What if the day
lasted 27 hours?

01Where this comes from

Observational
background.

Growers in the Supercycler network recorded light and dark cycles lasting more than 24 hours, in different rooms and with different genetics. Those observations were used to define the variables and the contrasts of the present trial.

One aspect that guided the design is that the 13/14 arm accumulates fewer light hours per calendar day than 12/12. That is 11.56 h against 12, around 3.7% less, together with 3.7% more hours of darkness. If a higher dry weight were still observed, the explanation would not lie in the amount of light received but in the use the plant makes of the carbon already fixed.

Network data

Alongside the main trial, the network gathers reports from independent growers. As of 16 August 2026, 113 active zones were recorded on 13/13 cycles, 22 on 13/14 and 132 on 12/12, and the protocol explorer published 32 reports, 36 genetics, 11 cycles and 3 regions. The figures are kept with their cut-off date and are updated with a new date.

These records describe the diversity of conditions under which the cycles are run and allow new questions to be formulated. They do not replace the controlled comparison, because the protocols, the rooms and the genetics differ between reports. Each set is analysed and presented with its own level of evidence.

02The hypothesis

Working
hypothesis.

The hypothesis proposes that the endogenous period of the circadian clock of Cannabis sativa could lie close to 27 hours. If that relation exists, an external cycle of 27 hours could produce a response different from the one observed with a 24 hour cycle.

A cycle whose total length is not 24 hours makes it possible to modify the length of the light and that of the darkness separately. Under a 24 hour day the two are coupled and there is a single degree of freedom, so fixing one determines the other.

The trial considers two variables associated with the change of period. The first is the amount of light received per calendar day. The second is the length of the darkness and its relation to carbohydrate availability during the night.

Senescence and cut criterion

In earlier observations, some plants subjected to extended periods continued to form floral tissue for longer than expected and did not enter senescence within the period observed.

One practical consequence is that the trichome population can remain mixed, with new flower and old flower at the same time. A threshold based on the percentage of cloudy trichomes would in that case describe the age distribution of the flower and not a state of maturity comparable between arms.

For that reason the harvest criterion is defined in advance, declared explicitly and documented plant by plant. The criterion adopted and its scope are described in the procedure.

Light and darkness variables

Cycles longer than 24 hours make it possible to modify the length of the light and that of the darkness separately. The working hypothesis considers that the two variables could have different effects on growth, carbon allocation and the production of secondary metabolites.

The additional light could be associated with the accumulation of mass. The additional darkness could be associated with the production of secondary metabolites, by the pathway described in the work on carbohydrate availability during the night.

The three regimes run previously are compatible with that description, although they do not allow the two effects to be separated. The trial compares four defined periods and assesses those associations together with the limitations described below.

03What is published

Background
in the literature.

The proposal rests on studies of circadian resonance, plant growth and carbohydrate availability during the night. This background comes from different organisms and experimental systems, so it is presented as context for the hypothesis and not as a demonstration of an effect in Cannabis sativa.

04Relevant evidence

Results that
have to be taken into account.

The review also includes studies whose results do not agree with a uniform response to cycles of unnatural length. They are presented because they form part of the current state of knowledge and because they constrain the interpretation of this trial.

05Design · pre-registered on 16 August 2026

Design
of the trial.

The study compares four photoperiod conditions. Each condition corresponds to one arm and runs in its own cubicle, with the same fixtures, the same substrate and the same irrigation scheme indexed to the cycle.

The 28 hour arm makes it possible to distinguish between two possible explanations. If dry weight increases up to 27 hours and falls at 28, the response would describe a curve with a maximum value, compatible with resonance. If it continues to increase at 28 hours, the compatible explanation would be that a longer duration of darkness is associated with a higher yield. Without that arm, the two would be indistinguishable.

Registered predictions

The predictions were published on 16 August 2026, before setup and with no data taken. They describe expected results and not observed results. In the editorial revision of 2 September they were reworded in a descriptive register, without modifying their content, and the earlier wording is recorded in the change log.

On the internal ordering of prediction 1. The 13/13 and 14/14 arms are both one hour from the 27 h period and deliver the same number of light hours per calendar day, so the hypothesis does not anticipate which of the two would occupy second place. What prediction 1 assesses is the position of the highest value and the fall on both sides.

06Materials and procedure

Biological
material.

Four genetics are used. Each one is represented by one plant in each arm, so the same clone is compared across the four periods. The replication unit is the genotype and not the plant.

Second species. Chrysanthemum.

Each arm includes one container of chrysanthemums as an exploratory observation. The chrysanthemum is a short-day plant with photoperiodic flowering described in the literature, which makes it possible to observe whether the response is limited to the main species of the trial.

The chrysanthemum does not form part of the primary variable or of the predictions. The sample is one container per arm, with no internal replication, so the data will be presented as a descriptive observation. The date the flower bud appears, the date of opening and the appearance are logged, with photographs.

The cubicle and its equipment

Each arm occupies an independent cubicle of 1.00 × 1.00 × 2.00 m, with a growing area of 1.00 m² and a volume of 2.00 m³. The interior is white and the space is kept closed, with forced air exchange. The four cubicles are identical in construction and share equipment, substrate, plant material and management. The only variable that differs between them is the length of the light cycle. The sheet that follows corresponds to the 12/12 arm and holds for the other three by changing that line.

Lighting. One 300 W LEDVANCE Plant Growth SP fixture per cubicle, also sold under the Sylvania brand. It delivers a photosynthetic photon flux of 750 µmol/s at an efficacy of 2.5 µmol/J, over a declared spectrum of 4000 K plus 5000 K with an added peak at 660 nm. The body measures 580 × 580 × 46 mm in a ten bar format, with a beam angle of 115° nominal and 117.9° according to the manufacturer's photometry. The fixture is not dimmable, operates on and off and admits no attenuation. The resulting power density is 300 W per square metre.

Over the 1.00 m² area, and assuming that around 90% of the flux stays contained in the cubicle, the estimated mean PPFD is 675 µmol·m⁻²·s⁻¹, equivalent to a daily light integral of 29.2 mol·m⁻²·d⁻¹ in the arms that accumulate twelve hours of light per calendar day. In the 13/14 arm the estimated integral falls to 28.1 mol·m⁻²·d⁻¹, 3.7% less, as an effect of the 27 hour period.

Switching and electrical logging. The four fixtures are governed from a single Shelly Pro 4PM, with one channel assigned to each cubicle, operated by Supercycler in supercycle mode. The device measures consumption per channel, so electrical spend is logged per arm and not per room. In the 12/12 cubicle the cycle is 12 hours of light and 12 of dark, with a total period of 24 hours anchored to 1 September 2026 at 17.00 Argentina time. Real adherence to the schedule is verified against the light action log, which keeps the expected transition and the confirmed one.

Air exchange and circulation. One 6 inch dual-turbine extractor per cubicle, running permanently, connected to a controlled socket. One 6 inch oscillating fan, also permanent, wired directly to the mains and with no remote control.

Environmental logging. One battery-powered temperature and humidity sensor, placed in the front left corner of the cubicle at 1 m height and designated as the primary environment sensor. It provides temperature, relative humidity and vapour pressure deficit. A camera is added that records one frame every five minutes, from which the comparative timelapse of the four arms is built.

Plant material and containers. Four cannabis plants per cubicle, one of each genetic, all photoperiodic and propagated by clone, in 10 litre plastic pots. To these is added one container of chrysanthemums, declared outside the primary variable. The five pots are arranged in a quincunx, with the four cannabis plants at the corners and the chrysanthemum container in the centre.

Substrate. Growers Original commercial mix, on first use, inoculated at setup with Great White from Plant Success, which contributes mycorrhizae, Trichoderma and bacteria of the genus Bacillus. The preparation was made on 17 August 2026 and is homogeneous across plants and across cubicles.

Irrigation. Manual until 16 September 2026. Since then, scheduled drip with two drippers per pot and one pump per cubicle, three irrigations per light cycle and the same hours without water in the four arms. Each irrigation is logged with its time and duration.

Cubicle sheet, 12/12 arm. The other three are identical except in the cycle line.

Cut criterion, drying and exclusions

The harvest criterion admits two formulations, which answer different questions and which, for dry weight, are mutually exclusive, because a plant is cut only once.

1. Yield at comparable maturity. Each plant is cut on reaching a maturity criterion defined in advance. The cut dates differ between arms and the days taken to reach the criterion are added as a further variable. This is the formulation the trial adopts.
2. Yield at a fixed calendar time. All four arms are cut on the same day. It answers how much each regime produces over the same number of days, and not how much each plant produces when it finishes. It cannot be reported in this run, because dry weight is measured once and per plant.

The declared criterion is the state of the trichomes in a fixed zone. The upper third of the apical cola is observed with a loupe, the same point declared for the chemical sample, and the plant is cut when the trichomes in that zone stop being mostly clear and the first amber ones appear. Every cut decision is documented with a photograph of the zone observed and with the date.

The caveat already described applies here. Under these regimes the trichome population can remain mixed, so the criterion describes the state of the declared zone and not that of the whole plant. For that reason each plant is also reported with its calendar days to the cut, the number of cycles executed, the accumulated light hours and the maturity signs observed.

Cut expectation by arm

The windows that follow are a prior assumption based on earlier runs. They are not part of the registered predictions, they are not scored as right or wrong, and they are published so that what was expected before a single plant was looked at is on the record. The real days to the cut are reported as a variable of the trial.

If a plant in the 28 h arm does not reach the criterion, a cut by calendar cap is declared, the date is reported and the weight is analysed apart from the rest. The cap is set before any plant is cut and is recorded in the change log.

Drying. Wine fridge at 14 °C and 65% relative humidity, with all the plants in the same space. Each plant is weighed when the flower moisture meter reads 12%, with the same meter and the same scale, of 0.1 g resolution. The reading of every measurement is kept. The moisture point, rather than a fixed number of days, prevents the remaining water from entering the comparison.

Exclusions. A plant that dies or develops hermaphroditism is excluded from the primary variable and reported with its arm, its genetic and the day of the event. No replacement plant is introduced. If the events concentrate in one arm, that concentration is reported as a result of that arm.

Variables recorded

07Analysis

Analysis
plan.

The design includes one plant per genetic and per arm. The analysis therefore gives priority to the paired comparison within each genetic and states clearly the uncertainty associated with the sample size.

The following is fixed before the dry weights are available.

1. The primary test statistic.
2. The normalisation criterion, if one is used, and what it is normalised against.
3. The way the four arms are compared within each genetic.
4. The handling of the chrysanthemum data as an exploratory variable.
5. The way excluded plants and missing data are reported.

The analytical decision will be added to the document with its date and authorship. The method is thereby defined before the results are observed, which is the condition that allows them to be interpreted.

08Scope

Scope
and limitations.

Known limitations of the design, with what each one implies for reading the results.

Interpretation criteria

The results will be assessed against criteria defined before the cut.

• The relation between the dry weight of the four arms within each genetic.
• The consistency of the direction of the effect across genetics.
• The comparison between 12/12 and 13/14.
• The comparison between 13/13 and 13/14.
• Days to the cut by arm and by genetic, together with the cycles executed and the accumulated light hours.
• The distribution of exclusion events and of the plants that did not reach the criterion.

A result that does not follow the predicted ordering also carries information. It can reduce the support for the hypothesis, point to an interaction with the genetic, or indicate that the design requires an additional contrast.

The results will be published on this page with the data, the method used and conclusions proportionate to the design, whatever their direction.

The next comparison

A future comparison between 13/14 and 14/13 would make it possible to hold the total period at 27 hours and modify the ratio between light and darkness. That design would help to separate the effect of the period from the effects associated with the distribution of the hours.

The comparison will be assessed in a later run, according to the results and the documented methodological decisions of the present trial. If 12/12 and 13/14 showed no differences, the question to be asked would be a different one.

09Participation

Independent replication
broadens the evidence.

The trial compares paired arms within a single room. Replication in rooms we do not control, with genetics we did not choose, is what makes it possible to assess whether the effect generalises. There are four ways to take part.

A cycle whose length is not 24 hours requires a programmable controller able to execute every light transition and to log the one that actually occurred. Supercycler performs that function and keeps that log, which is what makes it possible to verify adherence to the protocol afterwards. That availability is what makes replication accessible in rooms we do not control.

Proposals and records are sent through the form at the foot of this page, stating which regime is going to be run or which aspect of the method the comment concerns.

10The document

Preprint
in progress.

A preprint is the version of a document that precedes external review, published so that it can be read and commented on while the work is under way. The body of the document consists of the sections of this page. What follows is what occupies the first page of a paper.

Chronobotánica aplicada preprint · under construction

Circadian resonance in Cannabis sativa. Yield, morphology and resin under four periods with paired clones.

E. I. Vitor · Supercannabis Team · Supercycler network · collaborators

Version 0.3 of 2 September 2026 · pre-registration published on 16 August 2026 · results expected for November 2026 · free to use for personal and research purposes

Abstract

This trial evaluates four light and dark periods, of 24, 26, 27 and 28 hours, in four Cannabis sativa genetics with clones distributed across the arms. The hypothesis proposes that an external period close to 27 hours could be associated with differences in yield, morphology and chemical composition.

The primary variable is dry flower weight per plant on reaching a maturity criterion declared before the start, defined on the state of the trichomes in a fixed zone. The cut dates differ between arms and the days to the cut are analysed as a further variable. The environment, adherence to the schedule executed, the morphology and a chemistry series are also recorded. The predictions were registered before setup and the results will be published together with the limitations of the design.

Keywords. Chronobotánica aplicada, circadian resonance, T period, photoperiod, Cannabis sativa, supercycle, pre-registration, open science.

1. Introduction closed

Photoperiodism describes the response of plants to the relative length of light and dark within a 24 hour day. Chronobiology, by contrast, describes the relation between the period of the external cycle and the endogenous period of the organism's clock. That relation, studied on crop plants and manipulated as a management variable, is what we call Chronobotánica aplicada, and it is the framework of this trial and of the preprint that accompanies it. Under a 24 hour cycle both descriptions coincide and cannot be told apart, because the length of the day and that of the night are coupled and add up to a constant.

Circadian resonance, formulated in Drosophila melanogaster by Pittendrigh and Minis (1972), proposes that the fitness of the organism is maximal when the external period matches the endogenous one. In plants, Dodd and co-workers (2005) showed that Arabidopsis genotypes whose clock matches the external cycle hold more chlorophyll, fix more carbon and survive better. Anton-Sales and co-workers (2026) took the principle to production in lettuce and reported biomass increases of between 11% and 29% under a 27 hour cycle at an equivalent daily light integral. Núñez Ocaña and co-workers (2025) reported, in the same crop, no effect under periods of 20 to 28 hours, with carbohydrate rhythms acclimated to the applied cycle.

No literature was found evaluating periods other than 24 hours on a flowering crop while measuring yield and secondary metabolites. The present trial evaluates four periods in Cannabis sativa under a design blocked by genotype, with clones paired across treatments. The working hypothesis proposes that the endogenous period of the species lies close to 27 hours and that an external cycle of that length is associated with a higher yield per plant than a 24 hour cycle, even while receiving a smaller amount of light per calendar day.

2. Materials and methods closed

2.1 Experimental design

Complete block design, with genotype as the block and the period of the cycle as the treatment factor, at four levels. Each level runs in an independent cubicle, so cubicle is confounded with treatment. Each block contributes one plant to each treatment, so the experimental unit is the plant and the replication unit is the genotype, with n equal to four genotypes per treatment. The trial is carried out at a single site, with a single operator, between 1 September 2026 and the harvest date of each plant.

2.2 Treatments

The four treatments differ only in the length of the light and dark cycle. All other factors are held constant across cubicles. The temporal anchor of the four cycles is 1 September 2026 at 17.00 Argentina time, and the transitions are executed and logged by the control system described in 2.4.

Treatment	Period T (h)	Light / dark (h)	Light per calendar day (h)	Estimated DLI (mol·m⁻²·d⁻¹)
12/12	24	12 / 12	12,00	29,2
13/13	26	13 / 13	12,00	29,2
13/14	27	13 / 14	11,56	28,1
14/14	28	14 / 14	12,00	29,2

Light per calendar day is calculated as the length of the light phase divided by the total period and multiplied by 24. The daily light integral is an estimate derived from the flux declared by the manufacturer of the fixture and not a measurement, as detailed in 2.4.

2.3 Plant material

Four genotypes of Cannabis sativa, all photoperiodic and vegetatively propagated. Each genotype contributes one clone to each of the four treatments, so the individuals compared across treatments are genetically identical. The genotypes are Sweet 16 (Lit Farms, Project 4516 × Grandi Candy, declared flowering of 63 days), Lemon Cherry Fire F2 (Tiki Seeds, Lemon Cherry Gelato × Zerbert, F2, with no published flowering time), SC-G01 (accession of unverified lineage, received as clonal material with no documentation) and Hell-echo (Berryfreak × Freakshow, with no published flowering time). Each cubicle also holds one container of Chrysanthemum as an exploratory observation of a second short-day species, outside the primary variable.

2.4 Growing conditions

Each treatment occupies a closed cubicle of 1.00 × 1.00 × 2.00 m, with 1.00 m² of growing area, 2.00 m³ of volume, a white interior and forced air exchange. The four cubicles are identical in construction.

Lighting by one 300 W LEDVANCE Plant Growth SP fixture per cubicle, of declared flux 750 µmol·s⁻¹, efficacy 2.5 µmol·J⁻¹ and spectrum 4000 K plus 5000 K with an additional peak at 660 nm, in a ten bar format of 580 × 580 × 46 mm and 115° nominal beam angle. The fixture admits no attenuation. The power density is 300 W·m⁻². Assuming 90% containment of the flux inside the cubicle, the estimated mean PPFD is 675 µmol·m⁻²·s⁻¹. This value and the daily integrals in table 1 are derivations from the declared flux and not measurements. PPFD was measured at canopy height with a PAR meter. It was 600 µmol·m⁻²·s⁻¹ at the start of flowering and since 3 October 2026 it is stable at 750 µmol·m⁻²·s⁻¹ in the four cubicles. The containment assumption is probably optimistic, since with a 115° beam angle a fraction of the flux that reaches the centre of the cubicle comes from reflection off matt white walls.

Switching by a single Shelly Pro 4PM, with one channel per cubicle, governed by the Supercycler platform in supercycle mode, with electrical consumption measured per channel. Adherence to the schedule is verified against the light action log, which keeps the expected transition and the confirmed one for every event. Air exchange by a 6 inch dual-turbine extractor running permanently and circulation by a 6 inch oscillating fan, also permanent.

Growers Original commercial substrate on first use, inoculated at setup, on 17 August 2026, with Great White (Plant Success), prepared homogeneously for all the plants and all the cubicles. 10 L plastic pots. The five pots in each cubicle are arranged in a quincunx, with the four cannabis clones at the corners and the chrysanthemum container in the centre. Irrigation was manual until 16 September 2026 and since then is scheduled drip, with three irrigations per light cycle and the same hours without water in the four treatments, with time and duration logged for each irrigation. Feeding follows a short flowering schedule, applied with the irrigation and indexed to the cycle executed.

2.5 Variables recorded

The primary response variable is inflorescence dry weight per plant, determined on a scale of 0.1 g resolution when the flower moisture meter reads 12%. Drying takes place in a chamber at 14 °C and 65% relative humidity, with all the plants in the same space. The reading of every weighing is logged. Fresh weight is logged and is not used for inference.

Secondary variables. Days from the change to flowering until harvest, number of cycles executed and accumulated light hours per plant. Temperature, relative humidity and vapour pressure deficit, logged continuously per cubicle with a sensor designated as primary, placed in the front left corner at 1 m height. Electrical consumption per cubicle. Morphology, with photography with a scale and a record of flowering sites, calyx length and stigmas, complemented by a camera that captures one frame every five minutes. THC and CBD series by field NIR spectroscopy, read as a relative trend, with a sample from the upper third of the apical cola, of equivalent mass, one per genotype and treatment, taken at harvest, and a reference determination in an external laboratory.

2.6 Harvest criterion

Harvest is carried out per plant, on reaching a maturity criterion defined before the start of the trial. The criterion is the state of the glandular trichomes observed with a loupe in a fixed zone, the upper third of the apical cola, coinciding with the chemical sampling zone. A plant is harvested when the trichomes in that zone stop being mostly clear and the first amber ones appear. Every harvest decision is documented with a photograph of the zone observed and a date.

Under extended periods the trichome population can remain heterogeneous because of the continued formation of floral tissue, so the criterion describes the state of the declared zone and not that of the whole plant. For that reason the variables in section 2.5 relating to accumulated time are analysed together with the primary variable. If a plant does not reach the criterion, a calendar cap declared before the first harvest is applied and its weight is analysed separately. The prior expectation, not pre-registered and not scored as a prediction, places harvest between days 65 and 70 for the 24 h treatment, between days 68 and 70 for the 27 h one, between days 75 and 80 for the 26 h one, and with no defined window for the 28 h one.

2.7 Exclusions

A plant that dies or develops male flowers is excluded from the primary variable and reported with its treatment, its genotype and the day of the event. It is not replaced by another plant. A concentration of exclusion events in one treatment is reported as a result of that treatment and not as a loss of data.

3. Data analysis open

The design provides one observation per combination of genotype and treatment, so it does not admit a test of means with within-cell variance estimation. The planned analysis rests on the ordering of the four treatments within each block. With four treatments there are twenty four possible orderings and the hypothesis specifies one, so the probability of observing it by chance simultaneously in the four blocks admits an exact calculation under the null hypothesis of exchangeability. The procedure is equivalent to a permutation test of minimum size.

Still to be fixed are the primary test statistic, the normalisation criterion if any is applied, the handling of the second species data and the procedure for reporting excluded plants and missing data. These decisions are recorded in this document, with their date and authorship, before the first dry weight determination.

Open section. Methodological proposals can be sent through the form at the foot of this page. Those taken up are recorded with their date and authorship in the change log.

4. Results pending

Pending. The results are added to this document when the trial closes, with the primary data, the analysis applied and the limitations listed on the page. They are published whatever their direction.

References

1. Anton-Sales, C., Benckhuysen, L., Peker, B., Jeuken, M. & Bonnema, G. (2026). Matching circadian rhythms to light–dark cycles increases lettuce yield by 29% in vertical farms without additional energy input. Journal of Experimental Botany, 77, 5336–5349. 10.1093/jxb/erag222 ↗
2. Dodd, A. N., Salathia, N., Hall, A., Kévei, E., Tóth, R., Nagy, F., Hibberd, J. M., Millar, A. J. & Webb, A. A. R. (2005). Plant circadian clocks increase photosynthesis, growth, survival, and competitive advantage. Science, 309(5734), 630–633. 10.1126/science.1115581 ↗
3. Graf, A., Schlereth, A., Stitt, M. & Smith, A. M. (2010). Circadian control of carbohydrate availability for growth in Arabidopsis plants at night. PNAS, 107(20), 9458–9463. 10.1073/pnas.0914299107 ↗
4. Núñez Ocaña, D., Haanskorf, T., Yang, L., Sfondrini, E., Reddy, A. T., Marcelis, L. F. M. & Heuvelink, E. (2025). Non-natural day length does not negatively affect lettuce growth as a result of acclimated carbohydrate rhythms. Scientia Horticulturae, 350, 114291. 10.1016/j.scienta.2025.114291 ↗
5. Pittendrigh, C. S. & Minis, D. H. (1972). Circadian systems: longevity as a function of circadian resonance in Drosophila melanogaster. PNAS, 69(6), 1537–1539. 10.1073/pnas.69.6.1537 ↗
6. Vitor, E. I. (2025). The Supercycle Hypothesis. Foundations of Chronobotánica Temporal Morphogenesis in Plants. Zenodo, versión preprint-beta-8, 7 de agosto de 2025. 10.5281/zenodo.16763824 ↗

The six references were checked against doi.org on 2 September 2026. Each entry links to its DOI.

Document status

Part	Status
Background and literature	closed Reviewed and published with their scope declared.
Hypothesis	closed Registered on 16 August 2026.
Predictions and design	closed Registered on 16 August 2026, before setup and with no data taken.
Analysis plan	open Agreed and recorded before the first dry weight measurement.
Results	open Published when the trial closes, with the data, the method and the limitations.

The author list closes when the results are published. Those who contribute method incorporated into the document or run a declared replication will be listed as collaborators, according to their documented contribution.

Every modification made after publication is recorded in the change log at the end of the page, with its date, a description and the earlier wording.

11Corrections

Change log.

Every modification after publication is recorded here, with its date and with the earlier wording in plain sight. The pre-registered predictions are kept separate from the editorial text and from the later analysis.