Living-soil failures look different from mineral-nutrient failures. A pot fed on bottled nutrients shows trouble through EC and runoff readings. A living-soil pot goes wrong through pH drift, salt build-up from the water and the medium, or one badly chosen liquid feed. This article covers the failure modes specific to this method: how to recognise them, which ones you can recover from, and a checklist to run before you change anything.
Source. Much of the method here comes from True Living Organics: The Ultimate Guide to Growing All-Natural Marijuana Indoors by The Rev (Green Candy Press, first published 2012; later editions have followed). The thresholds, rules and anecdotes below are the author’s view from his own garden, not settled science. Where we have checked a claim against other sources, we say so.
1. First principle: one runoff reading tells you little here
If you come from mineral nutrients, adjust this first: a single high PPM/TDS reading from living-soil runoff means little on its own.
Living soil is full of organic matter, humic substances, dissolved organic carbon and microbial exudates. All of them register on a TDS meter, so runoff from a healthy pot often reads high. If you flush because of one reading, you may strip out nutrients you spent a month curing in.
Runoff EC is still useful as a trend. Measure your input water, take runoff readings the same way each time and record them. A steady rise over several waterings, or readings climbing well above your pot’s own baseline, is one of the few early warnings of salt build-up (section 3).
For day-to-day diagnosis, a soil pH meter tells you more.
2. Soil pH: the main diagnostic tool
The author’s view is that a properly set-up living-soil grow needs no pH meter at all. While you are learning, though, a good one saves months of guesswork.
What to buy: a soil pH meter with a long probe. The author uses a 30 cm probe so he can read pH at depth, not just at the surface. Don’t buy a cheap one. In the author’s view, cheap soil pH meters are worthless, and no meter is better than a bad one.
How to use it properly:
- Know where your core-feed holes are, because pH there differs from the rest of the pot. Take several readings to find the real range.
- Clean and dry the probe before and after each use with a plastic scouring pad and a clean paper towel. Never use steel wool.
- Never clean the probe with detergent or alcohol. Use water only.
- Store it in its case or a sealed bag, away from air.
Most useful application: checking recycled soil batches. The pH of the mix rises as organic material finishes decomposing, which is when the batch is cured. If you need soil before a batch has fully cured, the author’s practice is to pick batches that read 6.2 or above. He prefers around 6.5 for Hashplant-type indicas.
That gives you a concrete readiness test instead of counting days. This matters in a hot climate, where curing runs faster than the author’s cooler-climate timeline.
A solution pH meter is rarely needed in this system. The author uses one only to check new water sources and to see how liquid additives change the pH of a tea.
3. Salt accumulation: the slow killer
This is the most common chronic failure. It has four main sources.
3.1 Hard water
Water quality has its own article on the forum, so here is the short version. In the author’s account, dissolved minerals build up around the root zone over one to two months. They shift root-zone pH until the microbes stop working properly, with mycorrhizae hit early and phosphorus lock-up following.
The author’s thresholds: with tap or well water at around 300 PPM, he considers living soil not viable. At around 60 PPM he considers it workable, provided the dissolved elements are balanced and not dominated by magnesium, iron or sulphur. These figures are stricter than most guidance. Many soil growers do well on 200–300 ppm water. The FAO’s general irrigation guideline puts water below about 450 mg/L TDS (EC below 0.7 dS/m) in the “no restriction” class. That guideline was written for field crops, and pots accumulate salts faster, so treat the higher end with care. What matters most is what your water contains and whether runoff readings trend upward over time.
3.2 Coco coir
The author lists coir as a salt source to be careful with, and it needs more explanation than the book gives.
Raw coconut coir arrives with its cation exchange sites holding sodium and potassium from the husk. When calcium and magnesium arrive in your water or nutrients, they push the sodium and potassium off those sites and are held there themselves. The medium releases sodium into the root zone and pulls calcium and magnesium out of solution at the same time.
Practical rules:
- Buy washed and buffered coco, and check that it really is.
- Rinse it yourself anyway. The author specifies rinsed coir in every recipe.
- If you buy bulk agricultural-grade coir, washing is mandatory. It is often the cheapest option in Vietnam, Thailand, Sri Lanka and India.
Local sourcing cuts both ways: coir is abundant and cheap, and the cheap product is more likely to be unwashed.
3.3 Softened water
Never use it. A water softener swaps calcium and magnesium for sodium, and sodium builds up in soil and harms plants. Softened water belongs upstream of an RO membrane and nowhere else. The water quality article has more detail.
3.4 Worm leachate overuse
Worm bin leachate has a very high PPM, especially if you feed minerals to the worms as the author does. Overuse causes symptoms on the lower and middle leaves that get steadily worse.
Recovery: flush with distilled, rain or RO water. This is one of the few cases where flushing a living-soil pot is the right move. Prevention: dilute heavily, use it sparingly and leave at least 10 days between applications (the author’s interval).
Castings work the same way. Mineral-fed castings are dense in salts. The author sticks to roughly 3 parts soil to 1 part castings in bulk, not extra “for good measure”.
4. Acid shock and mineral salts: the one-mistake failure
This is the failure most specific to living soil, and growers usually cause it by accident.
Mechanism (the author’s description, chemistry corrected): many liquid fertilisers sold as organic contain acids, including some OMRI-listed products. Some are organic acids such as citric acid, used partly to chelate (bind) nutrients. Others are acidified with mineral acids such as phosphoric acid, which is inorganic, not organic. The problem is not organic acids as a category. Any strongly acidic product can cause a sudden pH shift: a mineral acid, or a heavy dose of organic acid. The author compares the effect to decompression sickness. The organisms are not poisoned, but the change is too fast for them to adapt to, and they work poorly for weeks.
The key distinction:
| Effect on soil biology | Recoverable? | |
|---|---|---|
| Moderate dose of an acidic liquid feed | Disruption, weeks of impaired function | Yes: soil can recover |
| Soluble synthetic NPK salts (high-salt bottled or granular fertiliser) | Suppresses and shifts the soil biology but does not wipe it out | Slowly: recovery can take weeks to months. The author treats the pot as committed to minerals for the rest of the cycle |
Not all minerals are the problem. The slow-release dry minerals used in living-soil recipes, such as gypsum, Epsom salt, oyster shell and greensand, are mineral salts too. They release nutrients gradually at modest doses. The risk comes from concentrated, highly soluble NPK salts that flood the root zone all at once.
Reading labels: EDTA (or DTPA/EDDHA) on the label means synthetic chelated micronutrients, which is a mineral formulation. Ignore marketing phrases such as “based on organic ingredients”. Read the ingredient list and guaranteed analysis instead. If the nutrients come from nitrate, phosphate or sulphate salts, the product behaves as a mineral fertiliser whatever the front label says.
If you have already put a mineral fertiliser on a living-soil pot, the author’s view is that you are committed for this cycle. Either carry on with mineral nutrients to harvest, or switch to a heavily chelated organic product. Then recycle the soil and rebuild the biology before the next run.
Nutrient overdose more generally comes by three routes, and each needs a different response:
- Liquid overdose: flush straight away and hope.
- Dry amendment overdose: be ready to start over. No flush removes a dry amendment already mixed through the pot.
- Uncured material: this is a curing failure; see section 6.
There is also a subtler route. A normally amended, properly cured pot can show overdose symptoms if you water in something that shifts soil pH, making nutrients already in the pot too available.
5. pH lockout: causes in this system
General lockout is covered in topic 1337. In living soil, deficiency symptoms usually mean lockout rather than a real shortage. The author lists these causes:
- Too much molasses, or too much kelp/seaweed extract. He specifically warns that too much seaweed extract can block uptake of other nutrients, nitrogen included.
- Hard, high-PPM, high-pH water from wells or the mains supply.
- Pure water with an acidic liquid fertiliser added (section 4).
- Minimalist setup: a large plant flowering in a small pot with no core feeding, where the soil really has run out. This one is real depletion, not lockout.
For the last case the fix is simple: tea plus top-dressing. The author reports the plant greening up within 6–10 days.
On high-peat bagged soils: the author reports that peat-heavy mixes tended to drift down in pH when he recycled them. He suspects fungal dominance, and says he lost several crops before he stopped using them. He adds that peat is probably not a problem if you recycle plenty of plant material, kitchen waste and root balls. This is one grower’s observation, not tested advice. It is plausible, since peat is acidic and fungal decomposition produces organic acids. If you recycle a peat-based mix, check its pH each cycle.
6. Compaction, anaerobic zones and uncured soil
These three are linked, and between them they explain a large share of unexplained decline.
Compaction. Coir and bark fines give structure when fresh. Over time they break down into finer particles and eventually humus, so the soil gets denser. Dense soil goes anaerobic and kills roots. The author’s rule is perlite at 20–25% of pot volume. Perlite and other aeration amendments have their own article on the forum.
A habit that causes compaction: lifting the pot to judge dryness, then setting it down hard. The author notes this can compact a pot noticeably within a month. Lift it gently and set it down gently.
Uncured soil. A batch used too early produces stunted plants and can kill them outright, usually through anaerobic conditions. The good news is that fully cured soil stores well. In the author’s view, nutrients don’t evaporate and over-curing does no harm. If in doubt, cure longer, and use the pH test from section 2 instead of guessing.
7. Environmental causes that look like nutrient problems
These are commonly misdiagnosed as feeding errors:
| Cause | What it looks like | Fix |
|---|---|---|
| Light too close / too intense | Dry, brittle leaf tips or bleaching on the top of the canopy. With HID lamps, canopy heat (the author caps canopy temperature at 30 °C) | Raise or dim the light. With LED, follow the maker’s hanging height and PPFD guidance. Lighting is covered in topic 1001 |
| Hot, dry air (high VPD) | Leaf-margin scorch and tip burn that look like potassium deficiency | Raise RH toward 50–60% or lower the temperature. Avoid strong, dry airflow blowing directly on leaves. Make sure the soil holds enough K (kelp, greensand, balanced dry amendments) |
| Cold lights-off temperatures | Slower uptake of K and P; purple streaking on stems | Raise lights-off temperature. This is rare in this region, outside strongly air-conditioned rooms at night or highland grows in the cool season |
About the middle row: plants do not “sweat out” potassium. Hot air plus low RH means a high vapour pressure deficit (VPD), and the plant transpires much faster. Water uptake can then outrun nutrient supply. Dissolved salts concentrate at the leaf edges and in the root zone, and the plant’s demand for potassium rises because potassium drives the stomata that open and close all day. The result is damage that looks like K deficiency, and a real K shortfall if the soil can’t keep up. Ventilation itself is not the problem. Very dry air moving fast across the leaves raises transpiration further.
This row matters most in this region because air conditioning removes moisture aggressively. A room cooled to a comfortable temperature can easily sit below 45% RH and produce potassium-type symptoms that look like a soil problem.
8. Things that look like injuries but are not problems
Two things look alarming and aren’t:
Lower-leaf yellowing in late flower. The plant is moving nitrogen out of its least productive leaves toward the canopy, which is normal. Let it happen, remove the leaves only once they are dry and brittle, and recycle them. If yellowing spreads unusually fast, suspect overwatering before deficiency.
Root damage after transplant. Symptoms are burnt, upward-curling leaf edges at the top of the plant and a generally lifeless look. The author’s advice is firm: do nothing. No vitamin B and no additives, which in his view only unbalance the soil. Give pure water at sensible intervals, keep stress low, and he expects full recovery in around 10 days.
9. The diagnostic checklist
When several plants are struggling and you can’t find a cause, the author suggests asking yourself:
- When did I last change the carbon water filter?
- How old is the RO membrane, and have I checked water PPM recently?
- Has anything changed in my lighting (height, dimmer setting or, for HID, bulb age)?
- Is there anything wrong with my ventilation?
- Have I been lazy about topping up perlite when recycling soil?
- Have I checked for light leaks: vent tape, tent seam tape, the light-block behind the door zip?
- Have I changed any ratios or tried new products or brands in the past few months?
- Have I checked the timer settings?
- How sure am I that my meters are accurate?
- How old is my mycorrhizal inoculant?
- Were my genetics bred under mineral nutrients?
The governing rule: change one thing at a time, then wait and watch. The author suggests one to two months. For rapid decline, look at what you did about two weeks ago. For slow decline, look at the past two months.
On hermaphrodites: the author’s view is that a plant turning hermaphrodite is more often grower error than genetics, unless the line’s origin is unknown. In his own garden the usual cause was light leaks. That is his experience, not a rule, but checking seals routinely costs nothing. Tent vent tape degrades, and tents flex as the ventilation cycles.
10. Fungus gnats: tolerable at low numbers, not harmless
The author takes the unusual position that fungus gnats are hard to avoid in living soil and do little harm at low numbers. His reasoning is that larvae help process organic matter. We only partly agree.
The documented risks:
- Larvae feed on roots and tunnel into stems at the soil line. Extension services describe them as especially destructive to seedlings, clones and young plants, and mature plants suffer at high numbers.
- Larvae can carry root-rot pathogens including Pythium and Fusarium. Their feeding wounds also give other soil-borne pathogens a way into the roots.
In a humid tropical room, especially a perpetual-harvest room with no crop break, gnat numbers never get a natural interruption. That risk is real.
Monitoring and control:
- Place yellow sticky traps just above the soil surface and count adults weekly.
- If numbers climb, drench with Bacillus thuringiensis subsp. israelensis (Bti), the strain that targets gnat larvae. Other Bt strains do not.
- Protect seedlings and clones first.
Judge by numbers and by plant stage, not by principle.
Which of these have you diagnosed correctly on the first attempt? We suspect salt build-up from unwashed local coir goes under-diagnosed across the region, because coir is cheap here and everyone uses it. If you have measured the EC of your coir before and after rinsing, please post the numbers; they would help a lot of people.
This article is educational horticultural information only. In Thailand, cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis) B.E. 2568. Cultivation must be licensed, and any flower sold or exported must come from a GACP-certified cultivation site. Flower may be dispensed only against a PT 33 prescription from an authorised practitioner. Selling or advertising flower online is not permitted, and recreational use is not permitted. The Cannabis Control Act is still a draft before the House. Check the law where you live; nothing here is legal advice.