Cannabis Nutrients: What to Feed Your Plants, How Much, and When

By Henrique Dias, CEO & Co-founder of BudTrainer
Last updated July 2026 · 20 min read

What Nutrients Does Cannabis Actually Need?

A cannabis plant builds most of itself out of thin air and water. Carbon, hydrogen and oxygen - the bulk of every plant - come free from the air and from what you pour in the pot. Everything else, the roughly fourteen mineral elements the plant cannot make itself, is what we mean by "nutrients," and it is what you are buying when you buy fertilizer, whether the bottle calls it cannabis fertilizer, plant food or a grow-and-bloom nutrient.⁶

Those elements sort neatly into three tiers by how much the plant uses, and understanding the tiers is most of the battle:

• Macronutrients - nitrogen (N), phosphorus (P) and potassium (K). The big three, used in the largest amounts, and the three numbers printed on every bottle of plant food. Get these roughly right and the plant is 90 percent fed.
• Secondary nutrients - calcium (Ca), magnesium (Mg) and sulfur (S). Used in real but smaller amounts. Most soils and many tap waters already supply them, which is why they cause trouble mainly for growers on soft or filtered water.
• Micronutrients - iron, manganese, zinc, boron, copper, molybdenum and a couple more. Needed in tiny traces. A complete nutrient includes them and you rarely think about them again.

That is the whole map. A "complete" base nutrient is simply one bottle, or one grow-and-bloom pair, that supplies all three tiers in sensible proportions. The elaborate twelve-bottle shelves at the grow shop are that same base plus a stack of optional extras, and we will get to how many of those extras actually earn their place. First, the words.

The words you will need

Cannabis feeding is drowning in jargon, and most guides never stop to define it. Here is the short glossary that unlocks the rest of this page:

• N-P-K: the three numbers on a nutrient label (like 3-1-2), giving the percentage of nitrogen, phosphorus and potassium by weight, always in that order.
• Base nutrient: the main food that supplies all the essential elements. Often sold as a "grow" (veg) bottle and a "bloom" (flower) bottle. This is the one product you actually need.
• Cal-mag: a calcium and magnesium supplement. Useful mostly if you grow in coco or use reverse-osmosis or very soft water, which is stripped of both.
• EC and PPM: two ways of measuring how strong your nutrient mix is (how much dissolved mineral is in the water). More on both below.
• pH: how acidic or alkaline your water is, on a 0 to 14 scale. It decides whether the plant can absorb the nutrients at all.
• Coco: coco coir, a soilless growing medium made from coconut husk. It grows fast but holds no nutrients of its own, so you feed every watering.
• Flush: running plain water through the pot, either to reset a plant you have overfed or to clear it out before harvest.

NPK Explained: The Three Numbers on Every Bottle

Pick up any bottle of plant food and you will see three numbers, like 4-2-3 or 2-1-6. That is the N-P-K ratio: the percentage of nitrogen, phosphorus and potassium inside. Learn what each letter does and you can read any bottle in the shop, cannabis-specific or not.

Nitrogen (N) builds leaves and stems. It is the engine of green, leafy growth, so a plant in its vegetative stage is hungry for it. Nitrogen is also mobile inside the plant, meaning the plant can move it from old leaves to new growth when it runs short - which is why a nitrogen-hungry plant yellows from the bottom up, sacrificing its oldest leaves first.³

Phosphorus (P) supports roots and flower formation. It is involved in energy transfer and in building the sites where buds form. Marketing leans hard on phosphorus as the "bloom" nutrient, and there is truth in it, but the amount the plant needs is much smaller than the industry implies. We will come back to that, because it is one of the clearest places our advice differs from the label's.

Potassium (K) runs the plant's plumbing. It regulates how the plant moves water and opens and closes the pores in its leaves, and it is heavily used during flowering to fatten buds. Potassium is the quiet workhorse of the bloom phase.

So the pattern most feeding schedules follow is simply this: more nitrogen in veg, more phosphorus and potassium in flower. A veg or "grow" bottle might read 3-1-2, leaning nitrogen; a bloom bottle might read 1-3-4, leaning the other way. You do not need to calculate anything. You need to feed the grow bottle in veg and the bloom bottle in flower, which is exactly what a two-part base nutrient is built to do.

That last point about mobility matters when something goes wrong: the plant strips its mobile nutrients (nitrogen, phosphorus, potassium, magnesium) from old leaves first, so shortages of those show at the bottom, while immobile nutrients (calcium, iron) show their shortages in the new top growth. You do not need this to feed a healthy plant, but the day a leaf turns a color you did not order, where the symptom sits is the fastest clue to what it is. That is a whole discipline of its own, and we have a dedicated guide on how to read a sick, discolored plant when it happens.

Secondary Nutrients, Micronutrients, and Cal-Mag

The big three get the attention, but a plant fed only N-P-K will eventually stall, because it still needs the supporting cast. The good news is that most of these you never have to think about, as long as you know which ones can bite.

Calcium and magnesium are the two that catch people out. Calcium builds the plant's cell walls, its structural scaffolding, and magnesium sits at the literal center of every chlorophyll molecule, which is what makes leaves green and photosynthesis possible. In soil and hard tap water these usually arrive for free. But two common setups strip them out: growing in coco coir, which grabs calcium and magnesium before the plant can, and using reverse-osmosis or very soft water, which has had its minerals removed. In either case you add them back with a cal-mag supplement.

Sulfur helps build proteins and some of the aromatic compounds in the plant, and it is almost always supplied by your base nutrient and your water. The micronutrients - iron, manganese, zinc, boron, copper, molybdenum - are needed in genuinely tiny amounts, and again, any complete base nutrient includes the lot. You are extremely unlikely to be short of copper or molybdenum; a controlled trial that starved cannabis of molybdenum for nine weeks could not even produce a visible symptom.⁷

Here is the discipline that saves beginners the most grief: a supporting-cast symptom is usually not a shortage of that nutrient. The plant looks short of calcium or iron far more often than it is actually short of them, because the wrong pH locks those nutrients out even when they are sitting right there in the pot. Reaching for a cal-mag bottle every time is the classic wrong first move. Before you add anything, you check pH - which is the next section, and which we cover in depth in the deficiency guide's section on why "just add cal-mag" usually backfires.

How Much to Feed: EC, PPM and the Half-Strength Rule

This is the section that will save more plants than any other, so if you skim the rest, read this. The single most common way a beginner kills a cannabis plant is by feeding it too much. It is not close. Overfeeding is easier to do, harder to spot, and slower to fix than underfeeding, and it is exactly what happens when a nervous new grower follows the dose on the bottle.

The rule that prevents it is boring and it works: mix your nutrients at half the strength the bottle recommends, then work up only if the plant asks for it. Bottle doses are written to sell nutrients and to cover the heaviest-feeding crops in the best conditions. A home cannabis plant in a pot is almost never that plant. Start at half, watch how the plant responds over a few days, and nudge up only if growth is pale or slow. Adding more next week is trivial; reversing a burn is a week of setback.

What EC and PPM actually measure

To feed by numbers instead of by guesswork, you measure the strength of your mix with a cheap meter. There are two units, and the difference trips up thousands of growers:

EC (electrical conductivity) measures how much dissolved mineral is in your water by how well it conducts electricity, in millisiemens per centimetre (mS/cm). It is unambiguous: an EC of 1.2 is an EC of 1.2 anywhere in the world. PPM (parts per million) tries to express the same thing as a single "total dissolved solids" number, but there are two conversion scales in circulation - the 500 scale used mostly in North America and the 700 scale used mostly in Europe and Australia. The identical water can read 600 PPM on one meter and 840 PPM on another, both correct. This is why forum PPM advice contradicts itself endlessly. Work in EC if your meter offers it, and you sidestep the entire mess. If it only shows PPM, find out which scale it uses before comparing your numbers to anyone else's.

A safe strength range by stage

Here is a conservative starting range in EC, with the 500-scale PPM in brackets. These are targets for the nutrient solution you feed in coco or a soilless mix; in rich potting soil you often feed weaker or not at all, because the soil is already holding food. Treat these as a floor to build up from, not a goal to hit on day one:

Autoflowers are the exception across the board: because they are small and fast, they want noticeably lighter feeding than these numbers, often half of the veg figures. When in doubt with any plant, feed on the low side. If you ever do overshoot and the leaf tips go brown and crispy - the signature of nutrient burn - the fix is to flush the pot with plain pH'd water, and we walk through that step by step in the guide to fixing an overfed plant.

pH: The Step That Makes the Nutrients Available

You can mix a perfect feed and still starve your plant, because nutrients are only absorbable inside a particular pH window. Drift outside it and the nutrient chemically binds up in the medium: still present, still in the pot, simply out of the plant's reach. That is called lockout, and it produces a textbook deficiency leaf while your reservoir is full of the exact nutrient the plant appears to be missing. Checking pH is therefore not an advanced move. It is the difference between your nutrients working and not working.

Target pH by medium:

• Soil: 6.0 to 7.0, aiming for 6.5 in the middle. Soil buffers, so it drifts slowly and forgives more.
• Coco and hydroponics: 5.5 to 6.5, aiming for 5.8 to 6.0. There is little buffer here, so it moves fast and punishes quickly.

The practical routine is simple: mix your nutrients into the water first, because adding fertilizer changes the pH, and only then measure and adjust. Nudge it into the band with a little pH Up or pH Down (cheap potassium-based solutions sold at any grow shop), stir, re-check, and pour. Set the pH last, every single feed. It takes thirty seconds and it is the highest-leverage habit in growing.

You need one cheap tool for this, a pH pen, and it needs calibrating with sachet solution about once a month or its confident numbers slowly become confident lies. Because pH lives at the exact seam between "feeding" and "fixing a sick plant," we keep the deep material - how to calibrate a pen, how to read your runoff, and how to unlock a plant that is already locked out - in the deficiency guide's pH section. A strong, well-aerated root zone also holds pH steadier and takes up nutrients more efficiently, which is half of why healthy roots matter as much as what is in the bottle.

Organic vs Synthetic vs "Just Use Good Soil"

There is no single "best" way to feed cannabis, but there are three genuinely different approaches, and picking one on purpose beats blending all three by accident. They trade off in effort, control and forgiveness.

Amended living soil (water only). You buy or build a rich "super soil" that already contains slow-release organic amendments - worm castings, bat guano, kelp, rock dusts - and for much of the grow you simply add water. Soil microbes break the amendments down and feed the plant. This is the most forgiving route and the hardest to burn a plant with, which makes it superb for a first grow. The trade-off is less moment-to-moment control and a bag of soil that costs more up front. You feed the soil, and the soil feeds the plant.

Bottled synthetic base nutrients. Mineral salts, already in the form the plant absorbs, mixed into the water at every feeding. This is precise, fast and cheap per grow, and it is what most indoor and coco growers use. The catch is that it demands the discipline of the last two sections: you measure EC so you do not overfeed, and you set pH so the plant can actually take it up. Get those two habits and synthetic base nutrients are the most controllable option there is.

Bottled organic nutrients and top-dressing. The middle path: liquid organic feeds or dry amendments you sprinkle on top of ordinary soil through the grow. Gentler than synthetics and very hard to burn a plant with, at the cost of being slower to correct a real shortage, because the nutrients have to be digested by soil life before the plant sees them.

For a first grow, our honest recommendation is either good amended soil and water, or one synthetic base pair used at half strength. Both work. What does not work is buying a bit of everything and hoping. If you want the wider walkthrough of how feeding fits into the whole grow, the how to grow weed guide puts it in context, and the indoor growing guide covers the coco-and-bottle setup most tent growers run.

A Simple Cannabis Feeding Schedule (by Stage)

A feeding schedule is just "what to feed, and how much, at each point in the plant's life." You can buy elaborate charts from every nutrient brand, but they all follow the same shape, and the shape is what matters. Match the feed to the stage the plant is in, which you can track in our cannabis growth stages guide.

Seedlings (first 2 to 3 weeks): little to nothing. A seedling has almost no root system and cannot use much. In rich soil it needs no added nutrients at all for the first couple of weeks - the soil has it covered. In inert coco you give a very light feed early because coco holds nothing. The number one seedling killer is overwatering and overfeeding a plant that simply cannot drink yet, which is why a self-draining starter like the BudCups helps: you can pop the base plate and actually look at the roots before you assume a droopy seedling wants feeding, when it usually wants the opposite.

Vegetative stage: nitrogen-forward grow feed, building up. Once the plant is growing fast and stacking leaves, start your grow bottle at half strength and work up toward the veg range from the table above over a couple of weeks. This is when the plant eats the most nitrogen, because it is building all the leaf and stem it will ever have.

How often you actually pour depends on your medium. In soil you alternate - feed, then give plain water, then feed again - because the soil holds onto nutrients between waterings, so you are not feeding every single time the way you would in coco or hydro. Let the pot get light before the next feed.

The flip to flower: switch to a bloom feed. When you flip a photoperiod plant to 12 hours of light (or when an autoflower starts flowering on its own), move from the grow bottle to the bloom bottle over a week or so. Bloom feeds carry less nitrogen and more phosphorus and potassium to build and fatten buds. The plant also stretches hard in early flower and its appetite climbs, so this is where your EC creeps to its peak.

Late flower into harvest: taper off. In the last week or two, most growers ease the feed back toward plain water, both because the plant is winding down and as a pre-harvest flush (more on that below). The full week-by-week detail of what the plant is doing through bloom, including the environment shifts that go alongside the feed, lives in the flowering stage guide.

Here is the whole schedule as a quick reference:

How to Mix and Give a Feed, Step by Step

Most guides tell you what to feed and skip the part where you actually stand at the sink and do it. The order you add things in genuinely matters, because some ingredients react with each other if they go in concentrated and out of order. Here is the sequence that avoids trouble:

1. Start with your water at room temperature. Note its EC before you add anything - tap water is rarely zero, and that starting number counts toward your total.
2. Add cal-mag first, if you use it (coco, or RO/soft water). Adding it before your base nutrient prevents some ingredients from reacting and dropping out of solution.
3. Add your base nutrient - the grow bottle in veg, the bloom bottle in flower - and stir. If it is a two-part base (an A and a B), add A, stir, then add B, stir. Never pour A and B together in concentrated form.
4. Add any extras last, and be honest about whether you need them at all. Stir again.
5. Check the EC against the target for the plant's stage. Too strong, add water; too weak, add a little more nutrient.
6. Adjust the pH last, into the band for your medium, then pour. Water until you get about 10 to 20 percent runoff out of the bottom in coco or hydro, which stops salts building up in the pot. In plain soil you water to the point of a little runoff, less often.

Fabric pots make that last step more forgiving, because they drain freely and let air into the root zone, so the medium dries evenly between feeds and mineral salts do not pool at the bottom. Reinforced fabric pots like the BudPots are built for exactly that cycle of wet-to-dry that keeps a root zone healthy and keeps your feeding honest. If you are still moving plants up through pot sizes, the transplanting guide covers the timing and the 3-to-5x volume rule.

When to Stop: Flushing Before Harvest

"Flushing" before harvest - running plain water for the last week or two of flower to rinse nutrients out of the medium - is one of the most repeated practices in growing, and one of the least supported by evidence. The theory is that it forces the plant to use up stored nutrients and yields a smoother, cleaner smoke. It is worth being honest about what we actually know.

The best controlled test we have of the idea comes from a nutrient testing company that ran a trial comparing zero, seven and fourteen days of pre-harvest flushing. It found no meaningful difference in yield, potency or the mineral content people worry about, and if anything the unflushed plants scored slightly better on smell and taste. That is a single industry study, not a body of peer-reviewed work, so hold it loosely - but it is a good deal more than the tradition it questions has behind it, which is essentially none.

The practical position we take: a short taper to plain water at the end does no harm, it is a sensible time to ease off anyway, and if it gives you peace of mind, do it. What you should not do is treat a two-week flush as a rule that overrides the actual harvest signal. The plant is ready when its trichomes are ready, not when a flush calendar says so. Time the cut off the resin, which we cover in the harvesting guide, and let the flush fit around that, not the other way round.

Do You Even Need Bottled Nutrients? The Honest Answer

We sell training clips, pots and branch supports. We do not sell a single bottle of nutrients and never will, which puts us in the rare position of being able to answer this without a sales motive: most home growers spend far more on nutrients than the plant will ever use.

This is not a hunch, it is what the controlled research keeps finding. When scientists actually varied phosphorus - the headline "bloom" nutrient that boosters are built around - they found that cannabis reached its full yield and full cannabinoid content at modest levels, on the order of 25 to 60 milligrams per litre, and that pushing phosphorus higher did nothing for yield or potency.¹²⁴ One trial noted that many growers supply more than 200 milligrams per litre of phosphorus, several times the optimum, where the excess simply washes out as pollution.¹ The same pattern shows up for nitrogen and for the N-P-K balance as a whole: there is a sweet spot, and past it, more fertilizer reduces quality rather than raising it.³⁵ The plant is not a bucket you fill; it is a system with an optimum, and the optimum is lower than the shelf implies.

So what actually earns its place in a home grow? Short list:

• One complete base nutrient (a grow-and-bloom pair, or good amended soil). This does the real work.
• Cal-mag, only if you grow in coco or use RO/soft water.
• A pH pen and an EC pen. The two cheap meters that make everything above possible. Genuinely the highest-leverage money in a grow.

Everything else on the shelf - the bloom boosters, the enzyme teas, the "bud candy," the six-part programs - ranges from mildly helpful in expert hands to pure marketing. None of it will save a plant grown at the wrong pH, and none of it substitutes for a healthy root zone and honest doses. If your budget is finite, spend it on the base, the meters and the pot before you spend it on bottle number seven. That is the whole game, and no one selling a twelve-bottle lineup is going to tell you.

The Most Common Feeding Mistakes

Nearly every feeding failure is one of these five, and each has a one-line fix:

• Overfeeding. Chasing the bottle dose and burning the plant. Start at half strength and read the plant, not the label. If you already burned it, flush and recover here.
• Ignoring pH. Feeding a perfect mix the plant cannot absorb. Set pH every feed. Most "deficiencies" are really pH lockout.
• Feeding seedlings too early. A seedling in soil needs no added food for its first couple of weeks. Let it grow into its appetite.
• Buying the whole shelf. A stack of boosters does not beat one good base at the right dose. Keep it simple until you have a reason not to.
• Feeding autoflowers like photoperiods. Autos are small and fast and want noticeably lighter feeding. When unsure, feed an auto less.

Frequently Asked Questions

What nutrients do cannabis plants need?

Cannabis needs three macronutrients in large amounts - nitrogen, phosphorus and potassium, the N-P-K on every bottle - plus three secondary nutrients (calcium, magnesium, sulfur) and a handful of micronutrients like iron and zinc in tiny traces. A single complete base nutrient supplies all of them. Nitrogen drives leafy growth in veg; phosphorus and potassium build flowers in bloom.

When should I start feeding cannabis seedlings?

In rich potting soil, not for the first two to three weeks - the soil already contains enough. In inert coco coir, start a very light feed within the first week or so, because coco holds no nutrients of its own. Either way, seedlings need very little, and overfeeding a tiny plant is far more common and more damaging than underfeeding it.

How much nutrients does cannabis need?

Less than the bottle says. Mix at half the recommended strength and work up only if the plant looks pale or slow. In numbers, aim for roughly EC 0.8 to 1.2 in early veg, rising to about EC 1.6 to 2.0 at peak flower, measured with a cheap EC meter. Autoflowers want lighter feeding than that throughout.

What does N-P-K mean on cannabis nutrients?

N-P-K is the percentage of nitrogen, phosphorus and potassium in a fertilizer, always listed in that order. A veg or grow feed leans toward nitrogen (for example 3-1-2) to build leaves; a bloom feed leans toward phosphorus and potassium (for example 1-3-4) to build flowers. The three numbers are all you need to tell a grow feed from a bloom feed.

What is the best nutrient for cannabis?

The best nutrient for most home growers is the cheapest complete base nutrient you can buy, whether that is a grow-and-bloom pair or a bag of good amended soil. Controlled trials show cannabis reaches full yield and potency at modest nutrient levels, so premium boosters rarely earn their price. Spend on a base, a pH pen and an EC pen before anything else.

Do I need cal-mag for cannabis?

Only in specific cases. If you grow in coco coir, or use reverse-osmosis or very soft water, you almost certainly need a cal-mag supplement, because those setups lack calcium and magnesium. If you grow in soil with hard tap water, you usually do not - and reaching for cal-mag when the real problem is pH lockout is a classic mistake that makes things worse.

Can I use regular plant food or tomato fertilizer on cannabis?

Yes. Cannabis is not chemically special; it needs the same mineral elements as any fast-growing crop. A general-purpose vegetable or tomato fertilizer with a sensible N-P-K will grow cannabis perfectly well, especially if you match a higher-nitrogen feed to veg and a higher-phosphorus-and-potassium feed to flower. Cannabis-branded nutrients are convenient, not magic.

How often should I feed cannabis?

It depends on your medium. In coco or hydro you feed most or every watering, at a light strength. In soil you alternate - feed, then plain water, then feed - because the soil stores nutrients between feedings. Let the top of the medium dry between waterings either way, and never feed a pot that is still heavy and wet.

When should I stop giving nutrients before harvest?

Many growers taper to plain water for the last one to two weeks of flower, the so-called flush. The evidence that flushing improves quality is weak, so treat it as optional. What matters far more is harvesting on the trichomes rather than a flush calendar. A short taper does no harm; a long flush that makes you harvest early does.

What are the signs of overfeeding cannabis?

The classic sign is nutrient burn: brown, crispy, curled-under leaf tips, usually starting on the biggest, healthiest upper leaves. Very dark green leaves with clawed-down tips point to too much nitrogen. If you see these, flush the pot with plain pH'd water and feed lighter next time. Overfeeding is the most common beginner problem, so when in doubt, feed less.

Are organic or synthetic nutrients better for cannabis?

Neither is better in the plant's eyes - it absorbs the same mineral ions in the end. Organic and amended-soil growing is more forgiving and harder to burn a plant with, which suits beginners. Synthetic bottled nutrients give precise, fast control if you measure EC and pH. Pick one approach and run it properly rather than mixing a bit of everything.

Why are my cannabis leaves yellowing if I am feeding?

Yellowing while feeding usually means the nutrients are present but unavailable, which is a pH problem, not a shortage - so adding more feed makes it worse. Check that your pH is in range (6.0 to 7.0 in soil, 5.5 to 6.5 in coco or hydro) before anything else. Bottom-up yellowing can also be normal late in flower as the plant pulls nitrogen from old leaves.

About the Author

Henrique Dias is the CEO and co-founder of BudTrainer. He is a mechanical engineer who also holds a graduate certificate in Commercial Cannabis Production from Niagara College in Ontario, Canada - the first college-level cannabis cultivation program in North America. Before founding BudTrainer, Henrique worked with Health Canada licensed cannabis producers, where he gained hands-on experience in cultivation, processing, and post-harvest management of cannabis at commercial scale. He started BudTrainer to bring that same level of craft to home growers through better-designed gardening tools and clear, science-backed education.

DISCLAIMER: Everything taught and sold by BudTrainer® is to be used strictly for legal purposes. We do not endorse the production of illegal substances and it is your duty to ensure that you are complying with the law. The words "hemp," "cannabis," "weed," and "marijuana" are used interchangeably to refer to the same plant (legal hemp with less than 0.3% THC) for the purposes of this lesson.