Advanced Irrigation & Crop Steering Guide

1️⃣ FUNDAMENTALS

Crop Steering Basics

Understanding how irrigation controls plant morphology, metabolism, and yield

🌿 What is Crop Steering?

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Crop steering is the practice of manipulating irrigation frequency, volume, and timing to direct plant energy toward either vegetative growth (stems, leaves, structure) or generative growth (flowers, fruit, reproduction). By controlling substrate moisture content (SMC) and electrical conductivity (EC), growers can influence plant morphology, yield, and quality.

Why Crop Steering Matters

Maximize Yield: Steer plants generative during flowering for bigger, denser buds
Control Stretch: Use vegetative steering during transition to prevent excessive height
Improve Quality: Generative steering increases resin production and terpene expression
Prevent Issues: Proper steering prevents nutrient lockout, salt buildup, and stress
Commercial Edge: Precision steering is the difference between 1.5 lb/light and 2.5+ lb/light

🌱 Generative vs Vegetative Steering

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⬆️ VEGETATIVE Steering

Goal: Build structure, leaves, and roots

Higher SMC: 55-65% water content
More frequent irrigation: Smaller, more frequent shots
Lower EC: 1.8-2.2 mS/cm
Smaller dry-backs: 2-5% overnight
Effect: Vigorous growth, larger leaves, more stretch

⬇️ GENERATIVE Steering

Goal: Maximize flowering and fruit production

Lower SMC: 45-55% water content
Less frequent irrigation: Larger, strategic shots
Higher EC: 2.4-2.8 mS/cm
Larger dry-backs: 8-15% overnight
Effect: More flowers, denser buds, better quality

⚠️ Critical Balance

Too vegetative = excessive stretch, leafy buds, lower yield
Too generative = stunted growth, stress, nutrient deficiencies
The key is steering at the RIGHT time for each growth phase

📊 Substrate Moisture Content (SMC) Targets

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Growth Phase	SMC Target (%)	Dry-Back (%)	EC Target (mS/cm)	Steering Direction
Propagation	70-80%	0-2%	1.0-1.4	Neutral (root development)
Early Veg (Week 1-2)	60-70%	3-5%	1.6-2.0	Vegetative (structure)
Late Veg (Week 3-4)	55-65%	5-8%	1.8-2.2	Vegetative (size)
Transition (Week 1-2)	50-60%	6-10%	2.0-2.4	Generative (control stretch)
Early Flower (Week 1-3)	50-55%	8-12%	2.2-2.6	Generative (site development)
Mid Flower (Week 4-6)	48-52%	10-15%	2.4-2.8	Generative (bulk/density)
Late Flower (Week 7-8)	50-55%	8-12%	2.2-2.6	Balanced (ripening)
Flush (Week 9+)	55-65%	5-8%	0.0-0.4	Vegetative (finish clean)

💡 Pro Tips

Monitor substrate sensors: Teros 12, Grodan GroSens, or Aroya for real-time SMC/EC
Field capacity: The maximum water substrate can hold after drainage (usually 65-70%)
Dry-back timing: Calculate from last irrigation to first shot (overnight or daytime)
Adjust by cultivar: Indicas tolerate more generative stress; sativas need more vegetative support

⚡ EC Management & Dry-Backs

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Electrical Conductivity (EC) measures the concentration of dissolved salts (nutrients) in your irrigation water and substrate. Managing EC through irrigation strategy is critical for crop steering.

EC Monitoring Points

1. Feed EC (Input)

Your nutrient solution going IN
Set based on growth stage
Typical range: 1.0-2.8 mS/cm

2. Substrate EC (Root Zone)

Measured by sensors or pour-through
Should be 0.2-0.5 higher than feed EC
Key indicator for steering

3. Runoff EC (Drain)

Measure from drain-to-waste
Compare to feed EC
High runoff EC = salt buildup

Dry-Back Strategy

Dry-back is the intentional reduction in substrate moisture content between irrigation events. It concentrates EC in the root zone, creating osmotic stress that drives generative growth.

Dry-Back Type	SMC Drop	Duration	Effect	When to Use
Overnight Dry-Back	3-15%	12-16 hours	Controlled stress, daily reset	Every night throughout grow
Daytime Dry-Back	2-5%	Between P2 shots	Maintains field capacity	Between mid-day irrigations
Aggressive Dry-Back	15-20%	24-48 hours	Strong generative push	Mid/late flower for density
Flush Dry-Back	10-15%	24 hours	Salt removal, clean finish	Final 1-2 weeks

⚠️ Dry-Back Warnings

Don't over-dry: Below 40% SMC causes permanent root damage
Monitor daily: Every cultivar responds differently—watch for stress signs
Slow down in heat: High VPD + aggressive dry-backs = severe stress
Increase gradually: Start with 5% overnight dry-back, increase 1-2% per week

2️⃣ SHOT STRATEGY

P1, P2, P3 Irrigation Timing

Master the three-shot system used by commercial cultivators worldwide

24-Hour Irrigation Cycle

Hover over segments to see details

Lights OFF

P1

P2 (Multiple)

P3

Lights OFF

P1 (First Shot)

At or shortly after lights ON

P2 (Mid-Day Shots)

3-8 shots during photoperiod

P3 (Last Shot)

1-2 hours before lights OFF

🌅 P1 Shot - First Irrigation

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Purpose & Timing

The P1 shot is the most critical irrigation of the day. It occurs at or shortly after lights ON and serves to:

Replenish substrate to field capacity after overnight dry-back
Deliver nutrients for the active photosynthetic period
Reset EC in the root zone by flushing accumulated salts
Signal the plant that it's time to begin transpiration and growth

Growth Stage	P1 Timing	Volume (ml per plant)	Target Runoff	EC Strategy
Early Veg	At lights ON	100-200 ml	5-10%	Match feed EC
Late Veg	Lights ON + 0-15 min	200-400 ml	10-15%	Slightly lower EC to flush
Transition	Lights ON + 30-60 min	300-500 ml	15-20%	Lower EC, drive dry-back
Flower	Lights ON + 30-90 min	400-600 ml	15-25%	Lower EC after dry-back
Late Flower	Lights ON + 60-120 min	300-500 ml	10-20%	Moderate EC for ripening

💡 P1 Shot Triggers

Time-based: Fixed time after lights ON (most common)
SMC-based: When substrate moisture drops to threshold (e.g., 50%)
Light-integral: After X amount of light accumulation (DLI-based)
Hybrid: SMC threshold + minimum time delay for generative steering

⚠️ Common P1 Mistakes

Too early: P1 before lights ON wastes the overnight dry-back
Too late: Delayed P1 in veg causes wilting and stress
Insufficient volume: P1 must reach field capacity + runoff to flush salts
High EC after dry-back: Use lower feed EC in P1 to compensate for concentrated root zone

☀️ P2 Shots - Mid-Day Irrigation

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Purpose & Strategy

P2 shots are multiple small-to-medium irrigations during the photoperiod. They maintain substrate moisture at field capacity, prevent excessive dry-down, and manage EC throughout the day. P2 frequency and volume are your primary tools for steering generative vs vegetative.

Vegetative Steering (More Frequent P2)

Frequency: 6-10 shots per day
Volume: 50-150 ml per shot
Interval: Every 60-90 minutes
Effect: High SMC, lower EC, promotes leaf/stem growth
When: Veg stage, transition if you need stretch

Generative Steering (Less Frequent P2)

Frequency: 2-4 shots per day
Volume: 100-300 ml per shot
Interval: Every 2-4 hours
Effect: Lower SMC, higher EC, promotes flowering
When: Flower stage, controlling stretch in transition

Growth Stage	P2 Frequency	Shot Volume	Target Runoff	Steering Goal
Early Veg (Week 1-2)	4-6 shots	75-150 ml	5-10% each	Vegetative - build structure
Late Veg (Week 3-4)	6-8 shots	100-200 ml	10-15% each	Vegetative - maximize size
Transition (Week 1-2)	3-5 shots	150-250 ml	10-15% each	Generative - control stretch
Early Flower (Week 1-3)	3-5 shots	150-300 ml	15-20% each	Generative - site development
Mid Flower (Week 4-6)	2-4 shots	200-400 ml	15-25% each	Strong generative - bulk up
Late Flower (Week 7-8)	3-5 shots	150-300 ml	10-20% each	Balanced - ripen & swell

💡 Advanced P2 Strategies

DLI-based P2: Trigger shots based on accumulated light (PPFD × time)
VPD-based P2: Increase frequency during high VPD to prevent stress
Pulsing: Multiple small shots (30-50ml) in rapid succession to improve nutrient uptake
EC ramping: Gradually increase feed EC through P2 shots to push generative
Split fertilization: Alternate high/low EC P2 shots for balanced steering

🌙 P3 Shot - Last Irrigation

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Purpose & Critical Timing

The P3 shot is the last irrigation before lights OFF. Its timing and volume directly control your overnight dry-back, which is the most powerful crop steering tool. P3 strategy sets up the next day's growth direction.

Early P3 (Generative)

Timing: 2-4 hours before lights OFF

Creates larger overnight dry-back (10-15%)
Concentrates EC in root zone
Drives strong generative response
Use in flower for density

Late P3 (Vegetative)

Timing: 30-60 min before lights OFF

Creates smaller overnight dry-back (3-6%)
Maintains higher SMC overnight
Supports vegetative growth
Use in veg or to support stressed plants

Growth Stage	P3 Timing	Volume (ml)	Target Dry-Back	Overnight Strategy
Veg	Lights OFF - 1 hr	150-300 ml	3-6%	Minimal dry-back, high SMC
Transition (Early)	Lights OFF - 2 hr	150-250 ml	8-12%	Moderate dry-back to control stretch
Transition (Late)	Lights OFF - 3 hr	100-200 ml	10-15%	Strong dry-back, finish stretch
Flower (Week 1-4)	Lights OFF - 2-3 hr	150-300 ml	10-15%	Strong generative, site development
Flower (Week 5-7)	Lights OFF - 3-4 hr	100-250 ml	12-18%	Maximum dry-back for density
Late Flower (Week 8+)	Lights OFF - 2 hr	150-300 ml	8-12%	Ease back, support ripening

⚠️ P3 Critical Considerations

Never skip P3: Going into dark period dry causes severe stress
Watch runoff: P3 should have minimal runoff (0-10%) to set up dry-back
Adjust for temperature: Cooler nights = slower dry-back, warmer nights = faster
Monitor by morning: Check SMC at lights ON to confirm dry-back target was hit
Cultivar variation: Heavy feeders need later P3; drought-tolerant strains need earlier P3

💡 P3 Advanced Techniques

Double P3: Two small shots 2 hours apart before lights OFF for controlled dry-back
EC spike P3: Higher EC in final shot to drive overnight generative response
Pulse P3: 3-4 tiny shots in last hour to maintain high SMC vegetatively
Skip P3 (extreme): In late flower, skip P3 for 24-hour dry-back to shock plants into final swell

📊 Substrate WC & EC Over 24-Hour Cycle

Typical patterns for rockwool/coco with P1/P2/P3 strategy in flowering stage

Lights OFF Lights ON Mid-Day Late Day Lights OFF

Water Content (WC%) — Higher = Vegetative

Electrical Conductivity (EC) — Higher = Generative

Reading This Chart:

Overnight: WC drops (dry-back), EC rises (salt concentration) — Generative stress
P1: WC spikes back to field capacity, EC drops with fresh nutrient solution
P2 Shots: WC maintained, slight EC fluctuations as plant feeds
P3: Final boost before lights OFF, sets up overnight dry-back
Inverse relationship: As WC decreases, EC increases — this is crop steering in action

3️⃣ GROWING METHODS

Irrigation Strategies by System Type

Tailored irrigation protocols for every growing method

🧱 Rockwool / Stone Wool Irrigation

Rockwool is the gold standard for commercial cultivation. Its fibrous structure retains water while providing excellent aeration, making it perfect for precision crop steering. Rockwool slabs/blocks require high-frequency fertigation with drain-to-waste or recirculating systems.

Key Rockwool Characteristics

Field capacity: 65-70% water content by volume
Air porosity: 15-20% (excellent root oxygenation)
Drainage: Requires runoff (15-25%) to prevent salt buildup
pH buffering: None — requires careful pH management (5.5-6.0)

Rockwool Irrigation Schedule

Growth Stage	Daily Shots	Volume per Shot	Runoff Target	EC Feed	Notes
Seedling/Clone	3-5	25-75 ml	10-15%	1.0-1.4	Hand water or mist until roots establish
Early Veg	5-8	75-150 ml	15-20%	1.6-2.0	Increase frequency as roots develop
Late Veg	6-10	100-200 ml	15-20%	1.8-2.2	High frequency for vegetative steering
Transition	4-6	150-300 ml	15-25%	2.0-2.4	Reduce frequency to drive generative
Flower (Weeks 1-6)	3-5	200-400 ml	20-30%	2.2-2.8	Larger shots, aggressive dry-backs
Late Flower	4-6	150-300 ml	15-25%	2.0-2.4	Support ripening, ease back on stress

Drain-to-Waste (DTW)

Feed solution flows through slab, drains to waste
High runoff (20-30%) prevents salt buildup
No risk of pathogens recirculating
Higher nutrient costs but simpler management
Ideal for beginners and small operations

Recirculating (Recirc)

Runoff collected, filtered, and re-fed
Lower nutrient costs (50-70% savings)
Requires EC/pH monitoring and adjustment
Risk of pathogens spreading through system
Best for experienced growers with automation

💡 Rockwool Pro Tips

Pre-soak slabs: Soak in pH 5.5 water for 24 hours before transplanting
Monitor slab EC: Use Grodan GroSens or Teros 12 sensors for real-time data
Gradient planting: Plant slightly above slab surface to prevent stem rot
Directional holes: Cut drainage slits on underside, not sides, for proper drainage
Slab orientation: Fibers should run horizontally for optimal water distribution

🥥 Coco Coir High-Frequency Fertigation

Coco coir is an inert, renewable growing medium made from coconut husks. It behaves like rockwool but requires calcium/magnesium supplementation due to its cation exchange properties. Coco excels with high-frequency fertigation (8-12+ times per day) for explosive growth.

Coco Coir Characteristics

Field capacity: 60-65% water content
Drainage: Excellent — 15-25% runoff recommended
Cal/Mag hungry: ALWAYS supplement calcium and magnesium
pH range: 5.8-6.2 (slightly higher than rockwool)
Reusable: Can be buffered and reused 2-3 cycles with proper sterilization

Coco Irrigation Schedule

Growth Stage	Daily Shots	Volume per Shot	Runoff Target	EC Feed (+ Cal-Mag)	Notes
Seedling	2-4	50-100 ml	10-15%	1.0-1.4	Buffer coco with Cal-Mag before planting
Veg (Week 1-2)	4-6	75-150 ml	15-20%	1.6-2.0	Start high-frequency as roots establish
Veg (Week 3-4)	8-12	75-125 ml	20-25%	1.8-2.2	Maximum frequency for explosive growth
Transition	5-8	100-200 ml	20-25%	2.0-2.4	Reduce frequency to steer generative
Flower (Weeks 1-6)	4-6	150-300 ml	20-30%	2.2-2.8	Allow dry-backs between shots
Late Flower	3-5	150-250 ml	15-25%	2.0-2.4	Ease back, support final swell

⚠️ Coco-Specific Warnings

Always buffer coco: Pre-charge with Cal-Mag solution before first use
Never let coco dry completely: Coco holds salts when dry, causing lockout
High runoff essential: 20%+ runoff to flush exchanged calcium from CEC sites
Watch for deficiencies: Calcium and magnesium deficiencies are common

💡 Coco Pro Tips

Coco quality matters: Use buffered, low-EC coco (Mother Earth Coco, Grow Junky, Mother Earth)
Mix with perlite: 70/30 coco/perlite for improved drainage and aeration
Automated fertigation: Use float valves or solenoids for precision timing
pH drift: Coco pH drifts up — feed at 5.8-6.0 to maintain 6.0-6.2 in root zone
Recharge between cycles: Flush, buffer with Cal-Mag, and sterilize with H2O2

💧 Deep Water Culture (DWC) Management

Deep Water Culture suspends roots directly in oxygenated nutrient solution. There is no substrate, so "irrigation" becomes water level management and dissolved oxygen optimization. DWC offers the fastest growth rates but requires precise environmental control.

DWC Key Parameters

Water level: 1-2 inches below net pot (roots submerged, crown dry)
Dissolved oxygen: 8+ mg/L (critical — use powerful air stones)
Water temperature: 65-68°F (root rot risk above 72°F)
EC range: 1.2-2.4 mS/cm depending on stage
pH range: 5.5-6.2 (check and adjust daily)

DWC Nutrient Schedule

Growth Stage	EC Target	Water Level	Res Change Frequency	DO Target	Notes
Seedling/Clone	0.8-1.2	Just touching roots	Every 5-7 days	8+ mg/L	High water level, gentle aeration
Early Veg	1.2-1.6	1" below net pot	Every 5-7 days	8+ mg/L	Explosive root growth phase
Late Veg	1.6-2.0	2" below net pot	Every 4-5 days	8+ mg/L	Plants drinking heavily
Transition	2.0-2.2	2" below net pot	Every 3-5 days	8+ mg/L	Begin bloom nutrients
Flower (Weeks 1-6)	2.0-2.4	2" below net pot	Every 3-4 days	9+ mg/L	Peak nutrient demand
Late Flower	1.6-2.0	2" below net pot	Every 3-5 days	8+ mg/L	Reduce EC for ripening
Flush	0.0-0.4	2" below net pot	Daily water-only changes	8+ mg/L	Flush 7-10 days

⚠️ DWC Critical Warnings

Root rot (pythium): #1 killer in DWC — keep temps below 70°F, use Hydroguard/Southern Ag
Oxygen starvation: Insufficient aeration causes slow growth and root browning
pH swings: Check pH 1-2x daily — DWC pH can swing rapidly
Res temperature: Above 75°F, dissolved oxygen drops below safe levels
Light leaks: Any light on res causes algae growth and oxygen depletion

💡 DWC Pro Tips

Use a chiller: Maintain 65-68°F for optimal DO and pathogen prevention
Air stone placement: 1 large air stone per 5-gallon bucket minimum
Beneficials: Add Hydroguard, Orca, or Southern Ag for root protection
Top-off daily: Add water (pH adjusted) to replace evaporation, maintain level
Recirc DWC (RDWC): Multiple buckets connected = stable pH/EC but higher risk
Sterile vs beneficial: Choose one — sterile (H2O2, chlorine) OR beneficial microbes, never both

🌊 Ebb & Flow (Flood & Drain) Systems

Ebb & Flow systems periodically flood a grow tray with nutrient solution, then drain back to a reservoir. Plants grow in pots filled with clay pebbles, coco, or rockwool cubes. This method combines the best of DWC (oxygenated roots) with the stability of container growing.

Ebb & Flow Characteristics

Flood frequency: 2-6 times per day depending on medium and stage
Flood duration: 10-20 minutes (until roots are saturated)
Drainage time: 5-10 minutes (complete drainage critical)
Medium options: Clay pebbles (Hydroton), coco, perlite, rockwool cubes
Reservoir size: 2-3x tray volume for adequate flood capacity

Ebb & Flow Timing Schedule

Growth Stage	Floods per Day	Flood Duration	EC Target	Best Medium	Notes
Seedling/Clone	1-2	10 min	1.0-1.4	Rockwool cubes	Gentle floods to prevent drowning
Early Veg	2-3	15 min	1.6-2.0	Clay pebbles / Coco	Morning, mid-day, evening floods
Late Veg	3-4	15-20 min	1.8-2.2	Clay pebbles	High frequency for fast growth
Transition	3-4	15 min	2.0-2.4	Clay pebbles / Coco	Maintain frequency through stretch
Flower	3-5	15-20 min	2.2-2.6	Clay pebbles	Peak water/nutrient demand
Late Flower	2-4	15 min	2.0-2.4	Clay pebbles	Reduce frequency slightly

💡 Ebb & Flow Pro Tips

Timer precision: Use cycle timers (1-minute intervals) for accurate flood timing
Pump sizing: Pump should fill tray to max level in 5 minutes or less
Overflow protection: ALWAYS install overflow drain at max fill level
Root zone DO: Oxygenation happens during drain cycle — ensure complete drainage
Medium choice: Clay pebbles = most reliable; coco = faster growth; rockwool = precision
Res management: Change reservoir weekly, monitor pH/EC daily

🌊 Nutrient Film Technique (NFT)

NFT systems continuously circulate a thin film of nutrient solution over bare roots in sloped channels. There is no growing medium—roots sit in air with constant nutrient flow. NFT offers the fastest growth but is unforgiving of system failures.

NFT System Parameters

Flow rate: 0.5-1.0 liters per minute per channel
Channel slope: 1:30 to 1:40 (1-2.5% grade)
Film depth: 2-3 mm (thin film is critical)
Channel length: 10-15 feet maximum (shorter = better oxygenation)
Continuous flow: 24/7 nutrient circulation (never stop)

NFT Management Schedule

Growth Stage	EC Target	Flow Rate (L/min)	Res Temp	pH Range	Notes
Clone/Seedling	1.0-1.4	0.5	65-68°F	5.8-6.2	Start in starter plugs, gentle flow
Veg	1.6-2.0	0.75-1.0	65-68°F	5.8-6.2	Explosive root and shoot growth
Transition	2.0-2.2	1.0	65-68°F	5.8-6.2	Monitor for deficiencies during stretch
Flower	2.2-2.6	1.0	65-68°F	5.8-6.2	Peak demand period
Late Flower	1.8-2.2	0.75-1.0	65-68°F	6.0-6.5	Reduce EC for ripening

⚠️ NFT Critical Warnings

Pump failure = death: NFT roots dry out in 30-60 minutes without flow
Root clogging: Excessive root growth can block channels — prune roots regularly
Uneven flow: First plants get most nutrients; balance with channel design
Temperature sensitivity: Above 72°F causes root rot and low DO
No buffer: EC/pH swings affect plants immediately — monitor constantly

💡 NFT Pro Tips

Backup power: CRITICAL — use battery backup for pump (UPS system)
Inline filters: Prevent debris from clogging emitters and channels
Root pruning: Trim roots every 2-3 weeks to maintain flow
Channel material: Use light-proof PVC or gutter systems
Plant spacing: 6-8 inches minimum to prevent overcrowding
Res size: Larger reservoir = more stable EC/pH/temp

🌱 Living Soil / Organic Irrigation

Living soil systems rely on microbial activity to break down organic matter and deliver nutrients to plants. Irrigation is infrequent (hand-watering or automated drip) with focus on maintaining soil moisture, not precision fertigation. This is the "low and slow" approach—less control, but superior flavor and terpene profiles.

Living Soil Fundamentals

Water source: Dechlorinated tap or RO water (chlorine kills microbes)
Frequency: Water when top 1-2" of soil is dry
Volume: Water to runoff (10-20%) to prevent salt buildup
pH: 6.0-7.0 (soil buffers pH naturally)
No EC measurement: Nutrients come from soil biology, not liquid feeds

Living Soil Watering Schedule

Growth Stage	Watering Frequency	Volume	Amendments	Notes
Seedling (Week 1-2)	Every 2-3 days	To saturation (no runoff)	None (rely on soil)	Gentle watering, mist if needed
Veg (Week 3-6)	Every 2-4 days	10-20% runoff	Compost tea 1x/week	Allow slight dry-down between waterings
Transition	Every 2-3 days	10-20% runoff	Top dress bloom amendments	Increase P/K inputs
Flower (Week 1-6)	Every 1-3 days	10-20% runoff	Compost tea + bloom top dress	Plants drinking heavily
Late Flower (Week 7+)	Every 2-4 days	10-15% runoff	Water only (no teas)	Let soil "finish" naturally

Hand Watering Technique

Water slowly to avoid channeling
Water entire pot surface evenly
Stop when runoff begins (10-20%)
Use dechlorinated water (24hr sit or ascorbic acid)
Room-temp water (60-70°F)

Automated Drip for Soil

Blumat carrots for passive watering
Drip emitters (1-2 GPH) on timers
Water 1-2x daily for 5-15 minutes
Adjust based on soil moisture
Always use dechlorinated water

💡 Living Soil Pro Tips

Mulch layer: Cover soil with straw or barley to retain moisture and feed microbes
No-till: Never disturb soil between cycles — top dress and plant directly
Compost teas: Brew with air stone for 24-48 hours, apply fresh
Cover crops: Plant clover between cycles to fix nitrogen and build soil
Soil moisture meter: Use a probe to check moisture 4-6" deep
Build your own mix: Peat/coco base + compost + aeration (perlite/pumice) + amendments

4️⃣ SUBSTRATE MANAGEMENT

Monitoring & Managing Your Root Zone

Precision substrate monitoring is the key to professional crop steering

💧 Water Content (WC) Monitoring

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Water Content (WC) is the percentage of substrate volume occupied by water. It's measured in real-time using sensors inserted into your growing medium. WC is the primary metric for crop steering—it tells you exactly how much water is available to the plant at any moment.

Understanding WC Measurements

Field Capacity

Maximum water substrate can hold after drainage
Rockwool: 65-70% WC
Coco coir: 60-65% WC
Your P1 shot should reach field capacity

Permanent Wilting Point

WC below which plants cannot extract water
Rockwool: ~35-40% WC
Coco: ~30-35% WC
NEVER let substrate reach this level

Target WC Range

Veg: 55-65% (higher for vegetative)
Flower: 45-55% (lower for generative)
Adjust based on steering goals
Monitor daily patterns for optimization

How to Use WC Data

Track overnight dry-back: WC at P3 minus WC at P1 = your dry-back percentage
Optimize P1 timing: Trigger P1 when WC hits your target threshold
Adjust P2 frequency: If WC drops too fast, increase P2 frequency
Steer with confidence: WC gives you objective data instead of guessing
Compare zones: Multiple sensors show if irrigation is uneven

⚡ EC Monitoring: Feed vs Substrate vs Runoff

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Monitoring EC at three points gives you complete control over your nutrient strategy: Feed EC (what goes in), Substrate EC (what's in the root zone), and Runoff EC (what comes out).

Measurement Point	What It Tells You	How to Measure	Target Relationship	Action Required
Feed EC (Input)	Nutrient concentration you're delivering	EC meter in reservoir or irrigation line	Baseline (1.0-2.8 mS/cm by stage)	Set based on growth phase
Substrate EC (Root Zone)	Actual nutrient availability to roots	Substrate sensor (Teros 12, GroSens)	Feed EC + 0.2-0.5 mS/cm	Primary steering metric
Runoff EC (Drain)	Salt accumulation or depletion	Collect runoff, test with EC meter	Should match or be slightly higher than feed	Adjust feed EC or increase runoff %

EC Troubleshooting Guide

🔴 Runoff EC Too High

Runoff is 0.5+ higher than feed

Problem: Salt buildup in substrate
Cause: Insufficient runoff, too high feed EC
Fix: Increase runoff to 25-30%, reduce feed EC by 0.2-0.4
Flush: Water-only shot to reset substrate

🟢 Runoff EC Too Low

Runoff is 0.3+ lower than feed

Problem: Plants consuming nutrients faster than replacement
Cause: Feed EC too low, or excessive runoff
Fix: Increase feed EC by 0.2-0.4, reduce runoff %
Monitor: Check for deficiency symptoms

🟡 Substrate EC Climbing

Sensor shows rising EC over 24 hrs

Good sign: Part of generative dry-back strategy
Bad sign: If unintentional, indicates salt accumulation
Fix: If too high (>3.0), flush and adjust
Normal range: 0.5-0.8 mS/cm increase overnight in flower

⚠️ EC Red Flags

Substrate EC above 3.5 mS/cm: Immediate flush required (nutrient lockout imminent)
Runoff EC 1.0+ higher than feed: Severe salt buildup (flush with low EC solution)
Substrate EC swinging wildly: Irrigation timing inconsistent or sensors placed poorly
EC dropping during dry-back: Unusual — check for sensor errors or root disease

📏 Dry-Back Percentages & Timing

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Calculating Dry-Back

Dry-Back Formula

Dry-Back % = [(WC at Last Shot) - (WC at First Shot)] / (WC at Last Shot) × 100

Example: P3 shot leaves substrate at 60% WC. P1 shot starts when substrate is at 51% WC.
Dry-back = [(60 - 51) / 60] × 100 = 15% dry-back (strong generative)

Dry-Back Targets by Growth Stage

Growth Phase	Target Dry-Back	WC at P3	WC at P1	Steering Effect	Duration
Early Veg	3-5%	65%	62%	Minimal stress, fast growth	8-12 hours
Late Veg	5-8%	62%	57%	Slight vegetative push	10-14 hours
Transition Week 1	8-12%	58%	51%	Generative (control stretch)	12-14 hours
Transition Week 2	10-15%	55%	47%	Strong generative	12-14 hours
Early Flower (1-3)	10-15%	54%	46%	Generative for sites	12-14 hours
Mid Flower (4-6)	12-18%	52%	43%	Maximum generative (bulk)	12-16 hours
Late Flower (7-8)	8-12%	54%	48%	Balanced for ripening	12-14 hours
Flush	5-8%	58%	53%	Ease stress, clean finish	10-12 hours

💡 Dry-Back Pro Tips

Start conservative: Begin with 5% overnight dry-back, increase 1-2% per week
Watch plant response: Wilting in morning = too aggressive; adjust P3 timing
Adjust for environment: Higher VPD = faster dry-back; lower VPD = slower
Cultivar differences: Test each strain — some handle 20%+, others stress at 12%
Weekend strategy: Reduce dry-back before days off to prevent stress
Sensor placement matters: Place sensors mid-slab depth for accurate readings

📡 Sensor Placement & Equipment

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Substrate Sensor Options

Sensor	Measures	Best For	Price Range	Notes
Teros 12	WC, EC, Temp	Rockwool, coco, soil	$150-200 each	Industry standard, highly accurate
Grodan GroSens	WC, EC, Temp	Rockwool slabs (optimized)	$200-250 each	Purpose-built for Grodan, excellent
Aroya Sensors	WC, EC, Temp	Rockwool, coco (cloud-based)	$200 each + subscription	Complete monitoring platform
Bluelab Pulse	WC, EC, Temp	Soil, coco (handheld)	$300-400	Portable, good for spot checks
Budget Option: Pour-Through	EC, pH (manual)	Any substrate	$0 (EC meter needed)	Pour water through, collect runoff

Proper Sensor Placement

Rockwool Slabs

Insert at 45° angle into center of slab
Depth: 2-3 inches (mid-slab)
Position: 1-2 inches from plant stem
Quantity: 1 sensor per 6-10 plants
Avoid: Too close to edges or drainage holes

Coco Coir Pots

Insert vertically into side of pot
Depth: Mid-depth of container
Position: Halfway between stem and edge
Quantity: 1 sensor per 4-6 plants
Avoid: Directly below drip emitters

Living Soil Beds

Insert vertically into soil
Depth: 4-6 inches deep
Position: Multiple sensors across bed
Quantity: 1 per 10-15 sq ft
Avoid: Directly in root mass

Calibration & Maintenance

Calibrate monthly: Use manufacturer's calibration solution or dry/saturated readings
Clean probes: Remove salt buildup with soft brush and distilled water
Check readings: Compare multiple sensors in same conditions for consistency
Replace annually: Sensors drift over time — replace every 12-18 months
Log data: Track trends over weeks/months to optimize irrigation strategy

5️⃣ ADVANCED STRATEGIES

Next-Level Irrigation Techniques

Integrate climate, lighting, and multi-zone control for maximum yield

🌡️ VPD & Irrigation Integration

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Vapor Pressure Deficit (VPD) is the difference between the water vapor in the air and the amount it could hold at saturation. VPD drives transpiration rate, which directly affects how quickly your substrate dries and how much water plants need.

VPD Level	kPa Range	Plant Response	Irrigation Adjustment	Crop Steering Effect
Too Low	< 0.8 kPa	Slow transpiration, humid stress	Reduce irrigation frequency by 10-20%	Risk of mold, reduce vegetative push
Veg Target	0.8-1.0 kPa	Optimal vegetative growth	Standard frequency (6-10 shots/day)	Ideal for structure building
Transition Target	1.0-1.2 kPa	Balanced growth, stretch control	Moderate frequency (4-6 shots/day)	Generative steering starts
Flower Target	1.2-1.5 kPa	High transpiration, generative	Allow larger dry-backs (12-18%)	Maximum flower production
Too High	> 1.6 kPa	Excessive transpiration, stress	Increase frequency by 20-30%	Risk of nutrient burn, slow dry-backs

💡 VPD-Based Irrigation Rules

High VPD days: Plants transpire more — increase P2 frequency to prevent excessive dry-down
Low VPD days: Plants transpire less — reduce P2 frequency to avoid overwatering
VPD spike response: If VPD jumps during day, add extra P2 shot to compensate
Night VPD: Keep 0.4-0.8 kPa at night for optimal overnight dry-back
Automation: Advanced controllers (TrolMaster, Priva) can trigger irrigation based on VPD

☀️ Daily Light Integral (DLI) Based Irrigation

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Daily Light Integral (DLI) is the total amount of photosynthetically active radiation (PAR) delivered in 24 hours. More light = more photosynthesis = more water consumption. Advanced growers trigger irrigation based on accumulated light rather than fixed timers.

DLI Irrigation Strategy

Concept:

Instead of irrigating every 2 hours, trigger irrigation after the plant has received X amount of light (e.g., every 5 mol/m² accumulated).

Light Integral = PPFD × Time (seconds) ÷ 1,000,000

Example: At 800 PPFD, plants receive ~2.88 mol/m² per hour. Set controller to irrigate every 3 mol/m² = irrigation every ~60-90 minutes depending on light intensity.

Growth Stage	DLI Target	PPFD Range	Light Integral per Shot	Expected Shots/Day
Veg	25-40 mol/m²/day	400-600 PPFD	2-3 mol/m²	8-12 shots
Transition	35-45 mol/m²/day	600-800 PPFD	3-4 mol/m²	6-10 shots
Flower	40-55 mol/m²/day	800-1000 PPFD	4-6 mol/m²	4-8 shots

Benefits of DLI-Based Irrigation

Consistency: Irrigation tracks actual plant demand, not arbitrary time
Cloudy day compensation: Fewer shots on low-light days automatically
Dialed timing: No more guessing — irrigation syncs with photosynthesis
Energy efficiency: Optimize water use based on plant activity

💧 Drain-to-Waste Percentages by Stage

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Runoff percentage is critical for managing substrate EC and preventing salt buildup. Too little runoff = salt accumulation. Too much runoff = wasted nutrients and environmental instability.

Growth Stage	Target Runoff %	EC Strategy	Purpose	Notes
Early Veg	10-15%	Match feed to runoff EC	Establish baseline, flush substrate	Higher runoff to stabilize new plants
Late Veg	15-20%	Maintain stable substrate EC	Prevent buildup during heavy feeding	Balance growth with EC control
Transition	15-25%	Flush salts from veg, start higher EC	Reset substrate for flower phase	Extra runoff week 1 of flower
Flower (Weeks 1-4)	20-30%	High EC + high runoff = stable root zone	Aggressive feeding without lockout	Peak runoff during bulk phase
Flower (Weeks 5-7)	15-25%	Reduce runoff as feeding intensity drops	Maintain EC, less waste	Balance economy with control
Late Flower	15-20%	Lower EC, moderate runoff	Support ripening without stress	Ease into flush phase
Flush	30-50%	0 EC water, maximum runoff	Remove all accumulated salts	High volume flushes 7-10 days

⚠️ Runoff Management Mistakes

No runoff in rockwool/coco: ALWAYS have runoff — these media have no buffer
Ignoring runoff EC: High runoff EC = your substrate is toxic, flush immediately
Excessive runoff (>40%): Wastes nutrients and destabilizes substrate EC/pH
Inconsistent collection: Measure runoff from multiple plants for accuracy

🎯 Multi-Zone Irrigation for Different Cultivars

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Not all cultivars have the same water needs. Multi-zone irrigation allows you to run different irrigation strategies for different strains, growth stages, or room sections simultaneously.

Zone Strategy Examples

Zone 1: Indica-Dominant

Traits: Compact, drought-tolerant
Strategy: Aggressive dry-backs (15-20%)
Frequency: 3-4 shots/day in flower
EC: Higher EC tolerance (2.6-3.0)

Zone 2: Sativa-Dominant

Traits: Stretchy, thirsty
Strategy: Moderate dry-backs (8-12%)
Frequency: 6-8 shots/day in flower
EC: Lower EC range (2.0-2.4)

Zone 3: Hybrids

Traits: Balanced growth
Strategy: Standard dry-backs (10-15%)
Frequency: 4-6 shots/day in flower
EC: Mid-range EC (2.2-2.6)

Setting Up Multi-Zone Irrigation

Hardware: Use multi-zone timers or controllers (TrolMaster Hydro-X, Priva)
Manifolds: Split irrigation lines with ball valves for independent control
Sensors: Place substrate sensors in each zone to monitor independently
Solenoids: Automated solenoid valves for each zone (controlled by timer/controller)
Programming: Set unique schedules per zone based on cultivar needs

6️⃣ DOSATRON INTEGRATION

Precision Nutrient Injection for Crop Steering

How to integrate Dosatron injectors into your irrigation strategy

💉 Dosatron Basics for Irrigation

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Dosatron injectors are water-powered metering pumps that inject precise ratios of concentrated nutrients into your irrigation water. They require no electricity and maintain consistent dosing regardless of water pressure or flow rate variations.

Why Dosatron for Crop Steering?

Consistent EC across all irrigation events
No mixing tanks (reduces labor)
Easy ratio adjustments by growth stage
Multiple injectors = complex feeding programs
Reliable for commercial scale

Common Dosatron Models

D14MZ2: 1:500 ratio (hobby/small commercial)
D25F2: Adjustable 1:50-1:500 (most versatile)
D45RE: High flow, commercial
D8RE: Low flow, precise control

Setting Injection Ratios by Stage

Adjust your stock solution concentration or Dosatron ratio to hit target EC:

Veg (EC 1.6-2.0): Set Dosatron to 1:200 for standard stock solution
Transition (EC 2.0-2.4): Adjust to 1:150 or increase stock concentration
Flower (EC 2.4-2.8): Set to 1:100 or maximum concentration
Flush (EC 0.0): Bypass Dosatron completely (bypass valve)

🔧 Stock Tank Management

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Stock Solution Calculation

Formula:

Stock Concentration = Target EC × Dosatron Ratio ÷ Nutrient Concentration Factor

Example: Target EC = 2.4 mS/cm, Dosatron ratio = 1:200, Nutrient = Athena Pro Bloom (300 mS/cm per gram/L)
Stock Concentration = 2.4 × 200 ÷ 300 = 1.6 g/L stock solution

Stock Tank	Contents	Dosatron Model	Ratio	When to Use
Tank A	Base Nutrients (Part A)	D25F2	1:100-1:200	All irrigation events
Tank B	Base Nutrients (Part B)	D25F2	1:100-1:200	All irrigation events
Tank C	Supplements (Cal-Mag, PK)	D14MZ2	1:500	P2/P3 shots only (optional)

💡 Stock Tank Pro Tips

Opaque tanks: Use black or dark tanks to prevent algae growth
Tank size: Minimum 50-gallon tanks for stability (less mixing frequency)
Mixing order: Add nutrients to water (never water to nutrients) to prevent clumping
Circulation: Use small pump or air stone to keep solution mixed
Label clearly: Mark each tank with contents, concentration, and date mixed
Weekly checks: Test stock EC weekly, remix if precipitation occurs

⚙️ Multi-Injector Setups for Crop Steering

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Advanced growers use multiple Dosatron units to create complex feeding programs, allowing different nutrient mixes for P1, P2, and P3 shots or for different cultivar zones.

Setup Example: 3-Injector System

Dosatron #1: Base Grow (Veg)

Stock: High-N vegetative nutrients
Ratio: 1:200
Controlled by: Solenoid valve + timer
Active: Veg room only

Dosatron #2: Base Bloom (Flower)

Stock: High-PK flowering nutrients
Ratio: 1:150
Controlled by: Solenoid valve + timer
Active: Flower room only

Dosatron #3: Supplements

Stock: Cal-Mag, Silica, PK boosters
Ratio: 1:500
Controlled by: Manual or automated valve
Active: Specific shots (P2/P3) or phases

⚠️ Multi-Injector Warnings

Pressure balance: All Dosatrons need equal inlet pressure for accurate dosing
Backflow prevention: Use check valves to prevent cross-contamination between lines
Series vs parallel: Install in series (one after another) for complex mixes, parallel for zone control
Verification: ALWAYS test output EC after plumbing changes

7️⃣ MONITORING & EQUIPMENT

Essential Tools for Professional Irrigation

Controllers, sensors, and automation for precision crop steering

🎛️ Irrigation Controllers

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Controller	Type	Features	Best For	Price Range
TrolMaster Hydro-X	Full environmental control	Climate + irrigation, VPD-based triggers, multi-zone	Small-medium commercial, serious hobbyists	$800-2,000+
Priva Office	Professional greenhouse	Complete automation, crop models, data logging	Large commercial operations	$5,000-50,000+
Argus Controls	Professional greenhouse	Climate + fertigation, touchscreen, cloud access	Medium-large commercial	$3,000-30,000+
Bluelab Pro Controller	Basic automation	pH/EC dosing, pump control, alarms	Small grows, recirculating systems	$600-1,200
Digital Cycle Timer	Simple timing	1-minute intervals, multiple programs	Budget builds, fixed schedules	$30-100
Rainbird/Hunter Irrigation Controller	Agricultural timer	Multi-zone, outdoor-rated, programmable	Large DTW systems, outdoor grows	$100-500

Choosing the Right Controller

Beginner: Digital cycle timer + manual adjustments (learn the basics first)
Intermediate: TrolMaster or Bluelab for VPD integration and data logging
Commercial: Priva or Argus for full automation and multi-room management
Budget: Start with timers, upgrade to sensors + controller as you scale

📊 Substrate Monitoring Equipment

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Teros 12 (Meter Group)

Measures: WC, EC, Temperature
Accuracy: ±1-2% WC, ±0.1 mS/cm EC
Interface: Requires data logger (ZL6, EM60)
Cost: $150-200 per sensor
Best for: Rockwool, coco, soil research

Grodan GroSens

Measures: WC, EC, Temperature
Accuracy: Optimized for Grodan rockwool
Interface: Standalone display or cloud platform
Cost: $200-250 per sensor
Best for: Rockwool slabs (commercial standard)

Aroya Cultivation Platform

Measures: WC, EC, Temp + VPD + DLI
Accuracy: Professional-grade
Interface: Cloud-based app, real-time alerts
Cost: $200/sensor + $99/month subscription
Best for: Commercial operations wanting complete data

💡 Monitoring Setup Tips

Start with 2-3 sensors: Place in representative plants across grow space
Data logging: Use controllers that log data for trend analysis
Set alarms: Alert when WC drops too low or EC climbs too high
Weekly reviews: Check 7-day graphs to spot patterns and optimize
Calibrate quarterly: Verify sensor accuracy every 3-4 months

🚰 Pumps, Valves & Flow Control

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Essential Plumbing Components

Component	Purpose	Recommended Models	Sizing Guidelines
Main Pump	Pressurize irrigation system	Grundfos, Flotec, Wayne (1-3 HP)	60-100 PSI output, 10-50 GPM flow
Solenoid Valves	Zone control, automation	Hunter PGV, Rainbird DV series (24V AC)	1/2" to 1" depending on flow needs
Pressure Regulator	Maintain consistent PSI	Watts LFN45B, Senninger PSR2	Set to 30-60 PSI for drip systems
Flow Meter	Monitor irrigation volume	Blue-White F-2000, Omega FTB600	Match to system flow rate (GPM)
Inline Filter	Prevent emitter clogging	200-mesh screen filter	Clean weekly or when pressure drops
Check Valve	Prevent backflow	Spring-loaded check valves	Install after pump and Dosatrons

⚠️ Plumbing Mistakes to Avoid

Undersized pump: Insufficient pressure = uneven irrigation and Dosatron failures
No pressure regulator: Pressure fluctuations cause inconsistent shot volumes
Clogged filters: Regular cleaning prevents catastrophic emitter failures
Wrong valve type: Use latching solenoids for battery backup systems
No flow meter: Can't troubleshoot without knowing actual flow rates

8️⃣ COMPLETE SCHEDULES

Week-by-Week Crop Steering Programs

Full irrigation schedules from veg through harvest for rockwool/coco systems

🌱 Vegetative Phase (Weeks 1-4)

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Week	Daily Shots	Shot Volume	P1 Timing	P3 Timing	Dry-Back %	EC Feed	Runoff %
Week 1	4-5	75-100 ml	Lights ON	Lights OFF - 1hr	3-5%	1.4-1.6	10-15%
Week 2	6-7	100-150 ml	Lights ON	Lights OFF - 1hr	4-6%	1.6-1.8	15-20%
Week 3	8-10	100-150 ml	Lights ON + 15 min	Lights OFF - 1hr	5-7%	1.8-2.0	15-20%
Week 4	8-10	125-175 ml	Lights ON + 15 min	Lights OFF - 1.5hr	6-8%	2.0-2.2	15-20%

Notes: Vegetative strategy = high frequency, minimal dry-backs, lower EC. Goal is rapid structure building and leaf development.

🌻 Transition / Flip (Weeks 1-2)

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Week	Daily Shots	Shot Volume	P1 Timing	P3 Timing	Dry-Back %	EC Feed	Runoff %
Flip Week 1	5-6	150-200 ml	Lights ON + 30 min	Lights OFF - 2hr	8-10%	2.0-2.2	20-25%
Flip Week 2	4-5	175-250 ml	Lights ON + 45 min	Lights OFF - 3hr	10-12%	2.2-2.4	20-25%

Notes: Transition strategy = reduce frequency, increase dry-backs to CONTROL STRETCH. This is critical to prevent excessive height gain. Push generative hard.

🌸 Early Flower (Weeks 1-3)

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Week	Daily Shots	Shot Volume	P1 Timing	P3 Timing	Dry-Back %	EC Feed	Runoff %
Flower Week 1	4-5	200-300 ml	Lights ON + 60 min	Lights OFF - 2.5hr	10-13%	2.2-2.4	20-25%
Flower Week 2	4-5	200-300 ml	Lights ON + 60 min	Lights OFF - 2.5hr	11-14%	2.4-2.6	20-25%
Flower Week 3	3-5	250-350 ml	Lights ON + 75 min	Lights OFF - 3hr	12-15%	2.4-2.6	25-30%

Notes: Early flower = continue generative steering for flowering site development. Larger shots, strong dry-backs, high EC to maximize bud initiation.

💪 Mid Flower / Bulk Phase (Weeks 4-6)

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Week	Daily Shots	Shot Volume	P1 Timing	P3 Timing	Dry-Back %	EC Feed	Runoff %
Flower Week 4	3-4	300-400 ml	Lights ON + 90 min	Lights OFF - 3.5hr	13-16%	2.4-2.6	25-30%
Flower Week 5	3-4	300-400 ml	Lights ON + 90 min	Lights OFF - 3.5hr	14-17%	2.6-2.8	25-30%
Flower Week 6	3-4	250-350 ml	Lights ON + 90 min	Lights OFF - 3hr	13-16%	2.6-2.8	20-25%

Notes: Peak generative = maximum dry-backs, highest EC, largest shots. This is where you push for density, weight, and resin production. Monitor for stress.

🍇 Late Flower / Ripening (Weeks 7-9)

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Week	Daily Shots	Shot Volume	P1 Timing	P3 Timing	Dry-Back %	EC Feed	Runoff %
Flower Week 7	4-5	200-300 ml	Lights ON + 60 min	Lights OFF - 2hr	10-12%	2.2-2.4	20-25%
Flower Week 8	4-6	200-300 ml	Lights ON + 30 min	Lights OFF - 1.5hr	8-10%	2.0-2.2	15-20%
Flower Week 9	5-6	150-250 ml	Lights ON + 15 min	Lights OFF - 1hr	6-8%	1.8-2.0	15-20%

Notes: Late flower = EASE BACK on generative stress. Increase frequency, reduce dry-backs, lower EC to support ripening and final swell. Avoid shocking plants near harvest.

💧 Flush Phase (7-10 Days Pre-Harvest)

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Day	Daily Shots	Shot Volume	P1 Timing	P3 Timing	Dry-Back %	EC Feed	Runoff %
Days 1-3	4-6	200-300 ml	Lights ON	Lights OFF - 1hr	5-8%	0.0-0.2	30-40%
Days 4-7	3-5	200-300 ml	Lights ON	Lights OFF - 1hr	5-8%	0.0	30-50%
Days 8-10	2-4	200-400 ml	Lights ON	Lights OFF - 2hr	8-12%	0.0	20-40%

Notes: Flush = plain water (0 EC), high runoff to leach salts from substrate. Maintain adequate frequency to prevent stress. Some growers add enzymes or flushers (e.g., FloraKleen) to accelerate salt removal.

💡 Flush Strategy Notes

Duration debate: 7-10 days is standard; some do 3-5 days, others 14 days
Watch trichomes: Don't flush so long that plants fade excessively before harvest
Enzymatic flush: Products like Florakleen or Clearex accelerate salt removal
Final dry-back: Last 48 hours, some growers do an aggressive dry-back (12-24hr) to stress plants for final resin push (controversial)