By Ben ‘Prodigal Primate’ Morris

“Fast” or “Fast Flowering” strains have been increasingly produced for the contemporary cannabis market. The purpose of this brief article is to explain the definition of “fast” strains and how they are typically created.

“Fast” strains are simply cannabis strains that grow and bloom in a shorter period of time than non-fast strains. Fast strains are usually created by crossing an auto-flower variety and a photoperiod variety of cannabis. For reference, a photoperiod strain is the most common kind of cannabis grown and they require a change in light cycle to initiate flowering, whereas auto-flower strains will enter their flowering phase regardless of the light schedule.

Photoperiod Gene is Dominant  / Autoflower Gene is Recessive

When mixed together, the progeny (offspring) of the photoperiod x auto-flower plants will be photoperiodic and still require a light cycle change to initiate flowering, but the flowering time will usually be reduced in these offspring when compared to a traditional photoperiod plant. The auto-flowering gene is recessive which means that the offspring of two parents must inherit the recessive auto-flower gene from both parents to exhibit auto-flowering, non-light dependent floral initiation. When a photoperiodic plant and an auto-flowering plant breed, their resulting progeny have a copy of the auto flower gene and a copy of the photoperiod gene. Since the photoperiod gene is dominant it will make the offspring of such a cross still dependent on light cycle changes to initiate flowering but can help to speed up the process. This is an oversimplification but still an accurate representation of the process.

For visual reference we will use a Punnett Square to show a simplified version of the genetic transmission of the recessive auto-flower gene when bred with a homozygous (both alleles inherited are the same version of gene variant) photo-period plant:

In this table ‘A’ is the dominant photo-period gene and ‘a’ is the recessive auto-flower gene. The top row shows the two alleles for photoperiodicity found in the homozygous photo-period parent. The column to the left of the table shows the two recessive auto-flower alleles found in the auto-flowering parent. When bred together they create progeny that are heterozygous (one of each of the different alleles present). Anywhere you see ‘A’ means the plant will have dependence on light cycle changes to initiate flowering. Since all the offspring in this table have the ‘A’ allele they all will be dependent on light cycle changes and they all will have one copy of the recessive auto-flower gene.

If we were to breed 2 of the best of these offspring, we would get a Punnett Square like this:

As you can see from this table about 25% of the resulting progeny will be homozygous for photoperiodicity (‘AA’) and another 25% will be homozygous for the recessive (‘aa’) auto-flower gene. The remaining 50% will be photo-periodic still but heterozygous meaning that although they do not show the auto-flowering trait they still carry one of the auto-flower genes ‘silently.’ In other words, ¼ of these offspring will be photoperiodic with no recessive auto-flower gene, ½ will be photo-periodic but ‘fast’ versions of the strain and ¼ of these offspring will be true auto-flowers.

Genetic transmission isn’t always this clear cut, however. What can occur sometimes is a ‘dose effect’ where the mixture of photoperiod and auto-flower genes can lead to an intermediate expression of the two and rely not only on age or light cycle but a version of both. This can be thought of as a kind of ‘mixing’ of the two flowering controls and can lead to some ‘fast’ strains flowering at a low rate even while under 18/6 or 24/0 light cycles due to the blending of the two alleles. This is akin to incomplete dominance in mendelian genetics where a red flower and a white flower breed pink offspring. The offspring are neither red nor white but a blending of the two.

On average a ‘fast’ strain can complete its flowering cycle 1-2 weeks faster than its original photoperiod parent which can be a major boon to any cultivator but especially outdoor cultivators as a shorter flowering time means the buds are ready to be processed sooner and may help to avoid mold issues that come with the changing temperatures and humidities in late summer – early fall.

For indoor cultivators, a faster flowering time means less time to flip a grow room and get new plants blooming out thus potentially increasing the productivity and output of that facility. 

It should also be noted that occasionally seed producers and cannabis breeders will label certain cultivars as “fast” due to breeding selection for fast flowering time without mixing their photoperiod strains with an auto-flower. As with any product, reading the manufacturer’s description can help illuminate the process used to create the advertised ‘fast’ strain. 

Regardless of the method used to create a ‘fast’ strain, if you’re looking for shorter flowering times these may be cultivars to try! 

Shop FAST Flowering Strains from breeders like Twenty20 Mendocino and Atlas Seeds here!