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Customer highlight
This company is absolutely fabulous. I've only done my first feeds with this and a few other choice ingredients from Dr Forest, and I can honestly say that my plants are growing better than ever! My tomatoes are growing faster than I thought possible, and I've been growing my whole, relatively long life!
Editorial highlight from marketplace and store reviews — separate from the full review list below.
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.
Seaweed extract powder: a soluble Ascophyllum biostimulant
Seaweed extract powder from Ascophyllum nodosum dissolves in cold water in seconds to make a seaweed drench or leaf spray: 1g per 1.2 to 1.5 litres to water on, 1g per 1.5 to 2 litres to spray.
It works alongside your normal feed, not instead of it: the useful fraction is alginic acid, natural seaweed compounds and potash. Sometimes sold as kelp powder, this is Ascophyllum nodosum, the North Atlantic wrack and the most researched seaweed in agricultural science, and the only ingredient in the bag.
100% Soluble
19.4% Alginic Acid
17.9% K₂O Potash
A. nodosum
For Plants & Soil
Gently Processed
19.38%Alginic Acid
17.89%K₂O Potash
48.33%Organic Matter
100%Water Soluble
What gardeners use seaweed extract powder for
- Rooting and transplant establishment: a root-zone drench at planting helps roots recover after potting on or planting out.
- Stress recovery: betaines and mannitol act as osmoprotectants, stabilising cell membranes through drought, frost and heat.
- Potash for fruit and flowers: 17.89% K₂O does nutritional work alongside the biostimulant effect.
- Soil biology: alginic acid and seaweed polysaccharides are a carbon source for soil bacteria and fungi.
- Leaf sprays: alginic acid lowers surface tension, so the spray wets the leaf properly.
- Lawns: a drench straight after scarifying, aerating or overseeding.
Seaweed powder, Brix+ liquid or kelp meal: which to buy
Seaweed Extract Powder (this one)
- Powdered seaweed you mix yourself, at the dilution you choose
- One small resealable pouch in place of a row of plastic bottles
- No water in the pack, so far less weight to ship per dose
- Keeps for years, sealed and dry
Brix+ liquid seaweed
- Ready to pour, for regular leaf sprays
- Ascophyllum plus triacontanol and other biostimulants named on the label, so it is more than a seaweed extract
Scottish kelp meal
- Ground seaweed that you dig in; it breaks down in the soil over weeks
- Builds organic matter; will not go through a sprayer
All three are in the seaweed fertiliser collection. Comparing with Maxicrop? See our Maxicrop seaweed alternative.
At a glance: 19.38% alginic acid · 17.89% K₂O · 1.20% N · 0.89% P · 48.33% organic matter · 100% water soluble · single ingredient · garden use only.
Dr Forest is a family-run fertiliser business in Stockport. We pack this seaweed powder in Stockport.
What Ascophyllum nodosum extract does for plants: the evidence
Ascophyllum nodosum lives between the tides, dried out and frozen twice a day, and is packed with protective compounds: alginates, mannitol, betaines and phenolics. On garden plants several of these act as signals rather than nutrients.
Alginic acid is the number to read
Alginic acid is a natural chelator: it binds mineral cations into forms roots can take up, and it improves crumb structure and water-holding in sandy and heavy ground alike. This powder declares 19.38%. Raw Ascophyllum carries around 28% alginate (Shukla et al., 2019), so this is a credible figure for a dried extract, and the first one to check on any other seaweed powder.
Three mechanisms
01
Root growth and hormone balance
A. nodosum extract changes the plant's own hormone balance rather than simply supplying hormones. Wally et al. (2013) showed that treating Arabidopsis with an A. nodosum extract changed cytokinin, auxin and abscisic acid production in the plant. The visible result is faster root establishment and more root surface for water and nutrients.
02
Drought and frost tolerance
Shukla et al. (2018) found better drought tolerance in soybean after A. nodosum treatment, through stress-response genes rather than any water-holding by the product. Rayirath et al. (2009) found that components of A. nodosum raised freezing tolerance in Arabidopsis. In a UK garden a late frost is often the difference between a crop and no crop on early potatoes, blossom and tender bedding.
03
Chelation, wetting and soil biology
Alginic acid holds mineral cations in the soil and lowers surface tension on the leaf, which is why a foliar feed tank-mixed with seaweed wets and covers better. In the soil, the polysaccharide fraction feeds bacteria and fungi and improves aggregate stability. Shukla et al. (2019) summarise the soil and root-zone evidence.
More is not better: the dose curve reverses
Seaweed biostimulant responses rise to an optimum and then fall away; strong concentrations can hold back the growth the correct dilution supports (Khan et al., 2009). Doubling the rate does not double the result, it usually costs you the result. Weigh the powder, and treat the stress-recovery rate as a short-term measure, not a new normal.
What it will not do
It will not green up a pale, hungry plant: that needs nitrogen, and this powder is 1.20% N. At garden dilution its 17.89% K₂O will not replace a dedicated potash feed for a heavy-cropping tomato or a mature rose. The mechanism studies above are lab and glasshouse work on Ascophyllum extracts, not trials of this powder.
Scientific references
- Khan, W. et al. (2009). Journal of Plant Growth Regulation, 28, 386–399.
- Rayirath, P. et al. (2009). Planta, 230(1), 135–147.
- Wally, O.S.D. et al. (2013). Journal of Plant Growth Regulation, 32, 324–339.
- Shukla, P.S. et al. (2018). AoB Plants, 10(1), plx051.
- Shukla, P.S. et al. (2019). Frontiers in Plant Science, 10, 655.
How to use seaweed powder: drench, spray, seed soak and lawns
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.
Stress recovery
Frost damage, heat or drought. 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
Most useful straight after scarifying, aerating or overseeding.
Drip irrigation
Add after the main nutrients are mixed. Fully soluble, so no filter or emitter issues.
Do not increase the rate
Seaweed biostimulant response is non-linear. Past the optimum the effect reverses and strong concentrations hold growth back instead of helping 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.
On fruit trees and soft fruit
At these rates seaweed is a supplement, not a main feed, so keep feeding as normal alongside it. On fruit it's most useful at planting and on strawberries.
- At planting (trees, bushes, canes, strawberry runners): dissolve 1 g in 1.2 litres of water and drench the root zone straight after planting. Repeat after 7 days. A newly planted tree takes 5–10 litres of the solution; a bush or cane 2–3 litres.
- Strawberries (ground or pots): drench at 1 g per 1.2–1.5 litres every 2–4 weeks, from new spring growth to the end of picking. You can also spray the leaves at 1 g per 1.5–2 litres, in the evening or on a dull day.
- Established trees and bushes: optional. A drench in spring and another after a hot, dry spell is plenty.
- Measuring: 1 g is about half a level teaspoon. Mix it into a little warm water first, then top up.
Honest expectations: in field trials on strawberries in Victoria, Australia, a liquid extract of two seaweeds, given as a monthly drench (with a leaf spray as well in one study), gave better root growth and about 8–10% more fruit. Both studies were funded by the extract's maker (one jointly with a university), and that extract isn't this powder, so don't expect the same figures. Results vary with soil, weather and variety.
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.
- Doubling the rate for a struggling plant. Use the stress-recovery rate, not a rate you invented.
- Spraying in full sun. 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.
Use it with
Fulvic Acid Powder for mineral chelation and uptake, Humic Acid Granules for long-term soil structure, and the Dr Forest feeds for tomatoes, chillies, strawberries and roses, where the seaweed is the biostimulant layer under the nutrition.
Seaweed extract FAQ
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.
Yes, it suits organic gardening and no-dig growing. It is a single natural ingredient: dried Ascophyllum nodosum, processed gently without harsh chemicals or heat, with nothing synthetic added and no fillers, carriers or preservatives. 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 label analysis is 1.20% N, 0.89% P and 17.89% K₂O: potash-led, with very little nitrogen. If your plants are pale and hungry, they need a nitrogen source, not more seaweed. A tomato or all-purpose fertiliser supplies the numbers; seaweed sits alongside it. For the longer explanation, see what seaweed fertiliser actually does.
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 or drought.
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 a drip line on the same day you open the bag. For a dig-in seaweed, see our Scottish kelp meal.
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. The dry powder is alkaline (pH close to 10), so avoid skin and eye contact and keep the dust out of eyes when weighing. Store it sealed and out of reach as you would any garden product, and do not let anyone eat it.
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