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In South Africa’s flourishing cannabis landscape, where the energy of grow season is palpable, and cultivators strive for excellence – from nurturing monster outdoor crops to dialling in precision greenhouse environments – every decision counts. We’ve celebrated the plant’s inherent value, delving into the nutritional power of hemp seeds, marvelling at discoveries like the flavoalkaloids in cannabis leaves by Stellenbosch University, and embracing the cosmic rhythms that guide traditional planting. Now, it’s time to address a foundational element critical to every grower’s success: fertilisation.

Choosing the right nutrients for your cannabis plants can feel like navigating a complex maze. The market is saturated with products, each promising optimal growth and bountiful harvests. To make informed decisions, it’s essential to understand the regulatory framework that governs these products in South Africa – specifically, the Fertilisers, Farm Feeds, Agricultural Remedies and Stock Remedies Act, 1947 (Act No. 36 of 1947), overseen by the Department of Agriculture, Forestry and Fisheries (DAFF). This framework categorises fertilisers into distinct groups, guiding their composition, claims, and application.

This week, we’ll demystify these fertiliser groups, with a particular focus on Group 3 fertilisers. Many growers might not fully grasp that certain organic-derived products, including powerful hormone extracts, fall into this fascinating category. Understanding these classifications is key to selecting the right products that support healthy, high-quality cannabis, in harmony with both scientific principles and regulatory compliance.

The Foundation: South Africa’s Fertiliser Groupings

Under Act 36 of 1947, fertilisers in South Africa are broadly categorised into three main groups based on their primary function and nutrient composition. This classification helps both regulators and growers understand a product’s intended purpose and the claims it can legally make. A “fertiliser,” as defined by the Act, is any substance or organism intended to improve or maintain plant growth, yield, or the physical, chemical, or biological conditions of the soil.

Group 1 and Group 2 Fertilisers: The Core Nutrient Providers

These two groups largely encompass what most growers recognise as conventional fertilisers, focusing on the direct supply of major plant nutrients.

Group 1 Fertilisers are those containing a total of 100 g/kg or more of Nitrogen (N), Phosphorus (P), or Potassium (K), or any combination thereof. These are your high-impact, chemically compounded or enriched organic fertilizers designed to provide substantial amounts of the essential macro-elements that cannabis plants require in large quantities for vigorous growth, flowering, and fruit development. Most of the time, these will be the synthetic nutrients you are used to seeing on the market. But note that there are group 1 blends that are organic blends. These products are more available in huge blends from major Agri farm suppliers.
Group 2 Fertilisers include those with a total of less than 100 g/kg of N, P, or K, or those that provide other recognised plant nutrients in acceptable amounts. These often include products focusing on intermediate macro-elements like Calcium, Magnesium, and Sulphur, or specific trace elements. While still nutrient providers, their concentration of NPK is lower than Group 1. Products like “Bonemeal” or “Iron Chelate”, which focus on specific nutrient delivery or soil amendments, would typically be found here if their NPK levels are below the Group 1 threshold. Thus, we normally associate group two with a more organic fertigation. But it is not to say that all group 2 fertilisers are organic in composition.

Both Group 1 and Group 2 fertilisers are vital for directly feeding your cannabis plants, ensuring they receive the NPK ratios necessary for healthy vegetative growth, robust root systems, and prolific flower development, as we discussed when exploring cannabis’s nutritional needs and terroir.

Group 3 Fertilisers: The Holistic Enhancers and Stimulants

This is where the distinction becomes particularly interesting for cannabis cultivators aiming for a truly holistic approach to plant health and maximising specific traits – from stress resilience to enhanced resin production. Group 3 fertilisers are defined as any natural or synthetic substance or organism that improves the growth or yield of plants, or the physical, chemical, or biological conditions of the soil, and does not qualify for registration as a Group 1 or 2 fertiliser based on NPK content.

Unlike Groups 1 and 2, which primarily supply nutrients, Group 3 products often enhance the plant’s ability to utilise nutrients, improve its environment, or directly stimulate physiological processes. This broad definition encompasses a diverse range of innovative products crucial for modern cannabis cultivation.

Within Group 3, we find several key categories:

Biofertilisers: These are living organisms that enhance plant growth by improving nutrient availability or uptake. This includes beneficial fungi (like mycorrhizae) and bacteria that colonise the root zone, improving nutrient cycling and pathogen resistance. For cannabis, this means a healthier root environment, leading to stronger, more resilient plants, a concept deeply aligned with nurturing terroir. Our FPJ and FFJ blogs would give a great guide to homemade biofertilisers.
Soil Enhancers (Soil Conditioners): These products improve the physical properties of the soil, such as water retention, cation exchange capacity (CEC), and hydraulic conductivity. They don’t directly feed the plant, but create a better medium for roots to thrive. Examples include humic and fulvic acids, which improve nutrient absorption and soil structure, or peat and palm peat for enhanced water holding capacity and aeration – crucial for cannabis root development, as we discussed in the context of the Spring Equinox. Also consider our work on IMO, Korean natural farming too. Some awesome guides for homemade quality.
Seaweed Containing Products: Extracts from seaweed, like KELPAK or NATRAGRO from Starke Ayres, are rich in natural growth hormones and trace elements. They are classified as Group 3 because their primary function is plant stimulation and stress alleviation, rather than major NPK provision. They assist plants through stresses like heat, drought, and disease, and improve NPK uptake.
Plant Growth Regulators (PGRs): This is a critical category, and one that often causes confusion. PGRs include both natural and synthetic substances like Auxins, Brassinosteroids, Cytokinins, and Gibberellic acid. These compounds directly influence plant physiological processes such as root development, cell elongation, branching, and flowering. A common misconception is that if a product is “organic” it can’t be a PGR or a Group 3 fertiliser. However, many hormone extracts are organically derived but still function as PGRs, falling squarely into Group 3 due to their role in regulating growth rather than primarily supplying bulk NPK. Our understanding of cannabis architecture and florogenesis, highlighted by studies like those from Spitzer-Rimon et al., underscores the intricate hormonal control over plant development, making PGRs potent tools for cultivators.
Fertiliser Coatings and Inhibitors: These products improve the efficacy of other fertilisers by controlling nutrient release or increasing their residency in the soil. Nitrogen inhibitors, for example, prevent nitrogen loss, making fertilisers more efficient.
Products of Plant and Animal Origin (excluding bone and blood meal): This category includes various natural materials that improve soil conditions or plant growth, provided they meet specific safety and efficacy standards. Any moringa-based product, for example, Phytostim.
Novel Products: This catch-all category allows for the registration of new, innovative substances that improve plant or soil conditions, ensuring the regulatory framework can adapt to scientific advancements.

Why Group 3 Fertilisers are Essential for Cannabis Growers

For South African cannabis cultivators, embracing Group 3 fertilisers isn’t just about compliance; it’s a strategic move to optimise plant health, yield, and the expression of unique cannabis terroir.

Holistic Plant Health: Group 3 products work in synergy with conventional fertilisers. While NPK fertilisers provide the building blocks, Group 3 enhancers improve the very environment and mechanisms through which these blocks are absorbed and utilised. This leads to overall healthier, more vigorous plants.
Enhanced Terroir Expression: As we discussed, terroir is influenced by climate, soil, and genetics. Soil enhancers, biofertilisers, and seaweed extracts can optimise the soil’s biological activity and nutrient availability, allowing your cannabis plants to fully express their unique genetic potential, including those intricate terpene and cannabinoid profiles that make our local strains so distinctive.
Stress Resilience: PGRs and seaweed-based products, like Kelpak, are particularly effective in helping plants cope with environmental stressors such as drought, heat, and disease – common challenges in many South African climates. Stronger, healthier plants are naturally more resistant to mould and pests, a wish for our outdoor growers.
Optimised Growth Cycles: PGRs can be invaluable for fine-tuning plant development. For instance, specific hormones can be used to promote robust root growth in seedlings or to encourage denser branching in vegetative plants, influencing the plant architecture we saw discussed in studies on cannabis florogenesis. This is especially relevant for our greenhouse growers looking for smooth tunnel flower and a dialled-in setup.
Root Development and Nutrient Uptake: Humic and fulvic acids significantly improve nutrient uptake efficiency and foster robust root systems. As we learned from the Spring Equinox discussion, strong root development is fundamental for a healthy plant.

Navigating Your Choices: A Responsible Grower’s Guide

Selecting the right fertilisers requires an informed approach.

Understand Your Plant’s Needs: Start with the basics. Cannabis has specific NPK requirements that change during its vegetative and flowering phases. We have written extensively on nutrients. How to ensure the correct NPK for your plants. So check those out if you are stuck.
Read Labels Carefully: All registered fertilisers must detail their composition, application rates, and usage instructions. Look for the NPK sequence (e.g., 2:3:2), percentages of macro-elements, and lists of micro-elements. Pay attention to application rates, whether for foliar spray or soil drench, and apply them diligently to avoid over-application or under-application. If there are none of these things on the label, then you need to ask more questions. Use with caution.
Prioritise Efficacy and Safety: For Group 3 fertilisers, DAFF requires rigorous efficacy studies (scientific reports based on statistical analyses, often conducted in field, greenhouse, or laboratory settings) and toxicological studies to ensure the product has no harmful effects on plants, humans, animals, or the environment. This includes testing for phytotoxicity (negative effects on plant development, colour, yield, etc.). Always choose products from reputable suppliers who can provide this documentation.

Cultivating Excellence in South Africa

The journey of growing cannabis in South Africa is a dynamic blend of traditional wisdom and cutting-edge science. By understanding the nuances of Group 3 fertilizers – from biofertilizers and soil enhancers to plant growth regulators derived from natural sources – growers can make informed choices that promote not just growth, but true plant vitality, stress resistance, and the full expression of their unique cannabis terroir.

As you prepare your setups and nurture your plants this season, let this knowledge empower you. Choose your fertilisers wisely, respecting both the plant’s needs and the regulatory framework that ensures quality and safety. May your cultivation efforts reach new heights, yielding healthy, high-quality cannabis products that truly reflect the spirit of South African excellence.

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