How Strong Should You Be Feeding?
Tell it the stage and what the plant is rooted in — soil, coco or a reservoir— and it returns an EC and PPM band to work inside. Conservative by design, because overfeeding is harder to undo than underfeeding.
Feeding, In Six Lines
Build Your Feed
The Short Version
Seedlings want?
0.2–0.5
Next to nothing; good soil covers it
In bloom?
600–1000
Depends on the medium and the week
Soil or coco?
Fewer vs daily
Soil holds a reserve; coco holds none
Autoflowers?
A fifth lighter
Smaller roots, shorter clock
What This Tool Is Doing
Tell it where the plant is in its life and what it is rooted in, and it returns a range to feed inside. That second question is the one most charts skip: soil, coco and hydroponics hold and release nutrient so differently that a single set of numbers cannot serve all three.
Strength gets read two ways — EC, an electrical conductivity figure, and PPM, a parts-per-million one. You get both, plus how often to feed, which nutrients to lean on, and when to stop. Everything skews low on purpose: climbing is easy, and recovering from salt damage is not. Choose autoflowering and every figure drops by a fifth, because a smaller root system on a shorter clock cannot take the same load.
Schedules for Soil, Coco and Hydro
A printed chart assumes everyone grows the same way. This one asks first. Soil gets fed intermittently because it holds a reserve; coco coir gets fed daily and watched at the runoff; a recirculating system gets fed continuously and lives or dies on EC discipline.
What comes back: how often, how strong in both units, which element to push at that point — nitrogen while it is building leaf, phosphorus and potassium once it is building flower — and when to taper. Running autoflowering seed? Everything comes down twenty per cent without you asking. The tool is at the top of the page.
What a Plant Wants at Each Stage
What a plant asks for at three weeks and what it asks for at eleven are barely the same conversation. Reading the stage correctly is most of the skill.
| Stage | EC Range | Primary Focus | Key Nutrient |
|---|---|---|---|
| Just up | 0.2–0.5 | Putting down roots | Almost nothing |
| Early growth | 0.6–1.0 | Leaf and stem | Nitrogen (N) |
| Filling out | 0.8–1.4 | Filling out the canopy | Nitrogen, phosphorus rising |
| Just flipped | 1.0–1.6 | Turning over to flower | Phosphorus and potassium up |
| Flower filling | 1.2–2.0 | Flower building | Phosphorus and potassium lead |
| Nearly there | 0.6–1.2 | Ripening, then tapering | Wound back |
A seedling wants almost nothing added; a decent potting mix carries it two or three weeks unaided. Through vegetative growth nitrogen does the work of putting up leaf and stem. Once flowering begins the demand swings to phosphorus and potassium. In the last weeks you wind it back, often to plain water, which most growers find improves the finish. Exactly when to cut, and how long to taper beforehand, comes down partly to the medium and partly to taste.
Three Mediums, Three Different Jobs
🌍 Soil
- • Holds a reserve of its own
- • Feed on alternate waterings
- • Absorbs your mistakes
- • pH stays put on its own
- • Where to start
🥥 Coco Coir
- • Holds nothing — every water is a feed
- • Wants cal-mag added
- • Quicker than soil
- • Watch the runoff EC
- • For growers chasing weight
💧 Hydroponic
- • Total control of the solution
- • Fed continuously from a reservoir
- • The fastest growth available
- • pH and EC checked every day
- • Assumes you have done this before
Soil holds a reserve and evens out your mistakes, which is exactly what a first grow needs. Coco holds nothing — every watering has to carry the feed — and it grows faster in exchange for a narrower margin. Hydroponics puts the solution straight onto the roots: the quickest growth available, and the setup least willing to forgive a day of inattention.
| Factor | Soil | Coco | Hydro |
|---|---|---|---|
| How often | Every 2–3 days | Every watering | Never stops |
| EC in bloom | 1.0–1.6 | 1.4–1.8 | 1.6–2.0 |
| Holds a reserve | Yes — it forgives you | None at all | None at all |
| Pace | Steady | Quick | Quickest |
| Asks of you | Very little | Some attention | Daily attention |
| Cal-mag | Seldom | Every time | Usually |
| Suits | Forgiving autoflowers | Heavy croppers indoors | Anything you can watch daily |
Pick the medium that matches how often you can actually be in the room. An autoflower in soil survives a weekend away; a reservoir does not. The heavier setups do return more — a heavy cropper in coco outruns the same plant in soil — and they charge for it in attention rather than money.
Target EC and PPM, Stage by Stage
Where the plant is in its life sets the target. These are the bands most growers work inside, whatever they are growing in:
🌱 Just up
0.2–0.5 EC / 100–250 PPM
Barely anything. A good mix will carry a seedling two or three weeks with nothing added. Coco and hydro need a very dilute solution from the outset. More first grows are lost here than anywhere else.
🌿 Growing frame
0.6–1.4 EC / 300–700 PPM
Nitrogen demand climbs as the frame goes up. Sit at the bottom of the band early and walk it upward as the canopy fills out. Heavy-yielding lines will take the top of it.
🌸 In flower
1.0–2.0 EC / 500–1000 PPM
This is where the plant eats hardest, phosphorus and potassium above all. EC tops out around weeks four to six of bloom and comes down from there as you head toward harvest. Hydro can run the upper end; in soil, stay in the middle.
Take about a fifth off every one of these figures for autoflowering plants. With an unfamiliar strain, begin at the floor of the band and let the plant tell you whether to climb. Adding is trivial; reversing salt damage is not.
Should You Read EC or PPM?
📊 EC (Electrical Conductivity)
- • One scale, used everywhere
- • Nothing to convert
- • What commercial growers read
- • Measured in mS/cm
- • Finer control of strength
📏 PPM (Parts Per Million)
- • Common on hobby meters
- • Comes in a 500 and a 700 version
- • Easier to picture
- • Convert: EC × 500 = PPM (500 scale)
- • Check your meter before trusting a number
What we would do: read EC if the meter offers it. There is only one EC, whereas PPM comes in two flavours and a figure quoted without its scale is nearly useless. Both are shown here regardless. The number itself matters less than feeding consistently and watching how the plant answers.
What the Two Measurements Actually Measure
EC is how well your solution conducts electricity, which rises with the amount of dissolved mineral in it. A bigger number means a stronger mix. The unit is millisiemens per centimetre, and it means the same thing everywhere.
PPM expresses the same concentration a different way, and it has a trap in it: two conversion scales are in circulation, one multiplying EC by 500 and one by 700. Everything on this page uses the 500 scale. Any PPM figure you read elsewhere is worth nothing until you know which scale produced it.
Work in bands, not points. Genetics, room and water supply all shift the answer, and water is the one people forget: a hard supply already sitting at 200 PPM before you open a bottle has to be counted, while filtered water starts at nothing. Begin at the bottom of the band and only climb if the plant asks — pale new growth, or growth that has simply stopped.
Where Feeding Usually Goes Wrong
Starting Too Strong
The one everybody makes. A seedling wants almost nothing. Quarter of what the label says, then work upward. Far more plants die of generosity than of neglect.
Feeding Seedlings Like Adults
There is barely any root there yet, and what exists cannot handle a concentrated solution. Hold off until three or four sets of true leaves are up. Good soil covers the first fortnight or so unaided.
Ignoring Runoff in Coco
In coco the runoff is your instrument panel. Coming out more than 0.3 above what went in means salt is building up in the pot. Run half-strength solution through until the two readings converge.
Confusing Deficiency and Toxicity
Too much and locked out look much the same on a leaf, and the fixes are opposites. Read pH and EC before you conclude the plant is short of anything. Nine times out of ten it cannot reach what is already there.
Same Feed for Every Medium
The three media are not variations on a theme. Run a soil schedule in coco and the plant spends half its life dry; run a hydro schedule in soil and you will burn it.
Not Adjusting for Autoflowers
About a fifth less, across the board. Less root, less time to recover from a mistake, and correspondingly less tolerance for a heavy hand.
Picking Genetics That Suit How You Feed
Appetite varies between cultivars far more than most charts admit. A few will take everything you give them and turn it into flower. Others sulk at the first sign of excess and do better on a thin schedule. Lining the plant up with the way you actually feed — or the reverse — is rarely discussed and quietly decides a lot of grows.
A short life and a small root system keep autoflowering plants at the light end. The bulk producers — Big Bud and Critical Mass among them — eat properly through bloom and pay you back for a disciplined schedule. Northern Lights and White Widow sit at the forgiving end, absorbing a heavy hand or a missed feed without much complaint.
New to any of this? Forgiving genetics, in soil. Chasing weight in coco or a reservoir? Pick something bred to produce and feed it accurately once bloom starts. The strain finder and the yield calculator will narrow it down.
A Week-by-Week Chart for Soil
Everything below assumes soil. Growing in coco? Add 0.2 to 0.4 to each EC and feed considerably more often. On a recirculating system? Add 0.3 to 0.5 and run it continuously.
| Week | Stage | EC in soil | PPM | What it wants |
|---|---|---|---|---|
| Wk 1-2 | Just up | 0.0-0.4 | 0-200 | Plain water, or barely anything |
| Wk 3-4 | Early growth | 0.6-0.8 | 300-400 | Nitrogen — it is building leaf |
| Wk 5-6 | Filling out | 0.8-1.2 | 400-600 | Nitrogen still, phosphorus rising; train now |
| Wk 7 | Turning over | 1.0-1.4 | 500-700 | Change over to bloom feed |
| Wk 8-9 | Just flipped | 1.2-1.6 | 600-800 | Phosphorus and potassium climbing; sites forming |
| Wk 10-11 | Flower filling | 1.2-1.6 | 600-800 | Peak phosphorus and potassium; flower filling |
| Wk 12 | Nearly there | 0.6-1.0 | 300-500 | Wind it back and start tapering |
| Wk 13+ | Water only | 0.0 | 0 | Nothing but water, 5–10 days |
An autoflower runs the same shape on a shorter clock, usually finished by week ten, with every EC figure a fifth lower than the table shows. The heavier croppers will take the top of each band once bloom is properly underway.
Four Worked Examples
Four setups people actually run, written out in full. For your own combination of stage and medium, use the tool higher up the page.
Soil, late vegetative
Nitrogen leading, with phosphorus climbing behind it. This is where the frame gets built, so the target is canopy width before you flip.
Coco, mid bloom
Phosphorus and potassium at their peak. Keep cal-mag going — coco binds calcium — and read the runoff EC once a week rather than guessing.
Reservoir, early vegetative
Nitrogen forward while the plant is putting up frame. Fresh reservoir every seven to ten days, and pH read daily — it drifts faster here than anywhere else.
Autoflower in soil, start to finish
Open very light indeed, climb to a peak around weeks five and six of bloom, then taper. Everything a fifth below what a photoperiod plant of the same stage would take.
Cautious Feeding and Precise Feeding
🌱 Beginner Feeding Approach
- • A quarter to a half of what the bottle says
- • Grow in soil and let it buffer for you
- • Feed on alternate waterings
- • Choose forgiving autoflower strains
- • Burnt leaf tips are the first warning
- • Unsure? Give it less
🌳 Advanced Feeding Approach
- • Find each strain's own ceiling
- • Coco or hydro, for the precision
- • Daily, or recirculating without pause
- • Choose heavy-feeding high-yield strains
- • Runoff EC and pH read at every feed
- • Ratios retuned as the stage changes
The left column first, the right one after a few seasons. Almost everyone who gets burned went right too early, before they understood how their particular strain, their room and their water behave together. Set your experience level in the tool and the ranges move with it; at the cautious end they are chosen to keep the plant alive rather than to maximise anything.
Where Feeding Sits in a Bigger Harvest
Feeding is one leg of a three-legged stool; the other two are light and how you shape the plant. Exceptional genetics starved through bloom will still finish light.
Weeks four to six of bloom are where demand peaks, and a plant bred to carry weight wants phosphorus and potassium at their highest there. Consistency through that window matters more than peak strength: a plant fed steadily at a moderate EC generally finishes better than one swung between heavy feeds and plain water.
Run the yield calculator for a sense of what your space can carry, then come back here for the feed that supports it. The two questions are the same question asked from opposite ends.
When Something Looks Wrong
Plants still go wrong on a sound schedule. Reading the symptom correctly is the skill, and the reading is usually counter-intuitive: the cause is far more often pH drift or too much feed than a genuine shortage of anything.
Nitrogen Deficiency
Old growth going yellow from the bottom up
Read guide →Phosphorus Deficiency
Stems darkening, bloom slowing down
Read guide →Nutrient Burn
Tips gone brown and brittle
Read guide →Nutrient Lockout
Several deficiencies appearing together
Read guide →Calcium Deficiency
Rusty spotting, usually in coco
Read guide →Overwatering
Everything drooping, nothing growing
Read guide →Fed It and Nothing Changed?
A plant that looks unwell on a full feeding schedule is almost never hungry. Look instead at pH, at how much you are giving it, at whether you are treating the medium correctly, and at the room itself. Work down this list before you reach for another bottle:
⚠️ pH has drifted
Uptake only happens inside a narrow band — roughly 6.0 to 6.5 in soil, 5.5 to 6.0 in coco or a reservoir. Outside it the plant cannot reach nutrient that is physically present in the pot, and a perfect EC changes nothing. Read pH first, every time.
🔥 There is simply too much in the pot
Strength and growth are not the same lever. Salt accumulating around the roots damages the fine tips, slows how much water the plant can take, and burns the leaf. Look for very dark green leaves and dry, brittle tips. Run plain water through and come back at half to three-quarters of what you were giving it.
🌍 You are treating the medium as the wrong one
Water soil on a coco schedule and the roots sit wet until they rot. Water coco on a soil schedule and it dries into pockets while salt builds in what is left. The two are not settings of the same system; each wants its own rhythm.
🌱 The roots are the problem, not the feed
Compacted medium, a pot the plant outgrew, water that will not drain, or a cold floor under the container will all stop uptake no matter what is in the solution. In a New Zealand winter the cold floor is the one people miss. Aim for 18 to 24°C around the roots.
With pH, strength and the root zone all eliminated, what is left is the plant. Sensitivity varies between cultivars more than most charts admit, and one will sulk at a strength its neighbour takes happily. Northern Lights Auto and White Widow Auto sit at the tolerant end, which is why they turn up so often in a first grow.
Where These Numbers Come From
These are published horticultural ranges, cross-checked against what the major nutrient lines print on their own bottles and pulled toward the cautious end. We have not run controlled trials and we are not going to pretend otherwise, so treat the figures as a sane starting point rather than a result.
The bias runs low on purpose. Water supply, room temperature, humidity, pot volume and the cultivar itself all move uptake, and no calculator can see any of them. Err high and the plant carries salt damage for weeks; err low and it is hungry for a day. Those are not equivalent mistakes.
The bias throughout is deliberate: a range that is slightly too weak costs you a little growth, and one that is too strong costs you the plant. New Zealand tap water varies enormously between a Christchurch bore and a Wellington reservoir, which is one more reason to start low. Stuck on something? Write to us through the contact page.