If you're getting started in the world of cultivation or simply want to better understand what you're buying when choosing cannabis seeds, you've probably come across acronyms like F1, F2, BX, or even IBL and S1. While they may seem like complex codes at first, they're actually key terms to understand a strain’s genetics and stability.

In this article, we’ll explain everything you need to know about these concepts, with clear examples, comparison tables, and practical tips so you can make more informed decisions when choosing your seeds.

What Is an F1 in Cannabis?

The acronym F1 stands for "Filial 1" and refers to the first generation resulting from the cross between two distinct and stable strains.

Example: If we cross a pure Afghan with a pure Haze, the result is an F1: Afghan x Haze (F1).

This type of cross is very popular because it produces what is known as hybrid vigor, meaning stronger, more resilient, and more productive plants.

Characteristics of F1 Strains:

• High uniformity among plants.

• They all share similar traits: size, aroma, and effect.

• High resistance to diseases and stress.

• Ideal for beginners and commercial grows.

✅ F1 seeds are perfect for those who want a predictable and uniform grow.

What Is an F2 in Cannabis?

F2 (Filial 2) strains are created by crossing two individuals from the F1 generation with each other. In other words, we start from an F1 and continue reproducing the line.

Example: Afghan x Haze (F1) × Afghan x Haze (F1) = F2

This step is common among breeders who want to select new phenotypes, but it’s also interesting for growers looking for variety within the same genetics.

Characteristics of F2 Strains:

• Greater genetic diversity.

• New phenotypes appear (visible variations between plants).

• Some specimens may stand out for their flavor, yield, or potency.

F2s are the starting point for creating new genetic lines, but they can also show instability if proper selection is not applied.

What Does BX or Backcross Mean in Cannabis?

BX stands for backcross, or retro-crossing, and refers to a technique where a hybrid plant is crossed with one of its original parents to reinforce specific traits (flavor, structure, effect…).

Example: Cream Caramel x Skunk (hybrid) × Cream Caramel (original parent) = BX1

This process can be repeated several times to fix desired traits, generating BX1, BX2, BX3, and so on. The more times the backcross is performed, the more the result will resemble the dominant parent.

Characteristics of BX Strains:

• Greater phenotypic stability with each backcross.

• Dominant traits of the selected parent are reinforced.

• Very useful for recreating classic or legendary genetics.

BX-type genetics are ideal for those seeking consistency and fidelity to a specific profile (for example, the flavor of an original OG).

What Is an IBL?

IBL stands for Inbred Line, or stabilized inbred line. It refers to a strain that has been crossed over many generations within the same lineage to achieve near-total uniformity.

In other words, an IBL doesn’t come from a random cross, but from meticulous selection over several generations.

Characteristics of an IBL:

• High estabilidad genética.
• Fenotipos casi idénticos entre plantas.

• Ideal base for creating stable commercial hybrids.

✅ Highly valued by breeders who want to work with solid and predictable genetics.

What Does S1 Mean?

S1 stands for Selfed 1, and refers to a plant that has been self-pollinated, meaning it was forced to produce seeds from itself (usually through reversal using STS or gibberellic acid).

This method is used to feminize seeds and to fix very specific traits of a mother plant.

Characteristics of S1 Strains:

• All seeds are feminized.

• High likelihood that the offspring will resemble the mother.

• Used to reproduce an elite clone in seed form.

⚠️ Pueden presentar menos vigor si se repite demasiado la autopolinización.

Comparison Table

Which Genetics to Choose Based on Your Goals?

• Looking for ease and uniformity?
  Go for an F1 or an IBL.
• Want to find a unique phenotype?
  F2 seeds are ideal for exploration.
• Fell in love with a specific strain and want to repeat it?
  Choose a BX or an S1.

Understanding Leads to Better Growing

Knowing the difference between F1, F2, BX, IBL, and S1 will help you make more informed decisions as a grower and understand why the same strain can produce such different results depending on its genetic origin.

If you're looking for seeds to grow for the first time or to work as a breeder, we always recommend checking this information on each strain's description or consulting the breeder directly.