Cannabis Plant Stages and Light (2024)

Quick Overview of Cannabis Growing Stages with Grow Lights

A growing cannabis plant has four main stages/life cycles: Germination, Seedling, Vegetative, and Flowering. Growing cannabis from seed to a mature plant can take anywhere between three-eight months, depending on the strain.


Cannabis Seed Germination Stage

The germination stage takes three to ten days. Start with healthy seeds. These should be hard and dry and light brown to dark brown. If the seeds do not look like this, chances are they will not germinate. It is best to start the seeds indoors for the best germination outcome. During the germination stage, cannabis seeds must be kept in the dark in a warm, damp, and humid environment. The seeds must be checked often to verify they are moist but not drowning.
When starting seeds using no medium (soil, peat, or coco), it is time to transfer the germinated seed to a growing medium when the taproot appears. When a plant emerges from the medium, it is now the seedling stage.
When germinating in a medium at the first sign of a plant emerging, it has moved into the seedling stage.


Seedling Stage – Introduce Blue Spectrum LED Light

The seedling stage takes about two to three weeks. The cannabis plants are very fragile, and it is essential not to overwater them. The plants need at least sixteen hours of light during the seedling stage, but eighteen is best with six hours of darkness. During the seedling stage, the LED blue light spectrum is preferred. Moist soil, high humidity, and eighteen hours of the LED blue light spectrum will ensure the rapid growth of cannabis. The LED blue light encourages root and leaf development to stabilize the plant as it grows bigger. Once the first true leaves grow, a leaf with five to seven blades, the cannabis plant then moves into the vegetative stage.


Vegetative Stage – Reduce the Amount of Light

The vegetative stage is from three to sixteen weeks long. The cannabis plants need between sixteen and eighteen hours of LED blue grow light spectrum. The vegetative stage is where the cannabis plant does all the development. The plant stem grows thicker and taller, and its root system is established, preparing to bloom. The plant grows taller and produces leaves and branches. During this time, the plants need more water and airflow. It is vital to allow the plants to dry out between watering to keep mold and mildew away and ensure they are not drowning. Giving the cannabis plants a substantial time in the vegetative stage will produce bigger plants and probably higher yields. Lighting is the key to encouraging cannabis plants to move into the flowering stage. Change the LED grow lights to twelve hours on and twelve hours a day off. This lighting change will trigger the plants to produce flowers.


Flowering Stage – Time for the Red Spectrum from your Grow Light

The flowering stage is from eight to eleven weeks long. During the flowering stage, the LED red grow light spectrum encourages flowering and the development of THC (the main active ingredient for a “high” in cannabis). Continued use of the twelve-hour LED red grow light schedule will produce the best results of THC. The flowering stage has three subcategories.

  1. First is flowering initiation, which can be from one to three weeks. The female cannabis plant pistils start to produce “white hairs” in this stage. By the end of the third week, buds will appear in clusters on the female plants.
  2. Second is the mid-flowering time which takes four to five weeks is where the buds fatten, the pistils begin to darken, and aromatic properties form.
  3. The third is the flowering/ripening of the buds, which takes six weeks or more. The buds grow trichomes that produce the resin containing cannabinoids, flavonoids, THC, and terpenes. These trichomes change color from clear/transparent to amber. When the trichomes turn a shade of amber is one indicator that the cannabis is ready for harvest.
Cannabis Plant Stages and Light (2024)

FAQs

Cannabis Plant Stages and Light? ›

During the vegetative stage, cannabis plants often thrive on an 18/6 light cycle (18 hours of light and 6 hours of darkness). Once the flowering stage is initiated, a 12/12 light cycle is common. This darkness is essential for the plant's metabolic processes, allowing it to rest, respire, and manage energy.

What is the light schedule for cannabis stages? ›

In general, it is recommended to use at least an 18/6 light schedule during the vegetative stage and switch to a 12/12 cycle during the flowering stage. However, growers can adjust the light cycle as long as plants receive more than 12 hours of light per day.

When to switch to 12 12 light cycle? ›

Height of plant: Depending on the strain, plants will generally double in size during flowering. So, if 'room' height is limited, the switch to 12/12 will need to be done no later than when the plant has reached 50% of the 'available' height (remember to consider the minimum gap distance between lamp and foliage).

How high should light be in vegetative stage cannabis? ›

Consider the cannabis plant's growth stage:

During the vegetative stage, the LED grow light can be placed further away from the plant, around 18-24 inches. During the flowering stage, the light should be closer, around 12-18 inches.

What are the 4 stages of a cannabis plant? ›

Growing cannabis can seem easier when the process is broken down into the 4 main cannabis growth stages. These are the cannabis seed germination, seedling, veg and bloom. At each stage the requirements for nutrients, light and water will vary.

When to flip lights to flower? ›

In controlled environments like indoor grows, manipulating the light cycle to 12 hours of light and 12 hours of darkness initiates flowering in photoperiod plants. In nature, cannabis plants begin to produce flowers once the daylight hours drop below 12.

Should grow lights be turned off at night? ›

A: In general, you should not leave grow lights on 24/7. Plants need a light-dark cycle to develop properly. It's believed that they truly do “rest” during periods of darkness, and probably use this time to move nutrients into their extremities while taking a break from growing.

What are the best hours for grow lights? ›

How Many Hours Should Grow Lights Be On? Illuminate interior plants for 12-14 hours a day. Seedlings grow best when supplied with light around the clock.

What to do the last 2 weeks of flowering? ›

Here's What You Can Expect During Those Last 2 Weeks of Flowering
  • To Flush or not To Flush? ...
  • Prune Those Leaves. ...
  • Drop the Humidity. ...
  • Drop the Humidity Even More in the Last 2 or 2 1/2 days. ...
  • Drop the Light Hours, Too. ...
  • Stop the Nutrients. ...
  • Crank Up the Sugar (Molasses) ...
  • Know When to Harvest.
Sep 18, 2020

How much light is too much for cannabis plants? ›

Is 24 Hours of Light Too Much for Cannabis? Continual light exposure can stress the plants and hinder growth. Most growers recommend a light cycle of 18 hours of light followed by 6 hours of darkness during the vegetative phase.

What is the best light for cannabis flowering stage? ›

Go with a full-spectrum LED panel with an actual wattage of 300 to 600 watts (our recommendation). It won't be cheap, but you'll save money in the long run and avoid a lot of headaches with heat. Supplement the LED with blue-spectrum fluorescent bulbs, or equivalent LED bars, hung vertically next to the plant(s).

How close should cannabis seedlings be to light? ›

Seedling Stage

For marijuana seedlings, LED grow lights should be between 24-36 inches above the plant canopy (a plant canopy is: the tallest branches of foliage of your marijuana plants). Seedlings are delicate, and placing lighting closer can cause bleaching or stunted growth.

Can I cut a bud off my plant? ›

Yes, you can harvest one bud at a time when it is ready to harvest, especially if you have a staggered harvest due to different maturation rates among your cannabis plants. Just be sure to use clean, sharp scissors or pruning shears to avoid damaging the surrounding plant material.

What stage does cannabis grow the most? ›

Once a male plant has been identified, it is generally destroyed by the grower. There is no medicinal value during the germination period. The vegetative phase of cannabis development exhibits the greatest increase in biomass and total growth.

At what stage do cannabis plants stop growing? ›

After about 3 weeks of flowering, their verticle growth will significantly slow and they will put a lot more energy into growing buds. They will still continue to grow usually a very small amount for another week or two before they completely stop growing in height.

What is the ideal PPFD for cannabis stages? ›

PPFD for Weed

For regular weed growing, the PPFD for seedling stage is 100-300 µMol/m2/S; the PPFD for vegetation stage is 400-600 µMol/m2/S, and the PPFD for flowering stage is 800-1,000 µMol/m2/S.

What is the best light cycle for cannabis seeds? ›

The plants need at least sixteen hours of light during the seedling stage, but eighteen is best with six hours of darkness. During the seedling stage, the LED blue light spectrum is preferred. Moist soil, high humidity, and eighteen hours of the LED blue light spectrum will ensure the rapid growth of cannabis.

How long should grow lights be on for cannabis? ›

Keep marijuana plants under a minimum of 18 hours of growth light (also known as 18/6), when they are in the vegetative stage. On the other hand, if you're one of the growers who want their plant to get as big as it can, you can maintain it under 24-hour (24/0) indoor lighting.

What is the best light schedule for auto cannabis? ›

Many growers just leave their lights on 24 hours a day when growing autos, but that is not what we recommended. For the most part, a lighting schedule of either 18/6 or 20/4 will work great with any auto strain.

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