The light cycle can change autoflower plant growth, the end yield, bud density, branch formation, and even the plant’s height so growers should know why plants in certain light cycles do best and in what stages of plants growth what cycles would be best!
And that’s what I’m aiming to answer with this post!
But firstly, you need to know that autoflowers will flower under any light cycle. Which means that you can grow them under a 24/0 light cycle or even on a 12/12 light schedule. However, there are other aspects to consider than just if the plants will grow!
What is the best light cycle for autoflowers?
Cannabis is a plant that requires no dark period which is why it is categorized as a C3 plant. Being a C3 plant means that it gathers and uses CO2 during the light period but it doesn’t gather CO2 during the dark period like C4 plants do.
From this, we conclude that cannabis plants thrive if they get continuous light through their growth stages so a non-stop 24/0 light cycle should be better for autos than say a 16/8 or 18/6 light schedule.
In the vegetative stage of the plant’s growth (that happens in the first few weeks of autoflowering plants growth) you can increase the growth by up to 30% if you leave the lights on all the time. But in later growth stages, this additional growth isn’t so evident therefore despite the fact that increased growth will be visible you won’t get a 30% higher yield.
Although this additional light is beneficial for autoflower plants, it will also cost more.
Let’s assume that a grower has a 400W HPS lamp and the electricity price is 10 cents for KWh. In this scenario, if the grower would run his HPS 80 days nonstop then they would be burning 768 kilowatts ((24 h * 80 days * 400 W)/1000) which would cost him $76.80. However, if they would use an 18/6 light schedule they would be burning just 576 kilowatts that cost $57.8 and they would save $19 just with this one HPS lamp.
On top of that, the non-stop light would also decrease the lamp’s life span that could also be a potential saving.
After seeing these numbers every grower can do the math and see how much more money they would burn for his setup.
However, keep in mind that, depending on the autoflower strain, the dark period can decrease the plants’ growth by about 20%. This means that you can calculate how much expected yield would you lose if the autoflower plant would get 20% less energy.
After doing some math, we can see that a full 24/0 light schedule is far more beneficial for autoflowers because they will grow bigger, and faster and you will ultimately get more yield. And the electricity costs aren’t that big compared to that increase in yield.
So I would suggest you run your lights non-stop since this way you will get more for your investment in energy as probably the plant is much much more valuable than those few dollars that you spend on electricity.
Using different autoflower light cycles for cooling your grow room
Light cycle changes can also decrease the overall heat signature of your grow room. So, if you have any heat problems you can slightly reduce them by using a light schedule with a dark period since the grow room will have time to cool off a bit during the dark period.
However, there are two potential pitfalls associated with not using a 24-hour light schedule for autoflowers to cool down your grow room.
The first is that your grow area should be well isolated and continuous light should not be a problem. Therefore, if a continuous light schedule can overheat your grow room you should definitely think about the grow room design and tweak it so the heat is not a problem anymore!
The second thing that’s wrong with the option of turning lights off for cooling the grow room is that autoflowers don’t like a temperature difference that’s more than 10 degrees, So, if your daytime temperatures are reaching 30°C but at night your temperature drops below 20°C you can severely stress your little plant and stun it.
So you can use light cycles for grow room cooling if you have no other choices but for most cases, I would not recommend it.
Using different light cycles to get bigger plants
In nature, autoflowering cannabis plants get different light exposure cycles and the most stretching usually happens in the night time. At night cannabis plant tries to find more light and it stretches toward the sky to do that.
This doesn’t mean that in the light cannabis growth stops, this just implies that at night cannabis stretches more.
Even if autos stretch more at night, the overall growth is much faster in daylight as cannabis produce energy only when it gets light shining on those green leaves.
So growers could use light cycle changes to get bigger plants by letting them stretch out in the dark period ultimately getting bigger plants. But a consistent dark period will not necessarily yield the most amount of bud.
I would say that if you really want to stretch your plant then a dark period should be mixed with continuous light periods so that the autoflower plant could stretch at the night and get a long light schedule for more vigorous growth to branch out, make more leaves, and produce denser buds.
But if cannabis produces energy only in the light then logically one might deduct that the best conditions for it are continuous light throughout its life to produce the most amount of energy to grow leaves, stems, and ultimately big buds.
Contrary to popular belief you should set the light schedule for more light if you want smaller plants. And keep in mind that smaller doesn’t mean that they will produce less – they would actually have denser buds with closer branches, and therefore have more total mass and they won’t be stretched.
Using differed light schedules for a bigger yield
Autoflowering cannabis plants will produce denser buds if the light period is continuous since the plant produce all its energy from photosynthesis and therefore more energy means more mass and denser buds.
The dark period between the light cycles can increase stretching that will lead to fluffier buds. However, this increased stretching can only be beneficial if you have a very humid environment where dense buds could easily sustain mold or fungus. And that can be easily treated by decreasing the humidity levels in your grow space.
A truly stable autoflowering seeds that are 100% autoflowers will definitely yield more if it is under a continuous light cycle.
But not all seeds are perfect and many first, second and some more generation unstable crossbred seeds will not completely flower under 24 hours of light and will produce small yields. In this scenario, the dark period between light is actually a good idea as you’re not so perfect autoflower will get some dark period and will produce better buds.
Should you deprive your autoflowers of light before harvest?
Many growers say that a dark period increases the resin gland production on cannabis plants and that plants which are deprived of light for the last couple of days will give you stickier and whiter buds.
Yet, this theory has not been proven scientifically. And as much as I can tell it really doesn’t matter if you give your plans a light shock in form of a two-day dark period or not. They will give you the same amount of buds.
If we think about this myth some more then we can boil it down to the truth – cannabis plants produce energy while they are exposed to light. Which means that you will get bigger and denser buds if you supply more light.
So for autoflowers if you give them 48 hours of light as opposed to the 48 hours of darkness at the end of their life cycle they should produce more from that extra energy!
The only real-world solution for the dark period at the end of the plant’s life cycle is in the situation when you need to harvest prematurely and you can’t wait for the real harvest.
In this situation giving your autoflower plants a complete light deprivation stress (also called light depping) may trigger them to form denser buds as the plants think their life is coming to an end so they produce more resin to protect their seeds!
What will an interrupted light cycle during veg do to my plants?
One more thing to remember here is to give your plants a stable light schedule and don’t change it during its growth so your autoflowers don’t get confused and can grow to their full potential.
It Is undoubtedly true that automatic plants will flower under any light schedule but cycle changes can reduce the yield and induce stress in those plants.
However, if you have frequent light leaks or unplanned electricity outages then autoflowers are undoubtedly more tolerant to those occurrences than regular photo-sensitive cannabis and they won’t convert back to vegetative growth as it can happen with regular weed plants.
Autoflower light cycle outdoors
For outside growers, light cycles aren’t a big deal since you can’t change the period when the sun shines and when it doesn’t. So the only thing you can do is calculate the best possible time to plant your weed.
Say your autoflower ganja plant will automatically flower after 25 days and it will be ready to harvest in 70 days. You can divide this time and plant your cannabis plant outdoors 35 days before the summer solstice (June 21st) since the nights are very short as midsummer approaches and it is the time when your plants will get the most amount of light.
If you need more help with growing your plants you can check out my complete autoflower grow guide where I give a thorough explanation of how to grow your autos!