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

Watering frequency
Autoflowering plants often thrive with more frequent but lighter water.
Substrate selection
Autoflowering plants prefer light, well-aerated substrates. Adding perlite to the soil can improve aeration and drainage.
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

Deficiency diagnosis
Understanding nutrient competition helps identify the root causes of deficiencies (e.g., magnesium lockout due to excessive potassium).
Optimising feeding programmes
Balancing synergistic nutrients improves efficiency, reduces waste, and maximises absorption.
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 feeding	Morning or early midday Supports nutrient uptake during active metabolism.
Foliar feeding	Early 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

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).
Moisture
Exposure to moisture can cause clumping in granular fertilisers and promote microbial growth in organics, reducing their effectiveness.
Light exposure
UV light can break down nutrients, particularly in transparent containers. Store fertilisers in a dark, dry area.
Air exposure
Oxygen exposure can oxidise nutrients in opened bottles, diminishing their potency over time.

Risks and considerations

Microbial contamination
Organic fertilisers, especially liquids, can harbour microbial growth if stored improperly. This can harm plants or even pose safety risks to handlers.
Nutrient precipitation
In mixed solutions, nutrients may precipitate out of the solution if left for extended periods, making them unavailable to plants.
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

Keep containers sealed
Tightly close lids after each use to minimise air and moisture exposure.
Label and date
Write the purchase or opening date on the container to track freshness.
Store in a controlled environment
Use a cool, dry, and dark space, such as a storage cabinet, away from direct sunlight.
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

What is the best time of day to water cannabis plants?

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

Why should I avoid watering at midday?

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.

Is it good to feed plants at night?

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

How can I tell if my plants need water?

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

What’s the difference between root feeding and foliar feeding?

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

When should I foliar feed cannabis plants?

Early morning or evening to avoid sunburn.

How often should I water cannabis plants?

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

What happens if I feed close to lights out?

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

Should I water more often during flowering?

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

How should I adjust watering for outdoor cultivation?

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

Why is morning feeding preferred for nutrients?

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

How can I time foliar feeding correctly?

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

What is the ideal pH for the flowering phase?

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

How does nutrient uptake change during the day?

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

Why should I avoid feeding at night?

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

What’s the risk of midday watering in outdoor cultivation?

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

How often should I check the pH and EC of runoff water?

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

What role does root temperature play in nutrient efficiency?

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

How do I manage watering in hydroponic systems?

Automate irrigation during light hours and monitor solution temperature consistently.

What’s the best way to flush plants during cultivation?

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

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