Adapted and edited from the book Organic Marijuana, Soma Style (2005) by Soma (Quick American Archives).
This guide covers the growing mix and feeding for a raised organic bed: a wooden box on wheels, 1.25 × 1.25 m and 35 cm deep, with a drained layer of clay pebbles at the bottom and an air pipe in each corner. The design comes from Soma, a grower and writer who built it for a climate-controlled room in Amsterdam. This version adapts it for hot, humid rooms in Thailand and Southeast Asia.
The bed works by putting most of the plants’ food into the mix at the start, then topping it up with a bat guano tea in mid-flowering. The book’s method is described as the book gives it. Changes for tropical rooms are marked “Translator’s note”.
This is Part 2. Part 1: A Tropical-Adapted Soma-Style Raised Organic Bed: LECA Base, PVC Air Columns, Substrate and Feeding Schedule
The growing mix
The book’s mix makes roughly 400 L. Most of it is peat-based and light potting mixes. Worm castings and coarse perlite are added. The mix is “front-loaded”: most of the fertiliser goes in at the start, so the plants feed from the mix for most of the crop.
| Ingredient | What it does | Amount in the book |
|---|---|---|
| Peat-based potting mix and light potting mix | Bulk of the bed; holds water and air | Most of the ~400 L |
| Worm castings | Slow food and soil life | A smaller share (see the book for the amount) |
| Coarse perlite | Keeps the mix open so air reaches the roots | A smaller share (see the book for the amount) |
| Bat guano | Dry fertiliser | A small amount (see the book for the exact figure) |
| Organic fertiliser blend, NPK 7-6-12 plus MgO (magnesium) | Dry fertiliser | A small amount (see the book for the exact figure) |
| Red marine algae (calcified seaweed) | Raises pH | See the book for the amount |
NPK on a label gives the percentage of nitrogen (N), phosphate (P) and potash (K), in that order.
This version makes three changes to the mix, and adds one point about labels.
pH raiser. The book uses calcified seaweed, also called maerl: seaweed that builds a chalky skeleton. As a substitute, it offers greensand (a green mineral from old sea beds that slowly releases potassium) plus hydrated lime. In that substitute, the lime does the pH work, because greensand releases potassium very slowly. A reliable regional supply of maerl could not be confirmed. So use agricultural dolomite (ground rock containing calcium and magnesium) by default. Avoid hydrated lime: it is caustic, burns skin and is strongly alkaline. Greensand is covered in topic 1401.
Translator’s note: the book gives no rate for dolomite. Before you blend 400 L, mix a small test batch with dolomite, wet it, and measure the pH after a few days. Adjust the amount until the test batch reads where you want it.
Peat. The mix is mostly peat. Replacing part of the peat with rinsed coco coir uses a product made in this region. It may also reduce pH drift when the mix is reused (see the reuse section). Rinsing removes salts left from processing.
Target pH. The book says to aim for pH 7 in the fresh mix. Separately, it says the ideal pH for cannabis is 6.2–6.6. These do not conflict. The mix is buffered upward when blended, and it drifts down in use. If you measure, 6.2–6.6 at the roots is the number that matters. Topic 392 explains pH targets and testing.
Reading labels. The book explains that a 14-12-24 product is twice as strong as a 7-6-12 product, but has the same N:P:K ratio. This helps anyone comparing fertiliser labels: same ratio means same balance, and a higher number means you use less of it.
Translator’s note: if you cannot find the book’s 7-6-12 blend, look for a registered organic blend with a similar ratio. Topic 1464 explains how to check that a fertiliser is legally registered in Thailand.
Your next step: write the ingredient list with your local substitutes, then mix and test a small batch before you blend the full 400 L.
The layering step: a gentle top layer for young plants
Before you blend anything, set aside one bag of the light potting mix. Mix everything else thoroughly and fill the bed with it. Then spread the bag you kept on top.
The top layer is now less rich than the rest of the bed. Seedlings and freshly rooted cuttings start in it, where their roots cannot burn. As they grow, their roots reach down into the richer mix. This solves a common conflict in one step. A bed must be rich enough to feed plants through ten weeks of flowering, but young plants burn in rich mix. Topic 1475 covers layering in more detail.
Your next step: put one bag of light mix aside before you open the fertiliser bags.
Reusing the mix
The book says the mix can be reused at least three times. After each crop, remove about ⅓ and replace it with fresh mix. The third you remove is still good fertiliser for other plants in the garden. Replacing a third dilutes problems that build up, but does not fix them. That is why the book sets a limit of three crops.
Test pH before each reuse. Another organic growing book, True Living Organics, reports that peat-rich mixes tend to drift down in pH when recycled. That is a growers’ observation, not tested research. It still applies directly to a mix with this much peat. Topic 1397 covers recycling living soil.
Your next step: write down the pH of the old mix at every crop change. After two or three crops you will see which way it drifts and how fast.
Planting out
- Raise seedlings or cuttings in small pots of about 2 L. Move them into the bed once they have rooted well. The book puts this at about three weeks, or 30 cm tall. Topic 1341 covers transplanting.
- Before planting, mark a planting grid on the surface with a stick. Even spacing gives every plant equal light.
- A rooting product at transplant can help plants settle in.
The book’s lighting dates from the HID era (high-intensity discharge lamps: metal halide and high-pressure sodium). Its power per square metre is very high by today’s standards. In a room without air conditioning in this region, the heat from that much HID would make 22–27 °C impossible to hold. Topic 1001 compares LED and HID lamps.
Your next step: size your lighting for modern LED efficiency, and plan the room’s cooling first. Topic 1445 covers sizing air conditioning and dehumidifiers for a Thai flowering room.
The feeding schedule
The principle. The mix holds most of the food, and the tea tops it up. In the book’s programme, plants get plain water through the vegetative stage and the first three weeks of flowering. They are fed only in weeks 4–7 of a 10-week flowering period, then get plain water until harvest.
Bat guano tea
- Concentrate: soak 100 g of dry bat guano in 2 L of hot water. Guano does not dissolve. Let it soak, then strain it or pour off the liquid.
- Working solution: mix about 250 ml of concentrate into 10 L of water at pH 6.0.
- How to apply: twice a week, poured onto the mix without splashing leaves or flowers. Wait until the mix is fairly dry. Let the speed at which the mix dries set how often you feed, not the calendar.
Products named in the book (2005 edition). The book uses Guanokalong bat guano and gives its NPK as 2-15-2. Current retailer listings range from a guaranteed minimum of 1-10-1 up to 2-15-2, with phosphate given as P₂O₅. So check the analysis on your own bag.
The bloom fertiliser used with the tea is Canna Bio-Flores. The book gives its NPK as 2.5-2.5-5, while current retailer listings show about 2-2-5, so check the current label. Either way, it is a very low analysis compared with typical bloom boosters.
The book’s alternative to the tea is Budswel, at 35 ml per 10 L of water at pH 6.0. It starts a week earlier than the tea, when white pistils (the hairs on young flowers) appear. Whether Budswel is still sold could not be confirmed.
Translator’s note: ask suppliers in Thailand whether Guanokalong and Canna Bio-Flores are currently available. Bat guano collected from local caves is also sold in Thailand and is easy to find. Its analysis varies with the source, and loose cave guano is often dusty. Ask for a nutrient analysis, prefer a registered product, and follow the safety steps in the guano section below.
| Flowering week | Feeding |
|---|---|
| 1 | None. Plants feed from the mix |
| 2 | None |
| 3 | None (the book’s Budswel alternative starts here) |
| 4 | Guano tea plus a low-analysis organic bloom fertiliser, twice a week |
| 5 | Same |
| 6 | Same |
| 7 | Same |
| 8 | Plain water |
| 9 | Plain water |
| 10 | Plain water, smaller amounts |
Watering. The book waters beds about every 3 days and pots about every 2 days, adjusted by feel. Push a finger deep into the mix and judge the moisture directly. In the final weeks, water less, not more. Roots need to dry out between waterings to get air. Overwatering late in flowering also invites bud rot (grey mould inside the flower). In the last week, the plant takes up very little water through its roots.
Translator’s note: bud-rot pressure in the Southeast Asian rainy season is high. A plant can look healthy while a bud rots from the inside. When in doubt, water less. On whether a pre-harvest flush does anything beyond stopping the feed, see topic 1136.
pH of the water. The book states that Amsterdam tap water is pH 8.3. Soma brings it down to 6.0 with citric acid and lets it rise again over about 8 hours. He argues that a drifting pH lets the plant reach more nutrients than a fixed value. It is well established that how much of each nutrient a plant can take up depends on pH. But no test could be found showing that a deliberately drifting pH beats a steady 6.3. Treat his idea as untested. The parts worth copying are simple: know your water’s pH, correct it, and aim for 6.2–6.6 at the roots. Citric acid is a cheap and reasonable acid for this.
Translator’s note: tap water and well water in Thailand vary from place to place. Measure your own source before you copy any number from the book.
Extras in the vegetative stage. The book adds almost nothing during vegetative growth, apart from three things:
- a rooting product at transplant;
- a seaweed spray on the leaves (BN-Algaemix, as named in the book);
- in week 2 or 3, a vitamin B tonic (Power Thrive or Super Thrive) at ¼ of the label dose.
Leaf spraying stops once buds form. After that, everything goes in through the roots. This is sound, because spraying developing flowers risks residue and mould.
The evidence for vitamin B1 against transplant shock is weak. Linda Chalker-Scott, a horticulture scientist at Washington State University in the United States, calls it a persistent myth. A review by the University of Arizona’s farm advisory service (Extension) notes that the early root benefits came from auxins (rooting hormones) mixed with the B1, not from the thiamine (B1) itself. At ¼ dose the tonic is cheap and harmless, but there is no proven reason it works.
Your next step: mark week 4 of flowering on your calendar as the latest day to start the tea, and check the leaf colour every few days from week 2.
Adjusting the schedule for a hot climate
- The mix dries faster. The book’s 3-day and 2-day intervals assume 22–27 °C. At 30 °C with strong airflow, expect shorter intervals. Use the finger test, not the calendar.
- Food is released faster. Warmer mix generally releases nitrogen from organic fertilisers faster, but by how much depends on the product. One study (de Jesus et al., 2024, in the journal Nitrogen) kept organic fertilisers in two US soils at different temperatures. Temperature mainly changed how fast nitrogen came out early on, and it affected feather meal the most. So a mix charged for ten weeks at 22–27 °C may run out sooner at 30 °C, but how much sooner is not known. Watch for early fading, and be ready to start the tea before week 4.
- Mould in the final weeks. Add airflow through the lower part of the plants, and run a dehumidifier if you can.
- Tea in the heat. Make only what you will use within a few days. A nutrient-rich liquid kept at 30 °C loses its oxygen and turns sour.
Your next step: write down the date you first see fading in each crop. That date tells you when to start the tea next time.
Handling guano safely
Dry bat and bird droppings can carry spores of Histoplasma, a fungus that causes the lung infection histoplasmosis. The US Centers for Disease Control and Prevention (CDC) and its National Institute for Occupational Safety and Health (NIOSH) rate cleaning up large piles of bird or bat droppings as high-risk work. For that work they suggest a powered air-purifying respirator (a battery fan that pushes filtered air into a hood or mask) or a full-face respirator with 100-series filters. They note that a disposable N95 mask gives only about 20% of that protection.
Weighing out 100 g for one batch of tea is a small exposure. Pouring bulk guano from sack to sack is not. Topic 1555 covers guano dust, histoplasmosis and choosing a respirator.
Your next step: spray the guano lightly with water before you scoop or pour it, to keep the dust down.
What is well supported and what is not
Well supported:
- lack of oxygen around the roots as the main cause of root rot;
- keeping the clay layer drained;
- using the mix as the plants’ food store;
- a low-analysis bloom fertiliser;
- pH 6.2–6.6 at the roots;
- less water in the final weeks;
- no leaf spraying once flowers form;
- the clay quantities and pipe lengths recalculated in Part 1.
Soma’s own practice, not proven:
- that the four-pipe layout in particular is what makes the bed work;
- the drifting-pH argument;
- the value of vitamin B tonics;
- the 100 g / 2 L / 250 ml / 10 L tea ratio as the best ratio, rather than one ratio that works;
- the three-crop reuse limit.
Treat everything here as a starting point, not a fixed recipe. The book itself says that different varieties feed very differently, and that no single method suits every genetic line.
Share your results
Has anyone built a bed like this in a tropical room? Three things would help other growers: how the timber held up, what you sealed it with, and in which flowering week your plants actually started to fade.
The editors expect a front-loaded mix to empty faster at 30 °C than at 22 °C, which would make week 4 too late to start the tea. A few real observations, posted below this topic, would settle it.
This article is technical growing information, not legal advice. In Thailand, cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568, in force since 26 June 2025. Flower may be sold only against a PT 33 prescription from an authorised practitioner, for no more than 30 days per prescription. Flower that is sold or exported must come from a GACP-certified growing site. Online sale and advertising of flower are prohibited, and recreational use is not permitted. Growing for medical or research use requires a licence. Two Ministerial Regulations of B.E. 2569 tightened licensing in April 2026: the extracts regulation came into force on 26 April 2026, and Controlled Herbs (No. 2) on 30 April 2026. The draft Cannabis Control Act is not law yet: the Cabinet approved the draft on 22 September 2026 and sent it to the House. See topic 1330 for the current legal position. Check the law where you live before growing.