What Is The Light Schedule For Growing Weed

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Yeah, growing weed is a really fun hobby, or in some cases a business too, but the fact of the matter is that people who do this enjoy it a whole lot. That said, of course there is a fair amount of work and knowledge involved here.

You can’t just plop a seed in some dirt, stick it under a light bulb, and wait for the sticky icky to grow 6 feet tall. One of the most important aspects for growing weed, good weed, and lots of it, is the light, specifically the light schedule.

Yes, marijuana plants need a specific amount of light to grow, and more importantly, to provide you with great yields. So, what is the light schedule for growing weed? Well, there are actually two different growth stages or periods, these being the vegetative and the flowering stages. A weed plant in its flowering stage needs between 18 and 24 hours of light per day, and plants in the flowering state need around 12 hours per day.

cannabis plant lighting

However, there is a bit more to it than this, so let’s get right to it.


Vegetative State vs Flowering Stage

The first thing that you need to be aware of here is that there is a difference between the vegetative state and the flowering state, and what this difference means in terms of the lighting schedule.

Vegetative State

The vegetative state of plant growth is where the weed plant is going to do most of its growing in terms of pure size. This is when the stems and leaves grow, with the vast majority of height being achieved in this state.

During the vegetative state, there is no THC being produced, and you won’t see any buds or flowers starting to grow yet.

This is all about getting a solid stem, lots of leaves, and growing as tall as possible. A marijuana plant does not develop any of its potency during this stage.

This is an important stage, as you want to get both height and width out of your plant, especially when it comes to a strong main stem.

Flowering State

Once the flowering stage of the marijuana plant gets going, this is when it will start to bud and grow flowers. In other words, this is when those sticky icky buds start growing.

During this stage, the plant will not grow quite as much in height anymore as during the vegetative state. Yes, it will still grow, but not nearly as much as during the vegetative state.

However, as the buds begin to form and grow, you will notice your marijuana plant filling out and getting wider, which is because of the weight and growth of the actual buds, what you are going to dry and smoke.

Most of the THC content or potency of your weed will be developed during the few final weeks of the flowering stage.

This is also a very important stage, because how you treat your plant here will go a long way in determining the size, flavor, and potency of the weed itself.

Light Cycle For Indoor Vegetative Stage

Ok, so first off, let’s talk about the light cycle for you weed plant in the vegetative state when you are growing your plants indoors.

Many people like to go with an 18/6 light schedule. This means that during the vegetative state, you will give your weed plants 18 hours of light per day, with 6 hours of dark.

However, many people also go for a straight 24 hour light period, which is fine too. In other words, some people choose to provide their weed plants with 24 hours of light per day, for the first 2 or 3 months, or however long you choose to keep the plant in its vegetative state.

The bottom line here is the more light you give it per day, the faster, stronger, and bigger it will grow during this vegetative state.

Some will claim that 24 hours of light is too much and that it can damage the plants, but there is absolutely not proof or evidence to support this.

What there is proof for, is that your plants will grow way more in the vegetative state with 24 hours of light than with 18.

Here is a good guide on the kind of lights you need for indoor growing.

Light Cycle For Outdoor Vegetative Stage

Ok, so the issue with outdoor growing is that you just cannot control the sunlight. It comes up when it chooses and it goes down when it chooses.

For this, if you can many people will therefore choose to grow their plants indoors during the vegetative state, and will follow either the 18/6 or 24 hour light schedule, or anything in between, as long as it is consistent.

This is usually done for the months of early spring, such as March, April, and sometimes into June. When you grow outdoors, you do have to keep frost and cold in mind.

You cannot put a plant outside and grow it during the vegetative state if the air is going to get cold at night, or at any time. However, you also cannot wait to plant your seeds until it is summer.

If you do this, you will have to wait until the end of summer to transfer your weed plants outdoors for the flowering state, but by this time, it is already getting colder and changing seasons. Therefore, you won’t have time to let your plant go through the flowering state.

There is a reason why outdoor growing results in lower yields, more dead or lackluster plants, and much lower potencies than when growing indoors.

If you need some pointers on growing bigger buds outside, here are the 6 most effective methods.

Light Cycle For Indoor Flowering Stage

Ok, now your plant has gone through its vegetative state and has grown in height as much as it is going to, for the most part. Most people will choose to leave their plants in the veg state for 2 or 3 months.

It really depends on how big you want the plant to be. Some people, if they have time, will go up to 4 months in the vegetative state, and the plant will keep growing.

Of course, spatial constrains and other issues arise from this, so 3 months is usually the maximum. Now, to get your plant to start flowering and producing the kush, you need to switch the light schedule.

It is the changing in light schedules, which mocks the changing of the seasons, which will cause your weed plant to start flowering. There are no discrepancies or debates here.

When your weed plant is in the flowering state, it needs 12 hours of light, and 12 hours of dark, and the schedule needs to be consistent.

There is no room for leeway or arguments here. 12/12 is what is needed for flowering plants when growing indoors.

Light Cycle For Outdoor Flowering Stage

outdoor flowering stage

There is not too much to say here, as the sun is in control. Your weed plants will get as much light as the sun and the surroundings allow for. So, it’s more or less out of your control.

As you will find out over and over again, growing weed indoors might be more work per say, but the fact that you can control factors such as lighting with great accuracy produces much better results.

Do keep in mind that if the plants don’t get 12 hours of light and dark, there could be problems.

However, generally speaking, 14 hours of light and 10 of dark, or the other way around, will still work when outdoor growing, but it does make things trickier.

Moving From The Vegetation To Flowering

Keep in mind that this is not just some arbitrary thing, and moreover, it is not like you need to use this much light during one stage, and that much during another.

When growing indoors, you are in control. Your plant does not change from one state to another, and then you adjust the light schedule based on that.

Your plants will change due to the light schedule, and therefore it is you who chooses when the weed plant starts flowering by changing the light schedule.

Regular Plants vs Auto-Flowering Plants

auto flowering plant

Now, having to worry about the lights and the schedule can be a bit of a pain. This is why many people get timers so that the lights go on and off on their own.

If you go to school, work, or just have a life in general, growing pot without a timer for your lights is not very fun at all. However, keep in mind that this is only for regular plants.

There is such a thing as the auto-flowering plant, otherwise known as automatically flowering marijuana plants.

For one, a normal pot plant takes between 4 and 6 months to fully grow from seed to harvest, which is quite a while. Yet, auto-flowering plants take roughly 3 months, or about half the time of a normal plant.

The really good thing about auto-flower plants is that they will go through their life, and change from the veg to the flower state, no matter what the light schedule is.

For these plants, many people will choose to go with a 14/10 light schedule the whole way through. Auto-flowering plants are much more versatile and easier to grow in this regard.

Just keep in mind that your average auto-flower weed plant will produce about half as much product as a normal plant, or less, plus it is not as strong either.


So, generally speaking, for the vegetative state, 24 hours of light for 3 months will do just fine, and for the flowering state, a good divide of 12 light and 12 dark is what you need.

It’s really pretty simple, but due to the constraints of outdoor growing, in terms of weather and light, this is all much easier to control when indoors.

And, if you don’t want to have to worry about light schedules at all, a nifty automatic flowering plant is the way to go.


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.