Understanding The Life Cycle Of Marijuana Plants

Close up shot of cannabis plants growing indoors
December 18, 2020

Marijuana plants, like all living creatures, go through a series of changes throughout their life cycle. For you to get what you want – potent, aromatic buds, and massive yields – you have to give them what they need. That means providing the best environmental conditions throughout the different growth stages.

The nutritional requirements and optimal environmental conditions are not the same across the different growth stages. Hence, understanding what the needs are in each stage is of utmost importance. By doing so, you can coax the most out of them during the developmental and blooming phases.

Each stage requires different types of light, nutrient mix and ratio, and amount of water. Temperature and humidity also play a significant role in the plants’ overall health. If you take the time to understand these factors and provide them, your efforts will be more than adequately compensated by happy and productive plants.

What Are the Different Growth Stages of Marijuana?

The life of cannabis starts as a seed and ends as a flower. It is a monocarpic plant, which means it dies after flowering. Unless you are using plant cuttings, you must start from a new batch of seeds every time. From there on, a seedling emerges and progresses to vegging before maturing into a full-grown, budding plant.

1. Seed

The first stage of the marijuana plant’s life cycle begins with the seed. Although it may not look like it’s alive, inside is a miniature plant with a root, a stem, and two leaves. That embryo has its nourishment supply, called the endosperm, which provides food to keep the little plant in a state of suspended animation within the seed’s husk.

Cannabis Seeds

The seeds will not sprout – not until exposure to water and heat. However, the shelf life of cannabis seeds is only about a year. After that, they have a lower chance of germinating, although some varietals still do.

The best place to keep your seeds is a dark place with a stable, cool temperature. A cellar or a refrigerator would be an ideal storage space. Just remember that a dry environment is crucial to preserving the seeds. Avoid using sealed plastic bags or airtight jars that could trap moisture. Otherwise, the seeds might grow moldy or sprout prematurely.

2. Germination

  • Duration: 3 to 10 days
  • Temperature: 21 to 32°C (70 to 90°F)
  • Humidity: 80 to 90%

When you are ready to start growing, take the seeds out of storage. Let them come to room temperature, especially if they have been chilling out in the fridge. Examine each one’s appearance. Viable marijuana seeds are light brown to dark brown in color, with a hard and dry texture. In contrast, squishy seeds with green or white color are considered “off” and probably won’t germinate.

There are two ways to germinate seeds. The first method is the one we all learned in school. Place the seeds on a damp paper towel and fold it up. The moisture should be enough to make the seeds pop.

Paper Towel Germination Method

Most growers prefer the second method, which entails placing the seeds in a cup of water. Let them soak for 10 to 12 hours, no longer than that. Initially, the seeds will float. But as they absorb water and become saturated, they will sink to the bottom of the glass.

The second technique allows you to identify viable seeds. You should discard floaters. Even if they do germinate, they will not grow as well as the sinkers. You will just end up wasting your time and money, and the results won’t be satisfying in the end.

After the seeds have popped, keep them on a damp towel between two dinner plates. They will need water and warm, humid air to continue germinating.

Keep in mind that each marijuana plant requires 1 square foot of space to grow and spread out. If your space is limited, you should only germinate the number of seeds that can fit in your grow room or garden.

3. Seedling

  • Duration: 2 to 3 weeks
  • Light schedule: 18 hours light, 6 hours dark
  • Temperature: 21 to 30°C (70 to 85°F)
  • Humidity: 75 to 85%

When the taproot emerges, it’s time to put the young plants in their growing medium – usually soil or coco. The taproot will push itself down, and two rounded cotyledon leaves will appear as a tiny stem unfolds from the seed.

Cotyledons are not the serrated leaves we associate with marijuana. They are baby leaves that are responsible for the initial intake of light that plants need to grow. Eventually, they will wither and fall off as the plants mature.

Cannabis Seedling

As more roots start to develop, the first ‘true’ leaves will emerge above the cotyledons. When this happens, the plants are officially in the seedling stage. They will grow between 4 and 8 fan-shaped leaves before entering the next phase.

Cannabis seedlings like warm, moist conditions. The best temperature for them is 21 to 30°C (70 to 85°F), with a relative humidity of 75 to 85%. They need 18 consecutive hours of light and 6 hours of darkness. However, the lights must not be too intense because the plants are still quite sensitive.

The best types of grow light to use during this period are compact fluorescent bulbs (CFL) or LEDs because they don’t emit plenty of heat. To check the temperature, place your hand under the lamps. Move them farther from the plants if it feels too hot, but not too far away. Your seedlings will grow thin and lanky if they have to try too hard to reach for the light.

Many growers recommend spraying your seedlings with water, instead of pouring water into the soil. The roots are still very delicate, and it’s easy to drown them with too much water. There is no need to add nutrients yet; the seedlings can get enough sustenance from the soil.

Your plants are more susceptible to disease and mold during this stage. Check for excess moisture and keep the surroundings clean to prevent problems from happening. You will know you have healthy seedlings by their bright green color.

4. Vegetative

  • Duration: 3 to 16 weeks
  • Light schedule: 18 hours light, 6 hours dark
  • Temperature: 21 to 26°C (70 to 80°F)
  • Humidity: 45 to 55%

The vegetative stage of marijuana is when your plants will exhibit explosive growth. Healthy plants can grow as much as 5 cm (2 inches) overnight! To control their size to a manageable height, you should top or train your plants during this period.

As the seedlings start vegging, you will notice roots beginning to poke out of the growing containers. That’s the signal to transplant them to their permanent homes. Be extra careful when you do this. Stressed or damaged roots could hinder growth.

As the plants’ roots expand, you should water them farther away from the central stalk. That allows the roots to stretch outward and absorb water and nutrients more efficiently. Give them water every other day, or more often, if the soil feels too dry. Ensure that you don’t overwater them so that the roots can still breathe.

Vegging Cannabis in Hydroponics

During the veg stage, your plants need plenty of nitrogen to develop thick foliage. Start giving them a nutrient mix that is high in nitrogen. You can buy fertilizers that are specially formulated for vegetating plants at a garden supply store or online.

Indoor growers know that this is the right time to switch to metal halide (MH) grow lights while maintaining the 18 hours on, 6 hours off schedule. MH lamps emit a bluish light that approximates the color spectrum of sunlight in the late spring/early summer months. That period is when marijuana’s vegging phase naturally occurs.

For vegetative plants, the ideal temperature range is 21 to 26°C (70 to 80°F). For indoor growers, the cooler end is for lights off (“night”), while the warmer end is for lights on or “daytime”. Don’t let the temperature dip more than 10 to 15° at night; otherwise, your plants might go into shock and decrease enzyme activity.

The humidity level should be lowered by 5% every week until it reaches 45 to 55%. If you observe wet spots on the leaves, the moisture level is still too high. To lower it, you can use a dehumidifier. Most of the time, though, a proper ventilation system is enough to do the job. You should also install an oscillating fan or two in the grow room, to promote air circulation. A fan also helps even out the temperature, preventing extreme hot or cold spots.

5. Pre-flowering

Pre-flowering is not a separate growth stage, per se. However, you should pay special attention to the plants during this period. That is when the plants begin to reveal their sex.

Marijuana plants can be male, female, or hermaphrodite. As a grower, your goal is to harvest resinous buds produced by females, whereas males are only useful if you want the plants to make seeds. Hermaphroditic plants, meaning they have both male and female reproductive organs, also produce seeds.

Depending on the marijuana strain you are growing, pre-flowering occurs around the fourth week of vegetation. Pre-flowers can be found between the fourth and sixth nodes. A node, by the way, is the area from which leaves and branches grow out of the stem.

Female pre-flowers look like white hairs (stigma) sticking out of a tiny green ball (calyx) – collectively, they are called pistils. These become the big, fat buds we are familiar with and contain the largest cannabinoid concentration.

Marijuana Pre-Flowering

On the other hand, male pre-flowers appear as little balls without hairs. The balls are actually pollen sacs and contain no THC or CBD. Males don’t produce any buds at all. Furthermore, they can “impregnate” the females with their pollen, so that the latter will produce more seeds and fewer buds.

The males may reveal themselves as early as 3 to 4 weeks from germination. When their pollen sacs open, they can scatter and pollinate plants within a 5km radius. It is imperative, therefore, that you isolate and dispose of them as you can identify them. The most practical method of identification is to check the pre-flowers.

You should also discard any hermaphroditic plants. Some hermies produce distinct pistils (female) and pollen sacs (male) within the same plant, while others grow banana-shaped sexual organs. Those “bananas” also contain pollen, and the females they pollinate end up producing hermaphrodite seeds, too. Just get rid of any plants that aren’t females, and save yourself from disappointment.

6. Flowering

  • Duration: 8 to 11 weeks
  • Light schedule: 12 hours light, 12 hours dark
  • Temperature: 18 to 26°C (65 to 80°F)
  • Humidity: 30 to 45%

Plants that were grown outdoors enter the flowering stage when the days grow shorter, at the onset of autumn. To simulate this indoors, change the light schedule to 12 hours on, 12 hours off. Growers who use high-intensity discharge (HID) lights can now turn on their high-pressure sodium (HPS) vapor lamps. They emit a pinkish-orange glow, which is particularly suited for the flowering stage.

Note: The 12-hour dark period must be uninterrupted! Even a small amount of light could make the plants revert to the vegetation stage, or become hermaphroditic. Check your grow room to make sure that light does not leak in from outside.

During week 1 to 3 of flowering, your plants will continue to stretch and double in size. That is something to consider if your grow space is small or has a low ceiling. From week 4 to 5, the plants stop growing and redirect their energy to fattening their buds. Towards the end of the flowering stage, the buds become smelly, dense, and sticky to the touch. That’s when you know harvest time is near.

Additionally, the plants’ pistils will signal that harvesting is imminent. They will darken and curl inwards. Shiny, fuzz-like trichomes will cover the pistils and the leaf surfaces. Those aromatic fibers are the source of the cannabinoids, terpenes, and flavonoids highly valued by marijuana cultivators and users.

Your plants will need lots of water and nutrients in the flowering period. However, you should shift from a high-nitrogen nutrient mix to one with more phosphorus at around the third week of flowering. During the sixth week, switch to a high-potassium fertilizer. Those additional minerals will help the buds harden and ripen.

Flowering Cannabis Plant

For best results, however, you should stop giving the plants any nutrients a week before harvesting. Flush them by giving them 6.5 pH plain water, so that the buds won’t pick up a bad flavor from the fertilizer.

Be mindful of humidity when your plants are flowering. You should gradually lower the humidity level by 5% every week until it hits 35 to 45%. In the last two weeks before harvesting, the ideal level is 30%. That low humidity prevents the growth of bud rot, mold, and powdery mildew, which can damage the flowers.

Finally, maintain the daytime temperature at a maximum of 26°C (80°F), and nighttime at 18°C (65°F).

How Long Is the Marijuana Plant’s Life Cycle, Really?

If the duration period of every growth stage seems vague, it’s because there are some variables involved. For example, marijuana plants grown outdoors are dependent on the sun and the seasons. Their natural life cycle starts in the spring and concludes before winter sets in. That could be as long as eight months.

Growers have more control indoors. You can prolong the vegetative stage as long as you want. When you’re ready, just trigger the flowering period by shortening the light schedule to 12 hours. From seed to flower, it will take 3 to 5 months.

The marijuana strain you are growing affects the life cycle’s length, too. Autoflowering strains begin to flower on their own after a short vegging period of only 2 to 4 weeks. They don’t have to wait for the light schedule to change. As a matter of fact, you can keep the lights on 24 hours a day. That helps them reach maturity in as little as three months.

Understand your Plants’ Needs throughout its Life Cycle

Marijuana cultivation can be a challenging but rewarding experience. Now that you have learned about the stages of the cannabis life cycle, you can plan and prepare your plants’ requirements in advance.

Each growth stage is different but equally important. By knowing what to expect, you can control the light, temperature, moisture level, and nutrients from seed to bud. Soon, you’ll be growing like a pro.