Put two packs of CBD seeds beside each other, one labelled 1:1 and the other 20:1, and they look the same: same brand packaging, same seed count, seeds which nobody’s eye can separate apart. Grow them in the same tent and they go their separate ways from the first step and do not converge again. The reason is a single gene, and the clearest way to see what it does is to track the two packs through each stage they go through: the breeding that produced them, the seed, the seedling, the flower tent, the cut, the jar, the lab report and the border. The lines used as examples throughout are taken from the range at https://calmcbdseeds.com, which goes 1:1, 2:1 and 20:1 with a highest line at around 30 to one; the genetics is the same regardless of which shop the seeds came from.
Before the Seed Exists
Cannabis decides whether it will make THC or CBD at one locus on the genome. The gene there comes in two versions: one builds the enzyme that turns the common precursor into THCA, the other the enzyme that converts it into CBDA. Every plant holds two copies, one inherited from each parent, and the pair sets the chemotype. Two THC copies give a THC-dominant plant. Two CBD copies make a CBD-dominant one. One of each gives a balanced plant, because the two forms are codominant and not one of them silences the other.
The balanced pack was bred by pairing two balanced plants, both holding one copy of each version. The CBD-dominant pack was made by pairing two plants that each carry two CBD copies and no THC copy in either of them. This one fact at the cross determines everything downstream, and the difference is already inside the seed long before it is packed.
Stage Two: Inside the Seed
Cross two balanced plants and the offspring fall themselves by the oldest arithmetic in genetics: a quarter inherit two THC copies, a quarter get two CBD copies, half inherit one of each. In a pack of 10 seeds that means, on average, around two THC-dominant seeds, two or three CBD-dominant seeds, and five true balanced ones. The pack is labelled by its parents, and for half its contents the label fits; for the other half it does not. Calm CBD Seeds prints the expected split on every balanced line, which means the buyer sees before sowing that a share of the plants will differ from the stated ratio.
The CBD-dominant pack has no such split. Every seed got a CBD copy from each parents, every plant will be CBD-dominant, and the ratio on the foil applies to all of them, within the small differences in the amount of much total cannabinoid any given plant builds. Breeders describe such lines “breed true” for chemotype; the phrase refers to exactly this absence of surprise.
Weeks One to Four
Here the two packs appear the same once more, and the resemblance holds further than many growers assume. Chemotype shows no mark on a seedling. Leaf, vigour, internode length and the speed of growth are controlled by different genes altogether, and the three chemotypes of plant in the balanced pack grow without any visible difference from one another and from every plant in the CBD-dominant pack.
One real distinction during this stage arises from ancestry not chemotype. Strains with recent hemp ancestry, which includes some older CBD-dominant strains, are inclined to grow taller and fill out less. A heavily selected 20:1 line behaves like any modern hybrid; a young one may still carry the field in its shape. Neither habit tells anything about the ratio in the flower.
Frost, Smell and the Wrong Conclusions
In flower the two packs begin to offer clues, and most of them point the wrong way. Trichome density is the first thing a grower reads, and it was a reasonable guide: early CBD-dominant lines showed visibly less frost than their THC counterparts, a inheritance from hemp. Current lines have largely closed that gap, and a less frosted plant from the CBD-dominant pack can perfectly well come in exactly where the foil promised. Trichome density and chemotype are carried separately.
Smell is worse. The terpene profile sits on still different genes, so the THC-dominant plant hiding in the balanced pack can smell identical to the balanced one beside it, and both can smell indistinguishable to a plant from the CBD-dominant pack. Growers who try to sort a balanced pack by nose at week eight are right about half the time, and that is no better than not unsorted at all.
Stage Five: The Harvest Window
At this stage the two packs differ in a manner that benefits the grower of the CBD-dominant pack and also the CBD-dominant plants sitting in the balanced pack. CBDA degrades rather slowly than THCA, so a CBD-dominant plant allowed a week beyond its ideal point keeps the bulk of its cannabinoid content, whereas a THC-dominant one under the same conditions has by then started shedding THC into CBN. The cloudy rules nonetheless holds; it holds on account of the terpenes, which degrade on any plant whatever the chemotype, and a late, over-dried CBD flower smells of very little however good the test result says.
Stage Six: The Jar
The CBD-dominant pack can go into one jar. Each plant from it holds roughly the same ratio, and blending them changes nothing worth measuring. The balanced pack should never be handled that way. Blend its 10 plants in a single jar and the result become a ratio that nobody’s foil ever predicted, skewed by which plants grew most, and nothing on a subsequent test can untangle what went in.
The discipline that saves the grief is almost tedious: harvest the balanced pack plant by plant, cure every one apart, label each, and try each one one at a time rather than after the crop is mixed. This is the only point in the whole grow where the different chemotypes of plant in the balanced pack can still be kept apart short of a laboratory, and only for the reason that each is still in its own container.
Reading the Two Results
Submit a sample from each jar to a laboratory and the two packs finally are legible. For the CBD-dominant pack the reports come back clustered closely around the advertised ratio, varying mainly in total cannabinoid content not in proportion. For the balanced pack they come back in three clusters: a few plants showing nearly all THC, some showing nearly all CBD, and the rest somewhere around one to one. Nothing of this result is a defect; it is the breeder’s cross written out as numbers.
Home test kits exist for growers who cannot reach a lab, and the majority of them show whether THC is present but not how much. That is sufficient to pull the THC-dominant jars away from a balanced pack and not enough to assign a ratio to the rest, which suits the commonest need: knowing what of the 10 jars will catch out someone.
Hemp Threshold Versus Chemotype
The last place at which the two packs separate is legal, and it trips growers who assumed “CBD” meant “hemp”. The majority of countries classify hemp by a THC limit, a small fraction of a percent of dry weight, and the precise figure differing from country and year to year. A plant from the CBD-dominant pack producing twenty percent CBD at twenty to one also makes around one percent THC, and that is many times above most thresholds. Compliant lines are bred to hold total cannabinoid output low so the THC share remains under the line at maturity; CBD flower lines are selected for rich content and allow the THC rise with it. A seller that gives only a ratio is describing a flower line; anyone who needs a legal hemp crop needs to look for a tested THC figure at maturity and buy nothing that does not show one.
Beyond the threshold issue, the chemotype alters very little about the law on the seed as such. In places where owning cannabis seeds is permitted and germinating them is not, the balanced pack and the CBD-dominant pack sit in the same position as every other pack. Where the plant is legal outright, the decision between them is the grower’s and nobody else’s. No part of this article is legal advice, and the rule which counts is the one in the place the seed is going to be grown, rather than the one in the place it was sold.