Autoflowering cannabis starts to flower at a fixed age of about 3–5 weeks from seed. It does not wait for the nights to get longer. The trait comes from Cannabis ruderalis, a wild plant of short northern summers. An auto’s cycle is short and you cannot pause it. So feeding, climate and harvest timing must all fit that fixed schedule. This part covers feed strength at each stage, then temperature, humidity and root-zone temperature. It also covers harvest timing, staggered harvests, yearly output and growing outdoors in Thailand.
Part 1 explains where the trait comes from, how to choose seed, and how pot size, light and training differ from photoperiod plants. Photoperiod plants are the ones that flower when the nights get longer.
This is Part 2. Part 1: Autoflowering Cannabis: Ruderalis Genetics, Light Independence, and How to Grow Autos Correctly
7. Feeding autos
7.1 A weaker feed than photoperiod plants
Autos generally need a weaker nutrient solution than photoperiod plants of similar size. The usual explanation is their smaller root mass and faster life cycle. A safe starting point is an EC 10–20% below a photoperiod feeding schedule. EC (electrical conductivity) measures how much dissolved fertiliser is in the solution, in mS/cm (pH and EC basics).
Guide EC values for autos in coco or hydroponics:
- Seedling (days 1–14): 0.4–0.8 mS/cm
- Vegetative (days 14–28): 0.8–1.2 mS/cm
- Early flower (weeks 4–6): 1.2–1.8 mS/cm
- Mid flower (weeks 6–9): 1.4–2.0 mS/cm
- Late flower (week 9 to harvest): 1.0–1.4 mS/cm, lowering week by week
Translator’s note: Measure the EC of your own water before you add fertiliser. Tap water, well water and rainwater in Thailand can differ a lot (irrigation water topic). The EC your water already has counts toward the target. Buy only fertilisers that are legally on sale in Thailand (how to check).
7.2 How often to water and feed
In coco, mature autos in hot weather may need watering twice a day. Use the EC of the runoff as your guide. Runoff is the water that drains out of the bottom of the pot. If runoff EC climbs above 2.5 mS/cm, fertiliser salts are building up around the roots. Water once with plain water to wash them out, then lower the feed strength.
7.3 Switching from nitrogen to phosphorus and potassium
Autos start flowering earlier than many growers expect. At day 25–28, change to a feed with less nitrogen (N) and more phosphorus and potassium (PK) (NPK explained). Do this even if you see no flowers yet. By then, the hormone change toward flowering has usually started, and the plant will use the new feed well.
What to do: each time you water, write down the EC of the feed and of the runoff. A rising runoff EC warns you of salt build-up before the leaves show damage.
8. Temperature, humidity and the root zone
8.1 Temperature
Ruderalis ancestry can make autos handle cold better than pure sativa varieties. Still, autos grow fastest in the same range as other cannabis:
- Best daytime temperature: 22–28 °C
- Best night temperature: 18–24 °C
- Below 15 °C: the plant’s metabolism slows sharply and growth stops
- Above 30 °C: heat stress appears. Leaves curl upward, and the stomata (tiny pores on the leaf) close.
Outdoors in the tropics, the main risk in the hottest months is heat, not cold. Shade cloth that blocks 30–50% of the light can lower canopy temperature by 3–5 °C in the afternoon heat. Use it in the afternoon only, so the plant still gets full morning light.
Translator’s note: Indoor rooms in Thailand without cooling often reach 30–35 °C, which is above the heat-stress line. Reaching the targets in this section and the table below generally needs air-conditioning and a dehumidifier. Before you buy equipment, log the lowest and highest temperature at canopy height for one week. The log shows how far you are from target. The forum topic on sizing cooling for a Thai room then helps you choose capacity.
8.2 Humidity through the auto’s life
VPD works the same way for autos as for photoperiod plants. VPD (vapour pressure deficit) combines temperature and humidity into one number. It shows how strongly the air pulls water out of the leaves. Autos pass through each stage faster, so the targets change faster too. In the table, RH means relative humidity.
| Week from seed | Stage | Target RH | Target temperature |
|---|---|---|---|
| 1–2 | Seedling | 70–80% | 23–25 °C |
| 2–4 | Early vegetative | 60–70% | 24–26 °C |
| 4–6 | Late vegetative / early flower | 55–65% | 23–25 °C |
| 6–10 | Mid to late flower | 45–55% | 22–24 °C |
| 10 to harvest | Final ripening | 40–50% | 20–23 °C |
Humidity in late flower matters as much for autos as for photoperiod plants. Botrytis (bud rot) attacks all genetics alike. A dense-budded auto in its final weeks at 70% RH or more is as much at risk as an indica in the same air.
Translator’s note: In the Thai rainy season, outdoor air and rooms without a dehumidifier often stay far above 50% RH. Damp buds also raise the risk of mould toxins (mycotoxins). Hang a hygrometer (humidity meter) at canopy height. Write down the reading every day in the last three weeks. If it stays above the table, add dehumidification or plan an earlier harvest.
8.3 Root-zone temperature
Growers often overlook root-zone temperature. It strongly affects how well roots take up nutrients and how active the helpful soil microbes are (root zone basics). Cannabis roots work best at 18–22 °C. In warm climates, heat around the roots can block nitrogen uptake. You then see deficiency signs even though you feed enough. The roots can be stressed even when the air around the canopy seems fine.
Measure root-zone temperature separately from air temperature, using a probe thermometer pushed into the growing medium. Keep direct sun off the containers. If you use a reservoir, cool it to 20 °C or lower.
Translator’s note: Keeping a reservoir at 20 °C in Thai heat usually means buying a water chiller and paying to run it. The topic on running hydroponics at 31 °C compares three options: a chiller, beneficial microbes or a different system. Power cuts also stop chillers and air pumps. In a deep-water system, the roots then quickly run short of oxygen. A battery backup (UPS, uninterruptible power supply) for the air pump reduces that risk. Start by measuring the reservoir temperature at the hottest hour of the day for one week.
9. When to harvest
9.1 Check the trichomes
Trichomes are the tiny resin glands on the buds and nearby leaves. The most reliable sign of ripeness is how they look under a jeweller’s loupe (a small 30–60× magnifier) or a digital microscope (trichome maturity explained). Trust the trichomes over the breeder’s stated harvest week. That week is a median from controlled conditions, and your conditions will differ.
What the trichome heads tell you:
- All clear: too early.
- 60–70% milky or cloudy, the rest clear: THC is approaching its peak.
- 80–90% milky with 5–15% amber: peak THC. Some THC is starting to break down into CBN (cannabinol).
- 20% or more amber: the cannabinoid mix has shifted, and the effect is more sedating.
9.2 Pistil colour
Pistils are the white hairs on the buds (flower stages). They are a second, less precise sign. When 70–90% have turned orange or red, the plant is nearing maturity. Pollination, handling and environmental stress can also change their colour. That makes pistils less reliable than trichomes.
What to do: check a few buds at the top and in the lower canopy. Each time, write down the share of clear, milky and amber heads. The record shows the trend, so you decide when to harvest from what you see, not from the calendar.
10. Planning several harvests
10.1 Staggered sowing for a harvest every 3 weeks
Autos flower without any change in the light schedule. So plants of different ages can share one room under the same light. You can sow a new batch every 2–3 weeks and harvest continuously.
A common schedule is to sow 2–4 new seeds every 3 weeks while the earlier plants are flowering. By week 10 you have plants at four ages:
- 10 weeks: ready to harvest
- 7 weeks: mid flower
- 4 weeks: early flower
- 1 week: seedling
After the first 10 weeks, you get a harvest every 3 weeks for as long as you keep sowing. According to the original article, keeping plants of staggered ages under one light gets the most production out of each lighting period.
Translator’s note: The original article calls this schedule “Sea of Green” (SOG). That name usually means something else: many small plants packed close together and flowered early to form one even canopy (SOG and SCROG compared). Sowing in batches for a steady harvest is usually called perpetual harvest (perpetual harvest schedule). Both methods work with autos.
Translator’s note: Plants at different stages need different humidity. Seedlings want 70–80% RH, and plants in late flower want 40–50% (section 8.2). One room cannot give both. Raise seedlings under a clear cover or in a small separate tent for the first two weeks, then move them into the room. Check each new batch for pests before it joins the room, because pests on older plants spread easily to young ones.
10.2 Growing all year
Autos can be grown all year without changing the light schedule. This makes them especially practical for:
- climates where controlling day length is impractical;
- small-scale continuous production;
- sites without separate rooms for vegetative growth and for flowering.
What to do: if you have only one room, start with 2–4 seeds every 3 weeks as above. After the first harvest, adjust the batch size to the space and the drying capacity you actually have.
11. Costs and output per year
11.1 Shorter cycles, more harvests
The main economic advantage of autos is the short time to harvest. More cycles fit into a year while fixed operating costs stay the same:
| Strain type | Days from seed to harvest | Cycles per year (back to back) |
|---|---|---|
| Fast autoflower | 60–70 | 5.2–6.1 |
| Standard autoflower | 70–90 | 4.1–5.2 |
| Photoperiod indica (6 weeks vegetative + 8 weeks flower) | about 100 | 3.7 |
| Photoperiod sativa (6 weeks vegetative + 12 weeks flower) | about 130 | 2.8 |
For a small commercial grower, electricity and space are usually the main fixed costs. More cycles a year means more total yield for the same costs.
11.2 Yield per square metre and per watt
Count yearly output, which is the yield per harvest multiplied by harvests per year. On that basis, modern autos compete with photoperiod varieties per square metre. Per harvest, a large photoperiod plant can still yield more than an auto. That gap narrows a lot once you count how many cycles fit in a year.
Translator’s note: The table assumes cycles run back to back, with no break for cleaning or drying. In Thailand, cooling can be a large share of the power bill. For each cycle, record the electricity used (kWh) and the dry yield in grams. Divide the grams by the kWh. The result shows, on your own bill, whether autos or photoperiod plants give more yield for the power you pay for.
12. Growing autos outdoors in Thailand
12.1 The legal position
The original article says autos are grown legally in Thailand under the hemp licensing system, where varieties with certified low THC are registered. We could not confirm that any autoflowering variety is registered as hemp in Thailand. That statement does not cover the high-THC autos in this article.
Translator’s note: The high-THC autos in this article (20–25% THC) are not hemp (the 0.2% and 1.0% THC lines). Cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568. The Notification was issued under the Thai Traditional Medicine Protection Act B.E. 2542 and has been in force since 26 June 2025.
Translator’s note: Flower may be sold only against a PT 33 (ภ.ท.33) prescription, for a maximum of 30 days. Advertising and online sale of flower are prohibited. 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 (what changed in 2026).
Translator’s note: Section 78 of the 1999 Act sets the penalty for research, export, sale or processing of a controlled herb without a licence. The penalty is 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. Cabinet approved the draft on 22 September 2026 and sent it to the House (where the draft stands). Before you sow, check that your licence covers what you plan to grow (which licence covers what).
12.2 When to plant
The best window is to sow in October–November and harvest in December–January. The crop then grows in the cool, dry season. Daytime temperatures are 22–32 °C, and it rains less often than in the monsoon.
Translator’s note: This window does not suit the Gulf of Thailand coast of southern Thailand. There, the northeast monsoon brings the heaviest rain from about October to December, and November is usually the wettest month. Readers elsewhere in Southeast Asia should use local weather records. Pick the three months with the least rain and daytime temperatures closest to 22–32 °C.
12.3 Choosing varieties for heat
The original article advises two things. Choose autos from breeders who have tested them in tropical conditions, or choose ruderalis-dominant lines that show heat tolerance. Many commercial autos were bred for indoor rooms in Europe and do poorly above 30 °C.
Translator’s note: Ruderalis comes from short, cold summers (Part 1, section 1). A large share of ruderalis genes is therefore no sign of heat tolerance. Judge a variety by grow reports from hot climates and by your own trial (genetics for rooms above 30 °C). Start by sowing a few seeds of each candidate in the same season. Then compare how each one grows in the hottest weeks.
12.4 Keep pots off the hot ground
Fabric pots on stands keep the roots away from ground that radiates heat. On a hot Thai afternoon, the soil surface can reach 45–55 °C, which kills roots. Raised pots with reflective insulation underneath keep the root zone at a safe temperature.
What to do: on a hot afternoon, put a probe thermometer into a raised pot and into one standing on the ground. The difference shows you how much the stands help on your own site.
12.5 Pests
The main pests of outdoor autos in Thailand are:
- spider mites, in dry periods (November–February);
- colonies of aphids on new growth;
- caterpillars of moths and butterflies, active all year.
The original article recommends a weekly preventive rotation of neem oil and Bt from week 2 onward. Bt (Bacillus thuringiensis) is a bacterium-based product that kills caterpillars (a Bt programme for flowering). According to the original, this rotation keeps pests down without the chemical load of rotating synthetic pesticides.
Translator’s note: Use only products registered with the Department of Agriculture (กรมวิชาการเกษตร), and follow the label for dose, interval and crop (what you may legally spray). Check the undersides of the leaves every week with a loupe. This shows you when mites or aphids arrive, before they cause damage (integrated pest management).
12.6 Harvesting in humid weather
Outdoor autos near harvest in January may meet sudden rises in humidity when night temperatures drop. Check the trichomes daily from week 9. If several days of rain are forecast, harvest at the first acceptable ripeness. Do not wait for the peak.
Translator’s note: Check the Thai Meteorological Department forecast before you decide. Prepare the drying space before you cut, because outdoor humidity in Thailand is high (drying at 85–95% humidity).
Summary: what to do with autos
According to the original article, years of breeding have made modern autos a workable way to produce a crop. Their advantages are a short cycle, simple light management and the freedom to grow all year. The trade-offs are less room for training and little tolerance of stress. Growers who use photoperiod methods on autos usually get poor results. Growers who plan around the fixed timeline get good results.
- Sow straight into the final pot and avoid every avoidable stress in the first four weeks.
- Feed 10–20% weaker than for photoperiod plants. Record feed and runoff EC, and switch to a lower-nitrogen, higher-PK feed at day 25–28.
- Log canopy temperature, humidity and root-zone temperature for one week before you buy cooling equipment.
- Harvest by trichomes, not by the breeder’s week. Harvest early if several days of rain are forecast.
- Record kWh and dry grams for each cycle to see what autos really earn on your site.
- Before you sow, check that your licence covers the plants you grow.
If you have questions, or results from growing autos in Thai or Southeast Asian conditions, post them as replies below this topic.
References
- Small, E. (1972). Interfertility and chromosomal uniformity in Cannabis. Canadian Journal of Botany, 50(9), 1947–1949.
- Russo, E. B. (2007). History of Cannabis and Its Preparations in Saga, Science, and Sobriquet. Chemistry & Biodiversity, 4(8), 1614–1648. https://doi.org/10.1002/cbdv.200790144
- ElSohly, M. A., et al. (2017). Phytochemistry of Cannabis sativa L. In Phytocannabinoids. Springer.