Why are my leaf tips turning yellow and dry?

This is a classic sign of "nutrient burn." It happens when the concentration of mineral salts in your feeding solution (EC) is too high. Dial back your bottle dosage by 20–30% and water with plain pH-adjusted water for a few days.

Do I need to flush my plants before harvest?

Flushing involves giving plants only plain water for the final 7 to 14 days before harvest. While heavily debated, it forces the plant to consume stored internal reserves, leading to a smoother burn and cleaner white ash in the final smoked flower.

Cannabis Nutrients Guide: NPK, EC/PPM & Deficiencies

Indoor cannabis plants rely entirely on you to supply the essential mineral elements required for cellular growth, photosynthesis, and resin production. Feeding too little stunts yields, while feeding too much causes salt buildup, root burn, and nutrient lockout.

1. NPK Ratios Throughout the Lifecycle

Commercial fertilizers display three numbers on the front label representing the percentage by weight of Nitrogen (N), Phosphorus (P), and Potassium (K).

Vegetative Stage (High N, Low P, Moderate K):

Target Ratio: Roughly 3-1-2 (e.g., 6-2-4 NPK).
Nitrogen powers amino acids and chlorophyll production, ensuring rapid foliage expansion and thick green stems.

Early-to-Mid Flowering (Low N, High P, High K):

Target Ratio: Roughly 1-3-2 (e.g., 2-6-4 NPK).
Phosphorus drives early floral initiation and root vitality, while Potassium catalyzes sugar transport and bud swelling.

Late Flowering & Ripening (Very Low N, Moderate P, High K):

Target Ratio: Roughly 0-2-3 (e.g., 0-4-6 NPK).
Excess Nitrogen during late bloom degrades final burn quality and causes harsh smoke. Drop Nitrogen to minimal levels while keeping Potassium high to bulk up resin heads.

2. Measuring Strength: EC vs. PPM

Measuring how concentrated your nutrient solution is prevents accidental overfeeding.

EC (Electrical Conductivity): Measures the ability of water to conduct an electric current, which increases as mineral salts dissolve. Expressed in millisiemens per centimeter (mS/cm). EC is the universal scientific standard.
PPM (Parts Per Million): Calculates estimated salt weight. However, meters use different conversion factors (500 scale vs. 700 scale), leading to frequent confusion.

3. Diagnosing Deficiencies: Mobile vs. Immobile

When plants lack a specific element, symptoms appear in very specific locations depending on whether the element can move through internal tissue.

Mobile Nutrients (Nitrogen, Phosphorus, Potassium, Magnesium)

The plant can steal these nutrients from mature, lower fan leaves and transport them to support vulnerable top growth.

Nitrogen (N) Deficiency: Lower, older leaves turn pale yellow while top leaves remain green. The plant slowly starves from the bottom up.
Magnesium (Mg) Deficiency: Interveinal chlorosis occurs on lower leaves—the tissue between leaf veins turns yellow while the veins themselves remain bright green. Fixed with Calcium-Magnesium (Cal-Mag) supplements.

Immobile Nutrients (Calcium, Iron, Sulfur, Boron)

Once deposited in plant tissue, these nutrients cannot relocate. Deficiencies appear exclusively on brand-new top growth.

Calcium (Ca) Deficiency: New leaves emerge twisted or deformed, developing tiny copper-colored spots or dead brown speckles.
Iron (Fe) Deficiency: Upper leaves turn striking bright yellow/white, but the main leaf veins stay dark green.

Nutrient Type Comparison

Criteria	Synthetic Bottled Nutrients	Organic Dry Amendments
Availability Speed	Immediate (Ionic salts absorbed directly)	Slow (Requires soil microbes to break down)
Control & Precision	High (Instantly adjust EC and NPK daily)	Low to Moderate (Pre-mixed into soil weeks prior)
Salt Buildup Risk	High (Requires regular runoff flushing)	Minimal (Low salt index, safe for living soil)
Impact on Terpene Profile	High yield; clean, neutral flavor	Maximum complexity in smell and aroma

Cannabis Nutrients & Feeding: NPK Ratios, EC/PPM, and Fixing Deficiencies

Key takeaways