Best organic fertilisers for cannabis cultivation

Cannabis growers have long relied on synthetic fertilisers to feed their weed. While effective to some degree, these products also cause nutrient burn, pH problems, dead soil, and damage to the environment. As a result, contemporary growers are switching to organic practices for better weed and a better world!

In this article, we explore how to start growing weed organically, as well as which products are best for the job!

Why organic matters in cannabis cultivation

Growing organic cannabis benefits you, your cannabis plants, and the wider environment. Not only does it boost the quality of your crop, but using organic fertilisers will actually make the growing process simpler and more relaxed too!

The benefits of growing organic include:

• Improved plant health and resilience
• Increased terpene and cannabinoid production
• No need to measure pH or EC values when using well-formulated organic products
• Reduced risk of nutrient burn and chemical buildup
• Healthier soil structure over time
• Increased beneficial microbial activity in the soil

For a deeper look at organic vs synthetic fertilisers, consult our dedicated article.

Key organic nutrient phases: Seedling to harvest

With the right biological inputs, you can guide seedlings to harvest without ever needing to touch a bottle of pH adjuster. Plagron’s organic product range supports a full grow cycle with minimal intervention, making it easier to maintain balance, resilience, and flavour from start to finish.

Here’s how that might look across a typical cannabis timeline, from the moment your seeds sprout until your buds are ready to harvest.

Early growth / seedling stage

During the seedling stage, above-ground growth might look modest, but critical development is happening beneath the surface. This is when root systems begin to form, and how well they establish now determines how efficiently your plant will absorb water and nutrients later.

Two products are particularly useful at this stage:

• Vita Start: This liquid stimulator is designed specifically for seedlings, cuttings, and mother plants. It encourages fast root development, while also promoting more branching and greater nutrient uptake. Using Vita Start from the outset helps your plants build a strong structural foundation.
• Power Roots: This root stimulator supports the same goal as Vita Start, but from a different angle. It contains humic acids, seaweed extract, and a mix of proteins and vitamins to accelerate root mass development. The result is a denser, more responsive root network that sets plants up for strong vegetative growth later.

Power Roots (Plagron)

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Power Roots (Plagron)

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Vegetative phase (weeks 2–5)

As plants move into the vegetative phase, the focus shifts to producing strong stems and lush foliage, building size and strength before flowering begins. Healthy leaf growth is key to photosynthesis, which in turn fuels flower production later in the cycle. To achieve this, organic products containing ample nitrogen are essential.

• Alga Grow: This algae-based fertiliser supports the veg stage with slow-release nitrogen and vital trace elements. Its formulation feeds plants steadily, supporting robust growth while improving overall resilience. You can use it consistently throughout vegetation to give your plants a strong, stable structure.
• Pure Zym: Improve the substrate’s biological performance at the same time by combining Alga Grow with Pure Zym. This product contains natural enzymes that break down organic matter in the soil, releasing locked-up nutrients and helping prevent substrate compaction. It also increases oxygen levels in the root zone, which is vital for ongoing root expansion and microbial activity.

Together, these inputs keep the soil alive and plants responsive without risking nutrient burn or salt build-up.

Alga Grow (Plagron)

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Alga Grow (Plagron)

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Flowering phase (weeks 5–10+)

Once flowering begins, proper nutrition emphasises phosphorus and potassium, which support bud formation, resin production, and overall plant metabolism.

• Alga Bloom: This delivers phosphorus and potassium in a plant-available, organic form, along with amino acids that assist both nutrient absorption and protein production. It contributes to denser buds and a stronger overall structure.
• Sugar Royal: This product includes 18 amino acids and natural stimulants that support terpene production and boost the final quality of your harvest. When used alongside Alga Bloom, it helps bring out the full potential of each strain’s genetic profile.
• Green Sensation: Though optional, it’s a powerful flowering additive that boosts yield and resin development without interfering with the organic balance of the soil. Used sparingly, it provides an extra edge.

Each of these products is fully organic and works without the need to monitor pH or EC. When used together, they create a low-stress system that allows your plants to thrive naturally.

Alga Bloom (Plagron)

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Alga Bloom (Plagron)

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Growing medium matters: Understanding organic substrates

Cannabis grows best in an organic substrate that aerates and drains well, and supports the development of beneficial microbes.

Here are some of the best Plagron substrates to use for organic cannabis cultivation:

• Batmix: This is best if you’re after flavour and performance above all else. Preloaded with bat guano and high in phosphorus and potassium, it’s designed to facilitate terpene and cannabinoid production.
• Royalmix: The airiest of the substrates mentioned here, Royalmix provides maximum aeration around the root zone. This quality allows roots to easily spread, and reduces the chances of root rot.
• Allmix: Blended to hold water for longer, Allmix is designed for cannabis growers operating in hot environments where frequent watering is necessary. This substrate retains moisture well, meaning you’ll need water less frequently (and can save money on your water bill).
• Promix: This mixture combines carefully chosen types of peat, and is perfect for custom setups or growers who want full control over plant nutrition.

Each of these organic-certified Plagron soils include:

• High-quality peat for maximum airiness
• Worm humus from Dendrobaena Veneta, rich in microbes and nutrients
• Mycorrhiza and Trichoderma fungi to boost root health

Organic soil enhancers & natural pH buffers

In addition to regular fertiliser, amendments that support microbial populations or naturally buffer pH can help to keep your soil healthy and your organic plants thriving.

With that in mind, the following amendments and enhancers can be used alongside your core nutrition plan to ensure a functioning, living substrate:

• Mega Worm: This product contains decomposed plant matter full of enzymes, minerals, and fungi, and acts like a microbial inoculant.
• Supermix: This all-in-one fertiliser blend boosts soil life and plant immunity.
• Calcium Kick: This natural pH buffer raises soil to the ideal 5.5–6.5 range and improves nutrient uptake.
• Bat Guano: High in phosphorus/potassium, guano promotes root and flower development and is thought to improve bud flavour.

Using products such as these not only means you can be confident in the health of your substrate, but you also don’t need to flush before harvest like you would with synthetic fertilisers.

Bat Guano (Royal Queen Seeds)

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Bat Guano (Royal Queen Seeds)

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Putting it all together: Building the ideal organic nutrition plan

But how do all of these products work in tandem? The perfect organic feeding regimen will vary based on the given strain and growing environment, but below is an overview that can be used to guide your organic feeding regimen.

An organic grow plan typically includes:

• A substrate
• A base nutrient (Alga Grow/Bloom)
• One or two additives/enhancers

Using the above Plagron products as an example, a setup could include the following:

• One of the four substrates (Batmix, Royalmix, Allmix, Promix)
• Alga Grow (if needed)
• Alga Bloom
• Power Roots
• Sugar Royal
• Pure Zym
• Optional: Green Sensation

There’s a reason we recommend this particular regimen: it is pH/EC-neutral, award-winning, and comes recommended by real-life growers on Grow Diaries!

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Growing organic: Easier than ever before

Growing weed organically is not simply about putting a label on your bud. It’s an entire system that begins with your soil mix and ends with the highest-quality flowers you can grow. Ultimately, it makes for an easier cultivation experience (no nutrient burn, no pH problems, pathogen-resistant plants) and it’s better for the environment.

Given that, why not try it? If you’re just getting started, begin with the products and structure mentioned in this article, and head over to our store to order the necessities today!

Max Sargent

Max has been writing for over a decade, and has come into cannabis and psychedelic journalism in the last few years. Writing for companies such as Zamnesia, Royal Queen Seeds, Cannaconnection, Gorilla Seeds, MushMagic and more, he has experience in a broad spectrum of the industry.

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