Products down the left, weeks across the top, and in each cell a number in millilitres per litre. That is what practically every feeding chart looks like, whoever made it.
This lesson explains none of those numbers. It explains how the chart is built – because that part is the same everywhere, and once you know it you can read any chart, including one you have never seen.
Just guessing is totally fine – it's only about a first impression.
2 ml per litre, unchanged. „Per litre" is a ratio, not a supply that gets spread thinner over more water.
For 10 litres you take 2 ml ten times – 20 ml in total, but the same strength. And strength is what the root experiences.
Take the wrong turn here and you end up at double or half – and go looking for the cause in the plant later on.
The columns say „week 1, 2, 3". They almost never mean the calendar – they mean a stage of development.
The first week of flowering starts when the plant starts flowering, not seven days after you changed the light. If it takes longer, it moves through the table more slowly. The table will not wait for it, so you have to.
Same principle as in the lesson Week zero: the signal comes from the plant, not from the date.
Many charts do not say „2 ml" but „1–2 ml". That range is not indecision – it is the most honest figure in the whole table.
It says: somewhere in this corridor it has worked for a lot of plants. Where exactly you land in it depends on things the author cannot know – your light, your substrate, your water, your variety.
Anyone who routinely takes the upper edge has used up the room above them before they need it. And the upper edge is exactly the direction in which excess looks like deficiency.
You compare two feeding charts for the same purpose. For the same stage, one gives roughly twice what the other gives.
One of them must be wrong. Or must it?
Both can be right. A chart is not a measurement, it is a recommendation under assumptions – and the assumptions are rarely printed alongside.
A chart written for soft reverse-osmosis water has to sit higher than one that assumes hard tap water: in the second case the water already brings something along. A chart for a pre-fertilised substrate starts later than one for a neutral medium, because the pot carries the first weeks itself.
So the key question to ask a chart you did not write is not „how much?" but „what does it assume – and is that true for me?"
Back to the opening question. Millilitres per litre describes how concentrated your water is – not how much fertiliser the plant gets in total.
More water at the same figure means: more fertiliser in total, same strength. The same amount of fertiliser in less water means: same amount, stronger solution.
That is also why EC is a concentration figure: it does not change when you mix more of the same solution. The root notices the strength, not the watering can.
15 ml – 2.5 × 6, that is all there is to it.
And that is the only place your volume appears at all: at the measuring cup. It has changed nothing about the concentration – 15 ml in 6 litres is exactly the same strength as 2.5 ml in one litre.
People who are unsure about this conversion usually slip in the middle of the chart, where three rows are dosed at once.
You read a chart row by row – the plant gets the rows together.
Dissolved salts add up: every dosed row raises the EC of the finished water, and what arrives at the root is the sum. Three rows that look unremarkable on their own can add up to a solution none of them would have produced alone.
So the last question before watering is never „is this row right?" but „what is in there in the end?"
No chart says what you are starting from. Your tap water gets added on top anyway.
If you water from a tap whose water already has a measurable EC, the same chart leaves you at a different end value than someone using near-empty reverse-osmosis water. The table counts up from zero; your bucket does not.
So the first figure worth knowing is not the one in the chart but the one from your tap – the course Your water is about nothing else.
A feeding chart answers exactly one question: how much of what goes into the water. Four things it leaves open, and not out of carelessness – they depend on your setup:
how often you water · how much runs out at the bottom · how big the pot is · what pH the finished water has.
pH is missing for a hard reason: it is not additive. Two products that each lower it slightly do not add up to a predictable value, because the buffering of your water interferes. Which is why no calculator can work it out for you – only a meter can tell you.
At the bottom. Hard water and a pre-fertilised substrate both deliver something already – the corridor is written for the case where they do not. You are not starting from zero but with two silent contributions.
And lagging is no proof of hunger: raising the dose first on a struggling plant treats a symptom whose cause you do not know – light, roots and climate are just as plausible. Too much looks like too little.
The most common answer to uncertainty about feeding is not the lower edge of the corridor. It is a number that does not appear in the chart at all: half.
Is that the same thing by another name?
No – and what „half strength" actually is turns out to be interesting. In the archive of the scene magazines it appears across thirty years, but never as a rule for one particular case: 1986 for flushing, 1987 for cuttings, 2009 for seedlings, 2010 for correcting a deficiency. Five situations, one number – and not a single passage gives a reason.
Half strength is not a dose but a sentence: „I am not sure." As an attitude that is entirely fine. Only your chart says the same thing more precisely: the lower edge of the corridor is also a cautious number – but one that somebody chose. Half of something was chosen by nobody. And halving the lower edge again puts you outside any range there is a recommendation for.
One detail almost always drops out in the retelling. The fullest version, from 2010, has two halves: „begin with a half-strength solution, then work up to full strength if the deficiency persists." Only the first survived.
🎯 Hands-on mission
Take the chart you are working with and run a single week through in full: your volume, every dosed row, and the EC your water starts at.
The dosage calculator does exactly that – forwards, additively, without expecting you to add it up in your head. What it shows you is not the right dose but what ends up in the can. The rest is your call.
✓
From here on you can read any chart you meet – and you know where it leaves you on your own.
Something still unclear?
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