How To Tell If You Have An Autoflower vs Photoperiod Plant

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Growing you own weed can be extremely rewarding and it’s a whole lot of fun too. That said, there are certain challenges which every home pot grower faces.

Of course, it all starts out with the cannabis seed, which needs to be germinated, planted, cared for, harvested, and more. (it’s well worth picking up this FREE grow bible, it has some great information).

However, something you might not know is that there are different kinds of weed plants out there, specifically to do with going from the vegetative to the flowering stage. There are photoperiod weed plants and autoflower weed plants, and there is a difference between the two.

So how to tell if you have an autoflower weed plant or a photoperiod weed plant? here is everything you need to know to tell the difference;

Autoflower vs Photoperiod: Differences

Before we get into talking about how you can tell if you have an autoflower or a photoperiod pot plant, it’s probably helpful for you to know what each one is.


So, first off you have the photoperiod weed plant, which can take up to 4 or even 6 months to fully grow.

Photoperiod refers to the amount of light or illumination a specific plant needs on a daily basis in order to grow. Photoperiod weed plants will stay in their vegetative state for as long as you provide them with ample daily light.

Generally speaking, photoperiod weed plants need between 18 and 24 hours of light per day during the vegetation stage.

In order to begin the flowering process, photoperiod weed plants require the amount of daily light to be decreased to 12 hours.

This change in lighting then causes a chemical reaction in the plant which signals that it is time to start flowering.


Autoflower weed plants grow much faster than photoperiod weed plants, and often only take 2 months to get from seed to harvest.

Now, just as the name implies, autoflowering weed plants start flowering all on their own when they are ready. This is regardless of lighting.

Therefore, they tend to be much easier to grow, less time consuming, and more beginner friendly.

This is because the grower does not have to make any changes to cause the weed plant to go from the vegetation stage to the flowering stage. With autoflower weed plants, this transition happens all on its own.

6 Ways To Identify An Autoflower Cannabis Plant

Alright, so now you probably want to know how you can tell if you have an autoflower weed plant, which is what we are here for right now.

Here are the best ways to tell if you have an autoflowering marijuana plant;

1. When You Buy the Seeds

The first way to tell if you have an autoflower weed plant is when you buy the seeds. Simply put, it’s best not to use seeds you find in your weed or to use seeds that are not labelled.

When you buy marijuana seeds from a professional place, they should always be labelled (here is a list of seed banks we recommend).

When all is said and done, you should know if your weed is autoflowering or photoperiod before you germinate your seeds, as this will determine how you treat the plant during growth.

However, you might not always know, which is why below, we have a list of ways to tell if your weed plant is autoflowering or not, all from the look of it, how long it takes to grow, and some other factors too.

2. The Size of The Plant

One of the main ways in which you can tell if you have an autoflowering weed plant is by the size of it. Generally speaking, because photoperiod plants grow longer, they also grow bigger.

In other words, autoflower weed plants tend to be much smaller than a photoperiod weed plant. Photoperiod weed plants can grow to 6 feet indoors and up to 10 feet outdoors.

On the other hand, an autoflower weed plant will usually top out at 3 feet in height indoors and 5 feet outdoors.

If you have been growing the weed plant for a full month and it’s still only between 1 and 2 feet high, chances are that it’s an autoflowering plant.

3. How Fast it Grows

Something else that can help you tell whether or not you have an autoflower plant is by the growth rate.

A photoperiod weed plant can take up to 8 or 10 weeks in the vegetation state, and then that long again in the flowering state.

Therefore, a photoperiod weed plant can take up to a half a year to go from seed to harvest. So, if it took you any longer than 3 months to get to the harvest, it’s probably not an autoflowering plant.

However, if you planted your seeds and are ready to harvest buds within 10 or 12 weeks of planting, chances are almost 100% that it’s an autoflower weed strain.

4. Automatic Transition to Flowering

The easiest way you will be able to tell that you have an autoflowering weed plant is if it makes the transition from the vegetation stage to the flowering stage on its own.

A photoperiod weed plant requires you to reduce the amount of light given to it in order to start flowering. Without a reduction in daily lighting, a photoperiod plant will simply continue on vegetating.

However, an autoflower weed plant will begin flowering on its own regardless of lighting. Withing 4 to 6 weeks of having been planted, an autoflowering plant will automatically transition to the flowering stage all on its own.

5. The Final Yield

Yet another way to tell if you have grown an autoflower plant is by the final yield. Yes, photoperiod plants grow for much longer and they get much bigger, and therefore they also produce a much larger final yield.

On average, a photoperiod plants can yield up to 700 grams per square meter. When growing indoors, you can expect a single photoperiod weed plant to produce anywhere from 6 to 12 ounces of weed.

On the other hand, an autoflower weed plant will usually produce no more than 500 grams per square meter. Your average autoflower plant will produce between 2 and 6 ounces of bud by harvest time.

6. Potency

Yet another way to tell if you grew an autoflower or a photoperiod weed plant is by the potency of it.

For the most part, photoperiod weed plants will always be much more potent than autoflower plants, with THC content differences as high as 15% or even 20%.

Now, we do have to say that it all depends on the specific strain and growth conditions too. If you choose a naturally potent autoflower strain and you grow it like a pro, it might end up being more potent than a naturally weak photoperiod strain that has been grown improperly.

Although, this is not often the case.


When all has been said and done, if you want to grow some weed, but don’t want to take 6 months until you can smoke something, you want to go with autoflowering plants.

No, they might not get as big or produce as much of a final yield, but they are much easier to take care of and take about half as long as photoperiod plants to get from seed to harvest.


My passion for the sticky icky started nearly a decade ago, and it all began when I first laid my eyes on the beauty that is the marijuana plant.

I cover all aspects of growing from equipment recommendations to plant health/care tips to help both new and experienced growers.