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light cycles for growing weed

4 stages of marijuana plant growth

Cannabis plants go through a series of stages as they grow and mature, and those different growth stages call for different amounts of light, nutrients, and water.

It’s important to know these stages and how long each lasts to know what the plant needs and when. Knowing where your cannabis plants are in their life cycle will dictate when to prune, train, and trellis your plants, and when to harvest.

How long does it take to grow a marijuana plant?

Generally speaking, it takes anywhere from 10-32 weeks, or about 3-8 months, to grow a weed plant from seed. It’ll be quicker if you start with a clone or an autoflower seed.

The biggest variability in how long a marijuana plant takes to grow will happen in the vegetative stage—after the seedling phase and before flowering.

If you’re growing indoors, you can force a weed plant to flower after only a few weeks when it’s small, or after several weeks when it’s big. If you’re growing outdoors, you’re at the whim of the seasons and will have to wait until the sun starts to go down in fall for it to flower and then to harvest.

When should you grow marijuana?

If you’re growing outdoors in the Northern Hemisphere, growers usually get their seeds between February and April, and you should start your seeds by the end of April. Some growers will start their seedlings inside in a more controlled environment because seedlings are more delicate, and then put their seeds in the ground outside once they’re a little bigger. If you’re growing clones or autoflowers, you have a grace period of another month or so. Plants usually need to be outside, in the ground, by the end of June.

Harvest happens sometime between September and November. This depends on your local climate, as well as the weather that particular year—one year it could be the end of September, the next, end of October, and growers in the Pacific Northwest will have to pull down their crops earlier than those in Northern California.

If you’re growing weed indoors, you can grow whenever you like. Keep in mind that the outside environment will affect your grow space—you may need to add heaters in the winter or fans and ACs in the summer. Other than that, you can start seeds whenever you like and flip them into flower whenever you like, depending on how big you want the plants.

Important dates for growing marijuana outdoors

The Spring Equinox is a good reminder that it’s time to kick off the outdoor growing process and start germinating your seeds.

As the sun reaches up high in the sky, your cannabis will want to as well. Make sure all of your plants are outside by the Summer Solstice.

The weather will start to turn and the sun will begin descending in the sky as your plants fatten up with sweet, sticky buds. It might be tempting, but wait until around the Fall Equinox to start harvesting.

Everything should be cleaned up, dried, and curing well before the Winter Solstice. Now’s a good time to make your own cannabutter, topicals, or tinctures with all that trim from the harvest. Kick your feet up, relax, and hunker down for the cold, it’s been a long growing season!

Notes on marijuana growth phases

We can’t stress enough that the timeframes in the above graphic are ranges of time for the Northern Hemisphere. You’ll need to adjust them based on your specific region and local weather and climate.

Be sure to keep a grow journal to track the progress of your plants. Looking back on your notes will help you learn from mistakes and maximize the quality and quantity of your buds.

Take meticulous notes on when and how you perform each step, as well as what the weather is like. Other notes can include how much water you give plants, at what intervals, and how much nutrients you give them. Pictures will also give you a better sense of how your plants look along the way.

What are a weed plant’s growth stages?

The growth stages of marijuana can be broken down into four primary stages from seed to harvest:

  • Germination (3-10 days)
  • Seedling (2-3 weeks)
  • Vegetative (3-16 weeks)
  • Flowering (8-11 weeks)

Seed germination

Seed germination length: 3-10 days

Marijuana light cycle: 16 hours a day

The first marijuana plant stage begins with the seed. A cannabis seed should feel hard and dry, and be light- to dark-brown in color. An undeveloped seed is generally squishy and green or white in color and likely won’t germinate.

Once your seed has germinated, or sprouted, it’s ready to be placed in a growing medium, like soil. The tap root will drive down while the stem of the seedling will grow upward.

Two rounded cotyledon leaves will grow out from the stem as the plant unfolds from the protective casing of the seed. These initial leaves are responsible for taking in sunlight needed for the plant to become healthy and stable.

As roots develop, the stalk will rise and you’ll begin to see the first iconic fan leaves grow, at which point your cannabis plant can be considered a seedling.

Seedling stage

Seedling stage length: 2-3 weeks

Marijuana light cycle: 16 hours a day

When your marijuana plant becomes a seedling, you’ll notice it developing more of the traditional cannabis fan leaves. As a sprout, the seed will initially produce leaves with only one ridged blade. Once new growth develops, the leaves will develop more blades (3, 5, 7, etc.). A mature cannabis plant will have between 5 or 7 blades per leaf, but some plants may have more.

Cannabis plants are considered seedlings until they begin to develop leaves with the full number of blades on new fan leaves. A healthy seedling should be a vibrant green color.

Be very careful to not overwater the plant in its seedling stage—its roots are so small, it doesn’t need much water to thrive.

At this stage, the plant is vulnerable to disease and mold. Keep its environment clean and monitor excess moisture. Be sure to give it plenty of light.

Even if growing outdoors, a lot of growers will start their seeds inside under an artificial light to help them through this delicate stage of marijuana growth.

If you buy a clone from a grower or breeder it will be a seedling, so you can skip the seed germination phase.

Vegetative stage

Vegetative stage length: 3-16 weeks

Marijuana light cycle: indoor—16 hours a day; outdoor—at least 8 hours of direct sunlight (“full sun”), plus several hours indirect sunlight

The vegetative stage of cannabis is where the plant’s growth truly takes off. At this point, you’ve transplanted your plant into a larger pot and the roots and foliage are developing rapidly. This is also the time to begin topping or training your plants.

Be mindful to increase your watering as the plant develops. When it’s young, your plant will need water close to the stalk, but as it grows the roots will also grow outward, so start watering further away from the stalk in the soil so roots can stretch out and absorb water more efficiently.

Vegetative plants appreciate healthy soil with nutrients. Feed them with a higher level of nitrogen at this stage.

If you need to determine the sex of your plants (to discard the males), they will start showing sex organs a few weeks into the veg stage. It’s imperative to separate males so they don’t pollinate the females.

Flowering stage

Flowering stage length: 8-11 weeks

Marijuana light cycle: 12 hours a day

The flowering stage is the final stage of growth for a cannabis plant. This is when plants start to develop resinous buds and your hard work will be realized. Most strains flower in 8-9 weeks, but some can take even longer, especially some sativas.

Outdoors, flowering occurs naturally when the plant receives less light each day as summer turns into fall. Indoor growers can trigger the flowering cycle by reducing the amount of light marijuana plants receive from 16 to 12 hours a day.

Within the flowering stage, there are three subphases:

  • Flower initiation (week 1-3): The plant will continue to grow and females will develop pre-flowers—pistils, or white hairs, will grow out, which are the beginnings of buds.
  • Mid-flowering (week 4-5): The plant itself will stop growing and buds will start fattening up.
  • Late flowering/ripening (week 6 and on): Trichome density will increase and plants will get very sticky; keep an eye on the color of the pistils to tell when to harvest.

There are a number of changes to consider once plants go from the vegetative stage to the flowering stage:

  • Don’t prune when plants are flowering stage, as it can upset their hormones
  • Plants should be trellised so buds will be supported as they develop
  • Consider giving plants bloom (phosphorus) nutrients

When do buds grow the most?

Buds typically grow the most toward the end of the flowering life cycle. You probably won’t notice much budding out at the beginning of the flowering stage, and it will slow down toward the end of the cycle, when buds become fully formed.

Once buds have reached full maturation, it’s time to harvest your marijuana.

Pat Goggins and Trevor Hennings contributed to this article.

Knowing where your cannabis plants are in their life cycle will dictate when to prune, train, and trellis your plants, and when to harvest. Learn more about marijuana growth stages today.

Best Light Schedule For Cannabis In The Vegetative Stage

The vegetative stage has the ability to prepare the plant to support the bud, while also making it grow more and more healthy. Failing to provide a good amount of light will result in an unhappy plant that will be more prone to diseases and bugs.

The proper amount of light in the vegetative stage has the ability to prepare the plant to support the bud, while also making it grow more and healthier.

1. What Is The Light Cycle In Vegetative Cannabis?

Light is extremely important for plants in the vegetative phase because it’s what they use to photosynthesize and grow sturdy and healthy, so if they get more light, the more and better they grow.

Generally, the most common light cycle for the vegetative stage is 18/6 (light/darkness) but it can be any combination of light and darkness (like 20/4, 19/5, 17/7) as long as they don’t get more than 12 hours of darkness per day as this will trigger flowering.

Have in mind that giving your plants less light will cause them to develop slower and if you’re not that experienced, you should follow the 18/6 light cycle and only give them more light (like 20/4) if you know your plant can take it.

Not always giving them more light is going to result in faster or more development and you can harm or really stress your plant by doing this, making them turn into hermaphrodites or showing other heat stress symptoms.

2. Light Cycle For Vegetative Cannabis Outdoors

Photoperiodic Plants

When growing outdoors, the light cycle will solely depend on the season you’re in. Each season has a different amount of light and darkness hours, and this will hugely influence when you can start growing your photoperiodic cannabis plants.

For example, in California, we have the following light cycles throughout the year:

Winter December (9/15) January (10/14) February (11/13)
Spring March (12/12 of light) April (13/11 of light) May (14/10)
Summer June (14:30/9:30) July (14/10) August (13/11)
Autumn September (12/12) October (11/13) November (10/14)

This means that when growing outdoor you have to know the amount of light and darkness you will receive in the next couple of months so your plant develops the way you want to.

Note: Have in mind the information above is exclusive to California, you should get information about how is it in your area. That information can easily be found on the internet.

Autoflowering Plants

On the other side, autoflowering plants do not have a vegetative stage and start flowering directly from seed, not depending on a light cycle to do so.

This means you can grow autoflowering strains outdoors all year long. Although the amount of light and other factors like humidity and temperature may have an influence on the development of your plant, they will definitely vegetate and develop properly outdoors at any given time, before flowering.

3. Light Cycle For Vegetative Cannabis Indoors

Photoperiodic Plants

As you may know, when growing indoors we are responsible for maintaining all the elements of the environment, in the beginning, it can be a little bit hard but when we get more experienced it can have various advantages.

Like we said above, photoperiodic cannabis depends solely on the amount of light and darkness to start flowering, which can be tricky for new growers outdoors but when growing indoors, we are in full control of everything, including the light cycle.

Unlike autoflowering cannabis, photoperiodic plants indoor can vegetate for a long time and will only flower when we change the light cycle.

This allows us to vegetate our plants as long as we want and then flip them to the flowering stage when we have met our goals in the vegetative phase.

Autoflowering Plants

Autoflowering cannabis will flower independently of the amount of darkness they get. Obviously, giving them too little light like a 5/19 light cycle will make them seriously underdevelop but they will flower either less.

More experienced growers can experiment with different light cycles, some growers even saying they got the best results by giving their autoflowers 24hs of uninterrupted light. We encourage you to experiment also, but be aware that too much or too little light may stress your plants.

Different light cycles with autoflowering cannabis are also used to save electricity, by giving your plant a little bit less of light (like a 16/8) it will sum up to an important amount at the end of each cycle.

Even though it can affect the yield, removing only 2hs of light per day shouldn’t make a big difference on the plant and can save you a couple of bucks.

If you are still new to growing cannabis and want to guarantee your harvest, start with an 18/6 light cycle, and after you get a little bit of experience, it will be easier to read your plant’s signs and you can start experimenting with other light cycles.

4. In Conclusion

The vegetative stage of cannabis is super important. In this stage cannabis is building up strength to be able to support all the buds in the flowering stage. There’s nothing as the best light cycle for the vegetative stage, the light cycle will depend on a lot of factors that are individual to each grow room.

It is crucial that you give the amount of light and nutrients it needs so she can develop properly and be ready for the next stage.

Even though it mostly depends on genetics, the amount of light your plant will be able to receive is a decisive factor in the amount and quality of flowers it will produce.

If you don’t know which one to follow, we recommend providing a 18/6 light cycle for your cannabis plants in the vegetative stage as this cycle has been proved by a lot of growers to work really well, allowing the plant to develop properly.

The vegetative stage has the ability to prepare the plant to support the bud, while also making it grow more and more healthy. Failing to provide a good amount