Why the top layer decides the yield

Light does not reach far into a plant. The upper leaves absorb most of it, and what continues downward is a fraction of what arrived — enough for a leaf to survive on, not enough to build a dense flower.

Everything a grower does to the shape of a plant follows from that one fact. Topping, training, screens, defoliation and the removal of lower growth are all attempts to put more of the plant where the light actually is.

This page covers why the falloff is so steep, what happens to growth below the canopy, what each technique does, when it must be done, and how the results reach a buyer as different grades of material.

⚠️ Scope. This page describes a process and what can be verified from documents. It does not describe what a product does to a person, gives no amounts, and does not replace a healthcare professional.

🔴 Why light falls off so steeply

Absorption

Each layer of leaves absorbs a substantial share of what reaches it. Two or three layers down, very little is left.

Distance

Intensity from a point source falls with the square of the distance. A flower thirty centimetres below the canopy receives a fraction of what the top receives from the same lamp.

The combination

The two effects multiply. Depth in a canopy is expensive in light in a way that is easy to underestimate.

What the plant does about it

It allocates resources toward the parts that are photosynthesising well. Shaded growth is not merely poorly lit; it is also poorly supplied.

What grows below the canopy

The material itself

Small, loose flower structures, low in density and in resin. It is genuinely different material rather than merely smaller.

Why it forms at all

Because the plant produces flower sites at every node. Whether they develop into anything depends entirely on the light they receive.

What it is worth

Considerably less than canopy material. It is generally sorted out, sold separately, or sent to extraction.

Why growers care

Because the plant spent resources on it. Material that will not be worth harvesting is a waste of the inputs that produced it.

The objective

An even canopy

Many growing points at a similar height, forming a flat plane at the distance from the lamp where intensity is right.

Why flat matters

Because a single tall point takes the light and shades everything else, and the parts nearest the lamp burn while the rest is starved.

What that produces

More sites receiving good light, fewer sites producing poor material, and a more uniform harvest.

The general principle

Redistribute the plant rather than grow more of it. The available light is fixed; what changes is how much of the plant can use it.

Topping

What it is

Removing the growing tip of the main stem, which ends its dominance and promotes the growth of the shoots below it.

What it produces

Two main shoots instead of one, and with repetition, four, eight and so on. The plant becomes wide rather than tall.

When it is done

During vegetative growth, with enough time afterwards for the plant to recover and for the new shoots to develop.

What it costs

Recovery time. Every topping sets the plant back by days, and the schedule has to allow for it.

A variation on topping

What differs

Instead of removing the tip cleanly, part of the newest growth is pinched out, leaving some of the tip behind.

The intended result

More than two new shoots from one operation, with less recovery time than a clean cut.

Why results vary

It is a less precise operation and the outcome depends on exactly how much was removed. It is inconsistent by nature.

Which growers use it

Those prioritising speed over predictability. Both approaches are in common use.

Training without cutting

The principle

Bending and tying shoots down rather than removing anything, so that lower shoots are exposed and no single point dominates.

What it avoids

Recovery time. Nothing is removed, so the plant does not have to rebuild, and growth continues throughout.

What it demands

Continuous attention. Shoots must be repositioned as they grow, over weeks, rather than in one operation.

What it produces

A wide flat plant with many equal growing points, achieved gradually rather than in steps.

Growing through a screen

The arrangement

A mesh is fixed above the plants, and shoots are woven through it as they grow, filling the mesh horizontally before flowering begins.

What it achieves

A canopy defined by the screen rather than by the plant’s natural shape. Every square of mesh becomes a growing site at the same height.

Why it is efficient

It fills the lit area completely with fewer plants, which reduces the number of containers, the feeding labour and the plant count.

What it costs

Time before the switch. Filling a screen takes weeks of vegetative growth, which lengthens the cycle.

Many plants, little training

The opposite approach

A large number of small plants, each grown briefly and flowered early, filling the space by number rather than by training.

What it achieves

A short cycle and a canopy that is even because every plant is small and similar.

What it costs

Plant count. More containers, more medium, more cuttings, and more handling at every stage.

Where it suits

Operations with cheap propagation and a premium on cycle time. It is a throughput strategy.

Removing leaves

What is argued

That removing leaves shading flower sites improves light penetration and airflow. It is one of the most contested practices in growing.

The case for

Shaded flower sites receive more light, and the plant redirects resources from maintaining leaves to building flower.

The case against

Leaves are the photosynthetic organs. Removing them removes the plant’s capacity to produce anything, and the plant must rebuild what was taken.

Where the argument sits

Both effects are real. The question is the balance, and it depends on how dense the plant is and how much is removed at once.

Removing lower growth

What it is

Stripping the lower portion of the plant of shoots and leaves that will not receive useful light.

The reasoning

Those sites will produce poor material regardless. Removing them redirects resources upward and improves airflow at the base.

When it is done

Shortly before or shortly after the switch, once the eventual canopy height is apparent.

What it costs

Nothing, if the judgement is right. If it is wrong, sites that would have produced well are gone.

The timing constraint

What must happen before the switch

All structural work. Topping, training and screen filling belong to vegetative growth, when the plant still responds by branching.

Why afterwards is too late

Because a flowering plant redirects its resources into flowers rather than into new structure. Cutting then costs yield without producing branching.

What can still be done afterwards

Limited leaf removal and the removal of lower growth, both of which are subtractive rather than structural.

The practical rule

Shape the plant before the switch and manage it afterwards. The two phases allow different interventions.

What the stretch does to the plan

The event

Rapid extension after the switch, in which many varieties roughly double in height.

Why it disrupts canopy plans

A canopy that was flat and correctly spaced at the switch is neither of those things two weeks later if the shoots stretch unevenly.

What growers do

Continue training through the stretch, tucking shoots that outpace the rest, until extension stops.

The variety dependence

How much a line stretches is genetic and known in advance to anyone who has grown it before. On an unfamiliar variety it is a guess.

Where over-training shows

The symptom

A plant that stops growing, with pale new growth and no vigour. It has been set back more than it can recover from.

What causes it

Too many operations too close together, or heavy leaf removal on a plant that was not dense enough to spare it.

Why it is easy to do

Because each individual operation looks small, and the cumulative cost is not visible until the plant stalls.

The correction

Doing less. Growers who train heavily and successfully generally do so on a schedule with recovery built in.

Outdoors, where the constraints differ

The light source

Sunlight arrives from a moving point at high intensity and penetrates a canopy far better than a lamp at fixed height.

What that changes

Depth is less punishing. Outdoor plants produce usable material further down than indoor plants of similar size.

What still applies

Airflow, which matters more outdoors because humidity is not controlled and dense growth holds moisture.

The technique that dominates

Opening the plant for airflow rather than for light. The objective shifts even though the operations look similar.

What reaches a buyer

Canopy material

Dense, well-formed flower from the top of the plant. It is what is sold at the highest grade.

Lower material

Small, loose structures from below the canopy. Sold separately at a lower price, or sent to extraction.

Why both exist in every crop

Because no canopy is perfect and every plant produces some shaded growth. The proportion is what canopy management changes.

What the grading reflects

Position on the plant, principally. It is a light story rather than a genetics story, and the composition of the two grades is frequently similar.

The composition question

What is often assumed

That smaller, looser material is weaker. It is a reasonable assumption from appearance.

What analyses of the two grades tend to show

Content figures that are closer than the price difference implies. The material differs in density and form more than in composition.

Why the price difference exists anyway

Appearance, handling and market expectation. Dense flower is what buyers want to see.

What follows for a buyer

Lower grades can be better value per milligram. The certificate is what establishes whether that holds for a particular product.

What none of this appears on

The certificate

Composition and contaminants on the sampled material. Nothing about how the plant was shaped.

The label

The variety, where it is stated, and the batch code. Neither relates to canopy work.

The listing

A grade description, sometimes, which is the only trace of any of it and is not a defined term.

The one visible trace

Consistency of size and density within a package, which reflects both the canopy and the sorting afterwards.

The measurement growers actually use

Yield per unit of light

Grams harvested per unit of electrical energy delivered to the lamps. It is the figure that makes different techniques comparable, because it divides out the size of the operation.

Why it is the right denominator

Light is the limiting input indoors and it is the largest running cost. A technique that raises total yield by adding lamps has achieved nothing; one that raises yield per unit of light has.

What it exposes

Techniques that look impressive on a single plant and add nothing per unit of light. A large trained plant under two lamps is not obviously better than two small plants under the same two lamps.

Why the comparison is rarely made properly

Because it requires measuring energy as well as harvest, over several cycles, on the same genetics. Most claims about training rest on single-cycle impressions instead.

A short glossary

Canopy

The upper layer of a growing space where light intensity is sufficient to build dense flower.

Topping

Removing the growing tip to end apical dominance and promote branching from the shoots below.

Screen growing

Weaving shoots through a fixed mesh so that the canopy is defined by the screen rather than by the plant’s shape.

Lower growth removal

Stripping shoots and leaves from the shaded base of a plant, redirecting resources upward and improving airflow.

The stretch

Rapid extension after the switch to flowering, which disrupts a canopy that was flat beforehand.

The five checks that apply to any product

The batch certificate

Request it with the number printed on the packaging. A general document for the product line does not cover this batch, and those differences are exactly what it should record.

Total THC

Delta-9-THC plus THCA multiplied by 0.877, because THCA becomes THC under heat and the limit applies to the sum, not to either value alone.

Price per milligram

A division, not an opinion. The only figure that makes two products comparable, whatever the format, process and pack size.

The claims

Without an authorisation number in the EU Register these are assertions, not data — and for cannabidiol that register contains no authorised entry to this day.

The seller’s details

Company name, address and contact. Without them there is also no counterparty to turn to if something turns out to be wrong.

How this connects to the rest

With photoperiod

The stretch after the switch is what makes canopy planning difficult, and its extent is genetic.

With flower size grades

Position on the plant is what produces the grades. It is a light story rather than a quality one.

With density

Light received during development is the main determinant of how dense a flower becomes.

With the certificate

None of this appears there. It measures the material rather than its position on the plant.

What this is for in practice

When you see grade descriptions

They reflect position on the plant more than anything intrinsic. The composition of the grades is frequently similar.

When comparing grades

Price per milligram, with both certificates. Lower grades are sometimes better value and sometimes not.

When a package varies in size

It indicates the sorting rather than the growing. Both are producer decisions.

When judging density

It reflects light during development, which is a growing outcome rather than a genetic one.

Frequently asked questions

Why does light not reach the lower plant? Upper leaves absorb most of it, and intensity falls with the square of the distance. The two effects multiply with depth.

What grows below the canopy? Small, loose structures low in density and resin. They are genuinely different material rather than merely smaller.

What is the objective of training? An even canopy: many growing points at a similar height, so that more of the plant sits where the light is usable.

What does topping do? Removes the growing tip, ending apical dominance and promoting branching. The plant becomes wide rather than tall.

Is removing leaves beneficial? It is contested. Shaded sites receive more light and the plant loses photosynthetic capacity. Both effects are real.

When must structural work be done? Before the switch to flowering. Afterwards the plant builds flowers rather than structure, and cutting costs yield.

What is the stretch? Rapid extension after the switch, roughly doubling height in many varieties, which disrupts a canopy that was flat beforehand.

Is it different outdoors? Yes. Sunlight penetrates better, so depth is less punishing, and the objective shifts toward airflow rather than light.

Are lower grades weaker? Not necessarily. Analyses tend to show closer content figures than the price difference implies. The certificate settles it.

Does any of this appear on a certificate? No. It measures the material, not its position on the plant.

What we check and what we do not

We check what can be checked from documents: official registers, declared contents, certificates of analysis, arithmetic. We test no products, rank nothing, and assert no effects.

Every technique described here does the same thing by different means: it moves more of the plant into the thin layer where the light is actually useful. None of them makes the plant produce more per unit of light; they change how much of the plant can compete for what is there.

That also explains the grades a buyer eventually sees. Small loose flower is not a different quality of plant — it is the same plant, in the part of itself that never got enough light, and the certificate frequently shows a composition much closer than the price gap suggests.