Dr Forest
Organic Seaweed Powder | 100% Soluble Kelp Extract | Natural Biostimulant | UK
Organic Seaweed Powder | 100% Soluble Kelp Extract | Natural Biostimulant | UK
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Organic seaweed powder — 100% soluble Ascophyllum nodosum with tested growth hormones
Seaweed is not a fertiliser in the conventional sense. It supplies very little nitrogen, phosphorus, or potassium. What it delivers — and what no synthetic fertiliser can replicate — is a concentrated package of natural plant growth hormones, complex polysaccharides, and bioactive compounds that prime the plant's own growth and defence systems. This is the difference between feeding a plant and activating it.
This powder is pure Ascophyllum nodosum — the most extensively researched seaweed species in agriculture, with over 70 years of published science behind it. It is not a liquid extract diluted with water and preservatives. It is the whole seaweed, dried and milled to an ultra-fine, fully water-soluble powder that dissolves instantly with no sediment, no clogging, and no residue. Every gram contains the full spectrum of bioactive compounds in their natural ratios: cytokinins, auxins, alginic acid, laminarin, mannitol, fucoidans, betaines, amino acids, and over 60 trace elements.
The growth hormones in this product are laboratory tested — cytokinins verified at <200 ppm and gibberellins at <100 ppm. Most liquid seaweed products on the market do not test or declare hormone content, meaning you cannot know what you are actually applying. This powder delivers consistent, verified biostimulant activity with every application.
What seaweed powder is used for in the garden
- Root development and transplant establishment — cytokinins and auxins stimulate rapid root cell division; applying seaweed at transplanting accelerates root recovery and establishment
- Stress resistance and recovery — betaines, mannitol, and proline act as osmoprotectants that stabilise cell membranes under drought, frost, heat, and salinity stress
- Yield and fruit quality improvement — peer-reviewed meta-analyses report an average 15% yield increase across crops, with improvements in sugar content, vitamin C, and flavour
- Soil biology activation — alginic acid and polysaccharides feed beneficial soil microorganisms, increasing rhizosphere diversity and nutrient cycling
- Seed treatment and germination — soaking seeds in dilute seaweed solution improves germination rates and produces seedlings with stronger root systems
- Foliar nutrient uptake enhancement — alginic acid acts as a natural wetting agent and chelator, improving absorption of any co-applied foliar nutrients
- Disease suppression — triggers systemic acquired resistance (SAR), upregulating defence genes against fungal and bacterial pathogens
- Flower set and fruit retention — cytokinin activity delays senescence in flowers and developing fruitlets, improving fruit set rates
Why powder rather than liquid seaweed?
Soluble Powder
- Whole dried seaweed — full spectrum of bioactive compounds in natural ratios
- No water added — you are not paying to ship water
- Shelf life measured in years, not months
- Minimal packaging — a small resealable pouch replaces bulky plastic bottles
- Dissolves completely — no sediment, no nozzle clogging
- You control the dilution rate precisely
- Lower carbon footprint per application
Liquid Seaweed Extract
- Extracted fraction — processing removes or degrades some bioactive compounds
- Typically 85–95% water by weight
- Shorter shelf life; may require preservatives
- Heavy plastic bottles — far more packaging waste per dose delivered
- Convenient but less concentrated
- Fixed dilution — less flexibility
- Higher shipping emissions per dose delivered
The science of seaweed biostimulation: how Ascophyllum nodosum activates plant growth and defence
Why Ascophyllum nodosum is not an ordinary seaweed
Of the thousands of seaweed species in the world's oceans, Ascophyllum nodosum — the knotted wrack of the cold North Atlantic — is the single most studied species in agricultural science. It grows in the intertidal zone, exposed twice daily to extreme environmental swings: desiccation, UV radiation, freezing, osmotic shock, and mechanical wave stress. To survive this, it has evolved an extraordinarily complex biochemistry rich in protective compounds that happen to be directly useful to land plants when applied as a biostimulant.
Published analyses of dried Ascophyllum nodosum report approximately 28% alginic acid, 11.6% fucoidans, 7.5% mannitol, and 4.5% laminarin as the dominant carbohydrate fractions. The protein content is approximately 5%, and the phenolic content approximately 1.4%. It also contains a full suite of phytohormones — cytokinins (primarily trans-zeatin), auxins, gibberellins, and abscisic acid — in concentrations sufficient to trigger measurable hormonal responses in treated plants.
The hormonal role — Cytokinins, Auxins & Gibberellins
- Cytokinins drive cell division in roots and shoots
- Auxins initiate and direct root tip elongation
- Gibberellins regulate stem elongation and fruit development
- Combined hormonal action increases total plant biomass
- Delays leaf senescence — keeps foliage photosynthetically active longer
- Improves fruit set and reduces flower/fruitlet abscission
The polysaccharide role — Alginic Acid, Laminarin & Fucoidan
- Alginic acid chelates soil minerals, increasing plant-available nutrients
- Improves soil water-holding capacity and aggregate structure
- Laminarin triggers plant immune defence pathways (SAR)
- Fucoidan acts as an elicitor of pathogen resistance genes
- Feeds beneficial rhizosphere microorganisms
- Acts as a natural wetting agent when applied as foliar spray
Six mechanisms of action
Root Growth Stimulation
Cytokinins and auxins present in Ascophyllum nodosum directly stimulate root cell division and elongation. Research using Arabidopsis thaliana confirmed that root application of A. nodosum extract upregulates cytokinin biosynthesis genes while increasing trans-zeatin concentrations in plant tissue within 24–96 hours. The practical result is faster root establishment, greater root mass, and improved nutrient and water uptake capacity.
Abiotic Stress Tolerance
Ascophyllum nodosum contains high concentrations of betaines, mannitol, and proline — osmoprotectant compounds that stabilise cell membrane integrity under drought, frost, heat, and salt stress. Shukla et al. (2018) demonstrated improved drought tolerance in soybean through upregulation of stress-response genes following A. nodosum application.
Systemic Acquired Resistance
Laminarin and fucoidan — polysaccharides unique to brown algae — act as elicitors that trigger systemic acquired resistance (SAR) in treated plants. This primes the plant's own immune system to respond faster and more strongly to pathogen attack, providing broad-spectrum protection against both fungal and bacterial diseases before infection occurs.
Nutrient Chelation & Uptake
Alginic acid is a powerful natural chelator. Applied to soil, it binds mineral cations into plant-available chelated forms. Applied as a foliar spray, it reduces surface tension and improves leaf wetting, increasing the absorption rate of any co-applied nutrients. This is why tank-mixing seaweed with foliar feeds consistently improves their effectiveness.
Soil Biology Activation
The complex polysaccharides in seaweed are carbon sources that feed beneficial soil bacteria and fungi. Regular seaweed applications increase rhizosphere microbial diversity, improve nutrient mineralisation, and enhance mycorrhizal colonisation. Alginic acid also improves aggregate stability, water-holding capacity, and aeration in both sandy and clay soils.
Fruit Quality & Flavour
A comprehensive meta-analysis reported an average 17.96% increase in soluble sugars, 18.07% increase in vitamin C, and 38.32% improvement in sugar-to-acid ratios in treated crops. These represent measurable improvements in the flavour, nutrition, and eating quality of fruit and vegetables through enhanced photosynthetic efficiency.
Scientific References
- Shukla, P.S. et al. (2019). Ascophyllum nodosum-Based Biostimulants. Frontiers in Plant Science, 10, 655.
- Zamarreño, A.M. et al. (2024). Plant growth-promoting effect of A. nodosum extract. Chem. Biol. Technol. Agric., 11, 190.
- Shukla, P.S. et al. (2018). Seaweed extract improves drought tolerance of soybean. AoB Plants, 10(1), plx051.
- Field meta-analysis: seaweed on crop yield and quality in China.
- Wally, O.S.D. et al. (2013). Phytohormone regulation in Arabidopsis following A. nodosum treatment. J. Plant Growth Regul., 32, 324–339.
- Khan, W. et al. (2009). Seaweed extracts as biostimulants. J. Plant Growth Regul., 28, 386–399.
How to use seaweed powder: preparation, application rates & guide
This is a fully water-soluble powder, not a meal or granule. Add the measured amount to water at any temperature and stir briefly — it dissolves completely within seconds, leaving no sediment or residue. Use fresh solution within 24 hours of mixing.
Application rates
Soil drench — general maintenance
Standard biostimulant rate for all plants during the growing season. Apply around the root zone and water in. Compatible with all Dr Forest fertilisers.
Foliar spray — growth & defence
Apply to both leaf surfaces using a fine mist sprayer. Spray in early morning or late evening — avoid full sun. Alginic acid acts as a natural wetting agent.
Transplant & potting drench
Drench the root zone immediately after transplanting or any root disturbance. Cytokinin and auxin content accelerates root recovery.
Seed soak
Improves germination rate and produces seedlings with stronger root systems. Drain and sow — do not rinse.
Stress recovery
Use the stronger rate for frost damage, heat stress, drought, or pest attack. Return to standard rate once recovered.
Lawn & turf
Improves root depth, drought tolerance, and green-up speed. Effective after scarifying, aerating, or overseeding.
Hydroponics & fertigation
Add to the reservoir after mixing main nutrients. Dissolves completely — no filter issues. Minimal EC contribution.
Step-by-step preparation
- Measure the powder. 1g is approximately half a level teaspoon. For a standard 10-litre watering can, measure 7–8g.
- Add powder to water and stir. Sprinkle onto the water surface and stir briefly. Dissolves within seconds — no clumps, no straining.
- Apply immediately or within 24 hours. Root drenches around the base; foliar sprays targeting both leaf surfaces.
- Combine with other feeds if desired. Fully compatible with all Dr Forest fertilisers. Alginic acid improves uptake of co-applied nutrients.
- Store dry powder sealed in a cool, dry place. Shelf life of several years. Avoid moisture ingress.
Seaweed is most effective at key developmental transitions: transplanting, onset of flowering, rapid vegetative growth, and before stress events. For most gardeners, a fortnightly drench or foliar spray from spring through autumn covers all of these windows.
Combine with Fulvic Acid Powder for chelated mineral uptake, Humic Acid Granules for soil CEC building, and Dr Forest's crop-specific fertilisers (Tomato, Chilli, Rose & Flower) where the seaweed acts as a biostimulant booster amplifying nutritional effects.
Frequently asked questions about seaweed powder
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