Cannabis (Cannabis sativa L.) is an annual plant, which means it grows from seed to ripe flower within one growing season. Each stage needs different light, feeding, temperature and humidity. If you know which stage your plant is in, you can make each change at the right time. Good timing protects your yield and your cannabinoid quality.
This guide groups the life cycle into four main stages: germination, vegetative growth, flowering and harvest. The overview table shows seedlings as a separate fifth step, because young seedlings need gentler care than older plants. Part 1 covers germination, seedlings and vegetative growth. It also compares photoperiod plants with autoflowers so you can choose seeds before you start. Part 2 covers flowering, harvest, drying and curing.
The life cycle at a glance
The full cycle depends on genetics, growing conditions and when you choose to harvest. Autoflowers are plants that start flowering at a certain age, whatever the day length. They finish in 8–12 weeks. Photoperiod plants start flowering only when the nights get long enough. They take 14–32 weeks.
Light schedules are written as hours of light / hours of dark. For example, 18/6 means 18 hours of light and 6 hours of darkness.
| Stage | Duration | Light schedule | What you see | What matters most |
|---|---|---|---|---|
| Germination | 2–10 days | 24/0 or darkness | First root appears, seed leaves open | Moist, warm 22–28 °C, no fertiliser |
| Seedling | 1–3 weeks | 18/6 | First true leaves with 1–3 fingers (leaflets) | Gentle light, little water |
| Vegetative | 3–16 weeks | 18/6 | Leaves with 5–7 fingers, strong branching | Plenty of nitrogen, training, strong light |
| Flowering | 7–12 weeks | 12/12 | White pistils (hair-like flower parts), buds forming | More phosphorus and potassium, less nitrogen, humidity control |
| Harvest | 1–2 weeks | — | Trichomes (tiny resin glands) turn cloudy or amber | Flush, cut, dry, cure |
Write the start date of each stage on the plant label or in a grow diary. After one run, you will know how long your own genetics and setup really take. You can then plan the next run from those dates instead of from the seed packet.
Germination
Germination starts when the seed soaks up water, a step called imbibition. The water triggers the embryo to make gibberellin, a plant hormone. Gibberellin switches on enzymes that break down the food stored in the seed. In cannabis seed, that food is mostly oil and protein, not starch. The embryo uses that energy to push out its first root, the radicle (taproot).
This stage decides whether you get a plant at all. If a seed does not sprout, you lose that plant and the money you paid for the seed. You can read more about this stage in the seed germination guide.
Conditions that work
- Temperature: 22–28 °C, best around 25 °C. Below 18 °C, seeds sprout slowly or die. Above 32 °C, the embryo can be damaged.
- Humidity: 70–90% RH (relative humidity, the amount of moisture in the air).
- Light: not needed while the seed takes up water. Once the seed leaves (cotyledons) open above the surface, give gentle light of 200–300 PPFD.
- pH (how acidic or alkaline the water is): 6.0–6.5 in soil, 5.5–6.0 in hydroponics.
PPFD (photosynthetic photon flux density) measures how much usable light reaches the leaves each second, in µmol/m²/s. You measure it with a PAR meter. If you do not have one, start from the light maker’s hanging-height chart. The topic on light spectrum and DLI explains the units.
Translator’s note: In the Thai hot season, a room without air conditioning often sits at 30–35 °C. That is close to the 32 °C limit, and a closed box near a window gets hotter. Swings can be large too: an air conditioner that turns off at night, or a power cut, can shift a small room by more than 10 °C. For the first two days, put a thermometer next to the seeds. If it reads above 28 °C, or the temperature jumps a lot between day and night, move the seeds to the steadiest indoor spot, out of direct sun and away from the air-conditioner outlet.
Germination methods compared
| Method | How to do it | Success rate | Strengths and weaknesses |
|---|---|---|---|
| Paper towel | Put seeds between 2 damp paper towels, seal in a plate or zip bag, keep dark and warm for 24–72 hours | 90–95% | Easy to check progress; the root can break when you move the seed |
| Water soak | Soak seeds in warm water for 24–48 hours until the root is 2–3 mm long, then plant | 85–90% | Fast; if soaked too long, the seed runs out of oxygen and dies |
| Direct in soil | Plant the seed 1–2 cm deep in moist soil and keep it warm | 80–85% | No root disturbance; moisture is harder to control |
| Jiffy pellet or rockwool | Put the seed in a Jiffy peat pellet or a rockwool cube soaked in water at pH 5.5–6.0 | 90–95% | Used by professional growers; you must control pH |
On your first run, use the paper towel or Jiffy method. With either one, you can see each seed’s progress and spot failures early.
Germination day by day
- Days 1–2: the seed takes up water and the shell softens.
- Days 2–4: the root appears and grows to 1–3 cm.
- Days 4–7: the stem pushes above the surface and the seed leaves open. The plant now starts photosynthesis, making its own food from light.
- Days 7–10: if a seed has not sprouted after 10 days, it is not viable. Replace it.
Write the start date on each seed’s tray or bag. You will then know exactly when day 10 arrives, and you will not lose time waiting on a dead seed.
Translator’s note: If many seeds from one packet fail under good conditions, the problem may be seed age or storage. Before you buy again, read the topics on vetting a Thai seed vendor and storing seeds and pollen.
Seedlings
The seedling stage lasts 1–3 weeks under 18/6 light. The plant grows its first true leaves, with 1–3 fingers each. The roots are still small and easy to damage. Keep three things gentle at this stage: light, water and fertiliser.
- Light: 200–300 PPFD, with the lamp about 30–45 cm above the plants. If the light is too far away or too weak, the seedling grows tall and thin and the stem stays weak.
- Water: water only when the top 3 cm of soil is dry. Too much water causes damping-off and root rot. Damping-off is a disease that rots the young stem at soil level until the seedling falls over.
- Fertiliser: give plain water with the correct pH for the first 2 weeks. Fertiliser given too early burns young roots (see nutrient burn).
Translator’s note: In the rainy season, soil in open or outdoor pots dries much more slowly. A fixed watering calendar can then drown the roots. Push a finger 3 cm into the soil before every watering, and water only when it feels dry at that depth.
Vegetative growth
The vegetative stage is when the plant grows fastest. It builds its roots, stems, branches and leaves. Under ideal conditions, a plant can grow 2–5 cm a day. For photoperiod plants, this stage lasts 3–16 weeks, and you decide when it ends. Autoflowers stay in it for 2–4 weeks and then switch to flowering on their own.
Light
Indoors, vegetative plants are usually given at least 18 hours of light a day, and 18/6 is the most common schedule.
- PPFD: 400–600 µmol/m²/s. Start seedlings at 200–300 and raise the light as the leaves fully develop.
- DLI: DLI (daily light integral) is the total light the plant receives over one day. In one Canadian study, vegetative plants got about 425 PPFD for 18 hours, a DLI of about 27.5 mol/m²/day (Rodriguez-Morrison et al., 2021).
Translator’s note: A mechanical timer stops during a power cut. When the power comes back, the timer is behind, so your lights now turn on and off at the wrong hours. After every outage, check the timer against the real clock, or use a digital timer with a battery backup. Outdoors, Thai days stay close to 12 hours all year. Photoperiod plants grown outside can therefore start flowering before they have grown much (see early flowering in southern Thailand).
Nutrients
In the vegetative stage, the plant needs nitrogen most. A good NPK ratio (nitrogen–phosphorus–potassium) is about 3-1-2. EC (electrical conductivity) shows how much dissolved fertiliser is in the water. A higher EC means a stronger mix.
| Nutrient | What it does | Deficiency signs | Recommended EC |
|---|---|---|---|
| Nitrogen (N) | Builds chlorophyll, amino acids and proteins | Lower leaves turn yellow, spreading upward | 1.0–1.6 mS/cm |
| Phosphorus (P) | Builds ATP (the cell’s energy carrier) and DNA; root growth | Purple or red leaves, weak roots | — |
| Potassium (K) | Controls water balance, enzymes and sugar transport | Brown leaf edges | — |
| Calcium (Ca) | Builds cell walls; needed for cell division | Brown spots and curled tips on new leaves | — |
| Magnesium (Mg) | Sits at the centre of the chlorophyll molecule | Older leaves yellow between the veins while the veins stay green | — |
If the lower leaves turn yellow, measure the pH and EC of your feed before you add more nitrogen. A wrong pH can block uptake even when enough nitrogen is in the pot. You can use the leaf diagnostic guide to read the other signs.
Shaping the plant (training)
Training means cutting or bending the plant so more branches get even light. There are two groups of methods. High-stress training (HST) cuts the plant, so it needs days to recover. Low-stress training (LST) only bends and ties the plant. See the guides to topping, FIM and mainlining and to LST and HST.
High-stress training
- Topping: wait until the plant has 5–6 nodes (the points on the stem where leaves and branches grow). Cut the main tip above node 4–5. This gives 2 new main tops. Allow 5–7 days for recovery.
- FIM: cut off 75–80% of the growing tip instead of all of it. This gives 3–4 new tops.
- Mainlining: top the plant twice to build 4–8 even branches.
Never use HST on autoflowers. Their vegetative stage is too short to recover. Use LST only.
Low-stress training
- Basic LST: bend the stems and branches and tie them down. The aim is a flat, even canopy (the top layer of leaves and buds).
- ScrOG (screen of green): fix a flat net above the plants and weave the branches through it. This spreads the canopy evenly. See SOG vs ScrOG.
- Defoliation: remove large fan leaves that shade the bud sites. Take off no more than 20–30% of the leaves at a time, and wait at least 1 week between sessions.
On your first run, choose one method only. Write down the date and how many days the plant took to recover. Next time, you can plan your training around those recovery days.
When to switch to flowering
Photoperiod plants: they start flowering when you change the light from 18/6 to 12/12. Switch when the plant reaches 50–60% of the final height you want. During the first 2–3 weeks of flowering, it will stretch by another 50–100%. For example, if your room allows plants of 120 cm at most, switch at about 60–72 cm.
Autoflowers: they switch on their own 3–5 weeks after germination. The sign is pre-flowers, which are small white pistils at the nodes.
Before you start a photoperiod run, measure the height you can use between the pot rim and the safe distance below the lamp. Halve that number. That is roughly when you should switch to 12/12.
Photoperiod or autoflower: comparing the timelines
| Feature | Photoperiod | Autoflower |
|---|---|---|
| Germination | 2–10 days | 2–10 days |
| Seedling | 1–3 weeks (18/6) | 1–2 weeks (20/4 or 18/6) |
| Vegetative | 3–16 weeks (18/6); you decide | 2–4 weeks; switches by age |
| Flowering | 7–12 weeks (12/12) | 5–8 weeks (20/4 or 18/6) |
| Total time | 14–32 weeks (3.5–8 months) | 8–12 weeks (2–3 months) |
| What starts flowering | You change the light to 12/12 | Plant age (gene from Cannabis ruderalis) |
| Average height | 60–200+ cm | 40–100 cm |
| Yield per plant | 100–500+ g indoors; 500–2,000+ g outdoors | 30–150 g indoors; 50–200 g outdoors |
| Can you take cuttings (clones)? | Yes; a cutting stays vegetative under 18/6 | Not practical; a cutting keeps the parent’s age and flowers on the parent’s schedule |
| Training | HST and LST: topping, FIM, mainlining | LST only; no time to recover from HST |
| Difficulty | Intermediate; you must manage the light schedule | Easy for beginners; fewer decisions |
| Suits | Professional indoor growers, traditional outdoor growing, breeding | Beginners, several harvests a year |
Translator’s note: Autoflowers do not respond to day length. Thailand’s near-12-hour days therefore do not push them into flowering early, which makes them simpler for outdoor runs. The cost is a smaller yield per plant. If you are unsure, grow a small trial batch of each type in the same season and compare the dates and dry weights.
Translator’s note: Clones only make sense with photoperiod plants. Buying clones from another farm is a common way to bring in mites, thrips, hop latent viroid (HLVd) or the wrong strain. HLVd is a tiny infectious agent that stunts plants and reduces resin. The safer path is to start from seed and keep your own mother plants. If you must bring in clones, keep them away from your main room. Inspect the undersides of their leaves under magnification before they go near your other plants.
Early-stage mistakes and how to fix them
| Stage | Mistake | What happens | Fix |
|---|---|---|---|
| Germination | Soaking seeds for more than 48 hours | The seed dies from lack of oxygen | Soak for 24–36 hours at most, then move it to a damp paper towel |
| Germination | Planting deeper than 3 cm | The seedling runs out of stored energy before it reaches the surface | Plant 1–2 cm deep in loose soil |
| Germination | Temperature swinging more than 10 °C in one day | The embryo is stressed and can die | Keep seeds in a spot with a steady temperature |
| Germination | Touching the root with bare hands | The root breaks and bacteria get in | Move the seed with clean tweezers or by lifting the towel |
| Seedling | Light too far away or too weak | Tall, thin, weak stems | 200–300 PPFD, lamp 30–45 cm above |
| Seedling | Overwatering, including just after transplanting | Damping-off, root rot | Water only when the top 3 cm of soil is dry |
| Seedling | Feeding too early | Fertiliser burns the young roots | Plain water with correct pH for the first 2 weeks |
| Vegetative | Nitrogen deficiency | Lower leaves turn yellow, growth slows | NPK about 3-1-2, EC 1.0–1.6 |
| Vegetative | Not adjusting pH | Nutrient lockout: the nutrients are there but the roots cannot take them up | pH 6.0–6.5 in soil, 5.5–6.0 in hydroponics |
| Vegetative | Topping autoflowers | Stunted growth, lower yield | LST only, no HST |
Print this table and keep it next to your plants for the first three weeks. Each time a problem appears, check the row for that stage first.
Thai rules that apply to this guide
This guide is for education and technical information only. It is not legal advice. If you grow outside Thailand, check the law where you live.
- Cannabis flower (ช่อดอกกัญชา) is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568. It was issued under the Thai Traditional Medicine Protection Act B.E. 2542 and has been in force since 26 June 2025.
- Flower may be sold only with a PT 33 (ภ.ท.33) prescription, for at most 30 days. Advertising and online sale of flower are prohibited.
- The Ministerial Regulation on Controlled Herbs (No. 2) B.E. 2569 has been in force since 30 April 2026. It tightens the licence criteria for cannabis flower.
- The Ministerial Regulation on Cannabis or Hemp Extracts B.E. 2569 has been in force since 26 April 2026. Licences for extracts above 0.2% THC go only to Thai juristic persons that are not “foreign” under the Foreign Business Act B.E. 2542, to state agencies and to the Thai Red Cross Society.
- Unlicensed research, export, sale or processing of a controlled herb carries up to 1 year in prison and/or a fine of up to 20,000 baht (Section 78). A licence can be suspended for up to 90 days per order (Section 52) or revoked (Section 54). After a revocation, you cannot get a new licence under the Act for two years.
- Cannabis products must stay within the THC limits set by current law. The topic on controlled herb vs Category 5 narcotic explains those limits and how samples are tested.
- The draft Cannabis Control Act is not law yet. The Cabinet approved the draft on 22 September 2026 and sent it to the House.
Before you plant, check which licence covers what you plan to do in Licensing and Compliance in Thailand. Read the original legal texts in Thai Cannabis Law and Compliance.
References
- Chandra, S., Lata, H., & ElSohly, M.A. (Eds.) (2017). Cannabis sativa L. – Botany and Biotechnology. Springer. doi:10.1007/978-3-319-54564-6
- Rodriguez-Morrison, V., Llewellyn, D., & Zheng, Y. (2021). Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science, 12, 646020.
- Bernstein, N., Gorelick, J., Zerahia, R., & Koch, S. (2019). Impact of N, P, K, and Humic Acid Supplementation on the Chemical Profile of Medical Cannabis (Cannabis sativa L). Frontiers in Plant Science, 10, 736.
- Jin, D., Jin, S., & Chen, J. (2019). Cannabis Indoor Growing Conditions, Management Practices, and Post-Harvest Treatment: A Review. American Journal of Plant Sciences, 10(6), 925–946.
- Backer, R., et al. (2019). Closing the yield gap for cannabis: A meta-analysis of factors determining cannabis yield. Frontiers in Plant Science, 10, 495.
- Caplan, D., Dixon, M., & Zheng, Y. (2019). Increasing Inflorescence Dry Weight and Cannabinoid Content in Medical Cannabis Using Controlled Drought Stress. HortScience, 54(5), 964–969.
- Saloner, A. & Bernstein, N. (2021). Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products, 167, 113516.
- Danziger, N. & Bernstein, N. (2021). Light matters: Effect of light spectra on cannabinoid profile and plant development of medical cannabis (Cannabis sativa L.). Industrial Crops and Products, 164, 113351.
- Stack, G.M., Toth, J.A., Carlson, C.H., et al. (2021). Season-long characterization of high-cannabinoid hemp (Cannabis sativa L.). GCB Bioenergy, 13(4), 546–561. doi:10.1111/gcbb.12793
- Eichhorn Bilodeau, S., Wu, B.-S., Rufyikiri, A.-S., MacPherson, S., & Lefsrud, M. (2019). An Update on Plant Photobiology and Implications for Cannabis Production. Frontiers in Plant Science, 10, 296.
Post your germination results, your stage dates or your questions below this topic. Please say whether you grow indoors or outdoors and which province you are in, because heat and rain change the answers.
Continued in Part 2: The Cannabis Life Cycle From Seed to Harvest: Flowering, Harvest, Drying and Curing (Part 2 of 2)