Fertilizers & nutrients
by Plagron
Plagron Alga Grow is a 100% organic liquid fertiliser designed to fuel your plants through their entire vegetative growth phase. Built around a base of algae extract, amino acids, and an NPK ratio of 4-2-4, it feeds both your plants and the soil they live in — strengthening root systems, boosting green growth, and building the kind of foundation that pays off big when flowering starts. If you grow in soil and want to keep things organic from seed to harvest, this is the bottle you reach for first.
Alga Grow delivers nitrogen, potassium, and phosphorus in a 4-2-4 ratio — the classic vegetative-phase balance where nitrogen leads the charge for leaf and stem development, while potassium and phosphorus quietly build root mass underneath. But the real differentiator here is the algae extract. Algae-based fertilisers don't just dump nutrients into the soil; they feed the microbial life that makes organic growing actually work. You're not just feeding the plant — you're feeding the entire ecosystem in your pot.
The amino acids in the formula act as natural chelators, helping your plants absorb those minerals more efficiently. The result? Thicker stems, denser foliage, and a root system that can actually support heavy flowering later on. We've seen growers skip the veg-phase feed and wonder why their plants look tired by week three of bloom. The vegetative phase is where you build the engine. Alga Grow is the fuel for that engine.
One honest limitation: this product is strictly for soil. If you're running a hydroponic setup — DWC, NFT, coco with heavy drain-to-waste — Alga Grow isn't formulated for that. The organic compounds can clog drippers and create biofilm in reservoirs. Stick to soil, and it performs brilliantly.
| Spec | Value |
|---|---|
| Brand | Plagron |
| Product | Alga Grow |
| Type | Organic liquid fertiliser |
| NPK Ratio | 4-2-4 |
| Key Ingredients | Nitrogen, potassium, phosphorus, amino acids, algae extract |
| Dilution Rate | Max 4 ml per 1 litre of water (1:250) |
| Growth Phase | Vegetative |
| Medium | Soil only |
| Organic | 100% |
| Available Size | 100 ml |
| SKU | HS1874 |
Complete your organic feed line with Plagron Alga Bloom for the flowering phase — same algae-based formula, different NPK ratio tuned for bud development. Using both together gives your plants a consistent organic diet from the first true leaf to harvest day. If you're growing in Plagron's own soil mixes like Batmix or Growmix, the combination works even better since the soil is already optimised for their nutrient line.
Here's what we see time and again from growers who walk into the shop: they spend all their budget on bloom boosters and flowering supplements, then wonder why their yields are underwhelming. The vegetative phase isn't the warm-up act — it's where your plant builds everything it needs to produce flowers. Skimp on veg nutrition and you get thin stems that can't support heavy buds, shallow root systems that dry out between waterings, and pale leaves that tell you the plant is running on empty before it even starts flowering.
Alga Grow addresses this directly. The 4-2-4 NPK ratio gives your plants the nitrogen they're hungry for during veg, without overloading phosphorus (which they don't need much of yet). The algae extract improves soil structure over time — it's not just a one-shot feed but something that genuinely makes your growing medium better with each watering. After a few weeks of use, you can actually feel the difference in the soil texture: it holds moisture more evenly and drains more consistently. That's the microbial life doing its job.
Compared to synthetic veg feeds, Alga Grow works more slowly — you won't see overnight colour changes like you might with a mineral fertiliser. But the growth is sturdier. Plants fed organically through veg tend to have thicker cell walls and better resistance to stress. If you're the type who grows for flavour and aroma rather than just sheer weight, organic feeding through the entire cycle makes a noticeable difference in the final product. The terpene profiles on organically grown plants are, in our experience, consistently more complex.
The 100 ml bottle is the entry point — it gives you roughly 25 litres of nutrient solution, which is enough for a small grow of 2-4 plants through their vegetative phase. If you're running anything larger, you'll burn through it quickly. We'd recommend sizing up if Plagron offers larger bottles in your budget, but the 100 ml is spot-on for a first run to see how your plants respond before committing.
One thing we always mention: don't exceed the 4 ml per litre maximum. With organic feeds, more isn't better. Overfeeding can create salt buildup even in organic formulas, and it throws off the soil pH. If your plants look healthy and green, the dose is working. If you see tip burn on the leaves, dial it back to 2-3 ml per litre and let the soil biology catch up.
The smell is earthy and distinctly algae-forward — not unpleasant, but you'll know it's organic. It doesn't linger in the room after watering, though. Texture-wise, it's a dark liquid, slightly thicker than water, with a consistency that pours easily from the bottle. No chunks or sediment issues in our experience, as long as you shake it properly.
| Feature | Plagron Alga Grow (Organic) | Typical Synthetic Veg Feed |
|---|---|---|
| Composition | Algae extract, amino acids, NPK 4-2-4 | Mineral salts, chelated metals |
| Soil Health | Improves microbial life and structure | Neutral to negative over time |
| Speed of Effect | Gradual — 3-5 days visible response | Fast — often within 24-48 hours |
| Risk of Overfeeding | Lower — organic buffers in soil | Higher — direct salt uptake |
| Flavour/Aroma Impact | Tends to produce more complex terpene profiles | Neutral — depends on flushing |
| Suitable Medium | Soil only | Soil, coco, hydro |
| Organic Certification | 100% organic | No |
No. Alga Grow is formulated exclusively for soil-based growing. The organic compounds can cause blockages in drip systems and create biofilm in hydroponic reservoirs. For coco or hydro, look at Plagron's mineral-based Hydro or Cocos feed lines instead.
At the maximum dilution rate of 4 ml per litre, the 100 ml bottle produces 25 litres of ready-to-use nutrient solution. For a small grow of 2-4 plants, that covers most of the vegetative phase comfortably.
Organic soil grows are generally more forgiving on pH than hydro setups, because the microbial life in the soil acts as a natural buffer. That said, keeping your input water between 6.0 and 6.5 is good practice. Alga Grow itself shouldn't throw your pH wildly off course.
It's not designed for that. Alga Grow's 4-2-4 NPK ratio is nitrogen-heavy, which is what plants want during veg. During flowering, they need more phosphorus and potassium. Switch to Plagron Alga Bloom when you flip to 12/12 — it's the matching product with the right ratio for bud development.
Absolutely. It works in any soil-based setup — indoor pots, raised beds, or directly in garden soil outdoors. The algae extract and amino acids actually benefit outdoor soil even more, since they support the existing microbial ecosystem that's already present in natural ground.
Plagron doesn't list a specific expiry for opened bottles, but organic fertilisers degrade faster than synthetics. Store it sealed in a cool, dark place and use it within one growing season for best results. If it smells off or has unusual sediment that won't dissolve with shaking, replace it.
Yes — Plagron designs their product lines to work together. Alga Grow pairs well with Plagron's organic additives like Power Roots or Pure Zym. Just follow the dosage schedules on Plagron's official grow guides to avoid overfeeding.
Last updated: April 2026
