Nutrients are the food your cannabis plants need to thrive. Understanding what your plants need - and when they need it - is crucial for healthy growth and maximum yields. This guide covers everything from basic NPK ratios to feeding schedules.
The Big Three: N-P-K
Every nutrient bottle displays three numbers (like 3-1-2). These represent the ratio of the three primary macronutrients:
- N - Nitrogen: Drives vegetative growth, leaf development, and chlorophyll production
- P - Phosphorus: Essential for root development, flowering, and energy transfer
- K - Potassium: Regulates water uptake, enzyme activation, and overall plant health
Secondary Macronutrients
- Calcium (Ca): Cell wall structure and nutrient uptake
- Magnesium (Mg): Central component of chlorophyll, enables photosynthesis
- Sulfur (S): Protein synthesis and enzyme function
Micronutrients
Cannabis also needs trace amounts of iron, manganese, zinc, copper, boron, molybdenum, and chlorine. Most quality nutrients include these in proper ratios.
Nutrient Needs by Growth Stage
Seedling Stage (Weeks 1-2)
Seedlings need very little food. Their cotyledons (first round leaves) contain enough nutrients to get started. If using quality soil like FoxFarm Ocean Forest, don't add any nutrients for the first 2-3 weeks.
Vegetative Stage
During veg, plants need high nitrogen to fuel leaf and stem growth. A typical veg ratio is 3-1-2 (N-P-K). Start at 1/4 strength and gradually increase. Watch for signs of nutrient burn (yellow/brown leaf tips).
Flowering Stage
When flowers form, reduce nitrogen and increase phosphorus and potassium. A typical bloom ratio is 1-3-2. Continue Cal-Mag supplementation, especially under LED lights.
Late Flower/Flush
In the final 1-2 weeks, many growers flush with plain water to improve taste. This uses up stored nutrients in the leaves. Yellowing during this period is normal and expected.
Sample Feeding Schedule (Soil)
| Week | Stage | Nutrient Focus | Strength |
|---|---|---|---|
| 1-2 | Seedling | None (soil nutrients) | - |
| 3-4 | Early Veg | High N (Grow) | 25% |
| 5-8 | Veg | High N (Grow) | 50-75% |
| 9-10 | Transition | Balanced | 75% |
| 11-16 | Flower | High P-K (Bloom) | 75-100% |
| 17-18 | Late Flower | Plain water (flush) | - |
The Importance of pH
pH controls nutrient availability. Even with perfect nutrients, wrong pH means your plants can't absorb them.
- Soil: 6.0 - 7.0 (ideal: 6.5)
- Coco/Hydro: 5.5 - 6.5 (ideal: 5.8-6.0)
Always pH your nutrient solution after adding nutrients. Test runoff occasionally to ensure the root zone pH is correct.
Common Nutrient Problems
Nutrient Burn
Symptoms: Yellow or brown tips on leaves, starting at the tips and moving inward.
Cause: Too much fertilizer.
Fix: Flush with plain, pH'd water and reduce nutrient strength.
Nitrogen Deficiency
Symptoms: Lower leaves turn pale green, then yellow, starting from the bottom up.
Cause: Not enough nitrogen or pH lockout.
Fix: Check pH first, then increase nitrogen-rich nutrients.
Calcium/Magnesium Deficiency
Symptoms: Brown spots on leaves, interveinal yellowing (magnesium).
Cause: Common with LED lights and filtered water.
Fix: Add Cal-Mag supplement. Very common issue - most growers should use Cal-Mag routinely.
Popular Nutrient Lines
- Fox Farm Trio: Grow Big, Big Bloom, Tiger Bloom - great for beginners in soil
- General Hydroponics Flora Series: Versatile 3-part system for any medium
- Advanced Nutrients: "pH Perfect" technology for hands-off pH management
- Biobizz: Organic option for living soil growers
Organic vs Synthetic Nutrients
Synthetic nutrients are immediately available to plants and offer precise control. Great for hydro and coco, fast-acting for fixing deficiencies.
Organic nutrients rely on soil microbes to break them down. Slower release, harder to over-feed, and many growers prefer the taste. Best for living soil setups.
Key Takeaways
- Start at 1/4 to 1/2 recommended strength - you can always add more
- Always check pH after mixing nutrients
- Less is more - it's easier to fix underfeeding than overfeeding
- Watch your plants, not the calendar - adjust based on what you see
- Cal-Mag is your friend, especially with LEDs and RO water
For a complete breakdown of feeding at each growth stage, visit our growing guide or check out our equipment recommendations for nutrient suggestions.