Seaweed Fertiliser

Seaweed fertiliser: liquid, extract and kelp meal

Seaweed extract is brown seaweed dried and processed so the useful fraction can be taken up quickly by leaf or root. Kelp meal is the same seaweed left coarse, worked into soil to release slowly. Both are seaweed plant food in the loose sense, though neither is really a fertiliser.

This is the whole seaweed fertiliser UK range in one place: three formats of one raw material, Ascophyllum nodosum from cold Scottish water, packed in small batches by Dr Forest in Stockport.

UK gardeners searching seaweed fertiliser, liquid seaweed, seaweed feed or seaweed plant food usually want one of three jobs: a soluble drench, a slow soil meal, or a ready liquid biostimulant. Same cold-water Ascophyllum — different form.

Feeds the plant and the soil at the same time

Look at the NPK on a bag of seaweed and you would wonder why anyone buys it. That is because the numbers are not where the value is. Seaweed works through its bioactive fraction: natural growth hormones (cytokinins, auxins and gibberellins), alginic acid, mannitol and a broad spread of trace minerals. Together those drive faster rooting, better heat and drought tolerance, chlorophyll retention and, in the better trials, measurable yield. The full picture, with the evidence, is in seaweed fertiliser, properly explained.

Three forms, depending on how you feed

• Scottish Kelp Meal. Slow-release granular seaweed, worked into soil or compost for a steady season-long supply. The one to use if you top-dress once and forget about it.
• Seaweed Extract Powder. 100% soluble Ascophyllum nodosum. Dissolves instantly for foliar feeds and root drenches. The one to use if you feed weekly.
• Brix+. A liquid seaweed biostimulant with triacontanol and six other growth promoters, formulated to support sugar levels, flowering and fruit set. The one to use when you are chasing flavour in the fruit.

Seaweed extract, kelp meal and seaweed powder: what the difference is

The names get used interchangeably in garden centres, which is unhelpful, because they describe three genuinely different things.

• Kelp meal is dried seaweed kelp milled coarse. It is not soluble. It goes into the soil, where microbes break it down over weeks and months, feeding soil life as well as the plant. Slow, cheap per application, and the format to choose if you would rather amend once in spring than feed every fortnight.
• Seaweed extract is the soluble fraction, drawn out of the raw weed and dried. Because the cell walls have already been opened, the bioactive material is available immediately rather than after decomposition. This is what most published seaweed trials have actually used.
• Seaweed powder usually means extract in dry form, and powdered seaweed sometimes means finely milled whole weed instead. The distinction that matters is solubility. Our powder is 100% soluble, so it dissolves clear in a watering can and will pass through a sprayer without blocking it.
• Liquid seaweed is extract already in solution, often with other ingredients alongside it. Convenient, heavier to ship for the amount of active material you get, and the format most people find easiest to dose accurately.

Cost per application generally runs cheapest for kelp meal, then soluble powder, then liquid. Speed of effect runs the other way round.

Why Ascophyllum, and why Scottish

Not all seaweed is equivalent. Ascophyllum nodosum is the cold-water brown alga that almost every published seaweed trial has used, which is the reason it became the standard rather than tradition. Cold North Atlantic water means slow growth and a denser bioactive fraction than warm-water species carry.

How to use it

Kelp meal goes into the soil or compost at planting, or as a top-dress in spring. Powder and Brix+ go on every seven to fourteen days through active growth, as a foliar spray or a root drench. Seaweed is the most forgiving biostimulant there is: overdoing it is difficult, and it layers cleanly on top of any feeding programme. Adding a wetting agent to a foliar spray noticeably improves how evenly it coats the leaf.

Dilution and application rates are on every product page, and how to apply seaweed fertiliser covers timing and method in more detail. In beds, borders, containers, greenhouses and on the allotment the approach is the same: little and often through the growing season, more attention around transplanting and heat, and nothing to gain from doubling the dose.

Seaweed supplements and seaweed plant food are not the same thing

Seaweed is sold in two quite separate markets, and the search results mix them up. Seaweed supplements for people are a food product, made, regulated and labelled as such. Everything in this collection is a garden input: seaweed plant food for use on plants, soil and turf, packed for the garden and nothing else. It is not for human consumption, and we make no health claims of any kind for it. If you arrived here looking for something to take rather than something to feed a tomato plant, this is not it.

On grass, seaweed is the summer supporting act to the main feed; see Lawn Care.

Common questions