Place two packs of CBD seeds next to each other, one marked 1:1 and the other 20:1, and the two look the same: the same breeder’s foil, the same seed count, seeds which no eye can tell apart. Grow them in the same tent and they go their separate ways at the very first step and do not meet again. The reason is one single gene, and the easiest way to understand what it does is to track the two packs along every stage they go through: the cross that produced them, the seed, the seedling, the flower tent, the cut, the jar, the lab bench and the law. The ratios used as examples below are drawn from the range at https://calmcbdseeds.com, which goes 1:1, 2:1 and 20:1 and a top line at about 30 to one; the biology is the same whichever shop the seeds came from.
How Each Pack Was Made
Cannabis decides whether it is going to produce THC or CBD at one locus on the genome. The gene there exists in two versions: one builds the enzyme that converts the common precursor into THCA, the other the enzyme that converts it into CBDA. Each plant carries two copies, one inherited from each parent, and the combination 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 versions are codominant and not one of them overrides the other.
The 1:1 pack was made by pairing two balanced plants, each holding one copy of each form. The CBD-dominant pack was bred by pairing two plants which each carry two CBD copies and not a single THC copy between them. This one fact at the cross decides all that follows downstream, and the difference is already in the seed long before it is packed.
Stage Two: Inside the Seed
Cross two balanced plants and the seeds fall out by the oldest arithmetic in genetics: a quarter inherit two THC copies, a quarter inherit two CBD copies, half inherit one of each. In a pack of 10 seeds that works out to, on average, around two THC-dominant seeds, around two CBD-dominant ones, and five true balanced seeds. The pack is sold by its parents, and in the case of half its seeds the label is accurate; in the case of the other half it does not. Calm CBD Seeds states the expected split on each balanced line, which means the buyer sees ahead of sowing that a share of the plants will depart from the stated ratio.
The CBD-dominant pack has no such split. Each seed got a CBD copy from both parent, each plant will be CBD-dominant, and the ratio on the foil applies to all of them, give or take the small variation in the amount of much total cannabinoid any given plant builds. The trade describe these lines “breed true” for chemotype; the term refers to exactly this absence of surprise.
Weeks One to Four
At this stage the two packs look alike once more, and the resemblance holds further than most growers assume. Chemotype shows no mark on a seedling. Leaf shape, colour, internode spacing and growth are controlled by different genes altogether, and the three chemotypes of plant in the 1:1 pack come up indistinguishably beside one another and from every plant in the CBD-dominant pack.
One practical distinction at this stage arises from ancestry not chemotype. Strains with strong hemp genetics, which includes a number of less developed CBD-dominant strains, tend to stretch rangier and branch more sparsely. A well-worked 20:1 line grows like a normal modern hybrid; a young one still shows the hemp in its shape. Not one of these tendency says anything about the ratio to come.
Frost, Smell and the Wrong Conclusions
In flower the two packs begin to give clues, and most of them point the wrong way. Resin density is the usual one a grower reads, and it used to be a fair guide: first-generation CBD-dominant lines carried markedly less resin than their THC cousins, a legacy from hemp. Current lines have mostly closed that gap, and a less resinous plant from the CBD-dominant pack may still come in precisely where the foil said. Trichome density and chemotype are carried separately.
Smell is worse. The terpene chemistry sits on still other genes, so the THC-dominant plant hiding in the 1:1 pack can smell identical to the balanced one next to it, and either can be identical to a plant from the CBD-dominant pack. People who try to separate a balanced pack by nose at week eight are right about half the time, which is no better than not sorting at all.
How Late Is Too Late
At this stage the two packs diverge in a manner that benefits the grower of the CBD-dominant pack and the CBD-dominant plants hidden in the 1:1 pack. CBDA breaks down rather slowly than THCA, so a CBD-dominant plant left a week beyond its peak keeps most of its cannabinoid content, whereas a THC-dominant one under the same neglect has already begun converting THC into CBN. The usual trichome guidance still holds; it holds because the terpenes, which degrade on every plant regardless the chemotype, and a late, rushed CBD flower tastes of little whatever the test result is.
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 alters nothing worth measuring. The 1:1 pack should never be treated that way. Pool its 10 plants in a single jar and the result become a mixture that no foil could have predicted, skewed by which plants yielded biggest, and nothing on a later test can pull apart the plants that went in.
The habit that saves the grief is almost tedious: cut the balanced pack plant by plant, dry each separately, number each, and try each one plant at a time rather than after the crop is combined. This is the one stage in the entire process where the different chemotypes of plant in the 1:1 pack can still be kept apart without a laboratory, and only for the reason that every one is still in its own container.
Reading the Two Results
Send a sample from each jar to a laboratory and the two packs at last are readable. For the CBD-dominant pack the certificates come back grouped closely near the advertised ratio, differing mainly in total output rather than in proportion. For the 1:1 pack they arrive back in three groups: a few reports showing nearly all THC, some with nearly all CBD, and the majority sitting near one to one. Nothing of this result is a failure; it is the breeder’s cross expressed as numbers.
Over-the-counter test kits are sold for growers without a lab, and most detect whether THC is present rather than how much. That is sufficient to pull the THC-dominant jars away of a balanced pack and insufficient to assign a ratio to the rest, and that suits the most frequent use: finding out which of the ten jars will catch out a guest.
Stage Eight: The Border
The last place at which the two packs separate is legal, and it trips growers who assumed “CBD” was shorthand for “hemp”. The majority of countries classify hemp by a THC ceiling, a fraction of a percent of dry weight, with the exact number differing from country and sometimes year to year. A plant from the CBD-dominant pack making twenty percent CBD at twenty to one also makes around one percent THC, and that is several times over the majority of limits. Compliant cultivars are bred to hold total cannabinoid output low so the THC fraction stays below the line at maturity; CBD flower lines are selected for high content and let the THC scale with it. A seller that gives only a ratio is selling a flower line; a grower who needs a legal hemp crop should ask for a tested THC percentage at harvest and order nothing that does not show one.
Beyond the threshold question, the chemotype changes very little about the law on the seed as such. In places where owning cannabis seeds is permitted and germinating them is not, the 1:1 pack and the CBD-dominant pack sit in the same rule as every other pack. In places where the plant is permitted without restriction, the decision between them is the grower’s and nobody else’s. No part of this article is legal advice, and the law that counts is the one where the seed will be sown, not the one where it was sold.