Two ways of delivering the same thing to a root

A root does not absorb soil, and it does not absorb fertiliser. It absorbs ions dissolved in water, and it does so identically whichever medium delivers them.

That is the starting point for a comparison that generates more argument than almost any other in growing. The chemistry at the root surface is the same. What differs is everything upstream of it: whether a buffer sits between the grower’s decisions and the plant, and what happens when a decision is wrong.

This page covers what each medium actually does, where the buffer matters, what each demands in attention, why organic certification excludes one of them, and whether any of it reaches the finished flower.

⚠️ 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.

🔴 What the root takes up

Dissolved ions

Nitrogen as nitrate or ammonium, phosphorus as phosphate, potassium, calcium, magnesium and the trace elements, all in solution.

Why the source is invisible to the plant

A nitrate ion released by decomposing organic matter is the same ion as one from a mineral salt. The root cannot distinguish them and does not try.

What that settles

The claim that a plant somehow knows or benefits from the origin of its nutrition at the point of uptake. It does not.

What it does not settle

Everything else, which is where the actual differences live.

What soil provides

A physical structure

Pore space holding both water and air, which a root needs simultaneously. Getting that balance right is most of what a growing medium does.

A chemical buffer

Clay and organic matter hold ions on their surfaces and release them gradually. The solution concentration around a root changes slowly rather than instantly.

A biological community

Bacteria, fungi and larger organisms that convert organic material into plant-available forms and interact with roots directly.

A reservoir

Nutrients held in forms that release over weeks. A soil-grown plant is not entirely dependent on what was applied today.

What hydroponic systems provide

A solution delivered directly

Nutrients in known concentrations, supplied to the root in water, with no intermediary holding or converting anything.

An inert medium, or none

Clay pebbles, rockwool, coir, or nothing at all. The medium supports the plant physically and contributes little chemically.

Precise control

The grower sets the concentration of every element. What is in the solution is what the root receives.

No buffer

The corollary of that precision. A mistake in the solution reaches the root immediately and at full strength.

🔴 Where the buffer matters

When a feed is wrong

In soil, an overdose is partly absorbed by the medium and released slowly. In hydroponics it reaches the root at the concentration it was mixed at.

When a pump fails

In soil, the reservoir carries the plant for a day or more. In a system with no medium, roots can dry within hours.

When the grower is away

Soil tolerates neglect on a scale of days. Hydroponic systems generally do not.

What that means practically

Soil forgives, slowly. Hydroponics does not forgive and does not delay either, which is also why it responds faster when something is corrected.

pH and why it is different

What pH governs

Which nutrients a root can take up. Several elements become unavailable outside fairly narrow ranges, regardless of how much of them is present.

In soil

The medium resists pH change. A grower checks periodically and adjusts occasionally.

In hydroponics

The solution has little resistance to change. pH drifts as the plant takes up ions, and it needs monitoring and correction continuously.

What that requires

A meter, calibration solutions, and the habit of using them. It is the most common point of failure in a hydroponic system.

Electrical conductivity

What it measures

The total dissolved salt content of a solution. It is a proxy for nutrient concentration rather than a measure of any specific element.

Why it is used

Because it is instant, cheap and correlates well enough with feed strength for practical control.

What it cannot tell you

Which ions are present. A solution depleted of nitrogen and accumulated in something else can read the same as a balanced one.

How each medium uses it

Hydroponic growers track it constantly. Soil growers use it occasionally, on run-off, as a rough check.

Oxygen at the root

Why it matters

Roots respire. A root sitting in water with no dissolved oxygen suffocates, and the damage is quick and largely irreversible.

How soil provides it

Through pore space. Well-structured soil holds air alongside water, and the balance is a property of the medium.

How hydroponics provides it

By aeration, by film techniques that leave roots partly in air, or by periodic flooding and draining. Every system has a strategy for it.

What happens when it fails

Root death, followed by pathogens that establish on the dead tissue. It is the characteristic hydroponic failure.

The systems in use

Recirculating solution

Nutrient solution pumped past the roots and returned to a reservoir. Efficient in water and nutrients, and it concentrates any problem across the whole system.

Flood and drain

The root zone is periodically filled and allowed to drain, which brings in air on each cycle. Simple and robust.

Drip to an inert medium

Solution delivered to the base of each plant, with excess draining away. It is the most common commercial arrangement.

Coir and similar

A middle position: an inert medium with some buffering capacity, fed like a hydroponic system. Much of what is sold as hydroponic production is actually this.

What each demands of the grower

Soil

Periodic attention. Watering when needed, feeding on a schedule, and occasional checks. It tolerates a grower with other commitments.

Hydroponics

Daily attention at minimum. Solution monitoring, pH correction, equipment checks, and a response plan for pump or power failure.

The skill difference

Soil rewards experience and forgives ignorance slowly. Hydroponics rewards precision and punishes error immediately.

What that implies

Neither is harder in the abstract. They are difficult in different ways, and a grower good at one is not automatically good at the other.

Water and nutrient efficiency

Recirculating systems

Substantially more efficient than open soil growing. Water and nutrients are reused rather than draining away.

Soil in containers

Between the two. Run-off is collected in indoor growing and lost in outdoor growing.

The environmental argument

Recirculating hydroponics uses considerably less water per unit of production. It is one of the stronger arguments for the method.

The counterweight

It requires continuous pumping and, indoors, continuous lighting. The energy cost is real and it is rarely part of the comparison.

Why organic certification excludes it

The rule

Union organic production rules require crops to be grown in and connected to living soil. Production in a solution or an inert medium does not qualify.

The reasoning behind it

Organic production is defined around soil biology and nutrient cycling, not solely around which inputs are permitted. A system without soil cannot participate in that cycle.

What that means practically

A hydroponic crop cannot be certified organic in the Union, regardless of the inputs used.

What it does not mean

That the crop is worse, less safe, or less clean. The exclusion is definitional rather than a judgement about the output.

Does the method reach the flower

What is measurable

Cannabinoid content and terpene profile can be measured on material from either method. Comparative studies exist for various crops and are limited for this one.

What growers report

Strong opinions in both directions, largely uncontrolled. The comparisons are usually between different growers rather than between methods.

What would settle it

The same genetics, grown in both media, under otherwise identical conditions, with laboratory analysis. That trial is rarely run and rarely published.

The honest position

The method is one of many variables, and it is not obviously the largest. Genetics, harvest timing and drying all have well-documented effects.

The claims that circulate

Soil produces better flavour

Widely asserted, poorly evidenced. It may be true and the comparisons made to support it do not establish it.

Hydroponics produces higher yields

Better supported, in the sense that controlled nutrition and rapid response allow higher productivity per unit of time and space.

Soil is safer

Not established. Both methods can produce clean material and both can produce contaminated material.

What to do with all of them

Read them as positioning. The certificate measures the output, and it does not care how the plant was fed.

Contaminants and where they come from

In soil

Heavy metals taken up from the substrate, and pesticide residues. Soil composition is a genuine input into what a plant accumulates.

In hydroponics

The nutrient salts and the water. Both can carry heavy metal impurities, and neither is inspected by the grower routinely.

What is common to both

The grower’s decisions about crop protection, which are independent of the medium entirely.

What the panel covers

Heavy metals and pesticides on the finished material, whichever way it was grown. It is the answer to the question the method does not settle.

What a buyer can verify

The certificate

Content, compliance, and whatever contaminant panels were commissioned. It applies equally to both methods.

The organic certification

Where present, it tells you the crop was grown in soil under the Union scheme, because the scheme excludes the alternative.

What is not verifiable

Any claim about the method’s effect on quality. There is no document and no measurement that addresses it.

What is worth asking

Which method was used, if it matters to you. It is an ordinary production fact and a grower answers it directly.

What the argument is really about

Not chemistry

Both sides agree on what a root absorbs. Nobody disputes that a nitrate ion is a nitrate ion.

Control against resilience

One method offers precision at the cost of a safety margin. The other offers a safety margin at the cost of precision. That is the whole trade.

Which suits whom

Precision suits operations with monitoring, redundancy and staff. Resilience suits everyone else, including most outdoor and small-scale growing.

Why it generates heat anyway

Because both camps have real experience of their method working, and comparing across growers compares the growers rather than the methods.

The middle ground most production actually occupies

What coir is

Coconut fibre, an inert medium with a modest buffering capacity — more than rockwool, far less than soil. It is fed like a hydroponic system and behaves partly like a container substrate.

Why it dominates

It combines a usable safety margin with most of the control a solution gives. For a commercial grower that is the practical optimum, and it is what a large share of indoor production runs on.

Why the debate ignores it

Because the argument is framed as two poles, and the answer most operations arrived at sits between them. Purity of method is a hobbyist concern more than a commercial one.

What that suggests

The question as usually posed has already been settled in practice, by people choosing a compromise rather than a side.

A short glossary

Buffer

The capacity of a medium to hold ions and release them gradually, damping the effect of any single feeding decision.

Electrical conductivity

A measure of total dissolved salts in a solution, used as a rapid proxy for nutrient concentration.

Inert medium

A growing substrate that supports the plant physically while contributing little chemically, such as clay pebbles or rockwool.

Recirculating system

A hydroponic arrangement in which nutrient solution is returned to a reservoir and reused rather than drained away.

Living soil requirement

The Union organic rule that crops be grown in and connected to soil, which excludes soilless production from certification.

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 living soil

That page describes the biological end of the soil route, where the medium does the most work.

With organic certification

The soil requirement is the reason a hydroponic crop cannot carry the Union organic mark, whatever its inputs.

With contaminant panels

Both methods have plausible contamination routes. The panel measures the outcome and ignores the method.

With the certificate

It records composition and contaminants, and nothing about how the plant was fed.

What this is for in practice

When a method is advertised

Read it as a production fact rather than a quality claim. Neither method establishes anything about the output.

When organic is claimed

It implies soil, because the scheme excludes the alternative. That is a real and verifiable implication.

When flavour claims are made

They are unevidenced in both directions. The comparisons offered generally compare growers.

When comparing products

The certificate and the per-milligram price. The method appears on neither.

Frequently asked questions

Does a root know the difference? No. It absorbs dissolved ions, and an ion from decomposing organic matter is identical to one from a mineral salt.

What is the real difference then? The buffer. Soil holds and releases nutrients gradually; a hydroponic solution delivers exactly what was mixed, immediately.

Which is more forgiving? Soil, substantially. It tolerates neglect and dilutes mistakes. Hydroponics does neither, and it also corrects faster.

Why does pH need more attention in hydroponics? Because the solution has little resistance to change. It drifts as the plant feeds and needs continuous monitoring.

What is electrical conductivity? A measure of total dissolved salts, used as a rapid proxy for feed strength. It says nothing about which ions are present.

Why can hydroponic crops not be certified organic? Union organic rules require production in and connected to living soil. Soilless systems are excluded by definition rather than by input.

Does the method change the flower? No controlled comparison establishes it. Genetics, harvest timing and drying all have better documented effects.

Which uses less water? Recirculating hydroponics, substantially. Its energy consumption is correspondingly higher and rarely mentioned.

Which is safer? Neither inherently. Both have plausible contamination routes, and the panel on the certificate is what addresses them.

What should I ask a seller? Which method was used, if it matters to you. It is an ordinary production fact rather than a secret.

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.

The chemistry at the root surface is settled and uncontroversial, which makes it striking how much argument the question generates. What is actually being argued about is not what a plant absorbs but what a grower can afford to get wrong.

One method removes the margin and offers precision in exchange. The other keeps the margin and gives up some control. Both descriptions are accurate, neither is a quality claim, and the certificate on the finished material is indifferent to which was chosen.