What does F1 mean?

F1 (filial 1) is the first generation produced by crossing two distinct, true-breeding parent lines. Both parents must be stable — meaning their offspring consistently express the same traits. Cross two such parents and you get F1.

F1 hybrids exhibit what's called hybrid vigor (heterosis): unusually consistent expression, faster growth, and stronger plants than either parent alone. This is why F1 packs are popular with commercial growers — the plants are predictable.

Important: an F1 cross is only a true F1 if both parents are stable (typically IBL — inbred line — or landrace). If one parent is itself a hybrid or polyhybrid, the offspring is more accurately called an F1 polyhybrid, and the consistency is reduced.

Selfing or crossing F1s together produces F2 — and F2 is where the recessive traits scatter, opening up phenotype hunting and selection work.

Going deeper: when an F1 isn't really an F1

In the strict botanical sense, an F1 cross requires both parents to be true-breeding (typically IBL or landrace). Most modern "F1" packs use parents that are themselves hybrids — making the cross an F1 polyhybrid in the language of working breeders.