the fruit receives more heat and sun.
Excerpted from UWEX publication A3687 – Growing tomatoes, peppers and eggplants in Wisconsin, a guide for fresh-market growers by K.A. Delahaut and A.C. Newenhouse. (Clicking this link will take you directly to the pdf which you can download.)
This publication is available at The Learning Store online as a free pdf download, or from the UW Extension office in the Rock County courthouse.