The fundamental difference between autoflowering and photoperiod plants is not in size, difficulty, or potency, but in the clockwork in their bodies. One type has an internal clock that tells it when to start flowering, while the other uses the changes in the duration of day and night to determine the same.
Two Clocks, Different Results
Photoperiod cannabis is triggered to start flowering by a change in the length of night. The critical point is generally accepted as 12 hours – if the plant senses that the period of darkness is longer than usual, it will switch to the flowering stage to ensure reproduction before the end of the growing season. Indoors, this mechanism can be used to control when the plant starts to flower – simply put it on an 18/6 cycle until the desired moment comes, then switch to 12/12.
Autoflowers do not depend on the photoperiod and were originally bred from Cannabis ruderalis, a species which came from the harsh environment of Siberia and Central Russia. There, the summers are short and cannot be relied upon to provide the plant with enough information about the upcoming winter. Ruderalis and its descendants, the autoflowering cannabis plants, have an internal clock that dictates when they should start flowering regardless of day/night lengths, so long as they get enough light. This is a critical point for discussion, as it is this characteristic that determines nearly all of the differences listed below.
Speed Dating
A cannabis autoflower will be ready for harvest 70-90 days after germination, which puts it in the range of nine to twelve weeks. This is actually a fairly conservative estimate, as breeders’ websites and growers’ experiences confirm that many autoflowering plants are ready in as little as two months. Photoperiod cannabis takes significantly longer to reach the mature harvesting stage, generally anywhere between three and five months. Part of that time is spent in the vegetative phase, which the grower can control to a certain extent.
If we tally the difference up for a single season, a grower in a place with long, stable summers, like warm parts of Australia, could theoretically fit two whole autoflower cycles in the time a single photoperiod plant would be growing. This is not a difference in capability, but rather in opportunity – autos give grower’s room to plan. A photoperiod grower does not count days, they count down.
Time vs. Space, Two Constraints
Autoflowers generally do not grow to be as tall and as bushy as their photoperiod counterparts due to the shorter vegetative phase. This makes them ideal for growers that have to work with limited vertical space. Someone with a small grow tent or a discreet outdoor growing site will benefit tremendously from an autoflower’s ability to stay within a manageable height and footprint.
Photoperiod strains require time and space to grow, and both are needed in equal measure. The more a grower can stretch the vegetative phase, the more the plant will grow – and the more it grows, the bigger the potential yield is. However, that also means that a photoperiod grower in a small space will be significantly limited in their results, compared to an autoflower grower who would have been able to utilise the space more efficiently.
For growers working with restricted conditions, this discrepancy between potential yields is the major difference between autoflowering and photoperiod strainsFor Australian growers working around specific space and time constraints, browsing autoflower seeds Australia can help them compare characteristics such as finish time and height before choosing a strain. These characteristics are far more useful in planning a crop around a specific area or season rather than the overall yield potential that photoperiod strains offer.
Yield and Potency, Real Differences
As mentioned, photoperiod strains have a longer vegetative phase, which gives them an advantage in terms of potential yield. If a grower were to put an autoflowering and a photoperiod plant of the same genetics in identical conditions, the latter would produce more buds simply because it had more time to grow. This difference compounds along with the additional time the photoperiod plant spends in the flowering stage, giving it another edge in terms of yield potential.
In the past, that advantage would have been close to double, or 1.5x at the very least, but modern autoflowering strains have come a very long way in terms of overall size and potential yield. For most growers, the additional two months (and the extra electricity) that go into a photoperiod strain are not worth the additional potential, but for someone who truly wants to get every ounce of flower out of their plant, there is no other option. Time is the ultimate deciding factor.
Climate
Australia is a big country with a wide range of climates – and its growers face very different conditions. Someone in far North Queensland will have a set of conditions that have virtually nothing in common with those in southern Tasmania. Northern Queensland has a humid subtropical climate with a wet season that brings lots of rain, while Tasmania’s climate is oceanic with short, chilly summers. The further south and west you go, the less predictable the weather becomes, with far fewer consistently warm days.
A quick-flowering autoflower has a significant advantage over a photoperiod plant when it comes to unpredictable, extreme weather. If the humidity rises too high and threatens to push the onset of grey mold/bud rot, an autoflower can be brought to a quicker finish, weeks earlier than the photoperiod plant would be ready. That is the primary reason why growers in the south and east of Australia choose autoflowering strains – their short, predictable season means there is no room for error. Growers further inland and in the north have more reliable, longer weather cycles, meaning a photoperiod plant can take advantage of the extra time and space.
Electricity
When calculating the costs involved in a grow, especially an indoor one, time spent under lights is as important as the cost of electricity itself. An autoflower grower who puts their plants in a 20/4 cycle will find that a significant chunk of the electricity they spend goes into keeping those lights on. Compared to a photoperiod grower in a 12/12 cycle, the autoflower grower could be paying anywhere between 2/3rds more and double the amount of electricity, depending on the size of their tent and the equipment they use.
Therefore, it is entirely possible for a photoperiod grower to get a better value out of their grow in terms of grams per watt spent, simply because a chunk of that 12/12 cycle falls under a shorter daily photoperiod. Autoflowers win in terms of total grow time and turnover but are slightly disadvantaged when it comes to electricity costs. Anyone serious about budgeting for an indoor grow should bear in mind that the 24/0 cycle of autoflowers can hide some very expensive wattage.
Making Mistakes With Grow Time
This is the part that many new growers overlook. If a photoperiod plant gets infested with pests, or suffers from a nutrient burn or cold shock during the vegetative stage, the grower can pause the flowering and simply wait for the plant to recover. The flowering will be postponed until the plant looks healthy, but it will otherwise proceed as normal. The grower had the luxury of time to deal with the issue because the vegetative phase is entirely controlled by the photoperiod.
An autoflowering plant in the same situation has far fewer options available to the grower. It will continue to follow the internal clockwork and the only way to mitigate the damage is to deal with the stressor and get on with the flowering as soon as possible. There is no extra time that can be spent waiting for the plant to recover because an autoflowering plant never really takes breaks – it will simply push through the adversity and move on to the next stage. Everything happens on a strict internal clock and any setback adds to the total grow time, which means an autoflower grower has to be far more precise and attentive than a photoperiod grower.
Training Tolerance
A photoperiod grower has far more options when it comes to training their plants. They can use SCROG, topping, supercropping, low-stress training, and a number of other techniques to manipulate the plant’s shape and boost yields. This is possible because the grower has time to let the plant recover from the stress of these interventions. The autoflower grower, on the other hand, has far fewer options and generally has to stick to very mild low-stress techniques. This is a direct result of the autoflower’s internal clock which does not allow the grower to stop the flowering to deal with a plant that is recovering from topping.
There is generally no room for error with an autoflowering plant. A grower who makes a mistake when training is going to see those consequences play out in the final size and shape of the plant. The same mistake made with a photoperiod plant would have far fewer repercussions but would also take much longer to recover from. It is entirely possible for a photoperiod grower to push through a setback and make up for lost time by extending the vegetative phase, but an autoflower grower has to plan their interventions with precision because there is no time to make up for mistakes.
Genetic Keepers vs. Fresh Seeds
When it comes to genetics, photoperiod growers have the option to clone their plants, while autoflower growers generally do not. A photoperiod grower can take cuttings from their favourite plant, root them, grow them to the desired size, then put them in the flowering stage. This process can be repeated indefinitely – as long as the grower can keep their mother plants healthy and happy, they can make clones from them. Obviously, there is a genetic diversity factor involved, but overall, cloning is an advantage because it lets a grower use the same genetics again and again.
An autoflower grower cannot really do this – taking cuttings from an autoflower plant will put them in the same stage as the donor plant, so in practice, autoflower growers have to deal with fresh seeds every time. Therefore, maintaining a stable genetics source is more important for autoflowering growers than it is for photoperiod growers because there is no real alternative if a grower is dissatisfied with a particular phenotype.
One Big Harvest or Steady Supply?
An autoflower grower has the option to continuously grow small batches of plants, rather than waiting for an entire crop to finish before starting a new one. This means that instead of waiting several months for a single harvest, the grower can have a steady supply of cannabis coming in every few weeks. This is much more convenient for some growers, who either prefer to have small harvests more often or do not have the time or resources to deal with a large one right now.
A photoperiod grower has fewer options in this regard. Their harvests tend to be bigger, but also further apart. If they want to grow more than one plant, they have to stagger them in order to have continuous harvests. This is far more resource-intensive in terms of time, space, and equipment for the photoperiod grower. Some growers are happy to wait for a bigger harvest to come in after several months of grow time – for them, that single, larger batch is worth the wait. For others, it is preferable to have smaller but more frequent ones. It is up to the individual grower to decide which approach suits them better.
Deciding on the Right Approach
If we take all of the differences above and boil them down to the simplest form, it all comes down to two questions: is space constrained, and is the growing season short? If the answer to either of these is ‘yes’, then it is a good idea to look into autoflowering strains. If a grower has enough space and a long enough season to make use of a photoperiod strain’s advantages, then going that route is the most beneficial.
In most cases, growers will already have a ‘yes’ or ‘no’ answer to at least one of these questions before they even start looking at seeds. The grower simply has to choose a strain that takes advantage of the resources they have, rather than stretching them thin.
