Understanding Cannabis Nutrients
Cannabis plants require a precise balance of macro and micronutrients to thrive. Understanding what each nutrient does is the first step to diagnosing problems and growing healthy, high-yielding plants.
Primary Macronutrients (NPK)
Nitrogen
Leaf growth, chlorophyll, proteins
The most important nutrient during vegetative growth. Nitrogen is a core component of chlorophyll, amino acids, and proteins. It drives leafy green growth, stem development, and overall plant vigour. Cannabis uses the most nitrogen during the vegetative phase and less during flowering.
Phosphorus
Root growth, bud formation, energy
Critical for root development, energy transfer (ATP), and flower/bud formation. Phosphorus demand increases dramatically during the flowering phase, where it drives bud size, density, and resin production. Insufficient phosphorus during bloom is one of the top yield-limiting factors.
Potassium
Water regulation, immunity, bud density
Regulates water transport, enzyme activation, and overall plant immunity. Potassium strengthens cell walls, improves drought resistance, and enhances bud quality and density. It works alongside phosphorus during flowering and is essential throughout the entire lifecycle.
Secondary & Micronutrients
Calcium (Ca)
Cell wall structure, root development, enzyme activity. Essential in coco coir grows.
Magnesium (Mg)
Central atom of chlorophyll. Without magnesium, photosynthesis stops. Also aids phosphorus uptake.
Sulfur (S)
Amino acid synthesis, terpene and oil production. Critical for flavour and aroma development.
Iron (Fe)
Chlorophyll synthesis and electron transport. Required in small amounts but causes severe chlorosis when deficient.
Nutrient Deficiency Identification
Use these visual reference cards to identify and fix nutrient deficiencies in your cannabis plants. Each card includes symptoms, where to look, common causes, and the recommended fix.
Primary Macronutrients (N-P-K)
Secondary Nutrients
Micronutrients
pH and Nutrient Lockout
pH is the single most important factor in nutrient availability. Even if you add the perfect amount of every nutrient, the wrong pH will prevent your plant from absorbing them. This is called nutrient lockout.
Soil
Soil naturally buffers pH fluctuations, making it more forgiving than hydro. Most quality potting soils start around 6.5. Check runoff pH weekly and adjust input water as needed.
Hydro / Coco Coir
Hydro and coco have no natural pH buffering. Check and adjust pH at every feeding. Coco coir naturally binds calcium and magnesium, making CalMag supplementation essential.
Basic Feeding Schedule
Cannabis nutrient demands change dramatically between growth stages. Here are the general NPK ratios and feeding guidelines for each phase.
General Feeding Tips
- Always start at 50% or less of the manufacturer's recommended dosage and increase gradually
- Check pH after mixing nutrients — adding nutrients changes the pH of your water
- Water to 10-20% runoff to prevent salt buildup in the root zone
- Keep a grow journal — record what you feed, when, and how the plant responds
- Less is more — it is far easier to fix a deficiency than to recover from nutrient burn
Overfeeding & Nutrient Burn
Nutrient burn (nute burn) is one of the most common problems new growers face. It occurs when you feed your plants more nutrients than they can use, causing toxic salt buildup in the root zone.
Symptoms of Nutrient Burn
- Brown, crispy tips on leaves — the earliest and most reliable sign
- Tip burn progresses inward along the leaf edges if not corrected
- Leaves may appear dark green, waxy, or unnaturally deep in colour
- Leaf tips may curl downward (clawing)
- In severe cases, entire leaves become crispy and die
- Buds may develop poorly with reduced trichome production
How to Fix Nutrient Burn
Stop Feeding
Immediately stop adding nutrients. Switch to plain, pH-adjusted water.
Flush the Root Zone
Run 3x the pot volume of plain pH water through the growing medium to wash out excess salts.
Monitor Runoff EC/PPM
Test runoff water with an EC/TDS meter. Continue flushing until runoff PPM drops to acceptable levels (below 500 PPM for veg, below 800 for flower).
Resume at Lower Dose
After 3-5 days of plain water, resume feeding at 50% of your previous dose and increase gradually. The plant will tell you what it needs.
Prevention is Better Than Cure
Always start at half the manufacturer's recommended dose and increase gradually. Use an EC/TDS meter to measure nutrient concentration objectively. Feed-water-feed cycles (alternating nutrient water with plain pH water) prevent salt buildup and give the plant recovery time between feedings.
Frequently Asked Questions
Common questions about cannabis nutrient deficiencies, pH management, and plant nutrition.
How do I tell the difference between a nutrient deficiency and nutrient burn?
Nutrient deficiency typically causes yellowing, pale spots, or discoloration that starts from specific areas of the leaf (between veins, at edges, or across the whole leaf). Nutrient burn, in contrast, always starts as brown, crispy tips on the leaves — progressing inward if not corrected. Deficiency gets worse when you feed less; nutrient burn gets worse when you feed more.
Why do my plants show deficiency symptoms even though I am feeding nutrients?
The most common cause is pH lockout. If your root zone pH is outside the optimal range (6.0–7.0 for soil, 5.5–6.5 for hydro/coco), nutrients become chemically unavailable to the plant regardless of how much you add. Always check and adjust pH before increasing nutrient dosage.
Should I fix cannabis nutrient deficiencies with foliar spray or root feeding?
For fast-acting relief, foliar spraying (misting the leaves with a dilute nutrient solution) can deliver micronutrients within hours. However, root feeding is the long-term solution. Use foliar sprays as a short-term fix while correcting root zone pH and nutrient availability for lasting results.
What is the best pH range for cannabis nutrient uptake?
In soil, the optimal pH range is 6.0 to 7.0, with a sweet spot of 6.2–6.8. In hydroponic and coco coir systems, the optimal range is 5.5 to 6.5, with a sweet spot of 5.8–6.2. Within these ranges, all essential macro and micronutrients remain available to the plant.
How long does it take for a cannabis plant to recover from a nutrient deficiency?
Once the underlying cause is corrected (usually pH), you should see improvement in new growth within 3–7 days. Damaged leaves will generally not recover — they may stay yellow or spotted. Watch the newest growth at the top of the plant for signs of recovery rather than waiting for old damage to heal.
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