A phenotype hunt means growing many plants from one seed packet under the same conditions, scoring each one, and keeping the best as a mother plant for cuttings. This part covers the second half of the hunt: checking plants after harvest, scoring them with weighted criteria, keeping records you can trust, laboratory testing, and keeping the chosen plant healthy for years. Every section ends with something you can do in your own room or field.
The growers who end a hunt with a plant worth keeping are usually the ones who wrote everything down. Part 1 covered how many seeds to start, how much of what you see is genetic, and what to record in the vegetative and flowering stages.
This is Part 2. Part 1: Phenotype Hunting: From a Packet of Seeds to One Keeper Mother
6. Stage Three: Screening After Harvest
Plants that looked the same at harvest often separate during drying and curing. This is why you keep a live, rooted cutting of every candidate until the hunt is over.
| Criterion | What to record |
|---|---|
| Drying speed | Days until small stems snap instead of bending, with the same drying conditions for every plant |
| Aroma when jarred and after curing | A score from 0 to 10 plus a description, at day 14, 30 and 60 |
| Smoothness and flavour when heated | Ash, smoothness and flavour, always tested at one fixed temperature |
| Effect | Onset, duration and character, recorded “blind” so the tester does not know which plant the sample came from |
Aroma retention is where plants separate most clearly. Two plants can smell equally strong on the day they go into jars and be far apart by day 60.
Effect scores are subjective: they record one person’s impression. Mark them as such in your notes. No cultivar treats or cures any illness, and no score from a hunt can show that one does.
Translator’s note: In Thailand, cannabis flower (ช่อดอกกัญชา) is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568, issued under the Thai Traditional Medicine Protection Act B.E. 2542 and in force since 26 June 2025. Flower may be sold only against a PT 33 (ภ.ท.33) prescription covering at most 30 days, and advertising or selling flower online is prohibited. Run any tasting or effect check only within what your licence and Thai law allow. In very humid months, drying time depends heavily on the room, so dry all candidates together in one room and log its humidity (see drying at 85–95% humidity).
What to do: put a calendar reminder for day 14, 30 and 60 after jarring, and score every candidate’s aroma on the same day.
7. The Scoring System
7.1 A table of weighted criteria
Score each criterion from 0 to 10. Multiply the score by the criterion’s weight, then divide by 10. The weights in each column add up to 100, so a perfect plant scores 100.
The three columns show three different goals:
- Medical-supply consistency: a plant that gives the same result batch after batch.
- Aroma focus: a plant with a distinctive aroma that survives curing.
- Commercial yield: a plant that gives the most output for the least labour.
| # | Criterion | Medical-supply consistency | Aroma focus | Commercial yield |
|---|---|---|---|---|
| 1 | Vigour, roots, structure | 8 | 6 | 10 |
| 2 | Clone-ability | 9 | 6 | 9 |
| 3 | Resilience to stress and pests | 9 | 6 | 10 |
| 4 | Predictable flowering time | 11 | 5 | 12 |
| 5 | Consistent stretch ratio | 5 | 3 | 6 |
| 6 | Bud density and structure | 6 | 8 | 10 |
| 7 | Mould resistance | 13 | 9 | 12 |
| 8 | Aroma: character and retention | 11 | 38 | 8 |
| 9 | Yield and trimming difficulty | 8 | 6 | 16 |
| 10 | Match to the laboratory profile you want | 20 | 13 | 7 |
| Total | 100 | 100 | 100 |
7.2 Worked example: two plants in the final
Two finalists, A and B, are scored with the medical-supply weights.
| Criterion # | Weight | A score | A weighted | B score | B weighted |
|---|---|---|---|---|---|
| 1 | 8 | 5 | 4.0 | 9 | 7.2 |
| 2 | 9 | 9 | 8.1 | 6 | 5.4 |
| 3 | 9 | 8 | 7.2 | 6 | 5.4 |
| 4 | 11 | 9 | 9.9 | 6 | 6.6 |
| 5 | 5 | 7 | 3.5 | 6 | 3.0 |
| 6 | 6 | 5 | 3.0 | 9 | 5.4 |
| 7 | 13 | 9 | 11.7 | 4 | 5.2 |
| 8 | 11 | 4 | 4.4 | 10 | 11.0 |
| 9 | 8 | 6 | 4.8 | 9 | 7.2 |
| 10 | 20 | 9 | 18.0 | 7 | 14.0 |
| Total | 100 | 71 | 74.6 | 72 | 70.4 |
If you simply add up the scores, B totals 72 against A’s 71. A grower counting points would keep B. With the medical-supply weights, A wins. The reason is that B is weak on criterion 7, mould resistance, and criterion 10, match to the laboratory profile. Those two criteria carry the heaviest weights in that column.
The same two plants give different winners under each set of weights:
| Set of weights | A | B | Winner | Margin |
|---|---|---|---|---|
| Plain sum of scores | 71 | 72 | B | 1 |
| Medical-supply consistency | 74.6 | 70.4 | A | 4.2 |
| Aroma focus | 62.4 | 80.7 | B | 18.3 |
| Commercial yield | 71.0 | 72.3 | B | 1.3 |
The scores of the plants are the same in every row. Only the goal behind the weights changed, and with it the winner.
7.3 Why the weights must match your goal
A medical-supply hunt gives most weight to repeatability, because a peak result is of little use if the next batch cannot reproduce it. An aroma hunt gives most weight to the aroma profile and how well it survives curing. A yield hunt gives most weight to output and to the hours of labour each crop needs.
Read the margin as well as the winner. A margin of 1.3 out of 100 is not a real difference; it is within the noise of a single grow.
What to do: write down your goal and your weights before you score the first plant, and do not change them afterwards. If the top two finish within a few points, grow both again side by side (section 9) before you choose.
8. Records: Tags, Photographs and Logs
| What to record | When |
|---|---|
| Plant number | At germination. Every other record hangs off this |
| Cross, breeder and seed lot | At germination, for example the lot code printed on the seed packet |
| Position in the room; pot and substrate batch | At planting. Position is the biggest source of false differences |
| Cutting taken, cutting rooted, success or failure | In the vegetative stage. This is the clone-ability score |
| Height, aroma and resin notes | On one fixed day each week, from the flip |
| Harvest week, dry weight, minutes of trimming | From harvest onwards |
| Curing notes at day 14, 30 and 60; laboratory results | After harvest |
Keep every input the same for every plant. Whatever nutrient line you use, every plant gets the same product, at the same strength, on the same day.
Numbering: use one scheme, such as H14-07 for hunt 14, plant 7. Put it on a tag tied to the plant itself, not to the pot, because pots get swapped. Carry the same number unchanged onto the cutting’s tag, the jar, the photo filename and the laboratory label.
Photographs only compare well when taken the same way each time. Use the same distance and angle, neutral white light, and keep the tag in the frame. Take one photo a week, plus close-ups at week 6, week 8 and harvest. The purple-pink (magenta) light of many LED grow lamps distorts colour, so switch to white light for photos.
Environment logs show that you compared plants and not small differences in the room’s climate. Record temperature and relative humidity at canopy height in two or more spots, and the volume of water each plant receives.
Translator’s note: power cuts and air-conditioning failures are common in Thai grow rooms, and a hot night can mark some plants more than others. Log each failure with its date, length and the plants near the worst spot. A plant that scores low just after such a night may have been unlucky in its position, not weak in its genes.
What to do: set up the record sheet and print the tags before you germinate the first seed.
9. Why One Plant Is Weak Evidence
A confounder is anything other than genetics that differs between plants and changes the result. If you grow only one plant of each genotype, its genes and its position in the room are mixed together. You cannot separate them afterwards, because the information needed to do so was never collected.
| Confounder | How to reduce it |
|---|---|
| Position: the centre gets more light and steadier air | Assign positions at random, rotate plants, and log where each one stood |
| Light spread: light falls off towards the edges | Measure light across the room; put finalists in zones with similar light |
| Pot size: more volume gives a bigger plant | Use identical pots and one batch of substrate |
| Watering: hand watering differs from plant to plant | Measure the volume each plant receives |
The fix is replication, meaning growing the same genotype more than once. Grow your finalists again from their stored cuttings, three plants each, in positions chosen at random. Then compare the spread within each genotype with the difference between genotypes.
If the three copies of one plant differ as much as the finalists differ from each other, you measured your room, not your plants. If a plant only wins when it stands in the centre, its win came from the position.
What to do: before you name a keeper, grow the top three or four finalists again as three cuttings each, in random positions.
10. Laboratory Analysis and the Certificate
| Analysis | Usual method |
|---|---|
| Cannabinoid content (potency) | High-performance liquid chromatography (HPLC), which separates compounds in a liquid without heating them |
| Terpene profile | Gas chromatography with mass spectrometry (GC-MS), which separates compounds as a heated gas and identifies them. Common targets: myrcene, limonene, linalool, pinene, caryophyllene, humulene, terpinolene, ocimene |
An article on cannabis testing in Inform, the magazine of the American Oil Chemists’ Society (a scientific society for oil and fat chemistry), makes two points worth knowing. It was first published in 2016.
- A proficiency survey, in which many laboratories analyse the same sample and their results are compared, found that 90% of the laboratories in it used liquid chromatography for potency. Gas chromatography needs an extra chemical preparation step (derivatisation) that is prone to error. Its heat also drives decarboxylation, the conversion of the acid forms of cannabinoids, which inflates the potency figure.
- Headspace gas chromatography, which measures the vapour above a heated sample, profiled 38 terpenes. It is still only semi-quantitative, meaning it ranks amounts reliably but does not measure them exactly. Some terpenes evaporate poorly and stick to solid surfaces, so part of them is never measured.
So terpene figures can rank plants, but they cannot settle small differences. A total of 1.8% terpenes is not shown to be better than 1.6% from another sample. Keep three cautions in mind:
- The sample is not the whole plant. The same review notes that potency figures jump around when samples are not representative. “Laboratory shopping”, sending samples to several laboratories and reporting the highest number, is also known to happen.
- Compare results from one laboratory only, and test again before you believe a small gap.
- Score how well the plant matches your target profile, not who has the highest number.
Translator’s note: before sending samples, ask the laboratory which method it uses for potency and terpenes, which terpenes it reports, and whether it takes part in proficiency testing. Send all candidates to the same laboratory at the same time, so differences between laboratories or test runs do not decide your keeper. How to read the result sheet is explained in How to Read a Cannabis Certificate of Analysis.
What to do: send samples of your finalists in one batch to one laboratory, and enter the results in the “laboratory profile match” row of your scoring sheet.
11. Keeping the Keeper Over Many Crops
Finding the keeper is half the work. Keeping it healthy and unchanged goes on for as long as you grow it.
| Task | How often |
|---|---|
| Health check of the mother plant, kept in vegetative growth and low stress | Weekly |
| Take and root a backup cutting | Monthly |
| Test for disease agents and viroids | Before any large round of propagation |
| Grow the keeper again side by side with the runner-up | Once a year |
11.1 Drift, somatic mutation and disease load
Growers often say “genetic drift” when a clone line kept for years seems to decline (see Cannabis Strain Degradation). Two different mechanisms sit underneath.
Somatic mutation. These are changes in the DNA of the plant’s body cells, which build up as a line is cloned again and again. Cannavigia, a company that makes compliance software for cannabis producers, published a review that blames clonal decline on these mutations. It invokes Muller’s ratchet: without sexual reproduction, there is no recombination to remove harmful mutations, so they only accumulate.
The review names stress as the trigger: irregular light cycles, the wrong pH in the substrate, too little water and too little feed. The longer a mother is kept and the more cuttings are taken from it, the higher the risk. The review advises replacing mothers with cuttings taken from the middle region of the plant. In the study it cites, the middle of the plant carried the fewest genetic variants, and the top carried the most.
Translator’s note: in Thailand, a power cut that interrupts the light cycle is exactly the kind of stress listed above. Put the mother room’s lights on a timer with battery backup, or log every interruption, and replace a mother early if it has been through many of them.
Disease load. Hop latent viroid, a tiny infectious RNA that spreads in plant sap, is the cause most often mistaken for genetic decline. Oregon State University Extension publication EM 9570 (Cynthia M. Ocamb, August 2024) reports four findings:
- Infected drug-type cannabis produces less flower mass and fewer trichomes.
- Its cannabinoid and terpene levels drop.
- The viroid travels in cuttings taken from infected mothers.
- Infected plants may show no symptoms, or symptoms so mild that they go unnoticed, so it cannot be reliably diagnosed by eye.
Test mothers before you take cuttings. A viroid infection can be dealt with; an accumulated mutation load cannot.
Translator’s note: hop latent viroid is usually detected by RT-PCR, a test that finds the viroid’s genetic material. Ask a laboratory in Thailand whether it offers this test for growers before you plan around it. Because you cannot diagnose the viroid by eye, the safer habit until you can test is to start mothers from seed or from tissue-cultured stock, and never to bring in clones from other farms.
Re-testing. Keep the runner-up alive as a cutting too. Every year, or every few crops, grow the keeper and the runner-up side by side in random positions. Score both on your original scoring sheet and send samples of both to one laboratory. Compare the results with your archived scores, not with your memory.
What to do: put the four maintenance tasks in a calendar today, with the yearly side-by-side run as a fixed date.
12. The First Step of Medical-Supply Work
A hunt is also the first stage of choosing a cultivar for medical supply. There, the requirement is not one spectacular batch but batch-to-batch equivalence: every batch must match the last.
| Home hunt | Selection for medical supply |
|---|---|
| Finds the most impressive plant | Finds the most repeatable plant |
| Notebook or spreadsheet | Records that an auditor can check, linked to each batch |
| Laboratory testing optional | Testing of every batch, with samples kept in storage |
Good agricultural and collection practice (GACP), and the good manufacturing practice (GMP) frameworks built on it, rest on traceability and reproducibility. Both start with the plant you chose and the records that show why you chose it.
Translator’s note: if you plan to supply licensed medical buyers in Thailand, a GACP audit will look at the records described in section 8, starting with where your mother plant came from (see GACP Farms: The Records a Certification Audit Checks).
What to do: if medical supply is your goal, keep your hunt records from the first seed in a form you could show an auditor, with plant numbers matching every later batch.
13. Share Your Scoring Sheet
Post your scoring sheet below this topic. Other growers learn most from the details, not just the winner:
- the weights you chose, and why;
- the criteria you dropped because they measured your room instead of your plants;
- the plant you were sure about in week 5 that lost after curing;
- your population size, how many plants reached flower, and your stretch ratios;
- how mould resistance held up in a real wet season.
If you have grown your finalists again side by side, say whether the winner stayed the winner. Almost nobody publishes that, and it is the most useful result a hunt can produce.
This article is for education. Grow only where, and as far as, your licence and the law allow.
Sources named in this part
- Laura Cassiday, “The Highs and Lows of Cannabis Testing”, Inform (American Oil Chemists’ Society), 2016: cannabis testing methods (potency by liquid chromatography, headspace terpene profiling).
- Cannavigia: review of clonal degradation, somatic mutation and Muller’s ratchet.
- Oregon State University Extension, EM 9570, “Hop latent viroid in hemp”, Cynthia M. Ocamb, August 2024.