Maxicrop and Envii seaweed alternative

• The lab numbers are on the pack. 19.38% alginic acid, 48.33% organic matter, 17.89% K₂O, 1.20% N and 2.04% P₂O₅. Maxicrop Original states 8% seaweed extract; Envii SeaFeed Xtra states NPK 0.9-0.6-0 and 0.98% iron. Neither gives an alginic acid, organic matter or potash figure.
• How it is made matters. Cheaper extracts are often made with heat and strong alkali, which is quick and high-yield but keeps less of the heat-sensitive growth compounds, cytokinins and auxins among them. Ours is processed without harsh chemicals or heat.
• Less plastic, less weight. One 1 kg pouch makes as much mix as 6 to 7.5 litres of Maxicrop. A liquid seaweed is mostly water, and water is heavy to post.
• Seaweed is a biostimulant, a signal for the plant rather than a main feed. Keep a proper feed going alongside any of them.

Why the lab numbers matter

Most liquid seaweed labels give a dilution rate, perhaps an NPK, and a phrase about trace elements. That tells you very little about how much seaweed you are buying, or how much of what does the work. The potash figure on a liquid can even come from the potassium hydroxide used to make it, so a higher K number does not mean a better product.

Alginic acid is the figure worth comparing. It chelates minerals into forms roots can take up and improves how soil holds together and holds water. Organic matter tells you how much of the product is seaweed rather than filler or water. We print both, from lab analysis, so you can check what you are paying for.

Commercial growers buy seaweed on its analysis, because across a farm the difference shows. Garden bottles tend to sell on the brand and the dilution rate. We print the analysis so you can buy the way a grower would.

How much seaweed is in a litre of mix

Our powder is dried seaweed extract, so 88.97% of what you weigh out is seaweed and the rest is moisture. Envii declares 7% seaweed solids, so most of each millilitre is water. On these figures, a litre of our mix carries roughly four to five times the seaweed of a litre of Envii's.

Our figure takes the powder as 88.97% seaweed, after its 11.03% moisture. Envii's takes 1 ml as about 1 g, at its declared 7% seaweed solids. Maxicrop declares 8% seaweed extract, which is not a solids figure, so we have not converted it.

Why cheaper seaweed often does less

Seaweed does not earn its place through nutrients. The benefit comes from its natural growth compounds, cytokinins and auxins among them, alongside betaines and alginates. Work on Ascophyllum nodosum extract has shown it shifts the plant's own cytokinin and auxin levels, which is where faster rooting and better stress recovery come from (Wally et al. 2013).

Those compounds are sensitive to heat. The quickest and cheapest way to make an extract uses heat and strong alkali, which gives a high yield but keeps less of them. Cold or gentle processing keeps more, but it is slower and yields less, so it costs more to make. A very cheap bottle is often either made the fast way or heavily diluted. Look for a stated seaweed or solids percentage, and work out the cost per litre of mix rather than per bottle.

We go through the extraction methods, and what to look for on a label, in our guide to seaweed fertiliser.

What a litre of mix costs

Rates: powder 1 g per 1.2 to 1.5 litres as a drench; Brix+ 2 to 2.5 ml per litre as a spray; Maxicrop 45 ml per 9 litres; Envii 1 litre to 500 litres. Working: the powder 1 kg makes 1,200 to 1,500 litres; Brix+ 1 litre makes 400 to 500 litres; Maxicrop 1 litre at 5 ml per litre makes 200 litres; Envii 1 litre makes 500 litres. Maxicrop prices for 1 litre from Charlie's (£9.99) and Boma (£16.99), checked 15 Oct 2026. Envii's £12.95 is the price shown on envii.co.uk on 18 Oct 2026, which we have taken as the 1 litre price; we have not priced the 5, 10 or 20 litre sizes. At these prices Envii is the cheapest per litre of mix. Smaller packs of ours cost more per litre: the 500 g powder works out at 3.3p to 4.2p, the 250 g at 4.0p to 5.0p, and the 500 ml Brix+ at 5.2p to 6.5p.

Less plastic, less shipping weight

A liquid seaweed is mostly water. Maxicrop Original declares 8% seaweed extract, so the other nine-tenths of each bottle is water, packed in plastic and carried by van to your door. A powder leaves the water out: you add it from the tap.

Weights for the liquids are approximate, taking a litre of liquid as about a kilo. Larger containers mean fewer bottles, but the water still has to travel.

Side by side

Maxicrop Original figures from the Maxicrop Original factsheet (8% seaweed extract, 45 ml in 9 litres, every 7 to 14 days, via Boston Seeds) and Boma, Charlie's and Long Acres listings (Norwegian Ascophyllum nodosum, prices), checked 15 Oct 2026. Envii SeaFeed Xtra figures from envii.co.uk and the B&Q listing (Irish Ascophyllum nodosum, 7% seaweed solids, 0.98% iron, plant-based amino acids, seaweed and vinasse, NPK 0.9-0.6-0, 1 litre makes 500 litres, lawn rate, 1 to 20 litre sizes, reapply every 7 days, £12.95 taken as the 1 litre price), checked 18 Oct 2026. Dr Forest figures from the live product pages. Prices and formulations change, so check the pack in front of you. Maxicrop is a trademark of its owner. Envii and SeaFeed Xtra are trademarks of their owner. Dr Forest is not affiliated with either.

What changes if you switch to powder

• Numbers you can check. Alginic acid, organic matter and potash, from lab analysis, on the pack.
• Grams, not bottles. 0.67 to 0.83 g of powder makes a litre of mix, where the liquids need 5 ml (Maxicrop) or 2 ml (Envii). One pouch in place of several plastic bottles, and a fraction of the weight in the post.
• You set the strength. Drench at 1 g per 1.2 to 1.5 litres every 2 weeks, or spray at 1 g per 1.5 to 2 litres. It dissolves fully in cold water.
• Keeps for years. Sealed and dry, the powder stores for years.
• Where we fall short. Ours is posted rather than on the garden centre shelf, you have to weigh it, and Envii costs less per litre of mix at the price we found.

Which one should you pick?

• You want the most seaweed in the least weight and packaging: the soluble powder. Dissolves in cold water in seconds, no sediment, keeps for years sealed and dry. Weigh it: 1 g is about half a level teaspoon.
• You want to keep the same liquid routine: Brix+. It is more than a seaweed extract: alongside the kelp it carries triacontanol and other growth promoters. Spray at 2 to 2.5 ml per litre every 10 to 14 days, or drench at 5 to 12.5 ml per litre every 4 weeks. Little and often beats a strong mix.
• You want better soil rather than another spray: Scottish kelp meal. Beds at 50 to 100 g per m², potting mixes at 5 to 10 ml per litre, lawns at 50 to 75 g per m².
• You want the full biostimulant kit: the Seaweed, Humic & Fulvic Trio puts Brix+ with humic and fulvic acids, from £29.95.

When to stay with Maxicrop or Envii

• You want the lowest cost per litre of mix. At £12.95 a litre and 1 litre to 500 litres, Envii works out at about 2.6p per litre of mix, less than any of ours at the prices we found.
• You need it today. Maxicrop is on many garden centre shelves and Envii is on Amazon. Ours is posted.
• You prefer pouring a liquid. Measuring from a bottle is quicker than weighing a powder. If you want to stay with a liquid but try ours, that is Brix+, which adds triacontanol and other growth promoters to the seaweed.
• You want something added in one bottle. Envii adds iron and plant-based amino acids, and some Maxicrop variants add nutrients. With us that would be two products.
• You know it works for you. If you have used either for years and you are happy, there is no need to switch.

Common questions

Is Dr Forest seaweed powder the same as Envii SeaFeed Xtra?

No. Both start from Ascophyllum nodosum, but SeaFeed Xtra is a liquid harvested in Ireland, with 7% seaweed solids, 0.98% iron and plant-based amino acids, made from seaweed and vinasse and used at about 2 ml per litre. Ours is a single-ingredient soluble powder with a lab analysis of 19.38% alginic acid, 48.33% organic matter and 17.89% K₂O on the pack, used at 1 g per 1.2 to 1.5 litres.

Why do the lab numbers matter?

They tell you what you are buying. A dilution rate or a small NPK says little about how much seaweed is in the product or how much of the active material. Alginic acid and organic matter do. Maxicrop Original states 8% seaweed extract and Envii states an NPK and iron, but neither gives an alginic acid or organic matter figure.

Why are some seaweed products so much cheaper?

Mostly how they are made. Extraction with heat and strong alkali is quick and high-yield, but keeps less of the heat-sensitive growth compounds, such as cytokinins and auxins, that give seaweed its effect. Gentler processing keeps more and costs more. A very cheap bottle may also be heavily diluted. Compare the seaweed or solids percentage and the cost per litre of mix.

Why a powder rather than a liquid?

Weight and packaging, mainly. A liquid seaweed is mostly water, so you pay to post water in plastic bottles. 1 kg of powder makes as much mix as 6 to 7.5 litres of Maxicrop, in one pouch. Sealed and dry, it keeps for years, and because you weigh it you set the strength. The trade-off is that a liquid is quicker to measure.

Is powder or liquid seaweed better value?

On our products, the powder goes further: under a gram makes a litre of drench, about 3.2p to 4.0p per litre from the 1 kg pack. Brix+ works out at 4.2p to 5.2p per litre of spray. Across brands, Envii SeaFeed Xtra is cheapest at about 2.6p per litre at the price we found, and Maxicrop Original is 5.0p to 8.5p.

Can I use seaweed instead of a tomato feed?

No. Seaweed is a biostimulant, and neither the powder nor Brix+ will replace a dedicated feed at garden rates. Use a potash-led tomato feed for the fruit and seaweed alongside it.

Can I use seaweed powder and kelp meal together?

Yes. They do different jobs. Put the kelp meal in the soil at planting and use the powder or liquid in the can through the season.

Is seaweed safe around pets and children?

Store any concentrate sealed and out of reach. Let sprayed foliage dry before children or pets go back on the lawn, and water kelp meal in rather than leaving it on the surface for a curious dog.

Reference: 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.

More: all brand alternatives · Maxicrop tomato feed · seaweed fertiliser guide · Gaia Green · BioBizz

Written by Joe Barrington, Dr Forest, Stockport. Maxicrop figures checked 15 Oct 2026; Envii figures checked 18 Oct 2026.