Generally speaking, it takes anywhere from 14-32 weeks, or about 4-8 months, to grow a weed plant. The biggest variability in how long a marijuana plant takes to grow will happen in the vegetative cycle—if you’re growing indoors, you can force it to flower after only a few weeks when it is small, or after several weeks when it is big. If you’re growing outdoors, you’re at the whim of the seasons and will have to wait until fall to harvest.
The plant will develop buds in the last 8-11 weeks. The life cycle of cannabis can be broken down into four primary stages from seed to harvest: Germination (5-10 days) Seedling (2-3 weeks) Vegetative (3-16 weeks) Flowering (8-11 weeks) How to grow marijuana indoors: a beginner’s guide. Seed germination (5-10 days) Light cycle: 18 hours of light. The first stage of life for a cannabis plant begins with the seed. At this point, your cannabis plant is dormant, patiently waiting for water to bring it to life. You can observe the quality of the seed by its color and texture. The seed should feel hard and dry, and be light- to dark-brown in color. An undeveloped seed is generally squishy and green or white in color and likely won’t germinate. To begin growing from a seed, learn more about germination here.
Once your seed has popped, it’s ready to be placed in its growing medium. The tap root will drive down while the stem of the seedling will grow upward. Two rounded cotyledon leaves will grow out from the stem as the plant unfolds from the protective casing of the seed. These initial leaves are responsible for taking in sunlight needed for the plant to become healthy and stable. As the roots develop, you will begin to see the first iconic fan leaves grow, at which point your cannabis plant can be considered a seedling. Seedling stage (2-3 weeks) Light cycle: 18 hours of light. When your plant becomes a seedling, you’ll notice it developing more of the traditional cannabis leaves. As a sprout, the seed will initially produce leaves with only one ridged blade. Once new growth develops, the leaves will develop more blades (1, 3, 5, 7, etc.). A mature cannabis plant will have between 5-7 blades per leaf, but some plants may have more. Cannabis plants are considered seedlings until they begin to develop leaves with the full number of blades on new fan leaves. A healthy seedling should be a vibrant green color. Be very careful to not overwater the plant in its seedling stage—its roots are so small, it doesn’t need much water to thrive. At this stage, the plant is vulnerable to disease and mold. Keep its environment clean and monitor excess moisture. Vegetative stage (3-16 weeks) Light cycle: 18 hours of light. The vegetative stage of cannabis is where the plant’s growth truly takes off. At this point, you’ve transplanted your plant into a larger pot, and the roots and foliage are developing rapidly. This is also the time to begin topping or training your plants. Spacing between the nodes should represent the type of cannabis you are growing. Indica plants tend to be short and dense, while sativas grow lanky and more open in foliage. Be mindful to increase your watering as the plant develops. When it’s young, your plant will need water close to the stalk, but as it grows the roots will also grow outward, so start watering further away from the stalk so the roots can stretch out and absorb water more efficiently. Vegetative plants appreciate healthy soil with nutrients. Feed them with a higher level of nitrogen at this stage. Flowering stage (8-11 weeks) Light cycle: 12 hours of light. The flowering stage is the final stage of growth for a cannabis plant.
Flowering occurs naturally when the plant receives less than 12 hours of light a day as the summer days shorten, or as the indoor light cycle is shortened. It is in this stage that resinous buds develop and your hard work will be realized. If you need to determine the sex of your plants (to discard the males), they will start showing their sex organs a couple weeks into the flowering stage. It’s imperative to separate the males so they don’t pollenate the flowering females. Differences in Growing Sativa, Indica and Hybrid Cannabis. There are a number of changes to consider once your plant goes from its vegetative stage to flowering: Your plants shouldn’t be pruned after three weeks into the flowering stage, as it can upset the hormones of the plant. Plants should be trellised so that buds will be supported as they develop. Buds typically grow the most toward the end of the flowering cycle, around week 6-7.
You probably won’t notice much budding out at the beginning of flower, and it will slow down toward the end of the cycle, when buds become fully formed.