Put two packs of CBD seeds next to each other, one labelled 1:1 and the other 20:1, and the two look the same: the same breeder’s packaging, same seed count, contents that nobody’s eye can tell apart. Run them in the same tent and they go their separate ways from the first step and never converge again. The reason is one single gene, and the easiest way to see what it does is to track the two packs through every step they go through: the breeding that produced them, the seed, the seedling, the flowering tent, the cut, the jar, the lab bench and the law. The lines used as examples below 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 whichever shop the packs come from.
Before the Seed Exists
Cannabis decides if it will produce THC or CBD at one locus on the genome. The gene there exists in two forms: one builds the enzyme that converts the common precursor into THCA, the other the enzyme that turns it into CBDA. Every plant holds two copies, one inherited from either parent, and the pair fixes the chemotype. Two THC copies make a THC-dominant plant. Two CBD copies make a CBD-dominant one. One of each makes a balanced plant, since the two forms are codominant and neither overrides the other.
The balanced pack was made by pairing two balanced plants, each holding one copy of each version. The CBD-dominant pack was bred by pairing two plants that both hold two CBD copies and no THC copy between them. This one fact at the cross decides all that follows downstream, and the difference is fully in the seed before it is packed.
The Mendelian Split
Cross two balanced plants and the offspring sort 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 works out to, on average, two or three THC-dominant seeds, two or three CBD-dominant ones, and five true balanced ones. The pack is sold by its parents, and for half its contents the label fits; for the other half it is a description of something else. Calm CBD Seeds states the expected split on each balanced pack, which means the buyer sees ahead of sowing that a portion of the plants will depart from the stated ratio.
The CBD-dominant pack has no such split. Every seed received a CBD copy from each parent, each plant is going to be CBD-dominant, and the ratio on the foil applies to all of them, within the small variation in how total cannabinoid an given plant builds. The trade describe these lines “breed true” for chemotype; the term refers to precisely this absence of variation.
Where Nothing Shows
At this stage the two packs appear the same once more, and the likeness holds longer than most growers assume. Chemotype leaves no trace on a seedling. Leaf shape, vigour, stem spacing and the speed of growth rate are controlled by different genes altogether, and the different kinds of plant in the balanced pack grow indistinguishably beside one another and from each plant in the CBD-dominant pack.
The one practical difference at this stage arises from ancestry not chemotype. Strains with recent hemp ancestry, which covers a number of older CBD-dominant lines, tend to grow rangier and fill out less. A well-worked 20:1 line grows like any indoor hybrid; a young one may still shows the field in its frame. Not one of these tendency tells a thing about the ratio in the flower.
Stage Four: The Flowering Room
In flower the two packs start to offer clues, and the majority of the clues mislead. Resin coverage is the first thing a grower reads, and it was a fair rule: first-generation CBD-dominant strains carried visibly less frost than their THC cousins, an unwanted legacy from hemp. Modern selections have mostly erased that gap, and a less resinous plant from the CBD-dominant pack may perfectly well come in exactly where the foil said. Resin density and chemotype are inherited separately.
Smell is worse. The terpene chemistry lives on still different genes, so the THC-dominant plant sitting in the balanced pack can be indistinguishable to the balanced one next to it, and either can smell identical to a plant from the CBD-dominant pack. People who attempt to separate a balanced pack by nose in week eight are guessing, and that is no any better than leaving the plants sorting at all.
Stage Five: The Harvest Window
At this stage the two packs differ in a way that benefits the grower of the CBD-dominant pack and also the CBD-dominant plants sitting in the balanced pack. CBDA degrades more slowly than THCA, so a CBD-dominant plant allowed a week beyond its ideal point retains the bulk of its cannabinoid load, where a THC-dominant one in the same conditions has already started shedding THC into CBN. The usual trichome guidance still holds; it holds on account of the terpenes, which fade on every plant whatever the chemotype, and a late, rushed CBD flower tastes of very little whatever the lab result says.
What Mixing Does
The CBD-dominant pack goes into one jar. Every plant from it holds about the same ratio, and blending them changes nothing worth measuring. The balanced pack cannot be handled that way. Blend its 10 plants in a single jar and the contents become a ratio that nobody’s foil could have promised, weighted by whichever plants grew biggest, and nothing on a subsequent test can untangle what went in.
The habit that saves the grief is almost tedious: harvest the balanced pack plant by plant, cure every one apart, label each, and try them plant at a time rather than after anything is mixed. It is the one stage in the whole process at which the different chemotypes of plant in the balanced pack can yet be kept apart short of a lab, and only because each is still in its own container.
What a Certificate Shows
Send a sample from every jar to a laboratory and the two packs finally are readable. For the CBD-dominant pack the reports arrive back grouped closely around the advertised ratio, varying mostly in total cannabinoid content not in proportion. For the balanced pack they arrive back in three clusters: some reports showing almost all THC, some with nearly all CBD, and the rest sitting around one to one. Nothing of that pattern is a failure; it is the breeder’s cross written out as numbers.
Over-the-counter test kits are sold for growers without a laboratory, and most detect whether THC is present but not how much. That is enough to pull the THC-dominant plants away of a balanced pack and insufficient enough to assign a ratio to the rest, and that suits the most frequent use: finding out which of the ten jars is going to catch out someone.
Hemp Threshold Versus Chemotype
The last place at which the two packs separate is in law, and it trips growers who assumed “CBD” was shorthand for “hemp”. The majority of countries classify hemp by a THC limit, a small fraction of a percent of dry weight, with the precise number varying by country and over time. A plant from the CBD-dominant pack making twenty percent CBD at twenty to one also produces about one percent THC, which is several times above the majority of thresholds. Certified hemp cultivars are selected to keep total cannabinoid content low so the THC fraction remains below the line right up to harvest; CBD flower lines are selected for high output and let the THC scale with it. A seller that offers only a ratio is describing a flower line; anyone who requires a legal hemp crop should look for a tested THC percentage at harvest and buy no line that does not provide one.
Past the threshold question, the word on the foil changes nothing 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 under the same rule as any other pack. In places where the plant is permitted outright, the decision between them is the grower’s and nothing else’s. None of this article is legal advice, and the rule that counts is the one in the place the seed will be sown, rather than the one in the place it was bought.