The F1 (first filial generation) grow-out is the very first chance you’ll have to see if the cross was successful. In this generation, the most dominant traits will appear, meaning many F1 plants will turn out to be regular leaf indeterminates bearing red fruit since those are the most dominant traits. So if I had crossed a red potato leaf dwarf plant (the mother) with a purple regular leaf indeterminate plant (the father), the F1 would look something like a regular leaf indeterminate plant bearing red fruit. And since that regular leaf fruit came off a mother plant that was dwarf and had potato leaves, we would know for certain in the F1 generation that the cross was successful.
Sometimes, though, when complex genes are involved, along with several recessive factors, some recessive traits may appear in the F1. For example, take a cross I made last year of a chocolate beefsteak regular leaf dwarf plant with an orange cherry-sized regular leaf micro plant: The only dominant factors involved here were a yellow epidermis and a regular leaf, which both appeared in the F1 grow-out, but the plant height was to be determined because one was a dwarf and one was a micro. It ended up growing to about 16 inches tall—somewhere in between the parent’s height differences of four feet and four inches. The fruit’s appearance was a mystery until it developed into a very small (mini) beefsteak cherry-looking fruit that was deep orange to almost red—not brown, like the mother, or orange, like the father. Figure 1 shows fruit from the mother; Figure 2 shows fruit from the father, and Figure 3 shows how the F1 fruit turned out.

Figure 1.                                      Figure 2.                                       Figure 3.

It is of extreme importance to photograph both parents and the F1 fruit, along with recording written names and dates of your cross and F1 fruit grow-out. With all these pieces of information, a breeder will have documented evidence of a completed successful cross.