How Many Hours of Light Do Weed Plants Need? | Optimal Lighting for a Perfect Yield

by Morgan

May 9, 2022

How To Choose The Right Lighting For Your Marijuana Grow Room

How many hours of light do weed plants need? There's a reason why most plants on earth have evolved to adapt to the rhythm of the sun. It's not just for fun! There is an actual purpose for it all, and that reason is photosynthesis.

Cannabis plants are constantly flowering, even when you're not smoking them. The marijuana plants need hours and hours of lighting to make sure they grow properly. So, how many hours of light do weed plants need? To find out, let's look at what light does for your plants; how light affects the growth, development, and yield of your cannabis.

Importance Of Light in Plants

Before we know how many hours of light weed need to know why light is beneficial for the plant. Light is the most important factor for photosynthesis, but not all light is created equal. The light spectrum that marijuana plants need the most is blue and red hues. These colors stimulate growth and influence your final product's looks, smells, and tastes.

The sun emits a full spectrum of light for the plants growing outdoors, but artificial lights only emit some of these wavelengths. It's why it's so important to get high-quality bulbs for your setup. If you want your weed plants to stay healthy, you need to give them enough light. But how much is too much? And what about different stages of growth? Let's take a closer look at each one below:

Seed to Harvest Light Guide for Indoor Growers of Cannabis Plants:

Germination Stage 2-4 Weeks

No direct light is needed during this stage. Your plants are just getting used to their new home and taking root. You can place your grow lights on a timer, so they're only on for 12 hours a day. It will give your plants the darkness they need to rest.

Seedling Stage 2-3 Weeks

Your plants grow fast and need more light as they stretch towards the sky. You can gradually increase the amount of time your lights are on to 18 hours a day during the seedling stage.

Vegetative Stage 2-8 Weeks

Once your plants have reached vegetative growth, you can start giving them more light. They'll need around 18 hours of light per day during this stage when your weed plants will start growing! Make sure you have enough space for them, as they can get big quickly.

Pre-Flowering to Flowering Stage 6 Weeks – Harvest

Your plants begin flowering and need less light than before. You can reduce the amount of time your lights are on to 12 hours a day during this stage. It will help your plants focus their energy on flowering.

Flowering Stage 6-16 Weeks

When your weed reaches the flowering period, they'll need 12 hours of light and darkness during this stage when they begin to generate buds, so make sure you give them plenty of room to expand.

Harvest 2-4 Weeks

After you've harvested your weed plants, you can start the process again! Start by giving them 18 hours of light per day during the germination stage. Then, increase the light to 24 hours per day during the vegetative stage. Finally, reduce the light to 12 hours per day during the blossoming stage.

So, how many hours of lighting do weed plants need? It depends on what stage of growth they're in. Seedlings and young plants need around 18 hours of lighting per day, while adult plants need 12-12 lighting systems. After harvest, you can start the cycle all over again. Give your plants the light they need to grow big and strong.

Photoperiod vs. Autoflowers Light Cycle (Outdoor Plants)

While indoor growers have to worry about light cycles, outdoor growers don't have to be as concerned. The sun provides a full spectrum of light that your plants need to grow. However, you still need to know some things about outdoor light cycles.

Photoperiod plants 

Photoperiod plants are the most common type of cannabis plant. They need a certain amount of light per day to flower. The time depends on the cannabis strain, but most photoperiod strains need 12 hours of darkness to flower.

Autoflowers

Autoflowers are a newer cannabis plant that doesn't rely on light cycles to flower. Instead, they flower based on their age, making autoflowers a great option for outdoor growers, as they can be grown in any season.

No matter what type of plant you're growing, it's important to give them the right amount of light. Too much light can damage your plants, while too little light will prevent them from growing properly. Make sure you know how much light your plants need and adjust accordingly.

a peron with white gloves taking care of the plant

Light Requirements for Clones

While your plants are in the clone, seedling, or vegetative stage, they'll need more than 18 hours of lighting per day. It will aid in their rapid development and realization of their full potential. You can gradually reduce the amount of light they receive to 12 hours each day after a few weeks. The hours of lighting will allow them to concentrate on blossoming.

Flowering Stage

When your plants enter the flowering or blossoming stage, they'll need half a day of light and half a day of darkness which is basically 12 hours each. They will then start to produce buds, so make sure you have plenty of space for them to grow. After a few weeks, you can harvest your plants and enjoy the fruits of your labor!

What's the Difference Between Sunlight and Artificial Light from Grow Lamps?

While the sun provides a full spectrum of light, artificial lights don't. You'll need to provide your plants with different types of light depending on what stage of growth they're in.

For example, your plants will need more blue than red light during the vegetative stage. Blue light promotes growth, while red light helps your plants flower.

However, your plants will need more red light than blue light during the flowering stage. Red light helps your plants produce buds.

So, when choosing to grow lamps, make sure you get ones that provide the right type of light for your plants. It will help them grow strong and healthy.

Different Types of Grow Lights for Your Marijuana Plants

There are a few different types of grow lights you can choose for your plant's growth. Each has its advantages and disadvantages.

HPS Lights

High-pressure sodium (HPS) lights are among the most popular grow lights. They're inexpensive and provide a lot of light. However, they produce a lot of heat, damaging your plants.

LED Lights

LED lights are becoming more popular as they're more efficient and don't produce as much heat. However, they're more expensive than HPS lights.

Fluorescent Lights

Fluorescent lights are another option you can choose from. They're cheaper than LED lights, but they don't last as long. They also produce less light, so you'll need more of them to light your plants properly.

Fluorescent Grow Lights (CFL)

Compact fluorescent lights (CFLs) are a type of fluorescent light. They're cheaper than other fluorescent lights and provide a good amount of light. However, they don't last as long as other types of fluorescent lights.

weed plant under the artificial lights

Lighting Schedules for Your Weed Plants

You can create a light schedule now that you know how much light your plants need. It will help ensure that your plants get the right amount of light.

  1. 12-12 lighting - For cannabis plants, this is the most typical lighting schedule. Each day, the weed plants will need exactly 12 hours of lighting and 12 hours of uninterrupted darkness to help them bloom properly.
  2. 18-6 lighting - This lighting schedule is employed for clones, seedlings, and vegetative plants. The plants will acquire 18 hours of lighting and six hours in darkness every day. They will be able to grow more swiftly as a result of this.
  3. 24-0 lighting - The lighting regimen is employed for mother and vegetative plants. Each day, your plants will receive 24 hours of lighting. It will assist them in growing swiftly, producing many leaves.
  4. 0-24 lighting - The lighting schedule is used for mothers and vegetative plants. Your plants will get 24 hours of darkness per day to help them focus on flowering and producing buds.

Signs Your Weed Plants Are Getting Less Hours Of Lighting Than Recommended 

If your plants are getting fewer hours of lighting than they need, you'll notice a few signs.

  • Your plants will grow slowly.
  • Your plants will be spindly and have thin leaves.
  • Your plants will produce fewer buds.

How to Fix It

If your marijuana plant is getting little light, you'll need to increase the amount of time they're exposed to light. You need to add more daylight hours or brighter grow lights to do this.


Signs Your Weed Plants Are Getting More Hours of Lighting Than Recommended 

If your arijuana plant is getting too much light, you'll notice a few signs.

  • Your plants will grow quickly.
  • Your plants will be bushy and have thick leaves.
  • Your plants will produce more buds.

How to Fix It

  • If your plants are getting too much light, you'll need to reduce the amount of time they're exposed to light. Add more hours of darkness or use dimmer grow lights.
  • You should also make sure that your plants are getting enough ventilation. It will help them stay cool and prevent them from getting damaged by the heat.
weed plant

FAQs

Is 24-Hour Light Good for Weed Plants?

No, a 24-hour cannabis light cycle is not good for weed plants. Your plants need a dark period to rest and rejuvenate. A 12-12 lighting schedule is the most common for cannabis plants.

What's The Difference Between Artificial Light and Sunlight?

While the sun provides a full spectrum of light, artificial lights don't. You will need to provide your plants with different types of light depending on what stage of growth they're in. For example, your plants will need more blue than red lights during the vegetative stage. However, your plants will need more red lights than blue lights during the flowering stage.

Does Weed Grow Without Light?

No, weed does not grow without light. Light is essential for photosynthesis, which is how plants make their food. Without light, your plants will not be able to grow healthy and strong with higher yields.

How Do I Know If My Plants Are Getting Enough Light?

If your plants are not getting enough light, they will start to stretch and become leggy. They may also produce fewer buds. If you think your plants are not getting enough light, try moving them closer to your grow lights. You can also try adding more lights to your grow room.

Are LED Lights Better for Weed Than HPS?

LED lights are becoming more popular as they're more efficient and don't produce as much heat. However, they're more expensive than HPS lights.

plant under the LED lights

Use Right Amount of Light

As you can see, there's a lot to know about how many hours of light weed plants need. But, as long as you provide your plants with the right amount of light, they'll grow healthy and strong. So, don't forget to create a lighting schedule and stick to it.

If you have any queries about providing light for your plants or any other weed-related topic, don't hesitate to ask us through our Green thumb website.

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About the author 

Morgan

I discovered the benefits of Cannabis at a young age in 2002, with years of trial and error, my knowledge grew just like my plants. As my love for cannabis unfolded I began to teach and learn, trying to gain as much information and practical growing experience.

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