This is the second half of a beginner’s guide to a first indoor cannabis grow. It covers the vegetative and flowering stages, harvest, drying and curing, and how to read the most common problems. It also covers the Thai rules, keeping a grow secure, and moving from seeds to clones. A short summary of what matters most comes at the end. Part 1 covered equipment, choosing seeds, germination, growing media, feeding, light and watering.
Translator’s note: Some targets in this part come from indoor growing in cooler climates, for example 23–25 °C in flowering and 15–21 °C for drying. In Thailand, rooms are often 30–35 °C, humidity is high in the rainy season and power cuts happen. The translator’s notes say what to do first when you cannot reach a target.
This is Part 2. Part 1: Your First Cannabis Grow: A Complete Beginner's Guide from Seed to Harvest
8. Vegetative stage
In the vegetative stage, the plant builds its structure of stems, branches and leaves. How you train the plant now decides the shape of the canopy (the top layer of leaves and buds). It also decides how many places buds can form. You can top the plant, which means cutting off the main growing tip so two shoots grow instead. You can use low-stress training (LST), which means bending and tying branches. Or you can let the plant grow naturally.
For a first grow, use low-stress training only. Tie the main stem down so the plant bends sideways. The side branches then grow upward and fill more of the canopy. Unlike topping, LST needs no recovery time, and you can undo it.
Give photoperiod plants 3–6 weeks of vegetative growth before you switch to 12/12. Autoflowers need no planned vegetative stage. Train them early, within 3 weeks from seed, and then let them flower on their own timetable.
Use soft, covered ties, and loosen them every few days as the stem gets thicker. This stops the ties from cutting into the stem.
9. Flowering
9.1 Early flowering (weeks 1–4)
In the first two weeks after the switch to 12/12, plants stretch upward fast. Keep training so no single branch shades the others. Follow your feeding schedule and move to a feed with less nitrogen and more phosphorus and potassium.
9.2 Mid flowering (weeks 4–7)
Buds grow fast now, and VPD becomes more important. VPD (vapour pressure deficit) describes how temperature and humidity together control how fast leaves lose water. From mid flowering until harvest, humidity above 65% creates ideal conditions for botrytis (bud rot), a grey mould that rots the buds. Aim for 45–55% relative humidity (RH) and a steady temperature of about 23–25 °C.
Check for pests every day. Spider mites and thrips breed faster in the warm, dry conditions of late flowering.
Translator’s note: In a Thai room at 30–35 °C, you need an air conditioner, and usually a dehumidifier, to reach 45–55% RH and 23–25 °C. If you cannot reach both, get humidity below 65% first, because bud rot risk rises above that level. This topic explains why one air conditioner can still leave a flowering room near 69%. If you can, plan your first grow so flowering falls in the cooler, drier months.
Translator’s note: Check the undersides of leaves with a loupe every day. If you need a pesticide, use only products registered with the Thai Department of Agriculture, and use them exactly as the label says. This topic explains what you may spray under Thai GACP (Good Agricultural and Collection Practice).
9.3 Final weeks and flushing
In the last 1–2 weeks before harvest, many growers give only plain water adjusted to the right pH. This is called flushing. The aim is to wash leftover fertiliser salts out of the medium. Research does not support it so far.
A 2025 trial tested two high-CBD varieties (Alden & Faust, 2025). Longer flushing lowered the weight of dried flower and the CBD yield per square metre. Flushing also lowered nitrogen, phosphorus and potassium in the flower, but the study did not test taste. No peer-reviewed study has yet shown that flushing improves taste or how cleanly the flower burns. So far, the evidence gives you no reason to plan a long flush for your first grow.
When to harvest: trichomes give the most reliable sign. Trichomes are the tiny resin glands on the buds, and they hold most of the cannabinoids. Look at their heads with a 30–60× jeweller’s loupe or a digital microscope.
- 10–20% amber heads: THC is at its peak, and a small part has started to turn into CBN.
- 20–40% amber heads: a later harvest, with more THC already turned into CBN. Growers choose this when the intended use needs a more sedating profile.
10. Harvest, drying and curing
10.1 Harvest
Cut the branches into pieces you can handle, 30–45 cm long. Remove the large fan leaves straight away. You can keep or remove the small sugar leaves around the buds. If you keep them, they hold more moisture around the bud and drying is slower. If you remove them, drying is faster.
Translator’s note: In humid Thai air, drying is more often too slow than too fast. Unless your drying space has air conditioning and a dehumidifier, removing the sugar leaves at harvest is usually safer.
10.2 Drying
Target conditions are 15–21 °C, 55–62% RH, darkness, and no fan blowing directly on the buds. Under these conditions, drying takes 10–14 days in total. Faster drying, from heat or low humidity, destroys terpenes (the aroma compounds) and makes a harsher, less aromatic product. Within reason, slower drying is better.
Translator’s note: Outdoor air in Thailand is often 85–95% humidity and above 30 °C. In that air, buds dry too slowly and mould can grow. Some moulds leave toxins on the flower. This topic explains the rainy-season risk. Five Thai drying setups are compared there with their costs. Before harvest day, run the hygrometer in your drying space for three days. If the space cannot stay below 62%, fix that first.
10.3 Curing
Put the dried buds into glass jars at 55–62% RH. Open the jars for 15–30 minutes to let fresh air in (“burping”):
- twice a day for the first 2 weeks
- once a day in weeks 3–4
- once a week after that, for at least 1–3 months.
Curing lets terpenes and cannabinoids keep developing, and it clearly improves flavour and smoothness.
Translator’s note: Burp the jars in an air-conditioned room. If you open a jar in a room at 85% humidity, moist air gets in, which is the opposite of what you want. Put a small hygrometer inside one jar to check that the buds stay at 55–62%.
11. Common first-grow problems
11.1 Yellowing leaves
Beginners notice yellow leaves more than any other symptom, and yellowing has more possible causes than any other. Find the pattern first (reading your leaves).
- Lower leaves turn yellow and fall off during flowering: this is normal ageing (senescence). The plant moves nitrogen from old leaves into the growing buds. You do not need to act unless the yellowing moves up the plant fast.
- New growth at the top turns yellow: the cause is usually pH-driven lockout of iron or zinc. It can also be a shortage of an element the plant cannot move from old leaves to new ones. Check and correct the pH first, before you add any trace-element supplement.
- Yellow between green veins: this is magnesium deficiency. It is most common with soft water, or in coco without enough cal-mag. A leaf spray of 1 g/L Epsom salt (magnesium sulphate) corrects it quickly.
- The whole plant is evenly pale yellow: this is nitrogen deficiency, which is most common in early to mid veg, or general underfeeding. Raise the EC of the feed.
Translator’s note: Buy magnesium sulphate sold as fertiliser, not bath salts with added perfume.
11.2 Brown leaf tips
Brown, crispy leaf tips are called nutrient burn. They mean the feed EC is too high for the roots the plant has now and for the amount of water it moves through its leaves. Lower the feed EC by 20–30% for two waterings and watch whether the plant recovers. Do not flush heavily. Heavy flushing swings the plant from too much fertiliser to too little and makes the problem last longer.
If brown tips appear only on the side closest to a hot lamp, the cause may be heat stress instead.
11.3 Drooping
- Leaves cupped upward and stems limp: heat stress. The plant has closed its leaf pores to save water. Lower the temperature or raise the light.
- Drooping while the pot is still heavy: overwatering. The medium holds too much water and the roots run short of air. They cannot take up water even though the medium is wet. Let the medium dry out more between waterings.
- Drooping while the pot is light: underwatering. Give more water each time or water more often.
11.4 Slow growth
In the first 3 weeks from seed, slow growth is usually a root problem, not a nutrient problem. Roots grow slowly in cold medium or in medium with poor airflow. Do not give more fertiliser. The roots are not big enough yet to take it up. Watch the root-zone temperature (aim for 20–24 °C) and avoid overwatering.
Translator’s note: In a Thai room, the root zone is more likely to be too warm than too cold. Push a probe thermometer about 5 cm into the medium and read it in the afternoon. If it is well above 24 °C, cool the room. Adding fertiliser will not fix it.
12. The law and responsible growing
12.1 Know the rules where you live
Cannabis laws differ greatly between countries, and they are changing across Southeast Asia. Vietnam and Cambodia keep strict prohibition. Philippine law sets specific penalties for cultivation. Growing without knowing the rules where you live carries serious legal risk. This guide gives growing information only. Check the legal position where you live before you start.
The original article says that Thailand allowed personal cultivation under certain conditions after it decriminalised cannabis in 2022. It also says that new restrictions on commercial flower followed in 2025–2026. This guide does not state the current conditions for growing cannabis at home for personal use in Thailand. Check them in the original legal texts before you start.
Translator’s note: The forum editors have checked these Thai rules against the original legal texts:
- Cannabis flower 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 (1999) and has been in force since 26 June 2025.
- Flower may be sold only with a PT 33 prescription, for a maximum of 30 days. Advertising flower and selling it online are prohibited. Do not offer flower on this forum or on social media.
- The Ministerial Regulation on Controlled Herbs (No. 2) B.E. 2569 came into force on 30 April 2026. It tightens the licence criteria for cannabis flower.
- The Ministerial Regulation on Cannabis or Hemp Extracts B.E. 2569 came into force on 26 April 2026. Only three kinds of applicant can be licensed for extracts above 0.2% THC: Thai juristic persons that are not “foreign” under the Foreign Business Act B.E. 2542, state agencies, and the Thai Red Cross Society.
- Section 46 of the 1999 Act requires a licence to research, export, sell or process a controlled herb. Doing so without a licence is punished under Section 78 with up to 1 year in prison, a fine of up to 20,000 baht, or both.
- The draft Cannabis Control Act is not law yet. The Cabinet approved the draft on 22 September 2026 and sent it to the House of Representatives.
Before you start, read the original legal texts. Post any legal question in the Licensing and Compliance section, and give the date and source of any rule you quote.
12.2 Security and discretion
Even where growing is legal, a discreet grow is less likely to be stolen. Theft is a serious problem for home grows that other people can see. Odour control with a carbon filter and inline fan is the most important single security measure. Other risks to manage are light from the tent showing through windows, noisy equipment, and social media posts that reveal your location.
Translator’s note: In Thai townhouses and condominiums, neighbours live close, so smell and fan noise reach them quickly. While the lights are on at night, go outside and look at your window for light leaks. If you can smell the grow outside the tent, check the carbon filter.
13. Clones or seeds for your next grow
After a first grow from seed, many growers think about using clones in later grows. Clones are cuttings taken from a favourite plant.
Seeds are a reliable start, are sold worldwide and need no mother plant. Each seed is a unique individual. This is useful for trying different plants, but plants will vary from one another (phenotype variation).
Clones are genetically identical copies of the mother plant. They are useful once you have found a plant that performs well. You need a healthy mother plant kept in the vegetative stage all year, which adds ongoing cost and work.
For a first or second grow, stay with seeds. Clones become worthwhile once you have grown your ideal plant through a full cycle and know it is worth copying. A mother plant under 18/6 light in a small vegetative space can give cuttings for as long as you keep it. The value of the genetics you keep must justify that space, light and upkeep.
How to root clones:
- Rooting medium: rockwool cubes soaked in water at pH 5.5, rapid rooter plugs (ready-made rooting plugs), or peat pellets (pressed peat discs that swell in water).
- Conditions: 70–80% RH under a clear propagation dome, at 22–25 °C.
- Timing: most varieties root in 7–14 days. When roots show through the cube or plug, transplant.
Translator’s note: Buying clones from another farm is the fastest way to bring problems into your grow room. The main risks are mites, thrips, plant diseases and hop latent viroid (HLVd). HLVd is a tiny infectious agent that can stunt cannabis and spreads through cuttings and tools. You may also get a different variety from the one you paid for. Keep new clones away from your other plants at first, and check the undersides of their leaves with a loupe every two days. Ask the seller which variety the mother plant is and how it was tested. Tissue culture is another source of clean plants. To keep clones at 22–25 °C in Thailand, you need an air-conditioned space.
Summary: what decides a first grow
A first grow succeeds or fails mainly on four basics:
- Stable temperature and humidity.
- The correct pH at every watering.
- Enough light, but not too much.
- Restraint in feeding.
If you get these four right in your first grow, yield and quality will follow. Once you know what healthy growth looks like, improve your genetics, training and feeding in later grows.
Keep a simple grow diary. Every day, write down the temperature, humidity, feed pH, feed EC and pot weight. When a problem appears, the diary shows which of the four basics changed. You can post your diary in the Grow Diaries section. If you have a question about this part, ask below this topic.
References
- Alden, M. J., & Faust, J. E. (2025). Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis (Cannabis sativa). HortScience, 60(10), 1818–1825. https://doi.org/10.21273/HORTSCI18752-25