The Life-Cycle of a Cannabis Plant Explained

Growing cannabis from seed to harvest may seem like an easy task. However, plants go through various stages during their life cycle. Each stage requires different temperatures, humidity levels, light intensities, and nutrients. In this article, I break down the different stages of a cannabis plant’s life cycle, the optimal conditions, and how to achieve the ultimate indoor harvest.

The Seedling Stage

The seedling stage lasts from the moment your cannabis seeds are germinated until the first 21 days of growth. During this time, the seedlings will focus on growing roots and their first set of leaves. Seedlings do not require a lot of light or nutrients during this stage and should be treated with extra care. They grow best under a light cycle of 18 to 20 hours of light per day.

Light intensity

• Cannabis plants can grow well under a low-powered LED or CFL light.
• A 250 – 400-watt high-pressure sodium or metal halide light will work well.

Nutrients

• Avoid using soils that contain too many nutrients to avoid burning the plants.
• Seedlings only require a mild amount of nutrients. Use 1-2 ml per litre.
• Using a high-nitrogen feed is best suited, and avoid anything high in P and K.

Temperature and humidity

• The temperature when the lights are on should be close to 75 degrees Fahrenheit.
• Humidity levels should remain between 65% and 75% relative humidity.

Plant training

• Avoid training cannabis seedlings to avoid stress and potentially killing them.
• Using a wooden stick and plant ties can help support tall and weak seedlings.

The Vegetation Stage

Once your seedlings have passed the 21-day mark, they will be ready to focus on growing roots, leaves, and side branches. When growing outdoors, the vegetation stage can last anywhere from 3 weeks to 15 weeks. It is during this stage that plant training techniques should be applied. Lights should be set to 18-20 hours during the vegetative stage.

Light intensity

• A 400w, 600w, or 1000w HID light will be well-suited for plants during this stage.
• The light distance from the plants should be between 60 cm and 120 cm.

Nutrients

• Cannabis plants prefer a higher level of Nitrogen and lower amounts of P and K.
• Increase the nutrient solution to 3 – 5 ml per litre, depending on how big they grow.

Temperature and humidity

• Aim for a consistent temperature of around 75°f for best results.
• Increase the temperature range from 75°f to 85°f if supplementing with carbon dioxide.
• Humidity levels during the vegetative stage should range from 65% to 80%.

Plant training

• Topping, fimming, super cropping, and lollipopping should be done during this stage.
• Always allow your plants plenty of time to recover and heal between plant training.
• Taking clones during the vegetative stage is advised, and the best clones will be produced.

The Transition Stage

This stage is when you change your timers to 12 hours on and 12 hours off to induce flowering. The transition stage lasts 21 days and is when your plants will start to stretch. Most photoperiod cannabis plants stop stretching after around 4-5 weeks. After that point, most of the growth happens on the buds, according to Dutch Passion.

Light intensity

• Plants prefer intense lighting, and using a 600-1000w HID light is recommended.
• Avoid using low-powered lights such as 400-watt HID and compact fluorescent lights.

Nutrients

• Using nutrients from the vegetation stage is recommended during the transition stage.
• You can increase your nutrient solution to 5 ml per liter and feed daily.

Temperature and humidity

• The temperature during this stage can range between 72 and 75 degrees Fahrenheit.
• Humidity levels should be lower during this stage, ranging between 55% and 60%.

Plant training

• Pruning and defoliation are best done during weeks 1 and 2 of the transition stage.
• Avoid high-stress techniques such as topping and super cropping.
• Taking clones during the transition stage is best advised during the first weeks.

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The Flowering Stage

Cannabis plants begin to show their sex and produce pre-flowers as early as 21 days. At this stage, use a nutrient solution higher in P and K and reduce the nitrogen levels. The flowering stage can last between 7 and 12 weeks, depending on the strain being grown.

Light intensity

• Plants need as much light as possible, so use a high-powered LED or 1000w HID light.
• The distance between the light and the plants should be between 60 and 75 cm.

Nutrients

• Plants can tolerate high EC levels during the flowering stage between 1.8 and 3.0
• Using P and K dominant nutrients, combined with a booster, is optimal during flowering.

Temperature and humidity

• The temperature should range between 72 and 75 degrees Fahrenheit.
• Humidity levels can be lowered to 40-50% relative humidity after week 6 of flowering.
• Check your plants for signs of mold and ensure good airflow around the buds.

Plant training

• Avoid any type of plant training once cannabis plants are producing flowers and buds.
• Stressed flowering plants will be sensitive to hermaphroditism and will produce seeds.
• Only take a clone from a flowering cannabis plant to save the genetic material.

My Final Thoughts

Having an understanding of what stage your cannabis plant is in while growing will give you an advantage. You can dial in the environment better, know which nutrients to use, the correct light intensity, and when to train them or take clones.

I always recommend using digital hygrometers and an EC pen to determine your nutrient solution’s exact temperature, humidity, and electrical conductivity (EC). Take extra care to avoid stressing seedlings, especially once your plants start producing buds. Good luck learning as much as you can about your plants and finding the perfect balance as an indoor grower!

Feature Photo: A cannabis plant in the flowering stage. Photo credit: Trichome Jungle Seeds.