The Cannabis Life Cycle

THE PLANT

From seed to harvest, an annual cannabis plant passes through four stages, germination, seedling, vegetative growth and flowering, and light is the switch between them. Knowing the stages explains why timing, and daylight, control everything a grower does.

Germination and seedling

A viable seed cracks open in warm, moist conditions and pushes out a root and its first pair of round seed-leaves (cotyledons). Over the next two to three weeks the seedling grows its first true, serrated leaves and establishes roots. It is fragile and needs gentle light and humidity.

Vegetative growth

With strong light (typically 18 hours a day indoors) the plant enters the vegetative stage: fast growth of stems, branches and fan leaves, building the frame that will later carry flowers. There are no flowers yet, and the plant is sexually immature.

Growers hold plants here as long as they want more size, then trigger flowering by changing the light.

Flowering

Cannabis is usually photoperiod-dependent: it starts flowering when nights get longer, which indoors means switching to about 12 hours of darkness. Autoflowering (ruderalis-derived) plants ignore this and flower by age.

Over roughly 7 to 12 weeks the female plant develops colas, the pistils mature, and the trichomes fill with resin. Harvest timing is judged by watching the trichomes.

The stages at a glance

Why the cycle matters

Every practical decision, when to train the plant, when to flip the lights, when to harvest, is a decision about where you are in this cycle. It also explains why an outdoor plant flowers in autumn as the days shorten.

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Photoperiodic Floral Induction, Meristem Architecture, and Trichome Maturation

Anatomical and developmental studies show that Cannabis sativa is a facultative short-day plant in which solitary floral primordia form at the nodes during vegetative growth, while terminal compound inflorescence branching is triggered when uninterrupted night length exceeds the cultivar's critical dark period (typically 10 to 12 hours) (Spitzer-Rimon et al., 2019, PubMed PMID 30949187). During the generative flowering phase, capitate-stalked glandular trichomes proliferate across the perigonal bracts and subtending sugar leaves, accumulating acidic cannabinoids (THCA and CBDA) and monoterpenes in their subcuticular storage cavities (Livingston et al., 2020, PubMed PMID 31696994). Photosynthetic capacity peaks during late vegetative and early floral development near leaf temperatures of 25 C to 30 C (Chandra et al., 2008, PubMed PMID 23572895).

Frequently Asked Questions

What triggers the transition from vegetative growth to flowering in photoperiod cannabis?

Short-day cannabis cultivars initiate compound inflorescence development when uninterrupted darkness exceeds their critical night length, which is managed indoors by switching the light timer to 12 hours of light and 12 hours of complete darkness.

How do autoflowering cultivars differ in their life cycle?

Autoflowering lines carry day-neutral genetics derived from Cannabis sativa subsp. ruderalis, so they transition from the vegetative stage into flowering based on chronological maturity (typically 3 to 4 weeks after germination) rather than night length.

What does trichome color change indicate at the end of flowering?

As capitate-stalked trichomes mature, their resin heads progress from clear (immature biosynthetically) to milky-opaque (peak THCA or CBDA concentration) and eventually to amber as THCA oxidizes toward cannabinol (CBN) precursors.