How Much Light Does A Weed Seed Need


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How much sunlight does a weed plant need? What’s the right amount for your strain? Learn how to fulfill your crops’ sunlight demands for a bountiful yield. When cannabis seedlings have grown their second or third set of serrated leaves they are usually hardy enough to flourish in direct sunlight. Learn when that is and how to do that now. What do I need to know about light cycles and flowering my marijuana plants? Plants keep getting bigger and bigger with long days, and start making buds when you give them long nights.

How Much Sunlight Does A Weed Plant Need?

We know that all things flourish when placed in the sun. The question remains, how much sunlight does a weed plant need?

The first thought that comes to mind is as much sunlight as possible. While you aren’t exactly wrong, your list of “how-to” questions should include this one: how many hours of light does a weed plant need.

The main reason we grow marijuana is to see the fruits of our labor once it produces the most beautiful buds. Getting enough sunlight is one of the key sources it needs to do so. Being clued up about it can only be beneficial to you and your crops.

Below we’ll discuss this further and determine how much sunlight plants need so that you can enjoy the finer things in life. Knowing your cannabis crops are getting the right amount of sunlight, just the way they like it.

Why does weed need sunlight?

Given all the benefits the sun-grown cannabis receives from sunlight, growers can walk away with a bountiful yield at harvest time. The natural rays maximize plant growth, encouraging quality buds.

The best part of the sun-grown weed is that it produces higher-quality marijuana and fatter buds with better taste.

The chlorophyll in the leaves absorbs the energy from the sun. This process breaks down water and carbon dioxide molecules that produce the energy necessary for the plant to grow.

How much sunlight does a weed plant need a day to receive this energy? Up to 12 hours is sufficient. Sunlight is an important energy source needed to develop healthy roots, branches, and crops.

Those pretty leaves on a marijuana plant are one of the main reasons this crop needs the right amount of sunlight. They have a large surface area, which means enough sunlight absorption needs to take place.

Can weed grow without direct sunlight?

Direct sunlight is by far the most effective way to fulfill the lighting quota of your marijuana plants. Can weed grow without direct sunlight? The answer is complex.

Understanding the difference between direct sunlight and reflected sunlight is essential. At times, growers cannot cultivate their crops in open spaces.

In this case, you may divert sunlight to your sun-grown cannabis by using a reflector.

With an outdoor grow in partial shade, the crop still seeks the sunlight and can develop long awry branches. The development of the bud is compromised, the yield is less, and so is the resin.

Weed can be grown without direct sunlight, with caution.

How does sunlight differ from artificial light for cannabis plants?

When cultivating marijuana, both lighting methods are optional. It all depends on grower preference.

Whether you choose to use artificial ones indoors or rely on the natural rays, one constant question remains: how many hours of light does a weed plant need? No matter the difference between them, cannabis crops still need the right amount of light to feed their growth.

Let’s compare the two in a brief outline:

Sunlight Artificial light
Free—uses UV illumination from the sun Not free—uses fluorescent, LED, and HID lights
Used for outdoor growing Used for indoor growing
Uncontrolled lighting exposure Controlled lighting exposure
Provides plants with natural full-spectrum lighting Mimics full-spectrum lighting
Sun-grown cannabis does well with 10–12 hours of sunlight Cannabis grown with artificial lights needs up to 18 hours of exposure

Weed outside

How much sunlight does a weed plant need?

Several factors determine how much sunlight you should give your weed. How much sunlight does a weed plant need a day is one of them.

It would be quite interesting to compare how different autoflowering and photoperiod strains react to the different amounts of sunlight each needs.

Let’s discuss a few of the most common factors which can help us determine this.

For photoperiod strains

Photoperiod strains are standard feminized seeds that are sensitive to light cycles. How much sun does this marijuana need?

Photoperiod seeds have two phases in their life cycle which can help answer this question:

During the vegetative phase, crops require about 18 hours of daily sunlight. During this stage, the weed starts developing its roots and branches only.

For the sun-grown cannabis to progress to the flowering stage, sunlight absorption requirements drop to 12 hours daily. It’s vital to know that the other 12 hours of the day, the marijuana plants need to be in uninterrupted darkness.

The crops remain in the vegetative stage for as long as it gets 15 hours or more of sunlight per day. These plants need “short days” with a lot of sunlight and “long nights” with darkness.

For autoflowering strains

It’s rather amazing how opposite autoflowering strains are to that of the photoperiod ones. How much sun does this marijuana need? As much as possible.

These wonder seeds can receive as much as 24 hours of continuous sunlight. There’s no such thing as too much sunlight for autoflowering seeds.

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Growers favor autoflowering cannabis strains, which have become popular sun-grown cannabis because they can be grown in almost any condition. It also doesn’t need uninterrupted hours of darkness for it to start its flowering process.

These crops grow to produce bushier buds with a much better yield, provided that it receives the right amount of sunlight.

How many hours of light does a weed plant need per day?

How many hours of light does a weed plant need a day? In a worst-case scenario, marijuana plants generally require up to 13 hours of light per day.

The correct amount of light that crops thrive on for growth are:

  • Vegetative stage: minimum of 18–24 hours per day
  • Flowering stage: minimum of 12 hours per day

The amount that weed plants require depends on a variety of factors:

  • Seed type
  • Location of seedlings
  • Stage of growth that your cannabis plant is at

How much direct sunlight does a weed plant need

Do you wonder how much direct sunlight a weed plant needs per day? Cannabis crops are happiest when they receive the right amount.

Weed plants should receive 10–12 hours of direct sun daily. No problem if your crops aren’t growing in a space where it doesn’t receive direct sunlight. Make sure that it receives approximately 6 hours of uninterrupted reflected sun.

Can weed grow without direct sunlight? If crops don’t receive any UV rays (directly or reflected), they grow slower and provide smaller yields. Get rid of branches and any obstruction to enhance light exposure.

What’s the difference between sunlight in the equator and the hemispheres?

Are you curious about how much sunlight plants need when grown close to the equator? Your location on either hemisphere is crucial since your location impacts how your crops grow.

Being close to the equator and receiving the sunlight from either side of the hemispheres influences the amount of outdoor plant light received by cannabis crops. When the Northern Hemisphere is closest to the sun, it’s called the summer solstice. Growers in this region experience their summer in June.

The germination of your sun-grown weed seeds should be between the start of spring in early March and summer. In the Southern Hemisphere, the earth faces the sun in December. Growers should start cultivating their seeds in early September.

How many hours of light a weed plant needs is usually not a concern for growers who live near the equator. Sun-grown weed flourishes at the equator, offering cultivators the opportunity to grow crops year-round.

The positioning of the equator from the sun never changes. It remains at the same distance, which means it gets 12 hours of sunlight daily. That’s music to a grower’s ears.


Knowledge is power. The information regarding marijuana cultivation is vast. While we have covered some of the most important facts, some frequently asked questions are common amongst growers.

Can weed plants get too much sunlight?

With the keyword being sunlight, the answer isn’t quite simple. Sun-grown cannabis thrives on the energy it receives from the sun to grow, so that’s a no. Considering the strains that need darkness to flower, too much sunlight would be a yes.

Do weed plants need light or heat?

Your sun-grown weed needs both. Sunlight is a source of light and heat. It’s important to remember that since your crops need a lot of sunlight to grow, it’s also receiving heat simultaneously. Keeping the temperatures regulated is a must for cannabis cultivation.

How long can weed plants go without light?

It’s dependent on the strain you’re growing and your sun-grown cannabis plant’s growth stage. It can’t go without light for extended periods. The longest your crop can go without uninterrupted light absorption is 24 hours. It won’t die instantly but may become stressed.

Weed under sunlight

Sun nourished weed!

Who knew that so many intricate details go into growing weed. It makes harvesting those buds a proud moment. Knowing how much sun marijuana needs helps you to optimize your crop’s yield.

The amount of sunlight that your crops receive depends on various considerations that might seem minor but play a vital role.

A question like how much direct sunlight does my weed plant need daily guides you with the decisions you need to make to sustain a generous yield.

There are multiple lighting options available to grow your weed, but direct sunlight is still the best one available.

Now that you’ve learned about the amount of direct sunlight marijuana crops need, why not put your newly acquired knowledge to the test? Head over to Homegrown Cannabis Co. and check out the wide selection of seeds available.

When can seedlings be put under lights or in the sun?

Not sure whether to grow your cannabis seeds in the sun or under lights? This article explains how much light you need, how to prevent your seedlings from falling over, and when to plant them outside.

“When can cannabis seedlings be put under lights or in the sun?” is a common and sensible question that is often asked by novice cannabis enthusiasts after germinating seeds indoors under lights.

For those who are growing indoors, cannabis seedlings may be put under lights as soon as they emerge from the soil or growing medium.

How much light for cannabis seedlings?

When using HID lighting (usually a metal halide lamp), young seedlings should be kept at least 50cm from the bulb.

With compact fluorescent lamps (usually 100w or more), a distance of around 15cm should be maintained between the top of the young seedlings and the bulb.

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If using normal fluorescent tubes (18-36w), seedlings can be kept within a few centimetres of the light source.

Cannabis seedlings growing under lights should always be given a gentle breeze from an oscillating fan (a small household fan on the lowest setting is fine), as constant gentle movement will strengthen their stems significantly.

Are your cannabis seedlings falling over?

If cannabis seedlings grow tall and then fall over, this is almost always a result of growing in an environment with static air.

Seedlings intended for outdoor growing should be kept by a sunny window for the first week or two after emerging from the soil.

When they have grown their second or third set of serrated leaves (after the the round cotyledons that initially emerge from the seed) seedlings are usually hardy enough to flourish in direct sunlight.

When to plant your cannabis seedlings outside?

If outdoor temperatures are suitable, seedlings may be acclimatised to direct sunlight by giving them progressively longer daily exposure to outdoor conditions.

Starting with about three hours outside, at the sunniest time of day, seedlings can be given an extra hour of outside exposure each day, so that within about two weeks they can be left outdoors permanently.

Laws and regulations regarding cannabis cultivation differ from country to country. Sensi Seeds therefore strongly advises you to check your local laws and regulations. Do not act in conflict with the law.

Cannabis Light Schedules: Vegetative Stage vs Flowering Stage

Cannabis plants keep getting bigger and bigger with long days, and start making buds when you give them long nights.

Cannabis is a “photoperiod” plant, which means the amount of light received each day decides when the plant starts flowering or making buds. This article explains how much light a day your photoperiod cannabis plants need to grow and start budding, so you get to a happy harvest day. What about auto-flowering strains?

Vegetative – Seedling or clone leads to Vegetative Stage –
Give 18-24 hours of light a day

Flowering – Flowering (Budding) Stage leads to Harvest –
Give 12 hours light & 12 hours dark each day

Seedling or Clone

While not technically a “stage,” all grows start with cannabis seeds or clones.


Plant your seeds or clones when you’re ready to start growing! What are clones?


Some outdoor growers start their plants indoors to give them a headstart before putting plants outside.

If you’re growing cannabis outdoors with seeds, you should wait until a few weeks after the spring equinox to put your seeds outside. In the northern hemisphere this means seeds go outside in-or-after April, In the southern hemisphere seeds go outside in-or-after October.

For growers starting with cannabis clones, generally you should wait a few weeks longer than with seeds. Cannabis clones are more prone to flowering early outdoors than seeds, so you might want to put your clones out in late Spring or early Summer. (What are clones?)

If you live in a cold climate, you must also wait until after the last frost before putting your plants outside. Freezing temps will kill cannabis plants. Strain choice is very important. Some strains flower earlier than others. For outdoor growers in cold climates, it’s important to make sure you grow a strain that is matched up with your local weather, so that plants are ready for harvest before temperatures drop.

Vegetative Stage

The vegetative stage is one of the most important parts of the life of your cannabis plant.

The vegetative stage is the growing stage of the plant. When in veg, cannabis plants grow bigger and taller, growing only stems and leaves. As a grower, you are able to control the size and shape of your plants in the vegetative stage using simple training methods.

During the entire vegetative stage the plant does not produce buds at all. It only grows stems and leaves. During the vegetative stage plants tend to grow very fast, especially when conditions are right.

What keeps cannabis in the vegetative stage?

Short nights keep cannabis plants in the vegetative stage. You can keep a cannabis plant in the vegetative stage for basically forever as long as the plant continues to get short nights (shorter than 1s-12 hours, depending on the strain).

Cannabis will stay in the vegetative stage as long as the plant gets short nights (less than 11-12 hours of darkness each day)

Whether you’re growing indoors or outdoors, you must make sure your cannabis plants get at least 13 hours of light each day to stay in the vegetative stage. If your plant gets a few long nights, it may start budding before you want.

The plant can receive as much as 24 hours of light a day while in the vegetative stage. Many indoor growers provide 18-24 hours of light a day (known as 18-6 or 24-0 light schedules) during the vegetative stage to encourage faster vegetative growth.

Don’t want to worry about light schedules? For growers that don’t want to pay attention to light schedules, there are auto-flowering strains of cannabis, which will automatically go through their whole life in about 3 months no matter what light schedule is provided. For some growers, an auto-flowering strain may be more simple than a traditional (photoperiod) strain.


Most indoor growers provide 18-24 hours of light a day (known as 18-6 or 24-0 light schedules). Giving your cannabis plants more hours of light each day in the flowering stage will encourage faster growth.

Lingo: When a grower provides 18 hours of light a day and 6 hours of darkness, this is commonly known as the 18/6 light schedule. For 24 hours a day, this is referred to as the 24-0 light schedule.

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As long as your plant is getting plenty of light a day, your plant will automatically stay in the vegetative stage from late spring until late summer. Every strain is a bit different.

Flowering Stage

Cannabis starts budding when plants get at least 12 hours of uninterrupted darkness each night. After plants start budding, they must continue to get long dark nights until harvest or they may revert back to the vegetative stage.


Indoors most growers put their plants on a 12-12 schedule to initiate flowering. Outdoors the plant will naturally start budding in late summer when nights are growing longer and longer as winter approaches. Just make sure plants aren’t exposed to light during their dark period!

What is 12-12 Lighting?

The indoor grower will need to artificially induce flowering/budding in plants by changing the light schedule so the plant receives only 12 hours of light a day, and 12 hours of uninterrupted darkness.

Once the plant is changed over to the flowering (12/12) light schedule, there is generally another 6 weeks-5 months (average 2.5 months) before the plant’s buds are ready for harvest.


Outdoor growers wait until their cannabis plants start naturally flowering on their own, usually after mid-summer when days start getting shorter than 12 hours.

It’s important to make sure plants aren’t exposed to light at night during their dark period, even street lights or spotlights, as this can prevent cannabis plants from flowering properly.

Growing Indoors? Not Sure When To Switch To Flowering?

So indoor growers have a choice to flower their plants whenever they want… When is the best t ime to start flowering your cannabis indoors?

The real answer is that it’s a matter of personal preference and also depends on what end result you’re looking for. There are two major considerations when choosing the right time to switch to 12/12, the age of the plant and the height of the plant:

Age: Some growers feel that a marijuana plant which has been grown from seed will not produce as many buds or have enough resin production if the plant is not given at least 60 days in the vegetative stage to mature before it’s changed over to the flowering stage. This is not true. many growers initiate flowering soon after germinating a seed in order to keep plants small and short. This is often called “12-12 from seed.” Just remember, no matter what you do, a young cannabis plant will not start flowering until it is 2-3 weeks old. Even if you put a seed on a 12-12 schedule from the beginning, it will not start properly budding for about 3 weeks. When growing with cannabis clones, age is not an issue and growers can switch directly to flowering once your clone has established roots. This is because even though a clone may be small, it’s still a ‘mature’ plant since it is made of a piece from a mature plant. Rooted clones tend to grow much faster for the first few weeks than plants grown from seed. In any case, age is not much of an issue, and you should switch your light schedule at the time that best fits your needs.

Height: A general rule is that your marijuana plant will double or triple in size during the flowering stage from the point where you first change over the light schedule to 12/12. Some plants will grow more, some will grow less, but a good rule of thumb is to change your light schedule over to flowering when your plants have reached half of their final desired height. Bending, known as “LST” or “low stress training” can be used to control colas that get too tall. Simply bend too-tall colas down and away from the center of the plant. Some growers will even slightly break or “supercrop” branches to get them to bend at a 90 degree angle. For those growing in a small space, height may be the primary concern. However, there are many techniques available to grow a short, bushy weed plant or basically train your cannabis plant to grow into any shape you want.

Here’s an example of LST to keep a plant short:

In optimal conditions if height and space is not an issue, you would probably want to vegetate your cannabis plant for 60 days or more before switching it over to flowering. This gives your plant plenty of time to grow big (so you get bigger yields), and allows new growers to dial in their grow before plants enter the sensitive flowering stage. In the vegetative stage, it is easy to recover from problems, but problems are a lot more serious in the flowering stage, where mistakes can dramatically hurt your final yields.

Giving cannabis plants more time in the vegetative stage, and taking time to train them to fit your space, will give you the best final yields. However, if space is tight, then it’s better to switch when the plant is half the final desired height, or even to just attempt to flower your cannabis plant straight from seed.


After the vegetative and flowering stage are over, it is time to harvest your plants!

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