If you are reading this article, then you are part of the clan that chooses to grow their own herb, and we salute you. Welcome to the tribe.

In this series of articles, we are diving into the topic of cannabis light cycles.

The Different Stages of Cannabis Growth depend on the Light Cycle

You may have heard before that cannabis is a photoperiod plant. What that means is that there are multiple stages, or periods, of growth during the life cycle of the plant. With marijuana, there are two periods: The Vegetative Period and the Flowering Period.

The First Stage of growth is the Vegetative Period

The Vegetative Period is the first of the two periods of cannabis cultivation. During the vegetative stage, the plant is growing, but remains “immature.” We refer to it as immature because it has yet to develop flowers or buds, which occur later in its life cycle.

During this period of immaturity, the plant is very flexible and pliable, which makes this an opportune time for training.

The Second Stage of growth is the Flowering Period

The plant reaches maturity during the Flowering Stage. This is when the plant firms up, can no longer be trained, and begins to bloom.  It is during the flowering period that the plant produces fruit, otherwise known as the buds that we all love to smoke.

But what does this have to do with light cycles?

The Light Cycle is what Causes the Different Stages of Growth

The two photoperiods represent different phases of the plant growth. The early phase is where the flexible, immature plant is green and simply grows. And the later phase is where the plant matures, begins to express color, and produces fruit.

These two cycles are a reflection of the amount of light the plant is receiving. When growing indoors, it doesn’t matter if it is summer, spring, fall or winter outside. By manipulating the light cycles, you control how the plant grows and when it can be harvested for bud.

The Natural Light Cycles of Cannabis Outdoors

In nature, there is spring, summer, fall, and winter. You plant cannabis in the late spring time, right as you are getting close to summer. The days are long, as the sun rises early, and sets later and later.

As the sun sets later in the summer, the plant receives more light than darkness in a 24-hour period. This is what causes the plant to remain in a vegetative state. During this summer season, the plant will continue growing every week, but it will not bloom or produce bud.

It is not until the sun starts setting earlier and earlier that the plant begins to mature and develop flowering sites for bud production.

By autumn, the days are finally equal to the nights, and the amount of sunlight starts to diminish until there is more darkness than light in a 24-hour period. During this period, the plants develop their bud sites. As the nights get longer, the plants develop evermore, with greater color expression and maturity of the flowers.

Using the Right Equipment to Control your Cannabis Light Cycles 

When growing indoors, you do not need to rely on the seasons or the rotation of the sun. You simply need a set of lights and a controller to switch them on and off.

After you have sprouted your plant from seed, you are ready to enter the vegetative stage. You should transplant your seedling into a small pot, and place it under your lights.

For veg, you do not need the same high-powered lights you need for flower. Low watt LED’s or T5 lights will work just fine.

Controlling the Light Cycle for the Vegetative Stage

You will want to keep the lights on for 18 hours, and off for 6 hours, per 24-hour period. This will ensure the plants remain in a vegetative state, and continue to grow without blooming. You will need a controller/timer that will turn the lights off after 18 hours, and kick them back on six hours later.

Some lights come with a timer/controller, but others do not. There are many aftermarket controls that can be purchased. But you can definitely purchase a light with controls included.

Controlling the Light Cycle for the Flowering Stage

When you are ready to start flowering your plant, you will need to change both the light cycle and the type of lights you are using. The flowering light cycle is 12/12, meaning the lights on are for twelve hours and off for twelve hours.

For maximum yield and quality, you will want a 1,000 watt HPS light or equivalent LED. Beware that many LED’s are not near the wattage of the HPS lights. The less photons of light, the less photosynthesis, and the lesser the bud development.

We recommend a High Pressure Sodium light, or an equivalent LED light that produces close to 1,000 watts or at least close to that.

Now, HPS lights can also be dialed back, sometimes to 600 or 400 watts, which makes them suitable for vegging plants. If you want to use the same light for both cycles, you can use an HPS light, set at the lowest wattage for 18/6.

When it comes time to flower the plants, switch the light cycle to 12/12, and increase the wattage. You can go straight to 1,000 watts right away, or you can slowly increase the watts week by week. For example, 600 watts in Week 1, 800 watts in Week 2, then 900 watts in Week 3 before finally bumping up to 1,000 watts.

If you light has more power, don’t be afraid to use it. Our HPS lights increase to 1,100 watts.

The Light Cycle is the thing that makes your marijuana plant produce bud

As you can see, the light cycle is everything. It is the one thing that makes your plant produce smokeable herb.

Use the vegetative light cycle — 18 hours on, 6 hours off — to grow your plant to the proper height and size. When you are ready, switch to the 12/12 light cycle to begin the flowering phase.

Your plant will double or triple in height during the first three weeks of the 12/12 light cycle, so be ready for some explosive growth.

If you want help on knowing when to make the switch from the veg light cycle to the flowering light cycle, check out this article on transitioning from veg to flower.


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