Weed is a flowering plant that produces its psychoactive and medicinal compounds naturally, but turning a cannabis seed into smokable bud involves a controlled growing process that typically takes 13 to 21 weeks from start to finish. The journey includes germination, weeks of careful vegetative growth, a flowering phase triggered by light changes, and a post-harvest drying and curing process that can make or break the final product.
How Cannabis Produces Its Active Compounds
Cannabis doesn’t simply “contain” THC or CBD. The plant builds these compounds through a chain of chemical reactions inside tiny, mushroom-shaped glands called trichomes, which coat the surface of the flowers. The process starts with a precursor molecule called CBGA, sometimes referred to as the “mother cannabinoid.” Specialized enzymes in the plant then convert CBGA into the acidic forms of the compounds you’ve heard of: THCA (which becomes THC) and CBDA (which becomes CBD).
These acidic forms don’t produce a high on their own. They only convert into their active versions, THC and CBD, when exposed to heat. That’s why cannabis is smoked, vaporized, or baked into edibles rather than eaten raw. This heat-driven conversion is called decarboxylation, and it’s a key step in making any cannabis product usable.
From Seed to Seedling
The process starts with germination, which takes 3 to 10 days. A viable seed cracks open and pushes out a tiny root called a radicle. Growers often start seeds in damp paper towels or small starter plugs to control moisture. Once the root emerges and the seed is planted, a pair of small, round embryonic leaves called cotyledons break through the soil and begin photosynthesis.
The seedling stage lasts another 2 to 3 weeks. During this time, the plant develops its first sets of true cannabis leaves, the familiar serrated, multi-fingered shape. Seedlings are fragile. They need gentle light, consistent moisture, and stable temperatures to survive. Most growers keep seedlings under 18 or more hours of light per day to fuel early growth.
Vegetative Growth: Building the Plant’s Frame
Once past the seedling phase, the plant enters a vegetative stage lasting anywhere from 2 to 8 weeks depending on the grower’s goals and the size they want the plant to reach. This is when cannabis grows rapidly, developing thick stems, broad fan leaves, and branching structure. The plant is essentially building the scaffolding that will later support heavy flowers.
During this phase, the plant needs high levels of nitrogen to fuel leaf and stem growth. Research on soilless cannabis production found optimal nitrogen concentrations around 160 mg per liter for conventional fertilizers, with potassium levels of at least 60 mg per liter needed to avoid deficiency symptoms. Phosphorus requirements are relatively modest during veg, with plants performing well at just 30 mg per liter.
Indoor growers keep lights on for 18 hours a day during this stage, mimicking long summer days. The more light energy the plant absorbs, the more biomass it builds. Some growers supplement with CO2 at 400 to 1,200 parts per million to push photosynthesis harder, though this only helps if light intensity is also high enough for the plant to use it.
Photoperiod vs. Autoflowering Genetics
Most cannabis varieties are photoperiod-sensitive, meaning they stay in vegetative growth as long as they receive long days and only begin flowering when light drops to roughly 12 hours per day. In nature, this happens as summer turns to fall. Indoor growers trigger it manually by switching their light timers.
Autoflowering varieties work differently. These strains carry genetics from Cannabis ruderalis, a subspecies that evolved in northern climates with unusual light cycles. Research from Aurora has identified the mechanism: a natural mutation in a gene called PRR37, which is part of the plant’s internal clock. This mutation disrupts the plant’s ability to track day length, causing it to begin flowering automatically 4 to 6 weeks after germination regardless of how much light it receives. Autoflowers are popular with beginners and outdoor growers in short-season climates because they simplify the process considerably.
The Flowering Stage
Flowering is where the plant shifts its energy from building structure to producing buds. This stage lasts 6 to 8 weeks for most varieties, though some can take longer. For photoperiod plants, it begins when indoor growers switch to a 12-hours-on, 12-hours-off light schedule.
Nutrient needs change during flowering. The plant demands more phosphorus and potassium to fuel bud development, while nitrogen needs decrease somewhat. Research published in Frontiers in Plant Science found that maximum flower yield occurred at roughly 194 mg per liter of nitrogen and 59 mg per liter of phosphorus. Potassium, interestingly, didn’t significantly affect yield within the tested range, though it remains essential for overall plant health.
As weeks pass, the flowers swell and become coated in trichomes. White hair-like structures called pistils darken and curl inward as the plant matures. CO2 supplementation during flowering, at levels of 800 to 1,500 ppm, can further boost bud production in well-lit indoor grows.
Knowing When to Harvest
Timing the harvest is one of the most important decisions a grower makes, and it comes down to examining trichomes under magnification. These tiny glands progress through three visual stages: clear, milky (cloudy), and amber. Clear trichomes mean the plant isn’t ready. According to cultivation expert Ed Rosenthal, peak cannabinoid maturity for most varieties occurs when 80 to 90% of trichomes are milky and 5 to 15% have turned amber. This window delivers maximum THC potency, fully developed terpene profiles, and balanced effects. Waiting too long shifts the chemical profile toward more sedating compounds.
Drying and Curing
Freshly harvested cannabis is roughly 75 to 80% water and needs to be dried slowly to preserve quality. The ideal drying environment sits at 65 to 70°F (18 to 21°C) with 50 to 55% relative humidity. Temperature shouldn’t fluctuate more than about 2°F and humidity no more than 3% throughout the process. Most growers hang whole branches or trimmed buds in a dark room with gentle air circulation for 7 to 14 days.
Rushing this step with fans blowing directly on the buds or higher temperatures destroys terpenes, the aromatic compounds responsible for cannabis’s smell and flavor. Some terpenes begin evaporating at temperatures as low as 70°F, with significant degradation starting around 100°F. Myrcene, the most common cannabis terpene, has a boiling point around 330°F, but partial evaporation begins well below that in an open-air environment.
Once the buds feel dry on the outside and stems snap rather than bend, typically at 8 to 10% moisture content, they’re placed in airtight glass jars for curing. Curing is a slow process, lasting at least two weeks and often longer, where residual moisture redistributes through the bud and remaining chlorophyll breaks down. Growers open the jars briefly each day (“burping”) to release excess humidity. Properly cured cannabis is smoother to smoke, more aromatic, and more potent than bud that was dried and sold immediately.
Concentrates and Extracts
Not all cannabis ends up as dried flower. A growing share of the market involves concentrates, which isolate the trichomes and their cannabinoids from the plant material. There are four broad categories of extraction.
- Dry methods like kief simply involve sifting trichome heads from the flower using fine screens. This is the simplest and oldest approach.
- Water-based methods use ice water to freeze trichomes and make them brittle enough to break off, then filter them through mesh bags of decreasing pore size. The result is ice water hash.
- Solventless heat and pressure is the basis for rosin, where cannabis flower or hash is compressed between heated plates at moderate temperatures. The heat and pressure squeeze out a sap-like concentrate rich in cannabinoids and terpenes. People initially made rosin with nothing more than a hair straightener and parchment paper, though dedicated rosin presses are now standard.
- Solvent-based methods use chemicals like butane or CO2 to dissolve cannabinoids out of the plant material. The solvent is then purged, leaving behind concentrated oil. These methods require professional equipment and carry safety risks if done improperly.
Testing and Quality Control
In legal markets, cannabis must pass laboratory testing before it reaches consumers. Labs screen for potency (THC and CBD percentages), terpene content, and a range of contaminants. Heavy metals are a particular concern because cannabis plants are efficient at absorbing metals from soil. State regulations set strict limits: Vermont, for example, caps arsenic at 0.2 ppm and lead at 0.5 ppm in flower, with mercury capped at the lowest level of 0.1 ppm.
Pesticide screening is equally rigorous. Labs test for dozens of compounds, with most restricted to 0.1 ppm or below. Even pesticides that are legal on food crops may be banned on cannabis because smoking or vaporizing can concentrate residues and deliver them directly to the lungs. Products that fail testing are pulled from shelves or destroyed, depending on the state’s regulations.