CONTENTS

CONTENTS

Watering

phase-by-phase essentials

Watering cannabis plants isn’t just about keeping them hydrated—it’s about creating the perfect environment for nutrient uptake, oxygenation, and root health. Here’s why watering is so critical:

  1. Hydration for growth
    Plants need water for photosynthesis, nutrient transport, and overall metabolism.
  2. Nutrient delivery
    Water acts as a vehicle to transport essential nutrients to the roots.
  3. Salt management
    Runoff helps flush excess salts from the substrate, preventing nutrient lockout. 
  4. Oxygenation
    Drying cycles ensure roots receive oxygen, promoting healthy root development.

pH and EC in watering

Proper management of pH and EC ensures efficient nutrient absorption and prevents plant stress.

pH dynamics

Watering pH should match the plant’s needs:

Grow medium Soil Coco Coir Hydroponics
pH range 6.0–6.5 5.7–6.2 5.5–6.0

EC dynamics

The EC value reflects the nutrient solution’s strength. Proper EC ensures plants get the right amount of nutrients without overfeeding or underfeeding.

Growth phase Soil EC (mS/cm)
Seedling 0.6–0.8
Vegetative 0.8–1.6
Flowering 1.6–2.2
Ripening 0.8–1.0
Runoff pH Slightly higher runoff EC than input is normal (±0.2–0.6).
Significant deviations suggest:
High EC Salt accumulation (requires flushing).
Low EC Overwatering or nutrient deficiency.

The role of runoff

Runoff plays an important role in determining your substrate’s health and nutrient balance.

Medium Target Runoff Purpose
Soil 10–20% Flush salts and maintain of input volume pH balance.
Coco Coir 20–25% Avoid salt buildup due to of input volume coco’s retention
Hydroponics No runoff
(replace reservoir)		 Maintain water and nutrient balance directly.

When and how to water

Understanding when to water is key for maintaining a healthy root system.

Weight Test Lift the pot when watered and again when dry to gauge moisture.
Topsoil dryness Check the top 2–3 cm of soil or coco for dryness.
Visual signs Underwatering
  • Limp, drooping leaves;
  • Dry, crumbly substrate.
Overwatering
  • Swollen, drooping leaves;
  • Persistently wet substrate.

Phase-by-phase watering guidelines

Phase Frequency Volume/L* (ml) Runoff
Seedling s: 1–2 days s: 50–100 s: 5–10%
c: daily c: 100–150 c: 10–15%  
Early Vegetation s: 2–3 days s: 200–300 s: 10–15%
c: daily c: 250–350 c: 15–20%  
(Main) Vegetation s: 2–3 days s: 300–400 s: 10–15%
c: daily c: 350–450 c: 15–20%  
Late Vegetation s: 2–3 days s: 300–450 s: 10–15%
c: daily c: 350–500 c: 15–20%  
Pre-Flowering s: 2–3 days s: 400–500 s: 10–15%
c: daily c: 500–600 c: 15–20%
Blooming s: 2–3 days s: 400–550 s: 10–15%
c: daily c: 450–600 c: 20–25%  
Ripening s: 2–3 days s: 300–400 s: 5–10%
c: daily c: 350–450 c: 10–15%  
Flush s: 1–3 days s: 3× pot volume s: 30–45%
c: daily c: 2× pot volume c: 35–50%  

* Volume per litres of substrate; s: soil, c : coco-coir.

Common watering mistakes and solutions

Overwatering Leads to root rot, poor oxygen uptake, and nutrient lockout.
Solution Ensure proper drainage; allow medium to dry slightly between watering.
Underwatering Stunts growth and causes nutrient deficiencies.
Solution Use a moisture metre to check levels and increase watering frequency if needed.
Ignoring Runoff Accumulated salts in coco or hydroponics harm root health.
Solution Flush medium periodically to remove excess salts.
Inconsistent timing Causes stress during sensitive growth phases.
Solution Use timers for regularity; adjust schedules as plants transition phases.
Incorrect pH levels AResults in nutrient lockout and poor plant health.
Solution Regularly test and adjust water pH to 6.0–6.5 (soil), 5.7–6.2 (coco) or 5.5–6.0(hydro).

Flushing between growth phases

Flushing is a crucial process in cannabis cultivation, especially between growth phases, to ensure optimal nutrient uptake, prevent build-ups, and enhance plant health. Proper flushing also plays a vital role in ensuring that your plants are ready for the next phase of their life cycle, whether it’s moving from vegetative growth to flowering or prepping for harvest.

How to flush between phases

  1. Use pH-balanced water
    Ensure the water used for flushing is pH-balanced (pH range 6.0–6.5 for soil, 5.7–6.2 for coco, and 5.5–6.0 for hydro).
  2. EC of 0.0–0.5 mS/cm
    Ensure the EC of flushing water is minimal, preventing any excess salts from remaining in the medium.
  3. Watering volume
    For Soil, use 3× the pot volume. For Coco and Hydroponics, use 2× the pot volume (e.g., 2L of water for a 1L pot).
  4. Resume feeding
    After flushing, continue with the new nutrient schedule once the runoff EC stabilises at a level consistent with the new feeding programme.

Flushing after nutrient overload

  1. Stop nutrient feedings:
    Immediately halt your regular feeding schedule.
  2. Prepare flushing water:
    Use pH-balanced water with an EC of 0.0–0.5 mS/cm to flush out excess salts and minerals.
  3. Flush thoroughly:
    Apply water equivalent to 2–3× the pot volume (depending on your medium).
  4. Monitor runoff:
    Measure the runoff’s pH and EC to ensure they match the input water (indicating the medium has been flushed properly).
  5. Resume feeding carefully:
    Once the runoff is stable, reintroduce nutrients at half-strength and observe plant’s response.

Signs of recovery

  1. Yellowing stops progressing:
    The yellowing of leaves (due to nutrient deficiencies) begins to reverse.
  2. New growth is healthy:
    New leaves and shoots are vibrant and healthy-looking.
  3. Leaves regain turgidity:
    Leaves become more rigid and less limp, regaining their natural texture and health.

Water and irrigation equipment in cannabis cultivation

Efficient water and irrigation systems are vital for consistent hydration, nutrient delivery, and optimal growth conditions for cannabis plants. This guide explores essential tools, maintenance practices, and tips for establishing a reliable water source and managing irrigation effectively.

Water pumps +Efficient distribution, versatile use.
–Risk of clogs; submersible pumps may overheat.
Irrigation systems +Saves time, reduces waste.
–Complex setup; requires cleaning.
Air pumps and stones +Prevents root rot, enhances nutrient uptake.
–Can be noisy; stones need regular cleaning.
Water filtration systems +Protects plants, improves consistency.
–Filters need replacement; RO wastes water.
Reservoirs and tanks +Batch preparation of solutions.
–Risk of algae if not maintained.
Heating/cooling elements +Prevents nutrient lockout, stabilises conditions
–Higher energy costs.
Timer boxes +Ensures consistency, reduces human error.
–Manual adjustment needed for seasonal changes.

Establishing a reliable water source

  1. Reverse Osmosis (RO)
    Filters impurities like chlorine and heavy metals for clean water.
  2. Water reservoir
    Stores filtered water for easy access and batch nutrient preparation.
  3. Submersible pump
    Transfers water efficiently with minimal labour.
  4. Tubing and connectors
    Direct water to plants; versatile for room configurations.

Best practices

  1. Regular maintenance
    Clean pumps, filters, and stones weekly to prevent clogs and maintain efficiency.
  2. Monitor water quality
    Test pH and EC levels regularly to ensure nutrient balance.
  3. Check connections 
    Inspect tubing for leaks or blockages.
  4. Algae prevention
    Use opaque reservoirs and treat water with hydrogen peroxide or beneficial bacteria.

Waterproofing the grow room floor

  1. Build a perimetre frame:
    Prevents water spillage from damaging floors.
  2. Use linoleum or waterproof material:
    Protects carpets or wood floors, ensuring durability.
Useful Tip

Consider using drip trays or floor mats in high-watering zones to catch excess water and prevent floor damage.

Automation: timer boxes and smart systems

1. Digital timers
  • Accurate programming for irrigation schedules.
  • Ensure backup batteries for reliability.
2. Smart irrigation systems
  • Integrate with sensors.
  • Higher upfront costs but greater control.
Useful Tip

Smart irrigation systems can be linked to a mobile app, allowing you to adjust schedules remotely and get notifications if there’s an issue with water flow or nutrient levels.

Reverse osmosis (RO) water provides unmatched purity, ensuring precise nutrient delivery and promoting optimal plant health across all growth phases, from Germination to Harvest. This guide details the benefits, challenges, and comparisons of RO water with other water types.

Reverse Osmosis (RO) water

Reverse osmosis (RO) water provides unmatched purity, ensuring precise nutrient delivery and promoting optimal plant health across all growth phases, from Germination to Harvest. This guide details the benefits, challenges, and comparisons of RO water with other water types.

How Reverse Osmosis works

  1. Sediment filtration
    Removes large particles like dirt and sand.
  2. Carbon filtration
    Eliminates chlorine and organic compounds.
  3. RO membrane
    Filters dissolved solids and microscopic impurities.
  4. Post-filtration
    Polishes water for final use.

Comparative table: types of water

Parameter TDS (ppm) pH Contaminants Consistency Suitability
RO water 5–10 Neutral
(~7.0)		 None High All phases  
Tap water 50–500+ Alkaline
(7.5–8.5)		 Metals, chlorine Low After
treatment
Bottled water 5–500+ Varies
(6.5–8.5)		 None Moderate Limited phases
Filtered water 5–200+ Varies
(6.5–8.5)		 Reduced
contaminants		 Moderate Most phases
Rainwater 5–100 Slightly acidic
(~6.0)		 Pesticides, microbes Low Early phases
AC Condensate 5–50 Slightly acidic
(~6.0)		 Dust, microbes Low Rarely suitable

Water suitability for Cannabis cultivation

Reverse Osmosis (RO) water
Best for Hydroponics, coco, and sensitive feeding schedules.
Key Benefits High consistency, no impurities, optimal for nutrient customisation.
Considerations Requires supplementation with calcium and magnesium (Cal-Mag).
Tap water
Best for Soil (after testing).
Key Benefits Readily available.
Considerations May require dechlorination and pH adjustment.
Bottled water
Best for Short-term use in emergencies.
Key Benefits Portable and safe.
Considerations Expensive, environmental impact from plastic waste.
Filtered water
Best for Soil or Coco Coir.
Key Benefits Removes basic impurities.
Considerations May not remove dissolved solids or heavy metals.
Rainwater
Best for Early phases like Germination and Seedling.
Key Benefits Natural and soft water.
Considerations Risk of pollutants and low mineral content.
AC Condensate
Best for Rare use in emergencies.
Key Benefits Readily available in hot climates.
Considerations Potential microbial contamination, lacks minerals.

Managing RO system waste water

RO WASTE For every litre (or gallon) of purified water, RO systems typically produce 3/5 litres (or gallons) of waste water.
Irrigation Water ornamental plants or lawns.
Cleaning Use for mopping, washing equipment, or flushing systems.
Pre-Filter Route through a sediment filter for partial reuse.
Storage Store in large containers for non-consumptive tasks.
Tips to minimise RO waste

  • Use a high-efficiency RO system with a 1:1 water recovery ratio.
  • Recycle waste water within the grow operation where safe.

Incorporating RO water in cultivation

Phase Water use
Germination Prevents seed contamination.
Seedling Supports root development without salt interference.
Early Vegetation Ensures optimal nutrient delivery for rapid growth.
(Main) Vegetation Enhances nutrient uptake with pH and TDS precision.
Late Vegetation Maintains growth consistency before flowering.
Pre-Flowering Avoids salt build-up during nutrient-heavy feeding.
Blooming Maximises terpene and cannabinoid production through clean hydration.
Ripening Ensures plant stability and quality.
Flush Purges salts and residues for a smoother final product.

Water recycling and heavy metal testing

Water conservation is vital for eco-conscious cannabis growers. Recycling techniques help reduce waste while maintaining water quality for plants.

Key methods for water recycling

1. Rainwater harvesting
Setup Install gutter systems and barrels to collect rainwater.
Filtration Use sand filters or activated carbon to remove impurities.
Usage Ideal for irrigation after testing pH and EC.
2. Greywater reuse
Setup Collect from non-contaminated sources like sink runoff (without harsh chemicals).
Filtration Filter and treat with UV sterilisers or biological filters to remove organic contaminants.
3. Runoff capture
Setup Use trays beneath pots to catch irrigation runoff.
Filtration Use sediment and charcoal filters to clean runoff before reapplication.
Signs of contamination

Cloudy water, foul odour, or sediment accumulation indicates a need for treatment.

Heavy metal testing

Heavy metals (e.g., lead, arsenic, mercury) can accumulate in cannabis through contaminated water or soil. Testing ensures safe consumption and prevents plant damage.

Phase Water use
Germination Prevents seed contamination.
Seedling Supports root development without salt interference.
Early Vegetation Ensures optimal nutrient delivery for rapid growth.
(Main) Vegetation Enhances nutrient uptake with pH and TDS precision.
Late Vegetation Maintains growth consistency before flowering.
Pre-Flowering Avoids salt build-up during nutrient-heavy feeding.
Blooming Maximises terpene and cannabinoid production through clean hydration.
Ripening Ensures plant stability and quality.
Flush Purges salts and residues for a smoother final product.

Heavy metal testing

Prevention tips

  • Use high-quality, tested water sources.
  • Install reverse osmosis (RO) systems to eliminate heavy metals effectively.
  • Regularly monitor soil and water inputs to catch contamination early.

How to test water at home

Affordable options to ensure water quality:

  1. pH test strips
    Simple and low-cost, dip them into water for a quick pH reading. Aim for 5.5–6.0 for hydroponics and 6.0–6.5 for soil.
  2. EC metres
    Measures the electrical conductivity of your water, which indicates dissolved salts. Essential for nutrient control in hydroponics.
  3. DIY sediment test
    Let water sit in a clear jar for 24 hours. Check for sediment accumulation at the bottom, which could indicate impurities.
  4. Water testing kits
    Comprehensive kits test for contaminants like chlorine, heavy metals, and nitrates. Available online or at gardening stores.

Final thoughts

Watering is one of the most important aspects of plant care. By following phase-specific guidelines, managing pH and EC, and being aware of common watering mistakes, you set your cannabis plants up for healthy root development, vibrant growth, and ultimately higher yields. With consistent monitoring and the right watering practices, your cannabis cultivation will thrive from seedling to harvest.

Frequently asked questions

A recap with plenty of useful information

Water every 2–3 days, depending on the plant's size, medium, and environmental conditions.

For soil, aim for 6.0–6.5; for coco 5.7–6.2 and for hydroponics, maintain a pH of 5.5–6.0.

Overwatered plants have swollen, droopy leaves and consistently wet substrate.

Runoff helps flush excess salts, preventing nutrient buildup and ensuring pH balance.

Use digital pH and EC metres to test the solution before watering and runoff afterward.

Frequent watering suffocates roots, leading to root rot and stunted growth.

Flush between growth phases or during ripening to remove nutrient buildup and improve quality.

Seedlings need light watering of about 50–100 ml every 2–3 days.

EC measures nutrient concentration, ensuring you feed the right amount without overfeeding.

Yes, but test and adjust pH levels, and dechlorinate the water if necessary.

Target 20–25% runoff to prevent salt buildup and maintain proper EC.

pH deviations often signal salt accumulation, nutrient imbalances, or poor medium aeration.

During flowering, aim for 1.6–2.2 mS/cm to meet the plant's high nutrient demands.

Use drip irrigation systems with timers or moisture sensors for consistent watering.

Flushing clears excess salts, resets the medium, and prepares plants for the next nutrient regime.

Maintain water temperatures between 18–22°C for optimal nutrient uptake and oxygen availability.

Look for pH spikes, high runoff EC, or symptoms like tip burn and nutrient lockout.

Runoff EC higher than input indicates excess salts; lower runoff suggests nutrient deficiency.

Recycle water using filtration systems or implement high-efficiency RO systems.

RO water ensures consistent purity, allowing precise nutrient adjustments without interference from contaminants.Nutrient management and fertiliser use in cannabis cultivation