Nutrients 101
What's in Your Feed?
How to Read NPK Ratios
Three letters on every bottle. Here's what they actually mean — and what to do when something goes wrong.
NPK ratios are on the back of every nutrient bottle — and most growers glance at them without really knowing what they mean. Once you get it, though, it changes how you feed. You stop guessing and start making decisions based on what your plants actually need at each stage of their life.
Here's the full breakdown: what each nutrient does, what a deficiency or excess looks like, and how to fix it fast.
N
Nitrogen — The Growth Engine
Most important during veg. Keeps things green and growing.
Nitrogen is what drives leafy, vigorous growth. It's involved in protein production, enzyme activity, and chlorophyll — basically everything that keeps a plant green and pushing upwards. Get it right during veg and your plants will look healthy, structured and strong.
Too little
Older leaves go pale and yellow, starting from the bottom up. Stems get thin. Growth slows noticeably. Classic sign: the plant looks washed out.
Too much
Leaves go very dark green and get brittle. Stems weaken. The plant keeps throwing out foliage instead of transitioning to flower — and fruit flavour takes a hit.
How to fix it
Deficiency: gradually increase feed strength and consider a foliar spray like Nitrozyme for a quick boost. Excess: flush with pH-balanced water for a few days, then come back in with a lighter feed.
💡 Yellowing leaves late in flower is totally normal — your plant is pulling stored nitrogen into the fruits. Don't panic and don't reach for more feed.
P
Phosphorus — Root & Flower Power
Critical from late veg through to harvest. Drives root development and flower sites.
Phosphorus handles the heavy lifting when it comes to root development, flower formation and fruit ripening. It's also involved in energy transfer inside the plant — without enough P, everything slows down. You'll typically push more of it during the transition to flower and peak bloom.
Too little
Slow overall growth. Leaves turn dark green or take on a purplish tint — especially on the underside of older leaves. Flowering is delayed or underwhelming.
Too much
Excess P locks out iron, zinc and magnesium — so you end up with secondary deficiencies that can look confusing. If you're seeing strange symptoms and your P has been high, that's likely the culprit.
How to fix it
Flush with pH-adjusted water, then reintroduce a PK booster like Shogun PK Warrior at a reduced base nutrient dose. Soil or coco growers can also try Bat Guano for a natural slow-release top-up.
💡 Cold grow room? Low temps can mimic a phosphorus deficiency — check your environment before adjusting your feed.
K
Potassium — Strength & Flavour
The finishing nutrient. Improves density, taste, colour and disease resistance.
Potassium is what separates a good finish from a great one. It strengthens cell walls, regulates water movement inside the plant, and has a direct impact on flavour, colour and how well your plants fight off pests and disease. Most growers increase K during late flower for this reason.
Too little
Yellow or brown edges on leaves, weak roots, curling or twisted leaves. Plants start looking stressed and become more vulnerable to pests.
Too much
High K blocks calcium, magnesium and nitrogen uptake. You'll see brown spotting, crinkled leaves and stunted growth — often confused with other deficiencies.
How to fix it
Flush for 3–4 days with pH-balanced water, then ease back into your base nutrients. Once stable, reintroduce Athena Blended PK or Monkey Nutrients PK 9/18 at a reduced rate. If Cal and Mag have dropped, bring in a CalMag supplement alongside.
Plants are always communicating — yellow leaves, purple stems, burnt tips, twisted growth. Once you learn to read those signs, you'll catch problems early and fix them fast instead of spending weeks guessing what went wrong.
Quick reference
N
Leafy growth & green colour. Push hard in veg, ease off in flower.
P
Roots, flowers & fruiting. Ramp up at flower transition.
K
Strength, flavour & resilience. Peak importance in late flower.
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