True F1 sativa crosses, where two unrelated stable parents are combined once, show hybrid vigour and grow uniformly, while inbred lines that have been selfed or backcrossed for many generations are more predictable but sometimes weaker. Most cheap seed bank sativas are neither, just F2 or later crosses with plenty of variation. The breeding glossary at https://hazesativaseeds.com explains the F1, F2, IBL and BX labels in plain terms, which helped me understand what I was actually buying. Uniform packs usually cost more for a reason.
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