CONTENTS

CONTENTS

Nutrient management and fertiliser use

in cannabis cultivation

Understanding Cannabis nutrients

Macronutrients

Cannabis requires three primary nutrients to grow healthily. These macronutrients are crucial for different stages of growth.

Calcium Ca Role Strengthens cell walls, promoting robust structure.
Magnesium Mg Role Central to chlorophyll production and photosynthesis.
Iron Fe Role Essential for enzyme function and chlorophyll synthesis.
Zinc Zn Role Facilitates growth hormones and enzyme activation.
Copper Cu Role Enhances reproductive processes and overall vitality.
Boron B Role Vital for cell wall formation and nutrient transport.
Molybdenum Mo Role Aids in nitrogen metabolism and enzymatic functions.

Micronutrients

Micronutrients are required in trace amounts but are just as critical for plant health.

Nitrogen N Role Vital for vegetative growth; promotes leaf and stem development.
    Phase Early to Late Vegetation.
Phosphorus P Role Essential for root health, flower formation, and energy transfer.
    Phase Pre-flowering and Blooming.
Potassium K Role Enhances water uptake, photosynthesis, and disease resistance.
    Phase Throughout the plant’s lifecycle.

N-P-K ratios and their importance

N-P-K refers to the three primary macronutrients found in fertilisers: Nitrogen (N), Phosphorus (P), and Potassium (K). Understanding their role is crucial for providing cannabis plants with the right nutrients at the right time.

The optimal N-P-K ratios may vary slightly depending on the strain and the specific needs of your plants. The following values are generally considered ideal for each growth stage:

Phase N-P-K Key focus
Seedling 2-1-2 Gentle root and early foliage development.
Early Vegetation 3-1-3 Promotes rapid leaf and stem growth.
(Main) Vegetation 4-2-3 Supports robust plant structure and health.
Late Vegetation 4-2-3 Prepares plant for flowering while maintaining growth.
Pre-Flowering 3-3-3 Balances vegetative and reproductive energy.
Blooming 1-4-4 Focuses on bud development and resin production.
Ripening 0-5-6 Enhances flavour, aroma, and final density.
Flush 0-0-0 Removes residual nutrients and salts from the growing medium.

pH and nutrient availability in relation to substrate

Nutrients and additives

Understanding which nutrients and additives to use is crucial for plant health. Here’s a guide to key nutrients and supplements.

Category Function
Base Nutrients Support basic needs during each growth phase.
Root Boosters Encourage strong root systems.
Bloom Boosters Boost flower production.
Cal-Mag Addresses calcium and magnesium deficiencies.
Mycorrhizae Enhance nutrient absorption and protect from pathogens.
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.

Organic vs Synthetic fertilisers

Feature Organic Synthetic
Source Natural (manure, plant residues) Chemical composition
Absorption Slow release Immediate
Environmental Eco-friendly impact Risk of pollution if overdosed
Cost Higher initial cost Lower purchase cost
Examples Compost, guano, seaweed Urea, potassium, sulfate, nitrates

Feeding by growth phase

Proper feeding varies with the plant’s growth phase. Tailoring nutrient solutions and ratios ensures optimal plant development.

Phase Key Nutrients
Seedling Minimal nutrients; root boosters are beneficial.
Tip Use diluted nutrient solutions (25–50% strength).
Early Vegetation High nitrogen with some phosphorus and potassium.
Tip Gradually increase feeding; monitor for nitrogen toxicity (dark green, claw-like leaves).
(Main) Vegetation Balanced but nitrogen-heavy blends.
Tip Regularly check plant response and adjust feeding levels.
Late Vegetation Maintain nitrogen but introduce higher potassium.
Tip Transition slowly to pre-flowering nutrients to avoid stress.
Pre-Flowering Balanced nutrients; phosphorus uptake begins to rise.
Tip Watch for the stretch (rapid vertical growth).
Blooming High phosphorus and potassium; reduce nitrogen.
Tip Introduce bloom boosters and Cal-Mag to support resin production.
Ripening Minimal nitrogen, higher potassium for bud density.
Tip Start flushing to remove nutrient residues.

Fertiliser mixing

Proper fertiliser mixing is essential to ensure that plants receive the correct balance of nutrients at every growth stage, avoiding issues such as nutrient lockout, pH imbalances, or chemical precipitations. Follow this detailed guide for accurate and consistent nutrient solutions.

Proper mixing: step by step

1. Start with clean water
  • Use filtered or reverse osmosis (RO) water, free from contaminants.
  • Maintain the water temperature at 20–22°C to avoid thermal shock to the roots.
2. Follow the correct order Add nutrients in a specific order to prevent chemical precipitation and ensure proper mixing:
  1. Silica →
→ 2. Base Nutrients (A & B) →
→ 3. Micronutrients →
→ 4. Additives
3. Adjust pH Soil: 6.0–6.5; Coco Coir: 5.7–6.2; Hydroponics: 5.5–6.0.
4. Oxygenate the solution Use air stones to oxygenate the solution, especially in hydroponic systems.
Useful Tips for Effective Feeding

  • Start small:
    Begin with 50% of the manufacturer’s recommended dosage and increase as needed.
  • Test regularly:
    Measure pH and EC regularly to monitor nutrient levels.
  • Flush as needed:
    Flushing periodically prevents salt buildup.
  • Monitor symptoms:
    Look for signs of deficiencies or toxicities and adjust feeding accordingly.

Changing fertiliser brands during cultivation

Changing fertilisers during cultivation is not recommended unless absolutely necessary. Consistency in nutrition ensures plant health, prevents imbalances, and minimises stress. However, situations such as issues with the current fertiliser, depleted supplies, or better alternatives becoming available might necessitate a change. A proper approach is crucial to avoid damage or reduced yield.

Challenges and risks
  • Nutrient imbalances: Each fertiliser brand has different NPK ratios and micronutrient profiles. Sudden changes can lead to toxicities or deficiencies.
  • pH instability: Different formulations may affect the pH of the solution, causing nutrient absorption problems.
  • Plant stress: Abrupt transitions may slow growth or cause symptoms of deficiency.
Smooth transition to a new fertiliser brand
  • Assess plant needs: Ensure the new fertiliser matches the requirements of the current growth stage (e.g., NPK ratios for vegetative or flowering stages).
  • Start with a reduced dose: Use the new fertiliser at 50–75% of the recommended dosage and increase it gradually.
  • Flush the system: In hydroponics or coco, flush the substrate or reservoir with clean water to remove residues from the previous fertiliser and prevent nutrient lockout.
  • Test on a small scale: Apply the new fertiliser to one plant or a small group and closely monitor their response before scaling up to the entire crop.
  • Monitor pH and EC: Regularly measure pH and electrical conductivity (EC) to ensure the solution remains stable.
When to Change Fertiliser Brands
  • Performance Issues: If the current fertiliser causes nutrient imbalances or if stabilising pH is challenging.
  • Product Unavailability: Depleted stocks or the discontinuation of the current fertiliser line.
  • Improved Solutions: Transitioning to products with added benefits, such as bloom boosters or better micronutrient absorption.

Nutrition for autoflowering Cannabis plants

Autoflowering plants are generally smaller in size and complete their lifecycle faster, meaning they require tailored feeding strategies.

General principles

1. Lighter feeding (compared to photoperiod plants) Autoflowering plants are more sensitive to overfeeding (nutrient burn). Start with 25–50% of the recommended dosage for photoperiod plants and gradually increase.
2. Faster phase transitions Autoflowering varieties quickly transition from vegetative growth to flowering. Therefore, the feeding schedule must adapt faster, with a greater focus on bloom nutrients.
3. Consistent lighting schedule Feeding should account for prolonged photosynthesis due to consistent lighting schedules of 18/6 or 20/4 throughout the entire cycle.
4. Stress management Avoid high-stress training (HST) techniques and prioritise gentle methods like low-stress training (LST), as these plants have limited time to recover.
Useful tips

  1. Watering frequency
    Autoflowering plants often thrive with more frequent but lighter water.
  2. Substrate selection
    Autoflowering plants prefer light, well-aerated substrates. Adding perlite to the soil can improve aeration and drainage.
  3. Stress management
    Avoid high-stress training (HST) techniques and focus on gentle methods like low-stress training (LST), as these plants have limited time to recover.

Phases and nutrition for autoflowering plants

Vegetative Phase (weeks 2–3)
Recommended nutrients:Increase Nitrogen (N) for leaf development. Use bloom nutrients in small doses.
EC/PPM: EC: 0.4–0.6 mS/cm and PPM: 200–300 (500 scale) or 280–420 (700 Scale). Start with a mild feeding regimen (1/4 or 1/2 of the recommended dose) and monitor plant growth.
Growth Phase (transition phase). This phase may begin as early as the 3rd week.
Adjust nutrition: Gradually increase Phosphorus (P) and Potassium (K), while reducing Nitrogen (N).
EC/PPM: EC: 0.8–1.2 mS/cm and PPM: 400–600 (500 scale) or 560–840 (700 Scale). Closely monitor plants for signs of stress or overfeeding and adjust accordingly.
Flowering Phase (weeks 4–8)
Recommended nutrients: High concentrations of Phosphorus (P) and Potassium (K).
EC/PPM: EC: 1.2–1.6 mS/cm and PPM: 600–800 (500 scale) or 840–1120 (700 Scale). Gradually increase nutrient concentration to support flower development but avoid overfeeding.
Flushing (final week). During the last week or 10 days, flush the substrate with clean water to remove accumulated salts and preserve the flavour and quality of the buds.
EC/PPM: EC: 0.0–0.2 mS/cm and PPM: 0–100 (500 scale) or 0–140 (700 Scale).

Mulder’s Chart: nutrient interactions

The Mulder’s chart illustrates the complex interactions between essential plant nutrients, highlighting two main relationships: competition and synergy. These interactions influence how cannabis plants absorb and utilise nutrients, making the chart an essential tool for fine-tuning fertilisation strategies.

Key Interactions

Competition Excessive levels of one nutrient can inhibit the uptake of another. For example:
  • High levels of potassium (K) can reduce calcium (Ca) and magnesium (Mg) absorption.
  • Excessive phosphorus (P) can block zinc (Zn) uptake.
Synergy Balanced levels of certain nutrients can enhance the absorption and utilisation of others. For example:
  • Μagnesium (Mg) supports nitrogen (N) uptake.
  • Sulphur (S) aids in the metabolism of phosphorus (P).

Mulder's chart

Application in Cannabis cultivation

The Mulder’s chart illustrates the complex interactions between essential plant nutrients, highlighting two main relationships: competition and synergy. These interactions influence how cannabis plants absorb and utilise nutrients, making the chart an essential tool for fine-tuning fertilisation strategies.

  1. Deficiency diagnosis
     Understanding nutrient competition helps identify the root causes of deficiencies (e.g., magnesium lockout due to excessive potassium).
  2. Optimising feeding programmes
    Balancing synergistic nutrients improves efficiency, reduces waste, and maximises absorption.
  3. Preventing lockouts
    Avoid excessive additions of competitive nutrients to maintain harmony in the nutrient solution or substrate.

Nutrient Interaction Table

Antagonistic Nutrient Synergistic
K N S, Mg, Mo
Fe, Ca, Zn, Cu, K P Mg
Ca, Mg, B, N, P K Fe, Mn
Mg, Zn, Fe, Mn, B, P, K, S Ca None
K, Ca Mg N, P
Ca, Cu, Mo S Mn, N
Cu, Mn, P, Ca, Zn Fe K
Fe, P, Ca Zn None
Mn, N, P, S, Fe Cu Mo
Ca, Fe, Cu Mn K, S
N, K, Ca B None
S Mo N, Cu

Optimal timing for nutrient delivery

The timing of nutrient delivery plays a pivotal role in cannabis plant health, nutrient uptake, and yield. Aligning your feeding schedule with the plant’s biological clock and environmental conditions ensures that nutrients are absorbed efficiently while minimising risks like root stress or mould. Here’s a breakdown of best feeding practices based on the time of day.

Feeding Cannabis plants: timing breakdown

Morning WHY? Cannabis plants are metabolically active after lights turn on (or sunrise), making mornings the ideal time for nutrient uptake.
ADVANTAGES
  • Supports photosynthesis and metabolic.
  • Reduces the risk of mould and root rot by allowing for evaporation.
CHALLENGES
  • Requires a consistent early schedule.
  • Less suitable for growers with limited morning availability.
BEST PRACTICES
  • Feed 1–2 hours after lights turn on (for indoor grows).
  • Monitor runoff to ensure proper drainage and avoid nutrient buildup.
Midday WHY? Convenient and avoids the hottest or most humid parts of the day for outdoor grows.
ADVANTAGES
  • Convenient for growers with daytime availability.
  • Useful for supplemental feeds in stable climates.
CHALLENGES
  • May lead to root zone overheating in poorly ventilated areas.
  • Nutrient uptake may not be as efficient compared to mornings.
BEST PRACTICES
  • Ensure root zone temperatures remain stable (20–25°C / 68–77°F).
  • Avoid midday feeding in outdoor setups under intense sunlight.
Evening WHY? Offers flexibility, but less ideal for plant health due to reduced metabolic activity at night.
ADVANTAGES
  • Convenient for growers unavailable during the day.
  • Easy to incorporate into nighttime routines.
CHALLENGES
  • Plants slow down nutrient uptake at night.
  • Increased humidity can lead to mould or pest issues.
BEST PRACTICES
  • Feed no later than 1 hour before lights go off (for indoor grows).
  • Provide proper ventilation to minimise excess humidity.

Root feeding vs. foliar feeding

Root feedingMorning or early midday
Supports nutrient uptake during active metabolism.
Foliar feedingEarly morning or evening
Avoid direct light to prevent leaf burn; ensure leaves dry before dark.
Factor influencing feeding schedules

Plant circadian rhythms: Nutrient uptake is most efficient during the plant’s active daylight cycle.

Environmental considerations

Indoor grows
  • Simulate natural light cycles by feeding after lights turn on.
  • Monitor temperature and humidity closely to avoid mould or pest risks.
Outdoor grows
  • Aligns with natural circadian rhythms and allows water to evaporate by afternoon.
  • High temperatures can stress roots and reduce nutrient efficiency.

Shelf-life and storage of fertilisers: maximising effectiveness and safety

Understanding the Shelf-life and storage requirements of fertilisers is crucial for maintaining their effectiveness and ensuring plant health. Fertilisers, whether organic or synthetic, can degrade over time, leading to reduced potency, contamination risks, or even harm to your plants. Here’s what you need to know about their longevity and proper handling.

Shelf-life of fertilisers

Type Sealed Opened Mixed
Synthetic Liquid 5–10 years
if stored correctly		 1–2 years
cap is tightly sealed		 24–48 hours
dispose after
Synthetic Granular Indefinite
in a cool, dry place		 Several years
without moisture		 n/a
dissolved on demand
Organic Liquid 2–3 years
unopened		 6–12 months
potential microbial activity		 Use immediately after mixing
Organic Dry 3–5 years 1–2 years
if kept moisture-free		 n/a

Factors affecting fertiliser longevity

  1. Temperature
    Extreme heat or cold can degrade liquid fertilisers and crystallise synthetic nutrients. Store in a temperature range of 5–25°C (41–77°F).
  2. Moisture
    Exposure to moisture can cause clumping in granular fertilisers and promote microbial growth in organics, reducing their effectiveness.
  3. Light exposure
    UV light can break down nutrients, particularly in transparent containers. Store fertilisers in a dark, dry area.
  4. Air exposure
    Oxygen exposure can oxidise nutrients in opened bottles, diminishing their potency over time.

Risks and considerations

  1. Microbial contamination
    Organic fertilisers, especially liquids, can harbour microbial growth if stored improperly. This can harm plants or even pose safety risks to handlers.
  2. Nutrient precipitation
     In mixed solutions, nutrients may precipitate out of the solution if left for extended periods, making them unavailable to plants.
  3. Salt accumulation
    Improperly stored granular fertilisers can attract moisture, leading to salt clumping that is harder to dissolve and can damage plants if applied unevenly.
Storage tips to maximise lifespan

  1. Keep containers sealed
    Tightly close lids after each use to minimise air and moisture exposure.
  2. Label and date
    Write the purchase or opening date on the container to track freshness.
  3. Store in a controlled environment
     Use a cool, dry, and dark space, such as a storage cabinet, away from direct sunlight.
  4. Avoid mixing in advance
     Mix only the amount you need for immediate use to prevent nutrient degradation.

By understanding the lifespan and proper storage methods of fertilisers, growers can minimise waste, reduce risks, and ensure consistent plant nutrition. Whether using synthetic or organic options, proper care extends the utility and effectiveness of your supplies, protecting both your investment and your cannabis plants.

Soil absorption (%) at different pH levels (5.5–7.0)

Nutrient / pH 5.5 5.6 5.7 5.8 5.9 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7.0
Nitrogen (N) 85 85 86 87 88 89 90 91 91 92 92 93 94 95 96 97
Phosphorus (P) 60 61 62 63 64 65 67 68 70 72 73 75 76 78 79 80
Potassium (K) 95 96 97 98 99 100 100 100 100 99 98 97 96 95 94 93
Calcium (Ca) 70 71 72 73 74 75 76 77 78 80 81 82 83 84 85 86
Magnesium (Mg) 75 76 77 78 79 81 82 83 84 85 86 87 88 89 90 91
Iron (Fe) 60 61 62 63 64 65 67 68 69 70 71 72 73 74 75 76
Manganese (Mn) 65 66 67 68 69 70 71 72 74 75 76 77 78 79 80 81
Boron (B) 60 62 64 66 68 70 71 73 75 77 78 80 82 84 85 87
Copper (Cu) 70 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
Zinc (Zn) 65 67 69 71 73 75 76 77 78 79 80 81 82 83 84 85
Molybdenum (Mo) 85 87 88 89 90 91 92 93 94 95 96 97 98 99 100 100
Nutrient / pH 5.5 5.6 5.7 5.8 5.9 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7.0

Coco Coir absorption (%) at different pH levels (5.5–7.0)

Nutrient / pH 5.5 5.6 5.7 5.8 5.9 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7.0
Nitrogen (N) 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99

100
Phosphorus (P) 60 61 62 63 64 65 67 68 69 71 73 75 76 77 78

79
Potassium (K) 95 96 97 98 99 100 100 100 100 99 98 97 96 95 94 93
Calcium (Ca) 70 72 73 74 75 77 78 79 81 82 83 85 87 88 90 92
Magnesium (Mg) 75 76 77 78 79 81 82 83 85 86 87 88 89 90 91 92
Iron (Fe) 60 61 62 63 64 65 66 67 69 71 73 75 77 79 81 83
Manganese (Mn) 70 72 73 74 75 76 77 79 80 81 83 84 85 86 87 89
Boron (B) 65 66 67 68 69 71 72 74 75 76 77 78 80 81 82 83
Copper (Cu) 75 76 77 78 79 81 82 83 84 85 87 88 89 90 91 92
Zinc (Zn) 70 71 72 73 74 75 77 78 79 80 81 82 83 84 85 87
Molybdenum (Mo) 90 91 93 94 95 96 97 98 99 100 100 100 100 100 100 100
Nutrient / pH 5.5 5.6 5.7 5.8 5.9 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7.0

Frequently asked questions

A recap with plenty of useful information

Morning is ideal, as plants are metabolically active, and water evaporates throughout the day, reducing the risk of mould.

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.

You can, but it’s less efficient because plant metabolism slows, and the risk of mould increases.

Lift the pot to check if it feels light and inspect the substrate surface for dryness.

Root feeding delivers nutrients to the roots, while foliar feeding is applied to leaves for quick absorption.

Early morning or evening to avoid sunburn.

Water every 2–3 days, depending on plant size, substrate, and environmental conditions.

Humidity rises at night, potentially leading to mould or pest issues if plants don’t dry in time.

Yes, flowering plants require more nutrients and water, but avoid overwatering.

Water in the morning to prevent stress from midday heat and monitor weather conditions.

Plants are metabolically active after sunrise, optimising nutrient absorption and reducing mould risks.

Spray early morning or evening when temperatures are cooler, and light is less intense.

Maintain pH at 6.0–6.5 for soil, 5.7–6.2 for coco, and 5.5–6.0 for hydroponics.

Plants absorb nutrients more effectively during the light cycle when metabolism is at its peak.

Humidity increases at night, leading to mould or fungal infections if plants don’t dry.

Intense sunlight and heat can stress plants, reducing nutrient uptake and causing water loss.

Check regularly—ideally once a week—to detect nutrient build-up or imbalances early.

Ideal root zone temperatures (20–24°C) ensure maximum absorption and root health.

Automate irrigation during light hours and monitor solution temperature consistently.

Use pH-balanced water (EC 0.0–0.3) and apply 2–3 times the pot’s volume to remove salts without overwatering.