A Look at Liquid Seaweed

Putting Seaweed Extract Feeds to the Test

Written by Daniel Woodley. Reviewed by Elizabeth Smith. Published to Products on 18th March 2023.

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Seaweed extract garden fertiliser has emerged as a highly effective, environmentally responsible alternative for plant nourishment within the United Kingdom’s horticultural sector.

This organic product, obtained from sustainably sourced seaweed, offers an array of benefits for gardeners seeking to optimise plant growth while minimising ecological impact.

I’ve been using Seafeed Xtra by Envii for several years and in 2020, I used it exclusively on my lawn and in my hanging baskets as part of a test.

This is my review of Seafeed Xtra and seaweed fertilisers in general.

envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L
envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L
envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L
envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L

Features/ Specifications 

Here are the key specs for Seafeed Xtra by Envii:

Pack Sizes: 1ltr, 5ltr, 10ltr and 20ltr bottles.

NPK: 0.9 0.6 0 plus added iron and plant-based amino acids sourced from sugar cane. (I must point out that there are many benefits beyond NPK)

Organic: Yes, certified.

Vegan Friendly: Yes, none of the ingredients come from animal sources.

Seaweed Content: 5% solids.

Shelf Life: 12 months.

Suggested Doses: Between 10ml and 25ml every 5-14 days for most vegetables, trees shrubs and plants. 10ml every 28 days for lawns.

Marketing Claims: “Harvested from UK waters” “In addition to these nutrients, seaweed also transfers anti-stress compounds to plants having produced them during growth at sea.”

My Experience With Liquid Seaweed Extract in 2020 and Since Then

Seaweed Lawn Feed

I used this lawn feed exclusively on my lawn throughout 2020 when no other fertiliser touched my grass.

Here are the key points:

  • I found it easy to dose the product as the 1ltr bottle comes with a measuring chamber at the neck (see photo above), and this was very precise and any excess liquid was drawn back into the bottle. This chamber also meant I didn’t spill any of the product, not even once.
  • The liquid seaweed mixed well with water and didn’t clog my watering can.
  • It didn’t smell unpleasant at all, unlike many other “organic” feeds I’ve tested over the years.

I didn’t use any other fertilisers on my lawn for the entire year. Here are a few photos:

Our lawn
Closeup of our lawn
Shaded lawn

Even though my lawn is in a shaded garden and the growing conditions are far from optimal, I was pleased with the results.

While liquid seaweed doesn’t have the highest concentration of NPK, it was obviously doing plenty of good for my lawn, as you can see from the photos above.

As part of my test, I also used it exclusively in several hanging baskets:

Flowers in a hanging basket
Petunias of several colours in a hanging basket

The hanging basket plants (petunias) responded well to the liquid seaweed and I didn’t experience any issues.

Most notably:

  • The liquid seaweed didn’t stain the patio under the hanging baskets.
  • None of the plants showed any signs of stunted growth, chlorosis or any other problems.
  • I felt the liquid seaweed feed went a long way, and the 1ltr bottle was enough for my small garden for the entire year.
envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L
envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L
envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L
envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L

What I Liked

  • Organic and vegan friendly.
  • Chemical free.
  • It didn’t clog the watering can or leave chemicals, sludge or pellets on the lawn (I have a dog, so I dislike slow-release fertilisers).
  • Choice of bottle sizes.
  • I liked the accurate measuring chamber in the 1 litre bottle.
  • The manufacturer (and others) claim that hormones produced by seaweed benefit and strengthen plants and grass.

What I Disliked

  • The larger 5-ltr, 10-ltr and 20-ltr bottles don’t have a measuring chamber, so it isn’t easy to get exactly the right amount of lawn feed from them.
  • The ratio of NPK (that’s Nitrogen, Phosphorous and Potassium) is very low, hence why it should be used as a supplement, rather than a replacement.
  • I found it a little weak compared to some of the chemical-laden alternatives out there, and I had to apply it more frequently to get the results; this could be an issue for the busy gardener with a very large garden.

Who Will Benefit The Most From Liquid Seaweed Feed

Liquid seaweeds aren’t the most powerful feeds in the world, and their NPK ratios are less favourable than chemical-laden alternatives, but well-known gardeners such as Monty Don and Alan Titchmarsh have publicly endorsed them and have highlighted the ecological benefits.

Based on my test and experience with Seafeed Xtra, I think it’s best suited to:

  • Those who value eco credentials.
  • Anyone who hates measuring out fertilisers (the 1 ltr bottle comes with a measuring chamber).
  • Those who value organic, vegan-friendly or safer products.
  • Those who value the other ingredients in the product (see the FAQs section below for a full list).

Advice

Despite having tested liquid seaweed exclusively on my lawn and hanging baskets for an entire year, I don’t recommend it as an alternative to a general fertiliser.

The NPK ratios are too weak and while it will be fine for a year, I think in the long term, gardeners should use something stronger as a base fertiliser and then use liquid seaweed as a supplement.

There are many benefits of seaweed extracts but they aren’t a replacement for fertilisers with higher NPK ratios.

Moving forward, I think I’ll try using fish, blood and bone as a base feed and then liquid seaweed as a supplement.

Alternatives

If you’re thinking about using Seafeed Xtra by Envii for its ecological benefits, consider these alternatives:

Alga-Sol: Stronger NPK ratios and comes in a 5-litre bottle with a standard screw cap.

MaxiCrop: Also stronger NPK, and comes in several bottle sizes, but after conducting independent research, I found that some buyers have complained about the cap leaking.

Maxicrop seaweed feed

I’ve also used Maxicrop – Buy on Amazon

Looking beyond liquid seaweed feeds, there are other garden feeds worth considering:

Blood, Fish and Bone: I’ve been using this for the last two years, and while it’s not vegan-friendly, it is organic and the granular powder goes a long in my garden. I also like the large 10kg tubs that last all year. See what I think of fish blood a bone here.

Also consider worm castings, chicken manure or bonemeal as alternatives, as they have some eco-credentials.

envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L
envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L
envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L
envii SeaFeed Xtra – Organic Liquid Seaweed Fertiliser - Multipurpose Outdoor & Indoor House Plant Food - 1 Litre Makes up to 500L

Liquid Seaweed FAQs:

What's in seaweed extract?

I’ve looked at several manufacturers and this is what I found:

Macronutrients: While not as concentrated as synthetic fertilisers, liquid seaweed feed contains essential macronutrients such as nitrogen (N), phosphorus (P), and potassium (K) that support plant growth, flowering, and fruit production.

Micronutrients: The solution provides trace elements like calcium, magnesium, sulfur, iron, manganese, copper, zinc, and boron, which are required in small amounts for various physiological functions in plants.

Vitamins: Liquid seaweed feed contains vitamins such as A, B1, B2, B3, B5, B6, B12, C, E, and K, which promote metabolic processes and overall plant health.

Plant hormones: Seaweed extract contains natural plant growth regulators like cytokinins, auxins, and gibberellins, which stimulate cell division, root growth, and overall plant development.

Amino acids: Seaweed extract provides a source of amino acids, which can be directly absorbed by plants, enhancing protein synthesis and supporting various growth processes.

Alginates and mannitol: These compounds can improve soil structure, water retention, and microbial activity, leading to healthier root systems and increased nutrient availability.

Bioactive compounds: Seaweed extract contains various bioactive compounds, such as phenolic compounds and polysaccharides, which can contribute to enhanced stress tolerance, pest resistance, and disease suppression in plants.

What is liquid seaweed feed?

Liquid seaweed feed, also known as seaweed extract fertiliser, is a nutrient-rich solution derived from sustainably harvested seaweed. It is an organic, eco-friendly alternative to synthetic fertilisers and provides a range of essential nutrients and growth-promoting compounds to support plant health and development.

How is liquid seaweed feed made?

Liquid seaweed feed is produced through processes such as cold pressing, enzymatic digestion, or alkaline hydrolysis, which extract the bioactive compounds and nutrients present in seaweed while preserving their beneficial properties.

Can liquid seaweed feed be used on all types of plants, including vegetables, flowers, and fruit trees?

Yes, liquid seaweed feed is versatile and can be used on a wide range of plants, including vegetables, flowers, fruit trees, and ornamentals.

What are the benefits of using liquid seaweed feed for my plants and garden?

Liquid seaweed feed offers numerous benefits, including improved plant growth, enhanced stress tolerance, better pest and disease resistance, and increased soil fertility and structure.

How do I apply liquid seaweed feed to my plants?

Liquid seaweed feed can be applied as a foliar spray, soil drench, or root soak, depending on your garden’s specific needs and the manufacturer’s recommendations.

Can I use liquid seaweed feed alongside other fertilisers or soil amendments?

Yes, liquid seaweed feed can be used in conjunction with other organic or synthetic fertilisers and soil amendments, as it complements their nutrient profiles and can enhance their overall effectiveness. However, it is important to monitor nutrient levels to avoid over-fertilisation.

Meet The Author: Daniel Woodley

Daniel has over 18 years of experience in the construction, home improvement, and landscape garden industries.

He previously worked as a project manager and has experience in managing teams of tradespeople and landscape gardeners on both small and medium sized projects.

Daniel is also a keen gardener and enjoys growing unusual plants and tending to his lawn.

More About Daniel Woodley.

Daniel Woodley

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1) We select a topic that we feel will help our readers.

2) The author creates the content based on their knowledge and experience of the subject. In this case, Daniel Woodley tested liquid extract feed over the course of an entire year on a lawn and in hanging baskets.

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This guide was reviewed and fact-checked by Elizabeth Smith, who is a qualified horticulturist.

Explore: Elizabeth’s profile and qualifications.

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