High nitrogen fertiliser: what it does, and when to use it
Plant nutrition
High nitrogen fertiliser: what it does, and when to use it
By Joe, Founder of Dr Forest · June 2026
A high nitrogen fertiliser is the right tool for one job: leafy, green growth. Knowing when that job is on, and when it is over, matters more than the number on the bag.
A high nitrogen fertiliser is any feed whose first NPK figure is well ahead of the other two, so it supplies far more nitrogen than phosphorus or potassium. Nitrogen is what plants build leaves, stems and chlorophyll from, so a feed weighted towards it pushes fast, green, leafy growth. That makes it the feed for leafy vegetables, brassicas, lawns and hungry crops early in the season, and the feed to put away once a plant turns its attention to flowers and fruit.
Our Nitrogen Extract supplies 13% nitrogen as amino acids and proteins, the building blocks plants assemble into leaves, stems and chlorophyll, drawn from fermented plant material and dried into a clean granule. It is plant-based, certified organic by two of the UK's leading certification bodies, and made in the UK. The form matters as much as the quantity, and that is most of what this guide is about.
In short
Use a high nitrogen feed for the leaf-and-stem stage: leafy greens, brassicas, sweetcorn, lawns, and any plant showing pale lower leaves. Stop once a crop sets buds, or you trade flowers and fruit for soft, sappy growth that flops and draws aphids.
Because the nitrogen is already in the form plants build their tissue from, the plant takes up these amino acids and puts them straight to work, greening growth quickly. The rest stays held in protein until soil biology releases it, so far less leaches away and there is little risk of scorch.
Figure 1 · How the nitrogen releases
Half feeds the plant now, half feeds it over the next six weeks
Cumulative nitrogen release from Nitrogen Extract: a fast green-up early on, then a slow tail as soil biology breaks the protein down.
What is a high nitrogen fertiliser?
Fertilisers are labelled with three numbers, the NPK ratio: nitrogen, phosphorus, potassium. A high nitrogen fertiliser is one where that first number dominates. A balanced feed might read 6-6-6; a high nitrogen feed reads more like 13-0-0 or 12-3-4. The bigger the gap between the nitrogen figure and the other two, the more the feed is built for leaf and stem rather than root, flower or fruit.
You will also see the same thing sold as a nitrogen rich fertiliser, a high nitrogen plant food, or a natural nitrogen feed for plants. The labels vary; what matters is that first number sitting well ahead of the other two.
Nitrogen is the nutrient plants need in the largest amount during growth. It is the backbone of amino acids and proteins, of chlorophyll, and of the enzymes that run photosynthesis. Short of it, a plant cannot build new green tissue, so growth stalls and older leaves go pale. Give a hungry, leafy plant nitrogen and the response is quick and obvious: deeper colour, bigger leaves, faster growth.
What counts as "high" is relative. Among organic feeds, anything above roughly 10% nitrogen sits at the top end. Our Nitrogen Extract is 13% N, which is about as high as organic nitrogen gets in the UK; blood meal, the usual organic benchmark, sits around the same 12 to 13%. Synthetic straights such as ammonium nitrate or urea run higher still, but as the rest of this guide explains, the form that nitrogen comes in changes how it behaves in your soil and what it costs you in waste and risk. For the wider picture of how feeds are put together, our guide to what a fertiliser actually is sets out the basics.
When your plants actually need nitrogen
Nitrogen demand is not steady through a plant's life. It runs high while a plant is building leaves and stems, then drops away as the plant shifts energy into flowering and fruiting. Feed with the curve and you get strong, productive plants. Feed against it and you waste fertiliser, or worse, push growth at the wrong time.
Figure 2 · Nitrogen demand through the season
Demand peaks in the leafy stage, then falls away at flowering
A rough shape, not a measured curve. The point is the timing: feed nitrogen early, ease off once buds form.
The jobs a high nitrogen feed is built for:
- Leafy vegetables and brassicas. Lettuce, spinach, chard, cabbage, kale and sprouts are grown for their foliage, so available nitrogen turns straight into bigger, deeper-green leaves.
- Spring green-up and stalled plants. A targeted boost for anything that has paled or sat still early in the season, before it turns to flower or fruit.
- Lawns. Nitrogen drives the green colour and dense growth a lawn is judged on. A slow-release tail keeps it fed for weeks rather than greening up and crashing.
- Hungry mid-season feeders. Sweetcorn, courgettes, squash and pumpkins draw heavily on nitrogen through their main growth phase.
- Correcting a deficiency. Pale lower leaves, slow growth and weak stems are classic nitrogen hunger, and a high nitrogen feed addresses them directly.
How to spot nitrogen hunger
Nitrogen moves around inside a plant. When supply runs short, the plant pulls nitrogen out of its old leaves to feed the new ones, so hunger always shows in the oldest, lowest leaves first. They turn pale, then yellow, evenly across the leaf, while the newest growth at the top stays greener. Growth slows and stems thin. If the yellowing is on new top growth instead, or it is patchy between the veins, the cause is usually something else, and our guide to yellowing tomato leaves walks through how to tell them apart.
Figure 3 · Reading the symptom
Nitrogen hunger starts at the bottom of the plant
Because nitrogen is moved from old growth to new, the lowest leaves pale and yellow first while the top stays green.
When to hold off
More nitrogen is not better. Once a plant has its leafy framework and starts setting buds, heavy nitrogen works against you. It pushes soft, sappy growth that flops in wind and rain, attracts aphids, and delays or suppresses flowering and fruiting. On a tomato, a late nitrogen feed buys you a forest of leaves and a thin crop.
So ease off nitrogen at these points:
- At first flower on fruiting crops. Tomatoes, peppers, chillies, aubergines, beans and peas need nitrogen only to build their early leaf framework. Once they set flower, switch to a high-potash feed.
- Late in the season. Feeding nitrogen into late summer pushes soft growth that will not harden before autumn. On lawns, stop nitrogen by late summer.
- On anything grown for its flowers, after the spring nudge. Roses and flowering shrubs take a single spring application for early foliage, then a balanced or high-potash feed for the flush.
This is the whole reason the timing matters more than the number on the bag. A high nitrogen feed used in the leafy stage and then put away does exactly what you want. The same feed used right through fruiting does the opposite. When a crop turns the corner into flower, our high-potash Bloom 2-4-8 takes over the job.
Organic vs synthetic nitrogen, and why the form matters
Two feeds can carry the same nitrogen figure on the label and behave nothing alike. A synthetic straight such as ammonium nitrate or urea is a soluble salt: it floods the root zone fast, but nitrate leaches readily into groundwater and urea can gas off into the air as ammonia, both well-documented loss pathways (Cameron, Di & Moir, 2013). It feeds the plant and nothing else, adding no carbon and no food for soil life, and it is not permitted in organic growing.
Plant amino-acid nitrogen works differently. The old textbook view was that plants take up nitrogen only as nitrate or ammonium, and that organic nitrogen has to be broken down into those minerals first. That view is out of date. Plants take up intact amino acids and small peptides directly through their roots, and in many soils organic nitrogen is a real part of what they use (Näsholm et al., 1998; Näsholm, Kielland & Ganeteg, 2009). Amino acids are the building blocks of protein, so a plant can build new tissue from them straight away. Mineral nitrogen takes the long way round: a plant fed nitrate has to spend energy reducing it and assembling it into amino acids before it can grow on it. Supply those amino acids ready-made and the plant skips that step. In a protein-bound feed, some nitrogen is taken up directly and the rest is released by soil microbes at a measured pace, so less leaches away between feeds and the carbon in the granule feeds the biology that cycles nutrients.
Among organic feeds, blood meal is the usual high nitrogen benchmark, at a similar 12 to 13% nitrogen. The difference is the form. Blood meal is whole protein, so soil microbes have to break it down before a plant can use any of it, and it releases in a fast, aggressive flush with a strong smell that can draw cats and foxes to dig. Our amino-acid nitrogen is already part-broken into the building blocks plants use, so some is taken up directly and the rest releases at a measured pace, with little odour.
Figure 4 · Same nitrogen, different behaviour
Plant amino-acid nitrogen against blood meal
Both are organic and high in nitrogen. What the plant has to do to use them is where they differ.
| Criterion | Amino-acid N (Nitrogen Extract) | Blood meal (another organic feed) |
|---|---|---|
| Form of nitrogen | Amino acids and proteins, ready to use | Whole protein, must be broken down first |
| Release | Fast start, then a slow tail over weeks | A fast, aggressive flush as it breaks down |
| What the plant does with it | Builds new tissue from it directly | Waits for microbes to release the nitrogen |
| Release control | Measured pace; little to leach between feeds | Released in one flush once it breaks down |
| Salt index, scorch risk | Low | Low, but the flush can be strong |
| Smell and wildlife | Little odour | Strong smell; can draw cats and foxes |
The form your nitrogen comes in decides what happens to the half you do not use that fortnight.
If you want a gentler, lower-strength plant nitrogen that cannot scorch, alfalfa is the classic choice. It releases slowly enough to be safe around seedlings, and carries a natural growth stimulant alongside its nitrogen. Our alfalfa meal pellets sit at 2.5-0.3-2, so they are a soil-building nitrogen feed rather than a hard push. The fuller story on amino-acid feeds is in our piece on amino acid biostimulants.
How much high nitrogen fertiliser to use
A 13% nitrogen feed is concentrated, so it goes on at much lower rates than a balanced blend or a soil conditioner. Scatter the granules evenly, keep them off leaves, stems and crowns, and water in well. Apply to moist soil during active growth, and feed little and often rather than one heavy dose. One application feeds for around six weeks, so do not reapply more often than every five to six weeks. The rates below are for Nitrogen Extract.
| Use | Rate | Frequency |
|---|---|---|
|
Base dressing before sowing or planting |
30–50 g/m² | Once, at bed prep |
|
Heavy leafy feeders brassicas, leeks, sweetcorn, squash |
40–55 g/m² | Every 5–6 weeks in growth |
|
Salad and moderate crops lettuce, beetroot tops, leafy herbs |
25–40 g/m² | Every 5–6 weeks |
| Established lawns | 25–40 g/m² | Spring to mid-summer, 1–2 times |
| New lawns / overseeding | 30–40 / 20–30 g/m² | Once, at sowing |
|
Fruiting crops tomatoes, peppers, beans, early only |
20–30 g/m² | Once or twice, before flower |
| Roses, flowering shrubs | 20–30 g/m² | Once, in spring |
| Pots and containers | 2–4 g/L of compost | At potting, or a light top-up every 6 weeks |
Rates for Dr Forest Nitrogen Extract (13% N). A rounded handful is roughly 30–40 g; a level tablespoon about 15–20 g. On light, sandy soils, split the feeds and keep to the lower end.
Once leafy growth is strong and well coloured, stop the nitrogen and move to a balanced or high-potash feed for the rest of the season. For most of the garden a balanced feed such as our All-Purpose 6-6-6 covers the job from there; for fruiting and flowering, switch to the high-potash Bloom. Even with a low salt index, too much nitrogen is the one mistake worth guarding against, so weigh the first few applications until you have your eye in.
From the Dr Forest range
High nitrogen feeds, for the leafy stage
Premium organic fertilisers, multi-input and made with organic ingredients, made in the UK.
- Nitrogen Extract, 13% NOur highest-nitrogen plant feed. Fast green-up, slow tail, very low salt.
- Alfalfa Meal Pellets, 2.5-0.3-2A gentle, seedling-safe slow-release nitrogen with a natural growth stimulant.
- All-Purpose 6-6-6The balanced feed to move to once leafy growth is established.
- Bloom 2-4-8High-potash feed for the flowering and fruiting stage.
Not sure where to start? Read what a fertiliser actually is for the groundwork.
Treat nitrogen as the feed for the first half of a plant's job. Leaves and stems early on, a quick green push, then put it away when the buds appear and let potassium and calcium carry the flowers and fruit. Get the timing right and a high nitrogen feed earns its place; get it wrong and you grow a lot of leaf and not much else.
Frequently asked questions
What is the best high nitrogen fertiliser?
For garden use, the best high nitrogen fertiliser is one that greens plants up quickly without leaching away or scorching, and that feeds the soil as well as the plant. Plant amino-acid feeds such as our Nitrogen Extract do that: at 13% nitrogen they are among the higher-nitrogen organic feeds available, and the protein-bound form releases fast then slow rather than all at once. Synthetic straights carry more nitrogen but leach readily and add nothing to the soil.
What is a natural or organic high nitrogen fertiliser?
Common natural high nitrogen sources are amino-acid extracts, alfalfa and seaweed, alongside animal meals such as blood meal, hoof and horn. Our Nitrogen Extract supplies 13% nitrogen as amino acids and proteins, certified organic, with a fast-then-slow release rather than a single flush.
When should I use a high nitrogen feed?
Use it during the leaf-and-stem stage of growth: on leafy vegetables and brassicas, on hungry crops such as sweetcorn and courgettes, on lawns through spring and early summer, and on any plant showing pale lower leaves. Ease off once a crop sets buds, because too much nitrogen at that point pushes leaves at the expense of flowers and fruit.
What are the signs of nitrogen deficiency?
The classic signs are pale or yellowing lower leaves, slow or stunted growth, and thin, weak stems. Nitrogen moves around inside the plant, so hunger shows in the oldest leaves first while new top growth stays greener. A high nitrogen feed corrects it: about half the nitrogen is available within a fortnight for a quick green-up, with the rest released over the following weeks.
Can too much nitrogen harm plants?
Yes. Too much nitrogen drives soft, sappy growth that flops, attracts aphids and resists flowering and fruiting, and very heavy doses on dry soil can scorch. A feed with a low salt index is gentler than a synthetic salt, but it is still a concentrated feed, so stick to the stated rates, keep granules off foliage, and water in.
Is a high nitrogen fertiliser good for lawns?
Yes. Nitrogen drives the green colour and dense growth a lawn is judged on. A slow-release feed greens the lawn up from the fast fraction and then keeps it fed for weeks from the slow tail, rather than a single flush and crash. Feed from spring to mid-summer at 25–40 g/m², and stop feeding nitrogen by late summer so you are not pushing soft growth into autumn.
Is a high nitrogen fertiliser good for tomatoes?
Only early on. Tomatoes need nitrogen to build their leaf framework before they flower, so a light feed during vegetative growth helps. Once the first truss sets, stop the nitrogen and switch to a high-potash feed, or you get lush foliage and a poor crop. This is also why a shop tomato feed such as Tomorite is deliberately low in nitrogen and high in potash: it is built for the fruiting stage, not the leafy one.
How is this amino acid feed different from blood meal?
Both are organic and high in nitrogen, but the form differs. Blood meal is whole protein that soil microbes must break down before the plant can use it, so it releases in a fast, aggressive flush and carries a strong smell that can draw cats and foxes. Amino-acid nitrogen is already part-broken into the building blocks plants use, so some is taken up directly, the rest releases steadily, and there is little odour.
Sources cited
- Näsholm, T., Ekblad, A., Nordin, A., Giesler, R., Högberg, M. & Högberg, P. (1998). Boreal forest plants take up organic nitrogen. Nature, 392, 914–916.
- Näsholm, T., Kielland, K. & Ganeteg, U. (2009). Uptake of organic nitrogen by plants. New Phytologist, 182, 31–48.
- Cameron, K.C., Di, H.J. & Moir, J.L. (2013). Nitrogen losses from the soil/plant system: a review. Annals of Applied Biology, 162(2), 145–173.