Science descrives photoperiod as an existing relationship between period of light and period of darkness alive organisms and plants are submited to. Each plants is affected by a photoperiod or another, being responsible that plants use their energy to develope a vegetative stage or flowering stage. In this chapter we will talk about how does photoperiod of light affect cannabis plants, and how small variations of it may cause huge changes in them.
In nature, photoperiod of light is mostly determined by season of the year, while growing indoors growers are who decide when to modify it, to make plants stay in vegetative stage or turn into flowering stage.
Photoperiod of light growing marijuana
Marijuana plants are also photoperiod-dependant, what makes them react to a certain photoperiod light/darkness we submit them. Nowadays exist large information about photoperiod for cannabis, that concludes that if we want to keep plants in vegetative stage we should use a photperiod of 18 hours of light and 6 hours of darkness (continuous). If we aim plants to start flowering we should use a 12 hours of light and 12 hours of darkness photoperiod.
These differences in daily hours of darkness is what induces plants to start flowering, what means that in any case where hours of darkness are inferior to 12 hours, plants will keep growing.
If we follow this growth pattern about photoperiod we'll be asuring that our plants have a good answer to it, doesn't matter what strain we are growing (indica or sativa).
* An exception to this law are autoflowering cannabis plants (wich are not photo-dependant). These type of cannabis plants can flower under any photoperiod contiditons and will bring their best yeald under a photoperiod of 20 hours of light and 4 hours of darkness (from germination to harvest).
Photoperiod for cannabis in vegetative stage
As we said above, photoperiod for growing cannabis is 18 hours of light and 6 hours of darkness (daily). Even being the most recommended method, some growers do change this photoperiod, by one reason or another, modifying the photoperiod to adapt it to their needings (photoperiod of 16/8 or photoperiod 20/4).
16/8 photoperiod could be used for two main reasons:
1.- Grower wants to keep mother plants in vegetative stage for the minimum budget possible (so using less hours of light decreases their bill).
2.- Grower wants to make cuttings that later on will be used in his outdoor garden.
20/4 photoperiod could be interesting if grower wants their plants to grow faster, due to those extra hours of light per day will translate in a quicker developement.
* We must advice that not all plants react equally to 20/4 photoperiod, showing symptoms of stress in some cases.
We also know that some growers use a 24 hours of light daily, pretending their plants to grow quicker. We highly recommend not to use 24/0 photoperiod due it may cause heavy stress in plants, causing them to avoid some functions they do along darkness period.
Photoperiod for cannabis in flowering stage
We have mentioned that all cannabis strains (indica, sativa or hybrids) will positively react to 12/12 photoperiod starting to flower. In Flowering stage we can also find some growers that, for some reasons (that we will discuss later on) decide to modify the photoperiod to adapt it to some certain strains, or special circumstances that may occur along cycle.
Indica: It could be the case where some indica strains could flower with only 10 ours of darkness and 14 hours of light. In these cases (very specific) grower can benefit from better yields, due to those two extra hours of light per day.
Sativa: The same way it happens with few indica strains that can flower with less hours of darkness, some sativa strains (from very specific areas, usually equatorial) flower better under more hours of darkness, being able to bloom with a 11/13 or 10/14 photoperiod. Using a longer night period can help these strains to mature.
Hybrids: The reaction of hybrids to photoperiod changings should vary (depending on a mostly indica or mostly sativa genotype), but by general law if days are longer that nights (13/11) the yields will be higher (taking longer to arrive to the optimal point to harvest), while when nights are longer (11/13), the yields will be lower, but plants will arrive sooner to the optimal point to harvest.
In this case, SantYerbasi recommends not to test with different photoperiods, and use the common 12/12 photoperiod, unless we stocked enough (tests can derive in possible problems, what could ruin our crop).
* We totally strongly discourage the use of photoperiods that don't adapt to natural 24 hours per day (day+night), due to results are not the expected, and usually derives in lower quality, and quantity harvest.
12/12 photoperiod from germination
In a previous post we talked about the possibility of doing a full cycle using 12/12, starting from seeds. This technique, fully valid to grow seeds, reduces up to 15 days the time to harvest, obtaining a more that good final yields, with a more compact-sized plants. In addition growers using this technique will be saving many hours of light use, what derives in a lower bill, what actually helps growing for a lower price.
Light photoperiod interruptions
For the moment we have discussed about different photoperiods we can use along cannabis cycle grown indoors. Even though this is the data we should use, it could happen light interruptions to occur (beyond our control) like electric cuts, or a timmer malfunctioning.
The magnitude of the problem will vary, mostly in the phase of the cycle we are currently running (growing or flowering) and to the long of that cut.
Vegetative stage interruptions: If the electrical cut happens in vegetative stage we will be suffering the smallest problem (if the cut is just for minutes/hours, if it lasts longer than one day this could turn into bigger problem, due to plants understanding of being turned to flower).
Flowering stage interruptions: If the problem means more hours of darkness, this won't be a huge stres (due to plants need days of continuous photoperiod to adapt to the new one). This stress, could be higher if the problem occurs when the lights are on, so the lighted time is enlarged. We aim you to control plants daily so you'll detect the same day if something occurs.
