Cannabis Nutrient Schedule: EC Table and Phase Plan for Every Substrate

Why a structured nutrient plan improves cannabis yields

Cannabis requires different nutrient ratios during different growth phases. Ad-hoc feeding creates stress and reduces yields. A structured plan enables precise dosing, reproducible results and early problem detection. Professional growers work with written plans—and you should too.

The idea behind a nutrient plan is simple: each growth phase has different optimal nutrient requirements. In the vegetative phase, the focus is on stem growth and leaf mass—nitrogen is dominant. In the flowering phase, the plant shifts to reproduction and cell wall stability—phosphorus and potassium become more important. A good nutrient plan orchestrates these transitions instead of ignoring them.

NPK ratios per growth phase: table for veg, early and late bloom

NPK stands for the three macronutrients Nitrogen (N), Phosphorus (P) and Potassium (K). Their ratio determines a fertilizer's character. Cannabis needs different NPK ratios in different phases—a universal 10:10:10 fertilizer is often not ideal.

A common mistake is not reducing nitrogen adequately in bloom. Cannabis that receives too much nitrogen in bloom delays maturity, produces less compact flowers and has reduced taste quality. Conversely, too little N causes leaf yellowing and reduced yields.

EC values for cannabis: targets for coco, soil and DWC compared

EC (Electrical Conductivity) measures solution conductivity and indicates how many dissolved salts it contains. EC is the numerical tool to control nutrient amount—not the bottle labels, but the actual measured EC.

Why do EC values differ between substrates? Coco and hydroponics are inert media—no buffering like in soil. Plants depend on the exact solution. Soil contains organic matter and biology that buffer nutrients—too high EC can cause salt burn.

A practical rule: Measure your input solution EC (what you feed) and later the runoff EC. If runoff EC is much higher than input, salt is accumulating in the substrate. Then flush with plain water.

Building your nutrient plan step by step

Follow this method to create your own functioning nutrient plan:

1. Step 1: Choose substrate and fertilizer

   First, decide on your substrate (coco, soil or hydroponics) and select a fertilizer optimized for it. Coco fertilizers are designed to tolerate higher EC. Soil fertilizers are often weaker. Hydroponics fertilizers are precisely balanced for optimal nutrient uptake. Check bottle labels for NPK ratio.

2. Step 2: Define base EC values for each phase

   Use the table above to choose EC targets for your strain and substrate. A good starting point: vegetative 1.2 EC (coco), early bloom 1.4 EC, late bloom 1.0 EC. Write down these values—they become your reference framework.

3. Step 3: Calculate fertilizer dose and calibrate

   Each fertilizer has different concentration. The manufacturer states how much mL per liter of water is needed to reach a certain EC (or EC increase per mL). Example: "1 mL A + 1 mL B per liter increases EC by 0.4." Start with the dose that reaches 80% of your target EC, then increase gradually. Measurement is critical—buy an EC meter (cheap and essential).

4. Step 4: Document, observe and adjust

   Keep a grow log (see Grow Data Logging). Note daily input EC, runoff EC, pH and plant condition. After 2-3 weeks, you'll see patterns: If runoff EC rises, you were too generous. If it drops, you can increase. Document multiple harvests—this data becomes gold for developing your personal masterpiece.

Common nutrient plan mistakes and how to avoid them

Many beginners make similar mistakes. Here are the most common—and how to prevent them:

1. Mistake 1: Not switching between veg and bloom

   Some growers use the same product throughout. This leads to nitrogen excess in bloom and poor flower quality. Plan a nutrient switch for the first week after light cycle change. For autoflowers: switch around weeks 4-5.

2. Mistake 2: Starting too high with EC and not adjusting

   A common reaction to deficiency symptoms is increasing EC. This usually makes it worse. Start conservative (80% target EC) and increase slowly based on plant condition and runoff measurements. Don't jump 0.5 EC at once.

3. Mistake 3: Not using an EC meter

   This is fatal. Without EC measurement, you work blind. EC meters cost $20-50 and save you hundreds in lost harvests. Buy a digital meter and calibrate monthly.

4. Mistake 4: Flush phase too short

   If you flush less than 7 days (e.g. 2-3 days), nutrient residues remain in the flower. This results in poor burn quality and unwanted taste. Always flush 7-14 days.

Flush phase and nutrient removal before harvest

The flush phase is a 7-14 day period shortly before harvest when you water only with plain water—no nutrients. The goal is to remove remaining nutrients from the substrate so flowers burn clean and taste better.

Timing: Start the flush phase about 10-14 days before planned harvest date (based on trichome maturity—see Harvest Timing and Trichomes). This is usually week 7-8 of bloom for 8-10 week strains.

Flush protocol: Water with pH-adjusted water (pH 6.0-6.5 for coco, 6.5-7.0 for soil). Amount should be 2-3x substrate volume to ensure thorough rinse. Many growers do two flushes: day 1 generous flush, day 3-5 another flush. Runoff EC should drop to 0.3-0.5 after flushing.

Nutrient schedule adjustment: reading plant signals

A printed nutrient schedule is a starting point, not a prescription. Cannabis plants communicate their actual needs through foliage, growth rate, and runoff data. Learning to read these signals and adjust your schedule accordingly separates experienced growers from beginners.

Week-by-week nutrient schedule: practical EC targets

The following EC targets provide a universal starting framework. Adjust based on runoff EC (target: ±0.3 of feed EC) and visible plant signals. This schedule assumes coco substrate with daily or near-daily watering. Soil growers should reduce EC values by 0.2–0.4 throughout.

How to use this schedule in practice

Week numbers are approximate—adapt to your strain and growth speed. Fast-growing sativas may transition to bloom after week 5; compact indicas may stay vegetative until week 8. Use the visible growth stage (not just the week counter) as your reference.

The EC values listed are input EC, what you feed into the substrate. Monitor runoff EC closely: if it exceeds input EC by more than 0.4, you're feeding too aggressively. If runoff EC drops below input EC, the substrate is being depleted—increase feeding strength or water more frequently.

Transition week strategy

The transition weeks (6–7) are critical. Some growers do a hard switch to bloom nutrient; others prefer a gradual transition. Gradual is safer: over 3–5 days, slowly reduce the veg nutrient and introduce the bloom nutrient. This prevents shock and nutrient lockout. Watch for temporary leaf yellowing during transition—it's often harmless, but if it spreads quickly, your transition was too aggressive.

Seedling EC management — why light feeding matters

Weeks 1–2 require extra caution. Seedlings have small root systems and low metabolic capacity. Overfeeding at this stage causes burned cotyledons and stunted growth. Many successful growers use just 0.6 EC with only water and a tiny amount of CalMag, or use seedling-specific nutrient formulations. The investment of 2–3 extra days of very light feeding pays dividends in robust early growth and fewer deficiency surprises later.

Flush phase EC targets and nutrient clearance

The final flush (weeks 12–13) is not just low EC—it's typically a complete nutrient removal phase. Running EC from 0.4 to 0.6 means minimal salts in the solution, with most applications using plain pH-adjusted water. Some growers add a commercial "flush" product which is mostly chelated micronutrients and sugars, helping the plant mobilize remaining nutrients out of the tissues. The goal is clean-burning flowers with minimal nutrient residue.

Mid-bloom peak feeding (weeks 8-10): maximum yield window

Weeks 8–10 are the critical yield-determining window. Flowers are sizing and resin production peaks. This is when you want EC at its highest (1.6–2.0 for coco) with maximum PK and supporting micronutrients. However, this is also where many growers over-feed. Monitor runoff EC carefully: if it exceeds 2.2–2.4, reduce slightly. A common professional approach: target runoff EC of 1.8–2.0 when input is 1.8—this signals active feeding without accumulation.

Micronutrient considerations throughout the cycle

While this schedule focuses on NPK and EC, don't forget supporting micronutrients: calcium, magnesium, iron, manganese, zinc, boron, molybdenum. Most commercial two-part or three-part nutrient sets include these, but coco growers must always add CalMag—it's non-negotiable. In hydroponic systems, some growers reduce CalMag slightly; in coco, use it at recommended dosage throughout the entire cycle. Micronutrient deficiency becomes apparent around week 4–5 of bloom; by then it's late to correct without yield impact.

Monitoring and real-time adjustment

This schedule is a starting point, not a rigid formula. Professional growers check runoff EC daily and adjust within 24–48 hours if needed. If runoff EC jumps suddenly, reduce feeding strength. If runoff EC drops below input EC, increase strength. This active management is what separates consistent yields from chaotic ones. You'll develop feel after 2–3 cycles, but always back it with measurements. Remember: data doesn't lie—follow your EC meter, not your intuition alone.

Summary: Your three-step framework

Start simple: (1) Choose EC targets per phase and write them down. (2) Measure input and runoff EC daily. (3) Adjust within 24–48 hours if runoff deviates by more than 0.3 from input. This system works for every strain, every substrate, every grower. It's the foundation of professional cannabis cultivation.