In a living-soil pot you cannot simply blend in all the nitrogen and phosphorus a flowering cannabis plant will need. Mix that much salt-free fertility evenly through the whole pot and it still overwhelms the microbial population you spent weeks building. The Rev’s answer in True Living Organics is geometric rather than chemical: put the concentrated food in a few small, defined places the roots have not reached yet, and let the plant walk to it. This article covers the two techniques behind water-only pots: core feeding (spikes) and layering. It gives the book’s recipes, hole dimensions and timing, and the parts of the method that deserve a caveat.
1. The problem core feeding solves
A 7.5 L pot of well-built living soil holds a large microbial population. That population competes with the plant for nitrogen and calcium. It is also what converts organic amendments into nutrients the plant can use. Two constraints pull in opposite directions:
- Mix enough blood meal and bat guano into the whole pot to carry a nine-week flower, and the concentration is high enough to burn roots and suppress the microbes.
- Mix a safe amount, and a small pot runs out of nitrogen and phosphorus somewhere around week four of flower.
Growers using bottled nutrients solve this by feeding a little at every watering. Living-soil growers generally avoid that route. High-EC mineral feeding can suppress parts of the soil biology, although the evidence is dose-dependent. The aim of a water-only pot is to let that biology do the converting.
Core feeding gets around the trade-off by changing where the fertility sits instead of how much there is. Concentrated dry amendments go into narrow vertical holes near the pot wall. The bulk of the soil stays at a low, microbe-friendly nutrient concentration. Over several weeks the roots grow outward and reach the holes one by one. They take up nitrogen and phosphorus on their own schedule while microbes break down the amendments in the holes.
2. Hole geometry — the numbers that matter
These figures come from True Living Organics (Ch. 5). They are the book author’s own practice, not measured research:
| Parameter | The Rev’s spec |
|---|---|
| Hole diameter | ~1 cm; never wider than 1.5 cm |
| Hole depth | ~3/4 of the soil depth (in a 30 cm-tall pot ≈ 22 cm) |
| Number per plant | 2 or 4, so they split evenly into N-holes and bloom-holes |
| Position | Near the pot wall, away from the stem |
| Timing | Only at the final transplant, before flipping to flower |
| Reference pot | 7.5 L, 9–10 week flower, ~1 m final height, 400 W HID |
Diameter matters more than it looks. A narrow hole keeps the concentrated amendment in a small volume with a large surface-to-volume ratio. Roots meet its edge gradually rather than a whole root mass suddenly sitting in a pocket of blood meal. The book’s 1.5 cm limit comes from experience, so treat it as a working rule, not a measured threshold.
The hard rule: never punch a hole into soil where roots are already living. That is why coring is done at the final transplant, into fresh soil the root ball has not colonised. Coring an established pot means driving a tool through working roots and then packing concentrated nitrogen against the wound.
Outdoors the diameter rule relaxes: the book says holes in ground beds do not need to stay narrow. The placement rule does not relax. Outdoors, core at the projected drip line of the mature canopy, not near the existing root zone.
3. The two core-feed recipes
Both recipes use equal parts by volume, so they scale to any batch size. Mix them dry, and store them dry and labelled.
All-purpose, nitrogen-dominant core mix
- 1 part blood meal
- 1 part bone meal
- 1 part high-N bird or bat guano (e.g. NPK 9-3-1)
- 1 part feather meal
- 1 part kelp meal
Flowering core mix
- 1 part feather meal
- 1 part high-phosphorus bat guano (low N, high P; check the label)
- 1 part bone meal
- 1 part kelp meal / alfalfa meal at 50:50
With four holes, two get the N mix and two get the bloom mix. With two holes, one of each.
Note what is absent: no dolomite lime and no gypsum in the holes. Powdered lime in a concentrated pocket does not behave like lime spread through cured soil. The book treats lime as a soil-mix ingredient that must be cured in, not as a spike ingredient.
After filling: cover the hole mouth with a little soil, press gently with a finger, put the bark mulch back, then water the pot thoroughly.
4. Layering — floor, top layer, mulch
Layering is the companion technique. Instead of one uniform pot, you build separate functional zones:
- Floor. Before any soil goes in, dust the bottom of the empty pot with a thin layer of the nitrogen-rich layering mix, plus a little all-purpose amendment.
- Soil column. Fill with your cured living-soil mix, then core-feed.
- Top layer. Dust the soil surface thinly with the same nitrogen-rich mix.
- Mulch. Cover the top layer with composted, shredded bark.
Nitrogen-rich layering mix (top and floor)
- 2 parts blood meal
- 1 part kelp meal (or kelp/alfalfa 50:50, which the book prefers)
- 1 part feather meal
- 2 parts high-N bird/bat guano
- 1 part finely ground oyster shell flour, or bone meal
Why put the nitrogen at the floor and the surface rather than through the middle? The book’s reasoning is that these are the two most aerobic zones in a container. High microbial activity there needs a lot of nitrogen and calcium, and if you do not supply it, the microbes take it from the plant. The book author dropped the “middle layer” from his older method because it added complexity without matching benefit. His current recommendation is top layer, floor layer and coring.
Mulch note: always put a light dusting of N-rich amendment under the bark mulch. Fresh bark ties up nitrogen as it decomposes on the surface, and the dusting stops the surface microbes from taking nitrogen from the plant. Avoid walnut-derived mulches. In warm conditions, expect most of the mulch layer to disappear within 30–45 days and plan to replace it.
5. Top-dressing during flower (summary)
Core feeding is not the only input. The book’s top-dressing pattern, in short:
| Flower stage | Top-dress with |
|---|---|
| Weeks 1–3 | Thin surface dusting of a balanced guano, only if needed |
| Week 4 onward | No more nitrogen. High-P guano only: ~2–3 teaspoons in small clumps on the mulch, away from the stem, misted so it breaks down. Repeat no more often than every 10–14 days, and only if needed. |
Placing the guano in small clumps rather than spreading it evenly is deliberate. It keeps the microbes that break it down concentrated in a small area, and it limits how much of the surface sees a strong phosphorus source at once. For a full week-by-week organic feeding plan, use the schedule in Bat Guano Tea and the 10-Week Organic Feeding Schedule rather than running two different schedules side by side.
6. When you do not need to core at all
The most useful line in the chapter is about pot size. Core feeding exists because the book author flowers in small pots. His stated rule of thumb:
The larger the pot relative to the plant, the less fertility the soil needs.
At 400 W HID, he treats a 13.25 L pot or larger as the threshold for a genuinely water-only grow using only layering and coring. At 7.5 L he cores and brews teas. At 11.5 L, for the same plant, he says he could often skip both.
Southeast Asian growers should take this seriously. Space is expensive, but so is the labour of a feeding schedule. If your room can take 15–20 L fabric pots, a bigger pot with good layering and no coring is often the simpler route. For choosing pot size and avoiding root-bound plants, see topic 1342 (pot size / root bound).
7. What is verified, and what is the book author’s experience
We keep these apart on purpose, because the book presents this method as proven practice, not as tested research.
Well supported outside the book:
- Concentrated nitrogen sources in direct contact with roots can injure them. This is a widely recognised horticultural risk, and fast-mineralising organic meals (see below) are not exempt.
- Fresh, high-carbon mulch ties up nitrogen while it decomposes on a soil surface, and putting nitrogen under the mulch is standard advice.
- Nitrogen from concentrated organic meals mineralises fast. Hartz TK & Johnstone PR (2006), “Nitrogen Availability from High-nitrogen-containing Organic Fertilizers”, HortTechnology 16(1): 39–42 (University of California), tested seabird guano, fish powder, feather meal and blood meal. The fertilisers were mixed into organically managed field soil and incubated in the laboratory at 10, 15, 20 and 25 °C. 47–60% of the organic nitrogen mineralised within two weeks at every temperature. The per-fertiliser figures are covered in our companion article on nitrogen release from organic meals. Caveat: this was a soil incubation in field soil, not a container trial in a living-soil mix. Applying it to a core hole is an extrapolation. Still, it suggests the material in your holes is not a season-long time capsule: most of its nitrogen is likely released within weeks, inside a single flower cycle.
The book author’s experience, not independently verified:
- The 1.5 cm maximum hole diameter, the 3/4-depth figure, the 2-or-4-hole rule and the exact part ratios in the recipes. No published trial compares core-fed living soil with evenly amended living soil in cannabis.
- The claim that feather meal releases nitrogen far more slowly than blood meal. In the incubation above, all four materials, feather meal included, mineralised roughly half their organic nitrogen within two weeks. Any gap between feather meal and blood meal is much smaller than the book implies. Do not plan a long-flowering sativa on the assumption that feather meal will still be releasing nitrogen at week ten.
8. Adapting the method to a tropical room
Three adjustments for Thailand, Vietnam and similar climates:
- Mineralisation at least as fast as the study. In the incubation above, release was rapid at every temperature tested, up to 25 °C. A room running 28–30 °C is above the tested range, so the exact rate is unknown. Do not count on the holes lasting longer than the study suggests. Start with the recipes as written, but expect to need the early-flower top-dress rather than treating it as optional.
- Faster mulch turnover. The book’s 30–45 day figure is for warm conditions. Budget for replacing the mulch mid-flower.
- Source substitution. Blood meal and steamed bone meal are the two ingredients most often hard to find locally at reliable quality. Fish meal can partly replace the nitrogen fraction, though it carries more phosphorus. Whatever you substitute, buy aged or dried commercial guano and use it at label rates. Fresh, unaged guano is rich in ammonium-forming compounds and can release enough ammonia to burn roots, especially in a small pot. Dry guano is also a respiratory hazard when handled: wear a dust mask and work in a ventilated space.
9. A short checklist
- Build and cure your soil mix first. Coring does not rescue an uncured mix.
- Dust the empty pot floor with the N-rich layering mix.
- Fill with soil; transplant the plant.
- Core 2 or 4 holes straight away: ~1 cm wide, ~3/4 of the soil depth, near the wall. Half get the N mix, half the bloom mix.
- Cap the holes with soil and press lightly.
- Dust the surface with N-rich mix; cover with composted bark mulch.
- Water thoroughly.
- Do not core again this cycle. Feed from the surface only.
Have you run a side-by-side test, with a cored small pot against a larger uncored pot, in a hot room? The pot-size threshold is the part of this method most likely to shift in a tropical climate, and it is the number we would most like to see growers in the region test. Post your pot volume, lamp wattage, and whether you had to top-dress.
Related reading: topic 1091, Organic vs Synthetic Nutrition: Living Soil & No-Till, and topic 1342 on pot size and root-bound plants. Compost teas are the other half of the feeding strategy when your pots are small.
This article is technical horticultural information for readers operating legally in their jurisdiction. Cannabis cultivation is regulated differently in every country. In Thailand, cannabis is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis) B.E. 2568, and cultivation falls under that notification and its licensing rules. The Cannabis Control Act is still a draft before the House. Check your local law before growing. Nothing here is legal advice.