What is the best organic fertiliser high in nitrogen?
A concentrated protein extract is the strongest practical option, at around 13% nitrogen. Milled meals such as alfalfa run at 2 to 3%, seaweed less again, and garden compost well under 1%.
Handcrafted in Stockport
Organic Nitrogen Fertiliser 13% N
13% nitrogen in a granule, low in salt and chloride. 1.5kg from £12.99
Shop Nitrogen 13% NWhy organic nitrogen is usually low
Nitrogen is the hardest of the three main nutrients to concentrate naturally. It arrives bound up in proteins, and a whole milled plant material is mostly not protein, so the figure lands at 2 to 3%. To get higher you have to concentrate the protein fraction, which is what a nitrogen extract is.
That is why a bag of alfalfa and a bag of concentrated extract are not interchangeable: you would need roughly five times the weight of the first to deliver the same nitrogen.
| Source | Nitrogen | Notes |
|---|---|---|
| Concentrated protein extract | About 13% | Roughly half available within a fortnight |
| Alfalfa meal or pellets | 2 to 3% | Slower, and adds organic matter |
| Rapeseed meal | 2 to 3% | Slow release |
| Seaweed meal | Under 2% | Bought for trace elements, not for N |
| Garden compost | Well under 1% | A soil builder, not a nitrogen source |
Figures are for the raw materials. Always feed to the rate on the product page rather than working backwards from a nutrient percentage.
When to use it, and when to stop
High nitrogen suits anything you grow for its leaves: salads, spinach, brassicas, and grass. It also suits the early stage of almost anything, when the plant is building the frame it will later flower on.
Stop pushing nitrogen once flowering begins. Excess nitrogen at that point gives you a large soft plant with little fruit, growth that flops and is attractive to aphids, and in heavy doses on dry soil a scorch risk. Late-season nitrogen is worse again, because it pushes soft growth into the first frosts.
The commonest mistake. Reaching for nitrogen when the plant is pale. Pale leaves are as often waterlogging, drought or root damage as a nitrogen shortage. Check which older leaves are affected first: a genuine nitrogen shortage shows in the oldest leaves, because the plant moves nitrogen to its new growth.
The concentrated option
Organic Nitrogen Fertiliser 13% N
13% nitrogen dried to a clean granule, low in salt and chloride, with about half of it available within a fortnight.
13% N · Half available in a fortnight · Rates published
Shop Nitrogen 13% NMore organic fertiliser questions
What organic fertiliser is high in phosphorus?What is the best organic fertiliser high in potassium?What is 4-4-4 organic fertiliser?Sources
- Royal Horticultural Society. How to feed plants. rhs.org.uk
- Cassity-Duffey, K. et al. (2020). Nitrogen mineralization from organic materials and fertilizers: predicting N release. Soil Science Society of America Journal 84(2), 522–533. doi.org
Soil notes
Get the evidence, not the marketing
Occasional notes from Stockport on feeding, soil structure and what the research actually supports, including the things that turn out not to work.
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