Cannabis Light

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. In order to reach a successful harvest day, this article explains how much light your photoperiod cannabis plants need to grow and begin budding. Do auto-flowering strains exist?

  1. Vegetative – Seedling or clone leads to Vegetative Stage –
    Give 18-24 hours of light a day
  2. Flowering – Flowering (Budding) Stage leads to Harvest –
    Give 12 hours light & 12 hours dark each day

Are indoor growing plans in the works? If so, it’s critical that you comprehend the various cannabis plant light cycles. And the basis for success is imitating the natural light pattern that plants would be exposed to should they be growing outdoors.

The growth or vegetative phase is a crucial time since this is when the stems and leaves start to grow. It is during this stage, when cannabis plants don’t produce any flowers, that you need to control their shape and size. This is where the light cycle comes into play: the more light your plants receive, the better they’ll grow, which will result in better yields.

During the vegetative phase, it is advisable to provide the plants with at least 18 hours of light per day (this is also known as the 18/6 photoperiod). Cannabis plants don’t start developing flowers until they are exposed to 12 hours of uninterrupted darkness. If not, the plants will continue to grow in a vegetative state.

Your plants will continue to be in this vegetative stage as long as they receive a minimum of 13 hours of light every day. But if you’re a producer eager to grow your plants as large as possible, you can even expose them to indoor lighting for 24 hours (24/0). The majority of growers, however, typically choose an 18/6 indoor vegetative period that lasts 4–8 weeks (or roughly 60 days).

Seedling Or Clone

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


As soon as you’re prepared to begin growing, plant your seeds or clones! What are clones?


Before putting their plants outside, some outdoor growers give their plants a head start indoors.

Wait a few weeks after the spring equinox to plant your cannabis seeds outside if you’re growing it from seeds outdoors. This means that seeds are planted outside in the northern hemisphere before or after April and before or after October in the southern hemisphere.

Beginning cannabis growers should typically wait a few extra weeks than those starting with seeds. You might want to plant your cannabis clones outdoors in the late spring or early summer because they are more likely to flower early than seeds are. (What are clones?)

When putting your plants outside if you live in a cold climate, you must also wait until after the last frost. Temperatures below freezing will kill cannabis plants. It’s crucial to choose the right strain. In comparison to other strains, some flower earlier. To ensure that plants are ready for harvest before temperatures drop, it’s crucial for outdoor growers in cold climates to grow a strain that is compatible with the local climate.

Vegetative Stage

One of the most crucial phases of your cannabis plant’s life is the vegetative stage.

The plant grows during the vegetative stage. Cannabis plants expand and become taller when they are in veg, producing only stems and leaves. In the vegetative stage, growers can use straightforward training techniques to regulate the size and shape of their plants.

The plant does not produce any buds at all during the entire vegetative stage. Only stems and leaves are produced. Plants typically grow very quickly during the vegetative stage, especially under ideal conditions.

What causes marijuana to remain in its vegetative state?

The vegetative stage of the cannabis plant is maintained by short nights. As long as the plant receives short nights (less than 1s-12 hours, depending on the strain), you can keep a cannabis plant in the vegetative stage for practically ever.

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

Make sure your cannabis plants receive at least 13 hours of light every day, whether you’re growing indoors or outdoors, for them to stay in the vegetative stage. Your plant might begin blooming earlier than you intended if it experiences a few long nights.

When in the vegetative stage, the plant can get up to 24 hours of light every day. In order to promote quicker vegetative growth, many indoor growers use light schedules that range from 18 to 24 hours per day (18-6 or 24-0).

Want to avoid worrying about light schedules? Cannabis strains that automatically flower in about three months, regardless of the light schedule given, are available for growers who don’t want to pay attention to light schedules. Compared to a conventional (photoperiod) strain, an auto-flowering strain may be easier to grow for some cultivators.


The majority of indoor growers use 18 to 24 hours of light per day (18-6 or 24-0 light schedules). Giving your cannabis plants more light each day during the flowering stage will promote quicker growth.

Lingo: The 18/6 light schedule is used when a grower gives their plants 18 hours of light per day and 6 hours of darkness. This is known as the 24-0 light schedule and lasts for 24 hours each day.


Your plant will naturally remain in the vegetative stage from late spring to late summer as long as it receives enough light each day. Each variety varies slightly.

Flowering Stage

When plants receive at least 12 hours of nighttime darkness without interruption, cannabis plants begin to bloom. Plants that have begun to bloom must continue to experience long, dark nights until harvest, or they risk returning to the vegetative stage.


The majority of growers indoors put their plants on a 12-12 schedule to start flowering. When the nights are getting longer and the onset of winter is near, the plant will begin to naturally bloom outside in late summer. Just be sure to protect plants from light when they’re in the dark!

What exactly is 12-12 Lighting?

By altering the light schedule so that the plant only receives 12 hours of light per day and 12 hours of uninterrupted darkness, the indoor grower will need to artificially induce flowering or budding in plants.

It usually takes another 6 weeks to 5 months (on average 2.5 months) for the plant’s buds to be mature enough to be harvested after switching to the flowering (12/12) light schedule.


Outdoor growers wait until their cannabis plants naturally begin to flower on their own, typically after mid-summer when days begin to get shorter than 12 hours.

It’s crucial to ensure that plants aren’t exposed to light at night during their dark period, not even from spotlights or street lights, as this can interfere with the way cannabis plants flower.

Therefore, indoor growers have the option to let their plants flower whenever they please. When is the ideal time to begin flowering your cannabis indoors?

In actuality, it comes down to personal preference and what kind of outcome you’re after. 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 believe that if a marijuana plant is not given at least 60 days in the vegetative stage to mature before it is switched over to the flowering stage, it will not produce enough resin or as many buds as a plant that has been grown from seed would. Contrary to popular belief, many growers start the flowering process as soon as a seed germination, which helps to maintain compact, short plants. This is often called “12-12 from seed.” Just keep in mind that no matter what you do, a young cannabis plant won’t begin flowering until it is 2–3 weeks old. A seed won’t begin to properly bloom for about 3 weeks, even if you start out by putting it on a 12-12 schedule. Age is not a concern when growing cannabis from clones, and once your clone has developed roots, growers can move right on to flowering. This is due to the fact that a clone is still a “mature” plant even though it may be small because it was created from a mature plant’s tissue. For the first few weeks, plants grown from seed typically grow much more slowly than rooted clones do. In any case, changing your light schedule at the time that best suits your needs is not particularly affected by your age.

Height: As a general rule, once you switch over to a 12/12 light schedule, your marijuana plant will grow by a factor of two to three during the flowering stage. As a general rule, switch your light schedule to flowering when your plants have grown to half their final desired height. Some plants will grow more, some less. Bending, known as “LST” or “low stress training” can be used to control colas that get too tall. Simply bend excessively tall colas downward and away from the plant’s center. Some growers will even slightly break or “supercrop” branches to get them to bend at a 90 degree angle. Height may be the main issue for those who are growing in a small area. A short, bushy weed plant can be grown using a variety of methods, or you can basically train your cannabis plant to take any shape you like.

If height and space are not a problem, you should ideally let your cannabis plant vegetate for at least 60 days before transitioning it to flowering. This gives your plant plenty of time to mature (resulting in larger yields) and enables novice growers to fine-tune their setup before plants reach the delicate flowering stage. Problems are much more serious in the flowering stage, where mistakes can severely reduce your final yields. Problems are much easier to recover from in the vegetative stage.

You will get the best final yields if you give cannabis plants more time during the vegetative stage and spend time training them to fit your space. If you don’t have enough room, it’s better to switch when the plant is half the height you want it to be, or even try to flower your cannabis plant from seed.

Cannabis Light

Which Type of Lighting Do I Need to Use?

What is the best light spectrum for your plants? is the first thing you should research before choosing a lamp. In order to recreate what happens in nature, cannabis plants basically need a blue light spectrum during growth and a red light spectrum during blooming. They are unaffected by the green spectrum, so if you want to use light in your grow that doesn’t change the photoperiod (for example, if you need to work in your grow while the plants are supposed to be in the dark), this type of lamp is best for you.

HID (high-intensity discharge) lamps are one of the most commonly used in indoor cannabis growing. There are two main types within this category: MH (metal-halide) and HPS (high-pressure sodium) lamps.

The difference between these two types of lamps is that MH provide a cold, blueish light, whereas HPS lamps are reddish and therefore warmer. This is why MH lighting is recommended for the vegetative phase, and HPS is better suited to the flowering phase. If you can only choose a type of lighting, best to use HPS with dual spectrum for both phases of growth.

HPS lamps are renowned for their high performance, but they generate a lot of heat, so you might need to install a ventilation system to help with this. In addition, all HID lamps deteriorate over time. HM lights degrade more quickly than HPS, but both need to be replaced after several harvests. Most reputed brands (Philips, Lumatek, Osram, and Sylvania) offer models adapted to each stage of growth, but they also include mixed types, which are dual spectrum HPS lamps that are valid for both the vegetative and the flowering periods.

LEC Lighting, the Next Frontier

LEC or CMH (An improved version of sodium lamps is ceramic metal halide. Nowadays LECs are the lamps that most closely resemble the spectrometry range produced by natural sunlight, which in turn translates into better results. Furthermore, LEC lamps also produce less heat.

Thanks to the great quality of the spectrum produced by LEC lighting systems, you can obtain better gram/watt ratios and greater production and preservation of terpenes.

Both the vegetative and flowering phases can be used with any of the LEC lamps currently available on the market. However, those with a colour temperature of 3100K are more appropriate for short-flowering cannabis. However, sativa-dominant or long-flowering strains respond better to CMH or LEC lamps with a color temperature of 4200K or higher.

And How About LEDs?

Due in part to their decreased electricity consumption and low heat emission, LED lamps have recently seen rapid growth. Although the initial cost is much higher, they ultimately save more energy and have longer working lives. You can use a full spectrum LED lamp for both the vegetative and the flowering phase, or you can get panels with different powers and spectrums that can be configured according to the different phases. Some LEDs even include infrared and UVB spectrums, which helps generate trichomes and thereby achieves a higher-quality cannabis.


It’s time to harvest your plants once the vegetative and flowering phases have passed.


How Long Should Veg Lights Be On?

18 hours

Cannabis plants begin to grow significantly during the vegetative light cycle. The plant will experience the majority of its vertical growth at this time, much like a teenager does. Lasting between 3 to 16 weeks, the vegetative stage requires full-spectrum light for 18 hours and 6 hours of darkness.

How Long Should You Flower Vs Veg?

In outdoor crops, the vegetative stage of cannabis plants may last up to 16 weeks, or even longer. Depending on the desired plant size, the majority of growers let their indoor plants vegetate for 4–8 weeks. The fourth week of the vegetative stage is typically when cannabis plants are able to begin flowering.

How Many Hours of Light Do Budding Need?


When you are ready for your cannabis plants to flower, a 12-hours of light and 12-hours of darkness schedule is standard.

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