A two-room perpetual harvest keeps a flowering room full all the time. You take cuttings on a fixed schedule and grow them in a separate veg room. Then you harvest a few plants every few days or every two weeks. This part covers what the arithmetic leaves out. It explains how to move plants and keep them at an even height, and what records to keep. It also covers the costs of a room that never empties: pests, odour, heat and the risk of losing mother plants. The last sections cover living soil, who the system suits, and the Thai licence rules. It is written for licensed small-scale and craft growers in Thailand.
Part 1 explains the two rooms and how to keep light out of the flowering room. It also gives the formula for how many clones to cut.
This is Part 2. Part 1: Two-Room Perpetual Harvest: The Cloning Schedule and the Arithmetic Behind It
Words used in this part
- Veg room: the room for leafy growth and rooting cuttings. Its lights run 18 hours on, 6 hours off.
- Flowering room: its lights run 12 hours on, 12 hours off. The long dark period makes plants flower.
- Clone: a rooted cutting from a mother plant. It is genetically identical to her.
- Mother plant: a plant kept in leafy growth only to supply cuttings (Mother Plants and Cloning, Part 1).
- Flip: moving a plant from the veg schedule to the flowering schedule.
- Batch system: the whole room is planted, flowered and harvested together, then emptied.
- Cultivar: a named cultivated variety of cannabis. Most growers call it a strain.
Practical limits
Each plant must move on its own
You will take out a plant every few days and move others around. Each plant must therefore come out without disturbing the rest.
These systems work well:
- pots of soil or coco coir (the simplest choice);
- drip irrigation, which feeds each pot through its own small line (Drip Irrigation for Cannabis in the Tropics);
- ebb-and-flow, where a tray floods with nutrient solution on a timer and then drains.
These systems make it hard to remove one plant without disturbing its neighbours:
- aeroponics, where roots hang in the air and are sprayed with a fine mist;
- NFT channels with fixed positions (nutrient film technique: roots sit in a channel with a thin flowing layer of solution; see Hydroponic Cannabis);
- any system where the roots of different plants grow into each other.
What to do: before you choose a system, make sure you can lift out any single plant without touching its neighbours’ roots.
Keep the tops of the plants level
Plants at different stages are at different heights. Stand shorter plants on upturned pots or crates. Remove these stands as the plants grow. A set of stands in assorted heights is all the equipment you need. This keeps every plant top at a similar distance from the lights. For general methods of controlling the canopy (the top layer of leaves and buds), see SOG vs SCROG and the Advanced Techniques category.
Labels and records
Write each plant’s cutting date and flip date on its pot and in your records. After two months you will not remember them. On a licensed site, these records must also match what the licence permits (see “The Thai rules” below).
What to do: label each clone on the day you cut it. Add the flip date on the day it enters the flowering room.
The rotation can never stop
The system only works if the cutting never stops. A missed cutting week leaves a gap that moves through the whole cutting-to-harvest time. In the published example from Part 1, that is about 90 days, roughly three months. Three months later, you have a gap in your harvests.
What to do: mark every cutting day on a calendar. Arrange in advance who takes the cuttings when you are away.
The costs the formula leaves out
The room never empties, so pests never lose their food
A perpetual room is never empty. Once pests get established, they always have plants to feed on. Their numbers can build up over months. In Southeast Asia, mites and mildew are a problem all year round. This is the strongest argument against the system, and you should weigh it honestly.
Ways to reduce the risk:
- Quarantine everything that enters the room, including mother plants. Keep new plants apart and check them before they join the rotation. This stops pests from reaching plants at every stage.
- Take cuttings only from your own quarantined mothers. Do not bring in clones from outside. Outside clones are a common way powdery mildew (Powdery Mildew on Cannabis), spider mites, aphids and thrips (Spider Mites & Thrips) get in.
- Deep-clean the room one section at a time, on a fixed schedule. You cannot empty the whole room, so this is how you remove pests and spores that build up in corners and on equipment.
- Write down a plan for breaking the cycle if you have to. This plan says how you would empty and clean the room during a serious outbreak.
If you have no plan for emptying the room, you have no plan for a serious infestation. Integrated pest management (IPM) combines prevention, regular checking and control methods, and uses sprays as the last step. It is covered in Integrated Pest Management for Cannabis, Part 1.
Translator’s note: In Thailand, growers often buy clones from other farms. Those clones can bring in pests. They can also carry hop latent viroid (HLVd). HLVd is a tiny infectious agent that can stunt plants and reduce yield. Infected plants may look healthy for a long time (Hop Latent Viroid). A clone sold under a copied name can also turn out to be a different cultivar. In a perpetual room, one bad clone can reach plants at every stage. Start your mothers from seed or from a source you trust. If you can find a laboratory that tests for HLVd, have your mothers tested. If you must spray, use only products registered with the Department of Agriculture (กรมวิชาการเกษตร), exactly as the label says (What You May Legally Spray on Cannabis Under Thai GACP).
Odour never stops, so the filters must run all the time
A batch room does not smell between crops. A perpetual room always smells. In Thailand, odour that reaches neighbours can lead to public-nuisance complaints.
Plan two things from the start:
- Carbon filtration: air leaving the room passes through a filter of activated carbon, which holds odour molecules.
- Negative pressure: the fan pulls more air out of the room than comes in. Air then leaks into the room through gaps, not out of it, so smell does not escape untreated.
Size both for non-stop use, not just the strongest-smelling weeks of a single crop.
The heat never stops
With no off period, the room never cools down. In a tropical climate, the cooling then runs non-stop. That makes it the largest running cost after lighting. This is the main reason to use LED in a perpetual room here. You do not pay to remove heat that your lights never make.
Two rooms still use your electricity better than one. Your highest-power lights run 12 hours a day over a full room, not over a half-empty one. To find the saving for your setup, use your own numbers. Multiply each light’s wattage by its hours per day and days per month.
Translator’s note: Room temperatures in Thailand often reach 30–35 °C without cooling. A batch room is sometimes empty, so you can plan air-conditioner repairs for that time. A perpetual room is never empty. Every power cut or cooling fault hits plants at every stage at once. If the air conditioner stops while the lights are on, the lights keep heating the room. Decide in advance that the lights go off first if cooling fails. Fit a temperature alarm so you hear about a failure quickly. For cooling and dehumidifying equipment, see Grow Room Climate Control, Part 2. Part 1 explains how to check light timers after a power cut.
If the mother plants fail, everything stops
Every clone comes from a mother plant. A perpetual system uses cuttings all the time, so you must keep mothers in leafy growth indefinitely. That is one more group of plants to plan space for. If the mothers die or get sick, you have nothing to cut from, and the whole rotation stops.
What to do: keep at least two mothers of any genetics you cannot replace.
Living soil in a perpetual room
Living soil is a soil mix in which soil organisms release nutrients to the roots (Organic vs Mineral Nutrients, Living Soil and No-Till). Freshly mixed living soil needs time to cure (rest, moist, so the organisms can break down the added materials) before plants go into it.
In a batch system, you prepare one big batch of soil between crops. In a perpetual room, soil preparation never stops. You need cured soil ready at every transplant date. Recycled soil suits this well, because root balls and used soil come out of the room continuously (Recycling Living Soil).
Here is how many curing bins you need with a 30-day cure and a transplant every 2 weeks:
- A bin mixed on day 0 is ready on day 30. Transplants happen every 14 days, so it is used at the next one, on day 42.
- Each bin is therefore busy for 42 days, which is three 2-week intervals. You need 3 bins, started two weeks apart. This works if you mix and close each batch within a day or two.
- Sometimes a bin takes the full two weeks to fill with used soil before its cure starts. Filling plus curing then takes 44 days, so the bin is used at day 56. Plan for 4 bins.
- Two bins started two weeks apart only work if filling plus curing takes 28 days or less.
Top-dressing (spreading dry fertilising materials on the soil surface) or core feeding (placing them in holes in the root ball) happens at each transplant (Core Feeding and Layering). It becomes a small job every two weeks instead of a big job every two months. Like harvesting, this work is spread out evenly.
What to do: count your bins from your own numbers. Add filling time and cure time, then round up to the next transplant date. Divide that number of days by your transplant interval.
Is it right for you?
It suits you if:
- you want to grow long-flowering sativas alongside shorter cultivars;
- drying and trimming space is what limits you;
- you can only prepare a limited amount of water at one time;
- you already have a separate veg space and your cuttings root reliably;
- your licence covers the number of plants the rotation holds.
It does not suit you if:
- you cannot yet judge each plant’s water needs reliably;
- you cannot run odour control all the time;
- your pest pressure is high and your quarantine is not strict;
- you need the room empty from time to time for any reason.
In short: this system changes your schedule. It has real benefits and one real cost: the room never gets a break. Every cost described in this part comes from that.
What to do: go through both lists. If any line under “does not suit you” applies, fix it first. You can also start with the simpler version from Part 1: flip half your plants, then the other half about a month later.
The Thai rules
- Controlled herb: cannabis flower (ช่อดอกกัญชา) is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568. It was issued under the Thai Traditional Medicine Protection Act B.E. 2542 and has been in force since 26 June 2025 (Cannabis as a Controlled Herb in Thailand).
- Licence and GACP: research, export, sale and processing of flower need a licence. Flower that is sold or exported must come from a cultivation site certified to GACP (Good Agricultural and Collection Practice, the standard for growing and handling medicinal plants; see Good Agricultural and Collection Practice for Cannabis, Part 1).
- Plant numbers and records: a perpetual room holds plants all the time by design. Your plant numbers, and the records behind them, must stay within what your licence permits. Check this before you build the second room.
- Sales: flower may be sold only through licensed channels. It may be dispensed only against a prescription on form PT 33 (ภ.ท.33) from an authorised practitioner, for a maximum of 30 days (The PT 33 Cannabis Prescription).
- Online: advertising flower and selling it online are prohibited. Recreational use is not permitted.
- 2026 changes: two Ministerial Regulations of B.E. 2569 tightened licensing this year (Thailand’s Two Ministerial Regulations of B.E. 2569). The Ministerial Regulation on Cannabis or Hemp Extracts came into force on 26 April 2026. The Ministerial Regulation on Controlled Herbs (No. 2) came into force on 30 April 2026 and tightens the licence criteria for cannabis flower.
- Draft Act: the Cannabis Control Act is not law yet. The Cabinet approved the draft on 22 September 2026 and sent it to the House of Representatives (The Draft Cannabis Control Act).
Cultivation is illegal in most other Southeast Asian countries. Nothing here encourages growing anywhere it is not permitted.
Share your experience below
If you run a licensed perpetual room in this region, please reply below this topic. Tell us which interval between cuttings or groups you chose. Also tell us what you did about the room never emptying. The efficiency side is just arithmetic. Pest control decides whether the system works, and grow manuals rarely cover it. If you have run both a batch room and a perpetual room through a wet season, please share how they compared. That comparison helps other growers more than the formula does.
This article is technical horticultural information for readers operating legally where they are. In Thailand, cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis) B.E. 2568, selling or processing flower requires a licence, and the Cannabis Control Act is still a draft (Cabinet approved 22 September 2026, sent to the House). Cultivation is illegal in most other Southeast Asian countries. Nothing here is legal, financial or business advice.