This guide takes you through a first indoor grow, from germinating a seed to curing the harvest. It uses equipment and fertilisers that are easy to buy. You do not need any growing experience. Each step explains why you do it, so you can adjust when your setup is different.
Most first grows go wrong because the grower does too much. They buy too much equipment, use too much fertiliser or water too often. The plant follows predictable biological rules. If you keep a few basic conditions steady, the plant does most of the work.
Translator’s note: The temperature and humidity targets in this guide are normal for indoor growing in cooler climates. In Thailand and much of Southeast Asia, rooms are often 30–35 °C, humidity rises in the rainy season and power cuts happen. Where a target is hard to reach here, a translator’s note tells you what to do instead.
Part 1 covers equipment, choosing seeds, germination, growing media, feeding, light and watering. Part 2 covers the vegetative and flowering stages, harvest, drying and curing, common problems, the Thai rules and growing from clones.
1. Before you start: what you actually need
1.1 The minimum for one to four plants
Beginners usually make one of two mistakes. Some buy too little and run into problems they could have avoided. Others buy too much and pay for features they do not understand yet. The table below is the real minimum for one to four plants. In the table, the “canopy” means the top layer of leaves and buds.
| Item | Specification | Why you need it |
|---|---|---|
| Grow tent | 60×60 cm to 120×120 cm | Fabric frame with reflective inner walls. It keeps the light in and lets you control the air |
| Grow light | 200–400 W LED, or 400–600 W HPS (high-pressure sodium lamp) | LED is preferred because it gives off less heat |
| Inline fan + carbon filter | Sized to the tent volume | Pulls old, hot air out through the filter. You need it for fresh air and odour control |
| Circulation fans | 2, clip-on or standing, oscillating | One at canopy height, one at floor level |
| Timer | Two outlets, 15-minute steps | Switches the light and any other equipment |
| pH/EC meter | Combined or separate | pH accurate to at least ±0.1 |
| Pots | 7–15 L fabric pots | Extra water and air escape through the fabric, so overwatering is harder |
| Growing medium | Coco coir or a good potting mix | See Section 4 |
| Fertiliser | 3-part base nutrient + cal-mag (a calcium and magnesium supplement) | See Section 5 |
| Thermometer/hygrometer | Placed at canopy height | Choose one that stores the day’s minimum and maximum |
Translator’s note: In a room at 30–35 °C, the light is your main heat source and the inline fan is your main way to remove heat. An LED with similar output adds less heat than an HPS lamp, so it is the safer choice here. The fan can only pull in air as cool as the room, so many home growers in Thailand put the tent in an air-conditioned room. A mechanical timer stops during a power cut, so afterwards the light schedule runs late by the length of the outage. Choose a digital timer with battery backup, or reset the timer after every outage.
1.2 On a tight budget: what to buy first
Translator’s note: The original article gives the minimum list but not the order to buy in. If you have to buy in stages, this order follows the reasons explained in this guide.
- Thermometer/hygrometer. It costs the least, and it shows whether your room can reach the ranges in this guide at all. Run it in the empty room for one week and write down the day and night readings.
- Light. No other equipment can make up for too little light.
- Tent, inline fan and carbon filter. Together they keep the light in, remove heat and humidity, and control odour. In Thai heat, removing hot air matters as much as the light.
- pH meter. Section 5.3 explains why wrong pH causes more problems than your choice of fertiliser brand.
- Timer. It keeps the light schedule exact. Photoperiod plants need an exact schedule to flower on time.
- Pots, growing medium and fertiliser. These items can be cheaper at the start. A pre-fertilised potting mix feeds the plant for 2–4 weeks (Section 4.1), so you can buy the fertiliser line and an EC meter a little later. This works only with soil, because coco needs fertiliser and cal-mag from the first watering (Section 4.2). Normal household clip fans can be your circulation fans.
1.3 What you do not need yet
Do not buy these for a first grow:
- CO₂ enrichment equipment, which adds carbon dioxide gas to the room
- automatic dosing systems
- clone machines
- humidity controllers that switch equipment on and off by themselves
- light spectrometers
- anything sold for “maximising yield” instead of keeping basic conditions stable.
Each extra device is one more thing that can fail. Learn on a simple setup first, so you know what normal growth looks like before you add more.
Translator’s note: Only the automatic controller can wait. You may still need to remove humidity. In humid Thai months, a plain dehumidifier or an air-conditioned room may be needed to keep humidity in range during flowering and drying (Part 2, Sections 9 and 10). Check your one-week hygrometer readings before you decide.
2. Choosing seeds
2.1 Photoperiod or autoflowering
Cannabis plants fall into two main groups. The groups differ in what makes the plant start flowering.
Photoperiod plants flower when you change the light schedule. While they grow leaves and stems (the vegetative stage), they get 18 hours of light a day. You then switch to 12 hours of light to start bud formation. This lets you control plant size and timing, but it adds steps.
Autoflowering plants flower by age, whatever the light schedule. They usually take 60–75 days from seed to harvest. They are smaller, faster and easier to manage. Each plant yields somewhat less, but they are still a strong choice for a first grow.
For a first indoor grow in a 60×60 or 80×80 cm tent, start with an autoflowering variety from a reputable breeder. Plan one plant per tent so it has enough space.
Translator’s note: Little published research compares how varieties cope with rooms above 30 °C and high humidity. This topic summarises the heat studies and explains why any Thai shortlist is still provisional. Ask in the Strain Reviews section which varieties members have grown in a room like yours, and how hot their room was.
2.2 Buying from a reputable breeder
Some seeds are genetically unstable or sold under the wrong name. Plants from them vary from one another. You then cannot tell whether a problem comes from your growing or from the seed. Buy from established breeders who:
- explain their breeding work openly
- have grow reports published by other growers
- give each seed lot a batch number you can trace.
Breeders whose seeds are often sold in Southeast Asia include Dutch Passion, 420 Fast Buds, Dinafem and RQS. These are examples, not recommendations. Check any breeder against the three points above.
Translator’s note: How to vet a Thai seed vendor covers copied strain names and old stock. Buying seeds in Thailand explains what the rules allow. Keep the seed packet with its batch number and your receipt. If the plants turn out wrong, these show whether the seed lot caused the problem.
3. Germination
Germination is when a seed cracks open and pushes out its first root, the taproot.
3.1 The paper towel method
- Wet two paper towels with water at pH 6.0–6.5. They should be damp but not dripping.
- Put the seeds on one towel and fold the second towel over them.
- Seal them in a zip-lock bag or between two plates to keep humidity high.
- Keep them in the dark at 22–26 °C.
- Check every 12 hours. Most good seeds crack and show a taproot within 24–72 hours.
Move the seed into the growing medium as soon as the white taproot shows, at 0.5–1 cm. Do not wait until it is longer than 1.5 cm. Longer taproots break easily and get tangled in the medium when you transplant.
3.2 Straight into the medium
Many growers prefer this simpler method. Wet the medium first and make a hole 1 cm deep. Put the seed in with the pointed end down and cover it loosely. Keep it at 22–26 °C and 70% humidity or higher until the seedling comes up.
Germination rates vary a little more than with paper towels. However, you never touch the fragile taproot, so you cannot damage it.
3.3 What kills seeds
- Overwatering. Seeds need oxygen as much as water. Soggy medium has no air, so the seed does not germinate.
- Temperatures that are too low or too high. Below 18 °C, germination slows down a lot. Above 32 °C, the embryo inside the seed is damaged.
- Old seeds. Fewer seeds germinate after each year of storage, especially in warm, humid conditions. Store seeds in the refrigerator, not the freezer, in a sealed container with a silica gel sachet to absorb moisture.
Translator’s note: A normal Thai room at 30–35 °C is right at the 32 °C damage limit. Germinate in an air-conditioned room, inside a closed drawer to keep the seeds dark. Avoid warm places such as the top of a refrigerator or near a lamp. Put the thermometer next to the seeds so you know their real temperature.
4. Growing media
4.1 Soil and potting mix
Potting mix forgives mistakes more easily than other media, so it suits beginners. Pre-fertilised mixes contain enough nutrients for the first 2–4 weeks. That means you do not have to feed while seedlings are most sensitive.
Choose a mix that:
- drains well and contains 20–30% perlite (light, white expanded volcanic rock that keeps the mix airy)
- is slightly acidic, pH 6.0–6.8
- stays loose and airy instead of packing down.
Avoid mixes for vegetable gardens that already contain a lot of nitrogen. They often cause nitrogen toxicity in cannabis seedlings.
pH range for soil: 6.0–7.0, best at 6.2–6.8.
4.2 Coco coir
Coco coir is coconut husk fibre. Sellers wash and buffer it (pre-treat it so it is ready for plants). It contains almost no plant food, so the plant depends fully on what you feed it. That takes more attention than soil, but it gives you much more control.
Advantages:
- Faster growth than in soil when you water correctly, because you can water coco more often.
- Much lower risk of overwatering when you mix it with 30% perlite.
- You can reuse it for the next grow.
pH range for coco: 5.8–6.2, best at 5.8–6.0.
The key difference from soil: coco fibre binds calcium and magnesium from the feed to its surface (cation exchange). This leaves less of these two elements for the roots. So any fertiliser line you use with coco needs a cal-mag supplement from week 1.
Translator’s note: Coco quality varies from batch to batch. Ask the official distributor in Thailand whether a product is washed and buffered, or ask other members in the Substrates section. At 30–35 °C, coco in a small pot dries fast. Lift your pots every morning and evening (Section 7) until you know how fast they dry.
4.3 Pot size
Pot size decides how fast the medium dries between waterings. If the pot is too big for the roots, the medium stays wet for a long time and overwatering becomes more likely. If the pot is too small, it dries fast, needs very frequent watering, and the roots can run out of room (root bound).
A practical sequence for photoperiod plants:
- Germinate in 1 L plastic cups with drainage holes punched in the bottom, or in rockwool cubes (blocks of spun stone fibre).
- Transplant into 3–5 L pots for the vegetative stage.
- Transplant again into 11–15 L pots for flowering.
Plant autoflowers straight into their final 7–11 L pot. Their life cycle is short, so they have no time to recover from transplant stress.
Choose your medium before you buy fertiliser. Pick soil if you want fewer feeding decisions. Pick coco only if you can check your pots twice a day.
5. Fertiliser basics
5.1 What the plant needs
Cannabis needs three main nutrients in large amounts:
- Nitrogen (N): the main driver of leaf and stem growth. Feed plenty during the vegetative stage and less in flowering.
- Phosphorus (P): needed for root growth, moving energy inside the plant, and the start of flowering.
- Potassium (K): controls the leaf pores (stomata), helps the plant resist disease and is needed to make terpenes, the aroma compounds.
Calcium (Ca), magnesium (Mg) and sulphur (S) are needed in moderate amounts. In hydroponics and coco, growers often add them separately because the base fertiliser may not supply enough.
Trace elements are needed in tiny amounts: iron, manganese, zinc, boron, copper and molybdenum. Commercial fertilisers usually already contain them.
Bernstein et al. (2019) studied how adding N, P, K and humic acid changes the chemical profile of medical cannabis (see References).
5.2 Feeding schedules for beginners
Most fertiliser companies, including Grotek, Advanced Nutrients, BioBizz and Canna, publish feeding schedules. A schedule shows which product to use, and at what dose, for each week. Schedules are set for typical conditions and are a reasonable place to start.
Three rules come before any schedule:
- With any new fertiliser line, start at 50% of the recommended dose for the first two weeks.
- Raise the dose only when the plant shows no signs of excess. These signs are burnt leaf tips, very dark green leaves, and leaf tips that curl down like a claw.
- Check the EC of your feed. EC (electrical conductivity) measures how much fertiliser is dissolved in the water. Most commercial schedules aim for 1.2–2.4 mS/cm in the vegetative stage and 1.4–2.8 mS/cm in flowering.
Translator’s note: Feeding schedules are usually written for cooler climates. At 31 °C and high humidity, plants can react differently, as this worked example shows. Start at the low end of the EC range and raise it step by step, using the signs in rule 2. Buy fertiliser with a Thai label from the official distributor in Thailand. This topic explains how to check that a fertiliser is registered.
5.3 pH matters more than the fertiliser brand
If the feed has the wrong pH, the roots cannot take up some elements, even when the water contains enough of them. This is called nutrient lockout. Many apparent deficiencies are really lockout: the nutrient is in the water, but the roots cannot use it.
Key ranges to remember:
- Above pH 7.0 in soil, iron, manganese, zinc and boron get locked out.
- Below pH 5.5, in any medium, calcium and magnesium become harder for the roots to take up.
- Phosphorus is easiest to take up at pH 6.0–7.0 in soil and 5.8–6.2 in coco and hydroponics.
Set the pH of every feed before you use it. Test your tap water too before you assume it is suitable. Tap water can be well above pH 7.
Translator’s note: Measure your own water instead of relying on what neighbours tell you. Town water, well water and stored rainwater can be very different. Write down the pH and EC of your plain water. This is your baseline, and it shows how much of the EC reading comes from the fertiliser.
6. Light
6.1 Light schedules
Vegetative stage: the standard is 18 hours of light and 6 hours of dark (18/6). Some growers use 20/4 or 24/0, and plants cope with these. 18/6 balances growth speed against electricity cost, and it gives the plant’s light-capturing system a rest.
Flowering (photoperiod plants): switch to 12/12 when plants reach 40–60% of the final height you want. In the first two weeks of 12/12, plants stretch and usually double in height. Switch early so they do not outgrow the tent.
Autoflowers: keep 18/6 or 20/4 for the whole life cycle.
Translator’s note: In hot climates, many growers run the light period at night, when the room is cooler. The air conditioner then works less, and the tent stays closer to the target temperature. Set the timer once and do not change the schedule after that.
6.2 Distance between light and plants
Manufacturers recommend different distances. A practical starting point:
- LED panels, 250–400 W: 45–60 cm from canopy to lamp for seedlings and early veg. 30–45 cm for mid to late veg. 25–40 cm in flowering, depending on how much light the variety tolerates.
- HPS, 400–600 W: at least 45–60 cm, to prevent heat stress.
Quick test: hold your hand at canopy height under the light for 10 seconds. If it feels uncomfortably warm, raise the lamp. A light meter or a smartphone PPFD app gives more exact data. PPFD is the amount of usable light that reaches the leaves each second.
Potter and Duncombe (2012) studied how lamp power and light intensity affect yield and potency in indoor cannabis (see References).
Translator’s note: When the room is already above 30 °C, everything feels warm, so the hand test is less reliable. Hang the thermometer at canopy height directly under the lamp. If it reads much higher than the rest of the tent, raise the lamp.
7. Watering
7.1 When to water
The most common beginner mistake is watering on a fixed schedule instead of when the plant needs it. The right signal is to lift the pot. A dry pot of coco or soil feels much lighter than a pot you have just watered. After two or three waterings you learn the feel, and then it comes naturally.
A second signal is that the top 2–3 cm of medium is dry. Also check that the leaves show no signs of heat stress, which can look like thirst.
7.2 How much to water
Water until 10–20% of the water drains out of the bottom (the runoff). This stops fertiliser salts from building up and wets the whole root zone. With less than 10% runoff, dry pockets can stay in the medium, and roots in those pockets cannot reach nutrients.
- Coco: water more often, with less water each time. In late flowering, this can be once or twice a day.
- Soil: water less often, with more water each time. Every 2–4 days, depending on pot size and room conditions.
Translator’s note: A kitchen scale or luggage scale turns the feel into numbers. Weigh each pot just after watering, then again when it is dry enough to water. Write both weights on the pot. In Thai heat, pots reach the dry weight sooner, and the numbers save you from guessing.
Before you start Part 2
- Run the thermometer/hygrometer in the empty room for one week and write down the readings. This shows which targets in this guide your room can reach.
- Measure the pH and EC of your tap water. This gives you a baseline for every feed.
- Choose soil or coco, then pots of the right size (Section 4).
- From the first watering, weigh your pots wet and dry. This shows you when to water.
If anything in this part is unclear, ask below this topic. Please include your room temperature and humidity.
References
- Potter, D. J., & Duncombe, P. (2012). The effect of electrical lighting power and irradiance on indoor-grown cannabis potency and yield. Journal of Forensic Sciences, 57(3), 618–622.
- 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. Frontiers in Plant Science, 10, 736.
Continued in Part 2: Your First Cannabis Grow: Vegetative Stage, Flowering, Harvest, Drying, Common Problems and the Thai Rules (Part 2 of 2)