What Is a Photoperiod-Derived Auto?
A photoperiod-derived auto is an autoflowering cannabis seed whose genetics come mostly from a photoperiod strain rather than from ruderalis. The breeder crosses the autoflowering trait into a photoperiod line worth keeping, then breeds back towards that photoperiod parent over successive generations, keeping only the lines that still flower on age. What survives that process behaves like the photoperiod parent and flowers on its own clock.
The term describes a position on a scale, not a separate species of seed. Every autoflowering line sits somewhere between the wild day-neutral plant and a photoperiod strain. Photoperiod-derived autos sit at the photoperiod end of it.
Where does the autoflowering trait come from?
From Cannabis ruderalis. Ruderalis grows in northern latitudes where the summer is too short to wait for the days to shorten, so it evolved to flower on age instead. Every autoflowering cannabis seed on sale anywhere inherits day-neutral flowering from that population. When a line is described as having no ruderalis in it, what is being described is how distant that ancestry has become, not a plant that never had any.
What differs between autoflowering lines is how much else came with it. In its wild form ruderalis is small and low in cannabinoids next to cultivated cannabis, so the breeding problem has always been the same: keep the flowering trait, lose the rest of the plant it arrived in.
How is a photoperiod-derived auto bred?
The autoflowering trait is recessive, which is what makes the work slow. Crossing an autoflower with a photoperiod plant gives a first generation that flowers on light, because the photoperiod parent’s version of the trait masks the other one. Autoflowering plants only reappear in the following generation, and only in a proportion of it.
So the breeder crosses back to the photoperiod parent, then selfs or sib-crosses that generation to bring the autoflowering plants back out, keeps the ones that flower on age and that also look and smell like the parent line, and repeats. Each pass halves what is left of the original ruderalis contribution while holding on to the one trait it was wanted for. Doing that properly takes years rather than months, which is why the quick route, a single ruderalis cross, is still the most common way autos are made.
How do the four seed types on this site differ?
TAG splits its catalogue by how the plant flowers and by how much ruderalis ancestry the line still carries, rather than lumping every auto together.
| Seed type | Flowers on | Ruderalis ancestry | Character of the line |
|---|---|---|---|
| Photoperiod Seeds | Light, at roughly twelve hours of darkness | None | The reference genetics. Largest plants, longest runs, grower decides when flowering starts |
| Photoperiod-Derived Autos | Age | Distant, bred back down over successive generations | Closest of any auto to its photoperiod parent in structure and aroma |
| Ruderalis × Photoperiod Autos | Age | One recent ruderalis parent | The standard autoflower cross. Fast and compact, with the photoperiod parent’s flavour showing through |
| Ruderalis Autos | Age | Dominant | Quickest and smallest, closest to the wild day-neutral plant |
Is a photoperiod-derived auto the same as a fast version seed?
No, and the two are easy to confuse because they start from the same cross. A fast version seed is a photoperiod plant. It comes from crossing an autoflower into a photoperiod line and then keeping the offspring that still flower on light, which shortens the flowering stage without making the plant day-neutral. A fast version still needs the light change. A photoperiod-derived auto does not.
If a seed description says the plant flowers in a set number of weeks from seed, it is describing an auto. If it says the plant flowers in a set number of weeks from the switch, it is describing a photoperiod or a fast version.
Why does TAG breed autos this way?
Because the complaint growers have always had about autoflowers is that the ruderalis shows: smaller plants, thinner aroma, less of whatever made the original strain worth growing. Breeding back towards the photoperiod parent is the direct answer to that complaint, and it is the slow answer.
It is also why the spec table on every TAG strain page is filled in from grow-tested results rather than copied from a supplier sheet, and why any figure that has not been verified is left marked as pending instead of estimated. A line bred over several years and then described with a made-up number would be a waste of the years. That principle has a name on this site: Plants Don’t Lie. How to Read a Cannabis Seed Spec Sheet sets out what each row of that table records.
For the underlying difference between flowering on age and flowering on light, see Autoflower vs Photoperiod Seeds.
Frequently asked questions
Does a photoperiod-derived auto contain no ruderalis at all?
Its day-neutral flowering came from ruderalis, so the ancestry is there by definition. What repeated backcrossing to a photoperiod parent does is reduce how much of the rest of the ruderalis plant remains, generation by generation. The honest way to describe a well-worked line is that the ruderalis contribution is distant, not that it is absent.
Are photoperiod-derived autos slower than other autos?
They tend to sit at the longer end of the autoflowering range rather than outside it, because more of the photoperiod parent means more of the parent’s flowering behaviour. The actual figure belongs on the strain page, not on the type.
Is “photoperiod-derived auto” a standard industry term?
It is used among autoflower breeders but not consistently, and no one polices it. Other sellers may describe similar lines as F5 or F6 autos, backcrossed autos, or simply as premium autos. TAG uses the plainer phrase because it says what was actually done.
Which type should a collector look at first?
That depends on what the collection is for. Photoperiod-derived autos preserve the character of a photoperiod line in an automatic plant, ruderalis crosses preserve speed and small size, and photoperiod seeds preserve the original line itself. All four types are listed in the seed shop.