F1, BX, S1: Cannabis Breeding Terms, Explained Without the Jargon
Last checked: October 27, 2026
Read enough cannabis product descriptions and you'll hit a wall of letters and numbers: F1, F2, BX1, S1, IBL. It looks like a chemistry exam. It's really a family tree, written in shorthand. Green Sundae, at 723 Lakeshore Rd E in Lakeview, Mississauga, keeps these cannabis breeding terms light and simple for adults 19+, with a cheat-sheet table you can screenshot.
The big idea behind cannabis breeding terms
Breeding is matchmaking. A breeder picks two parent plants, crosses them, grows out the seeds and keeps the plants they like. The letters and numbers just record which match happened and how many generations in you are.
Two quick building blocks:
- Cross: pollen from one plant fertilises the flowers of another. The seeds that form are the offspring.
- Generation: each round of crossing and growing out seeds.
Everything below is a variation on those two.
The cheat sheet
| Term | Say it like | What it means |
|---|---|---|
| Cross | "a cross" | Offspring of two different parent plants |
| F1 | "eff-one" | First generation from crossing two parents |
| F2 | "eff-two" | Next generation, from crossing F1 plants with each other |
| BX / BX1 | "backcross" | Offspring crossed back to one of its parents |
| S1 | "ess-one" | Seeds from a plant pollinated by itself ("selfed") |
| IBL | "inbred line" | A line bred within itself over many generations to stay consistent |
| Pheno | "fee-no" | One plant's visible traits within a seed batch |
| Polyhybrid | "poly" | A line with many crosses in its family tree |
F1 and F2, a little deeper
F1 is the first generation after two parents meet. The "F" comes from "filial," the old genetics word for offspring.
F2 comes from crossing F1 plants together. This is where things often get interesting: F2 seeds tend to show more variety, because the parents' genetics reshuffle. That variety is one reason breeders grow out lots of seeds and go hunting for phenos.
Backcrossing (BX)
A backcross takes offspring and crosses it back to one of its original parents. The goal is usually to lean the line toward that parent's traits. Do it again and it's BX2, then BX3, and so on. Each number is one more trip back to the same parent.
Selfing (S1)
S1 means a plant was pollinated by its own pollen. In cannabis, that typically involves getting a female plant to produce pollen, then using it on the same plant. The resulting seeds share that one plant's genetics in a new combination.
Inbred lines (IBL)
An IBL is a line bred within itself over many generations until the plants come out fairly consistent. Consistency is the selling point: grow several and they tend to look alike.
Why breeders bother with all this
- New lines start with a cross.
- Consistency comes from inbreeding or cloning a keeper plant.
- Steering traits happens through backcrossing.
- Variety shows up in F2 and beyond, which is where pheno hunts happen.
A 2017 review of cannabis domestication and breeding history in Critical Reviews in Plant Sciences notes that modern breeders combined populations from widely different regions and that heavy use of single-plant selection, inbreeding and cloning reduced genetic diversity in many present-day cultivars. Those breeding codes are the paperwork of that story.
What cannabis breeding terms do NOT tell you
Light, but firm:
- Not a THC number. Only Total THC and Total CBD on a legal label give you that.
- Not a quality grade. An F1 isn't "better" than an F2. They're different generations.
- Not a standard label line. Breeding codes come from producer or breeder descriptions, not the regulated label.
- Not proof of anything by themselves. Treat them as the producer's description.
Reading a description that uses them
- Spot the code. F1, BX, S1, IBL: now you know what each one means.
- Skip the hype words around it.
- Go to the label: product class, Total THC, Total CBD, net weight, packaging date.
- Look at the flower if the package lets you.
Questions we hear in Lakeview
Is "F1 hybrid" the same as "hybrid" on a menu? Not quite. In breeding, F1 is a specific generation. On menus, "hybrid" is often used loosely as a category word.
What does BX3 mean? Three rounds of crossing back to the same parent.
Are S1 seeds clones? No. They're seeds, so each one is a new genetic combination, even though only one parent was involved.
The bottom line
Cannabis breeding terms are a family tree in shorthand. F1 is the first cross, F2 is the next generation, BX is a cross back to a parent, S1 is a plant pollinated by itself and IBL is a line kept consistent over many generations. Fun to decode, but the label still carries the facts.
Questions before you visit? The Green Sundae contact page is the place to reach the store, and the Lakeshore Road East cannabis store page covers the neighbourhood. Green Sundae is for adults 19 and over. Bring government-issued photo ID.