Organic flowering fertiliser with seaweed

Regular price 5,50 €
Regular price Sale price 5,50 €
Size Price Price per L vs 100 ml
100 ml 5,50 € 55,00 €—
250 ml 7,90 € 31,60 €−43 %
500 ml 11,90 € 23,80 €−57 %
1 L 17,50 € 17,50 €−68 %
5 L 72,90 € 14,58 €−73 %
10 L 135,90 € 13,59 €−75 %

Plagron's Alga Bloom is an organic seaweed-based flowering fertiliser with an NPK analysis of 3-2-5, presented by the brand as suitable for organic growing. It feeds tomatoes, peppers, aubergines, courgettes and strawberries grown in soil, from the first flower to the harvest, at no more than 4 ml per litre, at every watering.

Ref. TK-PLAG-ABLOOM-100·Organic fertiliser
Size : 100 ml
Customer support 7 days a week by email
Delivery within 2 to 15 business days
100 % secure payment
Visa Mastercard American Express PayPalCartes Bancaires Apple Pay Shop Pay Bancontact EPS KlarnaMobilePaySatispay

The summary

Organic seaweed feeding for the flowering of vegetables grown in soil

Plagron's Alga Bloom is an organic seaweed flowering fertiliser, NPK 3-2-5, sold from the 100 ml bottle to the 10 litre container. It follows Alga Grow at the first flowers of tomatoes, peppers and strawberries, at 4 ml per litre. Its organic matter always rules it out for hydroponics as well as for the water of an aquaponic system.

When your tomatoes, peppers or strawberry plants are covered in flowers, their needs shift towards potassium, the element that swells the fruit and governs its sugar content. Alga Bloom, from the Plagron range, supports this phase with an organic formula with an NPK analysis of 3-2-5, which the brand presents as suited to organic growing. It follows on from Alga Grow, its growth-stage counterpart, and feeds the plant from the first flower to the last harvest.

The formula is based on three materials. Beet vinasse, a by-product of sugar refining, supplies most of the potassium in an organic form. Seaweed extracts provide trace elements and natural growth substances, while the amino acids and proteins are a source of nitrogen that soil life releases gradually. The French label classes it as an organic fertiliser of animal and plant origin, under standard NF U 42-001. For a vegetable garden certified as organic, the statement that counts is the one on your bottle's label.

Combine an organic potting compost with no mineral fertiliser

An organic fertiliser gives of its best in a living grow medium, where micro-organisms gradually convert its materials into forms the plant can absorb. Royalmix, a worm-castings compost whose starter feed is organic, provides this base without a mineral load that would upset the dosing. You thus start your fruiting vegetables on entirely organic nutrition, from potting on through to harvest.

🍓 From flower to fruit

Shake the bottle, then pour no more than 4 ml per litre of water into your watering can, i.e. 40 ml for a 10-litre can, at every watering from the opening of the first flowers. Prepare the solution just before use, as once diluted it only keeps for 24 hours. The fertiliser suits all watering methods, from the watering can to drip irrigation, and it can also be sprayed on the foliage at a reduced dose. During the growth phase that comes before, it is Alga Grow that feeds the plant, from transplanting until the first flower buds appear.

When

From the opening of the first flowers, at every watering until the last harvest.

How much

4 ml per litre of water at most, shake the bottle well before dosing.

Before

Alga Grow during growth, from transplanting to the first flower buds.

Who it's for

Vegetables harvested for their fruit, and the edible flowers of the vegetable garden.

Rinse the drip irrigation system after each feed

In an automatic watering system, organic matter eventually settles in the pipes and gradually blocks the drippers. Run clean water through the system after each use of Alga Bloom, and check the flow rate of the drippers furthest from the reservoir from time to time.

Alga Bloom was designed for growing in soil and potting compost. Soil life regulates the pH of the solution there, so you do not need to correct it, and the conductivity does not need to be adjusted either: part of the nitrogen is bound to organic matter, which the conductivity meter cannot read, so the measurement reflects only part of the dose. In a rich compost pre-fertilised for at least six weeks, soil life takes around two weeks to break down Alga Bloom, so the growing schedule starts it in the fifth week, without waiting for the bag's reserves to run out. However, it is not suitable for hydroponics, where no microbial life would be present to release its nutrients.

🐟 Outside the circuit, beside the system

Since it is not designed for hydroponics, Alga Bloom is not suitable for any form of water-based growing, whether a conventional aquaponic system, where the same water bathes both the roots and the fish, or a decoupled growing loop. In the pond, its organic matter would need oxygen to break down and would overload a biological filter sized only for the fish's waste. Its place is in the pots of potting compost set up around the system, where you grow the potassium-hungry fruiting vegetables that lack space in the grow bed.

In water shared with fish, potassium remains one of the elements most often in short supply, along with calcium and iron, and it is corrected differently. Potassium bicarbonate is added when the pH drops, which raises the pH and feeds the plants in a single step. Iron is supplied as iron chelate, at around 2 mg per litre every three weeks according to the aquaponics guide from New Mexico State University. Finally, you can water your neighbouring pots with the water drawn off the pond during water changes, topped up with Alga Bloom for flowering. The article on fertilisers in aquaponics details what the system will accept.

🧴 From bottle to drum

The 100 ml bottle makes 25 litres of solution at the maximum dose, enough to let you try the fertiliser on a few plants. The 500 ml size makes 125 litres and covers a season on a balcony of tomatoes, while the 1 litre bottle is enough for a vegetable bed. The 5 and 10 litre containers, which make up to 2,500 litres of solution, are intended for a greenhouse or a large fruiting-vegetable garden watered several times a week.

An opened bottle keeps for six months, so choose a size you will finish within the season rather than the cheapest one per litre. Close it tightly and store it away from frost and heat. Once diluted, the solution may turn cloudy and give off a smell, owing to natural bacterial fermentation, which is harmless to plants; this is one more reason to prepare it just before watering.

🌸 Flowering doses

On a light potting compost, the 100% NATURAL growing schedule brings in Alga Bloom from the third week, at 40 ml per 10 litres, that is, the full dose of 4 ml per litre. In the sixth week, the application is reduced to 30 ml, then to 35 ml in the seventh, while Green Sensation joins in at 10 ml per 10 litres. The dose returns to 40 ml until the tenth week, and the eleventh week is given plain water. On the range's rich composts, the same doses apply from the fifth week. Sugar Royal, an organic additive based on amino acids, is added at 10 ml per 10 litres throughout the crop. A single watering can therefore holds the flowering fertiliser and its additives, prepared on the day since the solution does not keep. At repotting, Bat Guano mixed into the compost, at 10 g per litre, adds a reserve of phosphorus that is released during flowering.

Technical specifications

The analysis

Type
Liquid organic flowering fertiliser
NPK
3-2-5Potassium-dominant for fruit set
Materials
Beet vinasse, seaweed, amino acids
Organic growing
Suitable, depending on the brand

Usage

Dose
4 ml per litre of water at mostThat is 40 ml for a 10-litre watering can
Grow media
Soil and compostsNeither hydroponics nor water culture
Diluted solution
24 hoursSmell and cloudiness are harmless
Opened bottle
6 months

The 100% NATURAL programme

Light potting compost
Week 3, 40 ml per 10 L
Rich pre-fertilised compost
Week 5, 40 ml per 10 L
Weeks 6 and 7
30 then 35 ml per 10 LGreen Sensation comes in at week 6
Final week
Clear water before the harvest

The preparation

Application
Bottle shaken, watering can of the day
Storage temperature
0 to 35 °CFrost-free, away from sunlight

6 further specifications are available in the detailed view.

In the box

  • 1 bottle or 1 container of Alga Bloom, from 100 ml to 10 L depending on the size chosen

Analysis, dose and certification taken from plagron.com (Alga Bloom page, technical data sheet of August 2026); programme based on the 100% NATURAL chart in French.

Manufacturer and product safety

Manufacturer
Bertels B.V.

Information provided under Regulation (EU) 2023/988 on general product safety.

Estimate your
delivery time

Bottles and cans are dispatched as parcels from a distributor's warehouse in France, with sealed caps and wedged against leaks. The exact shipping cost is shown in your basket.

Frequently asked questions

6 questions

6 key questions

How much Alga Bloom to pour

Enter the volume of the watering can. The result corresponds to the flowering dose, 4 ml per litre.

L
1 L100 L

0ml

of Alga Bloom in flowering

in the sixth week of the schedule, at 3 ml per litre
0 ml

A conductivity meter reflects only part of this dose, as its organic portion escapes measurement.

You may also like

Related articles

Let us talk about your project

A question about this product or your setup? Our team will answer and advise you.

Email usContact form

Interest-free instalment payments

Offered depending on the cart amount, at checkout.

Delivery in 2 to 15 working days

Depending on the products and shipping sites. Estimate by destination in the estimator on this page.

After-sales service 7 days a week by email or chat

Our team answers all your questions.

Shop responsibly

Become part of the change.