Understanding Cannabis Nutrition Basics
Like all plants, cannabis needs a range of nutrients to grow, develop, and produce flowers. Getting your feeding schedule right is one of the most impactful things you can do for your yield and plant health. Feed too little, and growth stalls. Feed too much, and you risk nutrient burn and salt build-up in the root zone.
This guide explains the core nutrients your plants need, how those needs change across the life cycle, and how to build a feeding schedule that works for your setup.
The Three Primary Macronutrients: NPK
Every cannabis nutrient product displays an NPK ratio — three numbers representing the percentage of Nitrogen (N), Phosphorus (P), and Potassium (K) in the formula.
- Nitrogen (N): Drives vegetative growth — stems, leaves, and overall plant size. Cannabis needs high nitrogen during the veg stage, tapering off in flowering.
- Phosphorus (P): Critical for root development and flower production. Demand increases significantly once flowering begins.
- Potassium (K): Regulates water movement within the plant, strengthens cell walls, and supports overall plant immunity. Stays high throughout flowering.
Secondary Nutrients & Micronutrients
Beyond NPK, cannabis requires a range of secondary and trace elements:
- Calcium (Ca): Vital for cell wall integrity and new growth. Deficiency causes tip burn and stunted tops.
- Magnesium (Mg): Central component of chlorophyll — essential for photosynthesis. Often deficient in coco/hydro grows.
- Sulphur (S): Involved in protein synthesis and terpene production.
- Iron, Zinc, Manganese, Boron: Required in trace amounts but critical for enzyme activity and healthy growth.
Most quality cannabis base nutrients include secondary elements, but Cal-Mag supplements are commonly needed in soft water areas or when growing in coco coir.
Feeding by Growth Stage
Seedling Stage (Weeks 1–2)
Seedlings are fragile and require very little nutrition. The seed itself provides enough energy for the first week. If growing in a pre-fertilised soil mix, hold off on any additional feeding for the first 2–3 weeks. In inert media like coco, begin feeding at ¼ strength once the first true leaves appear.
Vegetative Stage (Weeks 3–8)
Ramp up nitrogen-heavy feeds as the plant develops. A typical veg feed has an NPK of roughly 3-1-2. Gradually increase EC (electrical conductivity) over this period from around 0.8–1.2 mS/cm early veg up to 1.6–2.0 mS/cm in late veg. Water with plain, pH-corrected water between feeds to prevent salt build-up.
Early Flowering (Weeks 1–3 of Flower)
Reduce nitrogen, increase phosphorus and potassium. This is often called the "bloom switch." Many growers use a PK booster starting around week 3 of flower. EC can remain similar to late veg levels.
Mid to Late Flowering (Weeks 4–8+)
Peak nutrient demand. A PK-heavy formula (e.g., 1-3-2) plus a bloom booster keeps plants well-fed. Some growers introduce additional supplements at this stage:
- Carbohydrate/sugar supplements: May support trichome and terpene production
- Amino acid supplements: Support stress recovery and enzyme activity
- Silica: Strengthens cell walls and improves resistance to heat and pest damage
Flush (Final 1–2 Weeks)
Most growers flush with plain, pH-corrected water for the final 7–14 days before harvest. This is intended to clear residual nutrients from the medium and improve the final smoke quality, though opinions vary on its necessity. It's a low-risk practice worth including.
Sample Weekly Feeding Schedule (Soil)
| Week | Stage | Feed Type | EC Target |
|---|---|---|---|
| 1–2 | Seedling | Plain water or ¼ strength | 0.4–0.6 |
| 3–5 | Early Veg | Grow base nutrients | 0.8–1.4 |
| 6–8 | Late Veg | Grow base + Cal-Mag | 1.4–1.8 |
| 9–11 | Early Flower | Bloom base nutrients | 1.6–2.0 |
| 12–14 | Mid Flower | Bloom base + PK booster | 1.8–2.2 |
| 15–16 | Flush | Plain pH'd water | < 0.4 |
Key Tips for Successful Feeding
- Always pH your water after adding nutrients, not before
- Start at half the manufacturer's recommended dose and scale up
- Check runoff EC to monitor salt build-up
- Keep a grow journal — what you fed, how much, and what the plant looked like
- Less is usually more, especially for beginners