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Garden use only
This is a garden biostimulant for plants and soil. It is not a dietary supplement, not food grade, and not tested to supplement standards. Do not consume it. If you are looking for a seaweed or kelp supplement, this is the wrong product.
Organic seaweed extract powder for plants — 100% soluble Ascophyllum nodosum, 19.38% alginic acid
100% Soluble
19.4% Alginic Acid
17.9% K₂O Potash
A. nodosum
For Plants & Soil
Gently Processed
Seaweed is a biostimulant, not a conventional fertiliser. It carries almost no nitrogen or phosphorus. What it carries instead is alginic acid, complex polysaccharides, natural growth compounds and potash, all of which act on the plant's own growth and defence machinery rather than simply feeding it. That is the difference between a plant food and a plant activator.
This is an organic seaweed extract powder made from a single ingredient, Ascophyllum nodosum, the knotted wrack of the cold North Atlantic and the most heavily researched seaweed in agricultural science. The seaweed is processed gently, without harsh chemicals or heat, so the bioactive fraction survives the manufacturing rather than being cooked or stripped out by hot alkaline extraction. The result dissolves fully in cold water in seconds, with no sediment, no straining and no blocked sprayer nozzles.
The label is unusually strong for a soluble seaweed powder: 19.38% alginic acid, 48.33% organic matter and 17.89% K₂O. That potash figure matters. Most liquid seaweed feeds deliver a fraction of a percent of potassium once diluted, so gardeners assume seaweed is a poor source of potash. In a concentrated soluble powder it is not.
19.38%Alginic Acid
17.89%K₂O Potash
48.33%Organic Matter
100%Water Soluble
What gardeners use organic seaweed extract powder for
- Rooting and transplant establishment — drenching the root zone at planting speeds root recovery after the disturbance of potting on or planting out
- Stress recovery — betaines and mannitol act as osmoprotectants, stabilising cell membranes through drought, frost, heat and salinity
- Potash top-up for fruit and flowers — 17.89% K₂O supports sugar transport into fruit and firmer flower stems, alongside the biostimulant effect
- Soil biology — alginic acid and seaweed polysaccharides are a carbon source for beneficial soil bacteria and fungi
- Seed soaking — a dilute soak before sowing improves germination and produces seedlings with better root systems
- Foliar feeding — alginic acid lowers surface tension, so leaves wet properly and any nutrients in the tank mix are absorbed more readily
- Disease resilience — laminarin and fucoidan prime the plant's own defence pathways ahead of pathogen attack
- Lawns and turf — deeper rooting and faster green-up after scarifying, aerating or overseeding
Soluble powder or liquid seaweed?
Organic soluble seaweed extract powder
- Concentrated, so you are not paying to ship water
- Declared label: 19.38% alginic acid, 17.89% K₂O, 48.33% organic matter
- Shelf life in years, kept dry and sealed
- A small resealable pouch replaces a shelf of plastic bottles
- Dissolves completely in cold water, no sediment or nozzle blockage
- You set the dilution rate, from a gentle maintenance drench to a stress-recovery dose
Liquid seaweed feed
- Typically 85 to 95% water by weight
- Analysis often given as a diluted NPK, so the true concentration is hard to compare
- Shorter shelf life once opened, sometimes preservative dependent
- Heavy bottles, far more packaging per dose delivered
- Convenient to pour, but you are locked into the maker's concentration
- Higher shipping weight and emissions per dose
Made by Growers. Backed by Science.
Dr Forest is a small independent fertiliser business run from Stockport, Greater Manchester, founded in 2020 and named after Joe's grandfather Dr Forrest, a GP in a Lancashire mining town who kept a back-garden plot for the runner beans he turned into piccalilli. ★★★★★ 5-star across all platforms · 4,300+ reviews.
The science of seaweed biostimulants: what Ascophyllum nodosum does to a plant
Why this species and not any other seaweed
Ascophyllum nodosum grows in the intertidal zone of the North Atlantic and is exposed twice a day to desiccation, UV, freezing, osmotic shock and wave damage. Surviving that has driven it to accumulate an unusual density of protective compounds: alginates, fucoidans, laminarin, mannitol, betaines and phenolics. Applied to land plants, several of those compounds behave as signalling molecules rather than nutrients. This is the reason A. nodosum, rather than kelp or Sargassum, dominates the peer-reviewed biostimulant literature.
Alginic acid is the number worth reading
Alginic acid is the fraction that does most of the soil work. It is a natural chelator, binding mineral cations into forms roots can take up, and it improves aggregate stability and water-holding capacity in both sandy and heavy ground. It is also the reason a seaweed drench behaves as a soil conditioner as well as a feed. At 19.38%, this material sits above the alginic acid content typically declared by mainstream Ascophyllum powders, which is the single most useful comparison figure when you are looking at competing seaweed products.
The potash is real, and it is not chloride-heavy salt
Seaweed accumulates potassium from seawater. At 17.89% K₂O, alongside 1.20% N and 0.89% P, this is a potash-dominant analysis. It will not replace a dedicated potash feed at garden dilution rates, but it does mean the biostimulant is doing nutritional work at the same time, which is why seaweed has always earned its place in flowering and fruiting programmes.
Five mechanisms of action
01
Root growth and hormonal signalling
Ascophyllum nodosum extracts alter the plant's own hormone balance rather than simply supplying hormones. Wally et al. (2013) showed that treatment of Arabidopsis with a commercial A. nodosum extract changed cytokinin, auxin and abscisic acid biosynthesis and accumulation in plant tissue. The visible outcome is faster root establishment and a larger root surface for water and nutrient capture.
02
Drought and abiotic stress tolerance
Shukla et al. (2018) demonstrated improved drought tolerance in soybean following A. nodosum application, through upregulation of stress-response genes rather than through any water-holding effect of the product itself. Betaines, mannitol and proline in the seaweed act as osmoprotectants, stabilising membranes while the plant's own stress response comes online.
03
Frost and cold tolerance
Rayirath et al. (2009) found that lipophilic components of A. nodosum enhanced freezing tolerance in Arabidopsis. For a UK garden this is the most practically useful of all the stress findings, given how often a late frost is the difference between a crop and no crop on early potatoes, blossom and tender bedding.
04
Induced defence
Laminarin and fucoidan, polysaccharides specific to brown algae, act as elicitors that trigger systemic acquired resistance. The plant's defence genes are primed before infection, so the response to a fungal or bacterial attack is faster and stronger. Khan et al. (2009) review the elicitor evidence across crops.
05
Chelation, wetting and soil biology
Alginic acid chelates mineral cations in soil and lowers surface tension on the leaf, which is why tank-mixing seaweed with a foliar feed reliably improves the performance of the feed. In the soil, the polysaccharide fraction feeds bacteria and fungi and improves aggregate stability. Shukla et al. (2019) summarise the soil and rhizosphere evidence.
More is not better: the dose curve reverses
Seaweed biostimulant responses are concentration dependent and non-linear. The effect rises to an optimum and then falls away, and strong concentrations can inhibit the growth they promote at the correct dilution. Khan et al. (2009) note this concentration dependence across the biostimulant literature. Doubling the rate does not double the result, it usually costs you the result. Weigh the powder rather than guessing with a spoon, and treat the stress-recovery rate as a short-term measure, not a new normal.
Scientific references
- Khan, W. et al. (2009). Seaweed extracts as biostimulants of plant growth and development. Journal of Plant Growth Regulation, 28, 386–399.
- Rayirath, P. et al. (2009). Lipophilic components of the brown seaweed Ascophyllum nodosum enhance freezing tolerance in Arabidopsis thaliana. Planta, 230(1), 135–147.
- Wally, O.S.D. et al. (2013). Regulation of phytohormone biosynthesis and accumulation in Arabidopsis following treatment with commercial extract from the marine macroalga Ascophyllum nodosum. Journal of Plant Growth Regulation, 32, 324–339.
- Shukla, P.S. et al. (2018). Seaweed extract improves drought tolerance of soybean by regulating stress-response genes. AoB Plants, 10(1), plx051.
- Shukla, P.S. et al. (2019). Ascophyllum nodosum-based biostimulants: sustainable applications in agriculture for the stimulation of plant growth, stress tolerance and disease management. Frontiers in Plant Science, 10, 655.
- Zamarreño, A.M. et al. (2024). Plant growth-promoting effect of an Ascophyllum nodosum extract. Chemical and Biological Technologies in Agriculture, 11, 190.
How to use organic seaweed extract powder: rates, mixing and timing
Dissolves in cold water, no soaking needed
This is a fully soluble powder, not a meal or a granule. Sprinkle the measured amount onto the water surface, stir briefly, and it is gone within seconds with no sediment. The powder is alkaline, so in hard tap water expect a slight cloudiness on standing. That is normal and does not affect performance. Use the made-up solution within 24 hours.
Application rates
Soil drench, general maintenance
The standard biostimulant rate for anything in the ground or in a pot through the growing season. Apply around the root zone and water in. Compatible with all Dr Forest fertilisers.
Foliar spray
Both leaf surfaces, fine mist, early morning or evening. Never in full sun. The alginic acid acts as a wetting agent, so you need less spray volume than you think to get full coverage.
Transplanting and potting on
Drench the root zone straight after any root disturbance. This is the single highest-value application in the year.
Seed soak
Drain and sow directly. Do not rinse. Improves germination and produces seedlings with stronger root systems.
Stress recovery
Frost damage, heat, drought or pest attack. Drop back to the standard rate as soon as the plant is growing away again. This is a short-term rate, not a permanent one.
Lawn and turf
Deeper rooting, better drought tolerance, faster green-up. Most useful straight after scarifying, aerating or overseeding.
Fertigation and drip
Add to the reservoir after the main nutrients are mixed. Fully soluble, so no filter or emitter issues, and the contribution to EC is small.
Do not increase the rate
Seaweed biostimulant response is non-linear. Past the optimum the effect reverses and strong concentrations inhibit growth instead of promoting it. A stronger mix is not a stronger result. Weigh the powder, do not eyeball it, and if you have overdone it, water through with plain water and go back to the standard rate.
Mixing, step by step
- Weigh the powder. 1g is roughly half a level teaspoon, but density varies. For a 10-litre can at the standard drench rate, that is 7 to 8g. Kitchen scales are worth the thirty seconds.
- Add powder to water, not water to powder. Sprinkle onto the surface and stir. It dissolves within seconds, with no clumps and nothing to strain out.
- Add other feeds after the seaweed has dissolved. Seaweed goes in first, concentrated fertilisers second, then top up to volume.
- Apply within 24 hours. Root drenches at the base, foliar sprays to both leaf surfaces in the cool part of the day.
- Reseal and store dry. Kept sealed in a cool dry place the powder lasts for years. Moisture is the only thing that will spoil it.
Five common mistakes
- Treating it as a fertiliser. It is a biostimulant with useful potash. It still needs a balanced feed alongside it, not instead of it.
- Doubling the rate for a struggling plant. The curve reverses. Use the stress-recovery rate, not a rate you invented.
- Spraying in full sun. Scorch risk and rapid evaporation before anything is absorbed. Early morning or evening only.
- Mixing a batch and leaving it a week. Make it up fresh and use it within 24 hours.
- Applying only when something has gone wrong. The best returns come from fortnightly applications through the season, particularly at transplanting and at the start of flowering.
Works well alongside
Pair with Fulvic Acid Powder for mineral chelation and uptake, Humic Acid Granules for long-term soil CEC, and the Dr Forest crop-specific plant foods for tomatoes, chillies, strawberries and roses, where the seaweed acts as the biostimulant layer under the nutrition.
Organic seaweed extract powder: frequently asked questions
No. This is a garden biostimulant for plants and soil. It is not food grade, it is not manufactured to supplement standards, and it has not been tested to the heavy metal and contaminant limits that apply to products intended for human consumption. Do not consume it. If you want a seaweed or kelp supplement, buy one from a supplement supplier who can show you that testing.
It is a single-ingredient organic seaweed product. Dried Ascophyllum nodosum, processed gently without harsh chemicals or heat, with nothing synthetic added and no fillers, carriers or preservatives. Nothing goes into the bag except the seaweed. That is why it suits organic and no-dig growing, and it is what most gardeners mean when they search for organic seaweed fertiliser. We do not sell it as certified organic and we make no certification claim. If you grow under a certification scheme yourself, check with your certifier before adding any input to your programme.
No, and this is the most common misunderstanding about seaweed. The analysis here is 1.20% N, 0.89% P and 17.89% K₂O. Seaweed is potash dominant with very little nitrogen. If your plants are pale and hungry, they need a nitrogen source, not more seaweed. Use seaweed for rooting, stress tolerance and the potash contribution, and feed nitrogen separately.
For this soluble seaweed extract powder, 1.20 – 0.89 – 17.89 on the label, expressed as N, P and K₂O. Liquid seaweed feeds usually declare something like 0.1 – 0.0 – 0.6 because they are mostly water, which is why comparing a powder to a liquid on NPK alone is misleading. Compare the concentrate, or compare what actually reaches the plant per pound spent.
In concentrated powder form, yes. 17.89% K₂O is a genuinely potash-rich analysis. At garden dilution rates it will not replace a dedicated potash feed for a heavy-cropping tomato or a mature rose, but it does mean you are getting nutritional value alongside the biostimulant effect rather than the biostimulant effect alone.
This powder is alkaline, with a pH close to 10 as supplied. At garden dilution rates the effect on soil or growing-medium pH is negligible, because the amount of powder in a full watering can is a gram or two. If you are dosing a small volume of low-buffer solution and monitoring pH closely, add the seaweed first and check the pH afterwards rather than before.
Every two weeks through the growing season, as either a drench or a foliar spray. The effects are cumulative, so a regular fortnightly routine beats an occasional heavy dose. Add an extra application at transplanting and at the start of flowering, and switch to the weekly stress-recovery rate for two or three weeks after frost, drought or pest damage.
No. Kelp meal and seaweed meal are coarsely ground dried seaweed that has to break down in the soil over weeks before anything becomes available, and they will not go through a sprayer. This is a soluble extract powder that dissolves in cold water in seconds and can be used as a foliar spray, a drench, a seed soak or through fertigation on the same day you open the bag.
Liquid seaweed is typically 85 to 95% water. You pay for that water, the bottle it sits in and the weight of shipping it. A soluble powder gives you a declared concentrate analysis, a shelf life measured in years rather than months, a fraction of the packaging per dose, and the freedom to set your own dilution rate for maintenance or stress recovery.
Yes, and it is better that way. Seaweed extract is compatible with all Dr Forest fertilisers. Alginic acid improves the uptake of whatever else is in the tank, so combining is more effective than applying separately. Dissolve the seaweed first, then add the concentrates.
Hormonal and gene-expression changes begin within days, but they are invisible. What you actually see is better colour and stronger growth after one to three weeks of fortnightly applications, and much more obviously, faster recovery from transplant shock or a cold snap compared with untreated plants alongside.
All garden plants. Vegetables, fruit, herbs, tomatoes and chillies, roses and flowering ornamentals, trees, shrubs, lawns, containers and raised beds. The mechanisms involved are basic plant processes, so nothing is off limits and there is no withholding period on edible crops.
It is dried seaweed with nothing synthetic added, and at garden dilution rates it presents no hazard to pets, wildlife or pollinators. It is not a pesticide and has no insecticidal action. Store it sealed and out of reach as you would any garden product, keep the dust out of eyes when weighing, and do not let anyone eat it.
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