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. How much light does a weed plant need? Discover the answers plus cannabis light schedule tips, how to choose the best lights, helpful FAQs, and more. 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.

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.

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
See also  Fast Growing Marijuana Seeds

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.

How much light does a weed plant need?

How much light does a weed plant need? A difficult question for many new growers. Light is one of the vital elements of all life forms, including weed plants, so you must get it right for your plants to thrive.

Keep reading as we unpack everything you need to know about cannabis lighting, from picking the best lights to optimum schedules. Let’s get started.

How much light does a weed plant need?

How you use grow lights determines the success of your marijuana plants. Answering the question, how much light does a weed plant need is complex. There are four lighting basics to master for the best results.

  • Light intensity
  • Type of light and placement
  • Light spectrum
  • Light schedule

Outdoors, the sun showers your plants in natural light, but indoors you’re in control of the cannabis light cycle.

Let’s take a closer look at each factor to consider.

Light intensity

Higher light intensity is generally associated with better growth. If you continue to increase the intensity of light that a plant receives, what happens? You might over-saturate your cannabis, which causes burns. However, your crops also risk stretching and stunted growth if you dim the lights too much.

Two common ways to measure light intensity are:

  • Lumen — measures the light flow that a source emits. The higher the lumen, the brighter the light.
  • Lux — measures the light intensity that reaches a plant’s surface.
Measurements of intensity

Growers typically use lux to measure intensity in their cannabis light schedule since plants only use the light that reaches its surface.

Here’s a simple table showing the best lux levels for two essential life stages:

Life stage Minimum Good Maximum
Vegetative ~15,000 lux ~40,000 lux ~70,000 lux
Flowering ~35,000 lux ~60,000 lux ~85,000 lux

Choosing the right lights

Using specific marijuana grow lights for your weed allows you to maintain the plant’s health and progress to the next growing season.

The more plants you have, the more lights you’ll need for a successful marijuana light schedule. Average home growers use around one or two lights since most states permit no more than 12 plants.

To improve the growth and flowering of your plants, you may invest in an infrared grow light. It’s not necessary but works well with HID and LED lights.

Before you figure out how much light a weed plant needs, you must choose the right lights. HID (High-Intensity Discharge) lamps, such as MH and HPS bulbs, have a hood that reflects light.

Metal-halide lamps (MH) are ideal for the vegetative stage of the cannabis light schedule, while high-pressure sodium (HPS) lamps are perfect for flowering. Using both bulbs allows you to reap double the benefits.

See also  Germinating Old Weed Seeds

Most HID lights display a particular hue compared to the best LED grow lights, which may show many colors. Using LED lights is a fairly new practice compared to traditional HID lamps. LEDs use lower wattage but provide the same quality light spectrum as HID’s.

Before starting your cannabis light schedule, pick the best lighting options for you. Here are some pros and cons of HID and LED bulbs to help you decide:


Pro’s Con’s
Extremely bright, emitting up to 130,000 lumens Need extra equipment like an electronic ballast and reflector
Efficacy rates of 150 lumens per watt Emit an intense heat that may burn plants or spike room temperature
Relatively low maintenance Degrade over time needing routine replacement
Lower outright cost Power-hungry so higher electricity bills
Easy set up/beginner-friendly
Options for different marijuana lighting cycles


Pro’s Con’s
Energy-efficient/saves money in the long run No industry standard for LED lights
Runs cooler than HID’s, so low risk of burn Cheap models on the market may give inferior results
Mostly plug and go, no extra equipment Potentially lower yields than HID
Streamlined—supports veg and flower phase
Can last up to ten years

Distance from plants

Distance from the light can make or break your plants. Too close, and there’s a risk of light burn on weed, too far, and they won’t get the light they need. The optimum distance during your marijuana light schedule depends on the type of light and growing space.

During the seedling phase of the cannabis light schedule, grow lights should be kept around 24–36 inches away. Keeping an adequate distance prevents the seeds from drying out.

For the vegetative stage, lights should be 12–24 inches away. This phase of the cannabis light cycle requires more light for photosynthesis, so keeping them closer helps.

The light times for growing weed increase when flowering, and they should be kept around 16–36 inches away.

Here’s a handy guide for recommended distance depending on light wattage:

Grow light wattage Closest distance Furthest distance
150W 5 inches 11 inches
250W 6 inches 13 inches
400W 8 inches 19 inches
600W 9 inches 25 inches
1000W 11 inches 31 inches

Light spectrum for cannabis

Did you know the color of the lights influences your plants’ development? Different tones display certain hues based on the length of their waves. These varying shades suit the diverse stages, including a particular light spectrum for vegetative growth or the flowering phase.

The light spectrum for cannabis is the wavelengths between 380-750 nm. The colors represent the light wavelength. For example, if a light has a 400 nm wavelength, it appears purple to the human eye.

Light spectrum for seedling weed

During the seedling phase of your cannabis light schedule, use low-intensity light. Aim for 4000 lux—15% red, 30% blue, and white light.

Once your seedlings sprout their first leaves, you can double the intensity. When you spot more than two sets of leaves, it’s time for the vegetative stage.

Light spectrum for vegetative growth

For the vegetative stage of your marijuana light schedule, the main goals are root growth and tight internodes, so blue light is best. This shade stops your plants from growing too fast and developing long internodes, which causes light-blocking during flowering.

What is the best color spectrum for vegetative growth? For best results, use 27000 lux—100% blue light and less than 60% red.

Best light spectrum for flowering

In the flowering phase of the cannabis light cycle, your plants need more photons, so turn up the lux to 107,500—100% red while maintaining blue light at a lower level.

Lighting schedule

Excessive light increases your electricity bill and burns your plants.

Having a cannabis light schedule gives your flora a break. In the dark, your plants produce hormones that help them form buds.

Light and dark work together like yin and yang to form healthy greenery. How much light does a weed plant need? The answer depends on what stage the herb is in. Here’s a handy guide for the ideal light cycle for weed in different growth stages:

How many weeks does this stage last Lighting schedule
Seedlings 1–2 weeks 24 hours
Vegetative 3–5 weeks 18 hours on/ 6 hours off
Flowering 7–10 weeks 12 hours on/ 12 hours off
Light cycle for seedling marijuana

Seedlings are babies—they need all the care and nourishment you can give. In this phase of the cannabis light schedule, feed them 24 hours of light. After 1–2 weeks, your seedlings will sprout leaves and be ready for vegetation.

Light cycle for vegetative weed

The vegetative phase is the stage where plants grow bigger and taller. They need long days and short nights. To prevent early flowering, ensure they get at least 13 hours of light in your marijuana light schedule. 18 light hours and 6 dark hours will encourage healthy and steady growth.

Light cycle for flowering cannabis

In the flowering phase, weed plants start forming buds. If they don’t get at least 12 hours of darkness, they may revert to the vegetative phase. During this stage of the cannabis light schedule, you must ensure that plants get absolutely no light during the dark times.

Optimizing lighting for maximum yield and minimal cost

Powering the grow room brightness can pull copious amounts of energy and cost you money. There are some ways to ensure you use lighting properly without going bankrupt. Here are some techniques to maintain the marijuana lighting cycles efficiently:

  • Use lower wattage, LED, or energy-efficient bulbs

Energy-efficient bulbs tend to be pricey upfront but save you money in the long term. HID bulbs can use lots of power, whereas LEDs use less.

Reflective walls bounce light allowing you to make better use of your grow lights. To make walls reflective, you can use materials like mylar and plastic.

Nighttime tariffs are lower in many states, so you can save money by using grow room lights at night. Indoor growing gives you control of the cannabis light cycle, and using lights at night won’t make a difference. As long as you follow the cannabis light schedule, your plants will thrive.

See also  Cannabis Seeds Not Germinating

Providing ventilation

Ventilation is just as important as marijuana lighting cycles, water, and nutrients. Adequate airflow helps maintain the proper humidity levels, temperature, and CO2 levels in the room.

The most efficient method is to have two ventilators opposite each other and the exhaust system on a different side of the room. This way, you’ll have a balanced atmosphere with stable humidity levels and temperature.

FAQ related to how much light does a weed plant need

To help you a little more, we’ve put together the most frequently asked questions on marijuana light schedules.

What types of bulbs are best during vegetative and flowering stages?

Metal-halide lamps (MH) are the best option for the vegetative stage, and high-pressure sodium (HPS) lamps are ideal for flowering. During different phases of the cannabis light schedule, bulb settings with different lux are used. Bulbs with lux 27,000 work for vegetative and lux 107,500 for flowering.

How many hours of light do marijuana plants need?

It depends on the stage that the plants are in. In the vegetative stage, they need 18 hours of light and 6 hours of darkness. During the flowering phase of the cannabis light cycle, weed plants need 12 hours of light and 12 hours of darkness.

Can you leave grow lights on 24 hours a day?

You can only leave grow lights on for 24 hours a day during the seedling stage. Seedlings need all the nurturing they can get, and more light helps them sprout faster. During this phase of the marijuana light schedule, low-intensity light helps seedlings grow.

How much sunlight does a weed plant need?

How much sunlight does a weed plant need? The more, the merrier. Cannabis plants need at least 10–12 hours of direct sunlight to thrive. They can still grow healthy with a minimum of 6 hours of daily sunlight, but you’ll get a smaller yield.

What is the best color spectrum for vegetative growth?

Blue light bulbs with 27,000 lux—100% blue light and less than 60% red are best during the vegetative stage. It works best because blue light produces chlorophyll—a chemical that helps plants grow stronger and move to the next stage.

If you continue to increase the intensity of light that a plant receives, what happens?

If you increase light gradually following the recommendations for the cannabis light schedule, then your plant will flourish. Increasing intensity outside of the guidelines can cause your weed to burn. Cannabis plants need the most intense light when flowering, and too much before that can be detrimental.

Key Takeaways

How much light does a weed plant need? Cannabis plants have different light needs depending on their stage. Seedlings need 24 hours, vegetative stage weed needs 18 hours, and flowering plants need 12 hours of light.
There are many factors to consider, such as color spectrum, light type, marijuana lighting cycles, and intensity. Remember, healthy plants start with quality seeds. Shop our selection at i49 of the finest weed seeds now.

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    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.

    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.

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