High nitrogen lawn feed: when grass needs it, and when to stop
Lawn care
High nitrogen lawn feed: when grass needs it, and when to stop
By Joe, Founder of Dr Forest · June 2026
A high nitrogen lawn feed pushes the dense, deep-green growth a lawn is judged on. The skill is feeding hard while the grass is growing, then easing off before autumn.
A high nitrogen lawn feed is a grass fertiliser weighted heavily towards nitrogen, the first number in the NPK ratio and the nutrient grass needs in the largest amount. Nitrogen builds leaf blades and chlorophyll, so a feed weighted towards it gives a lawn thicker growth and a stronger colour. You will see the same thing sold as a high nitrogen lawn fertiliser, nitrogen for lawns, or a high nitrogen feed for grass. They all mean a feed with that first number sitting well ahead of the other two.
Most lawn feeds draw their nitrogen from synthetic salts. Our Nitrogen Fertiliser supplies 13% nitrogen as plant amino acids and proteins, the building blocks plants assemble into leaves and chlorophyll, drawn from fermented plant sugars and dried into a granule. It is plant-based, certified organic, and made in the UK. On a lawn the form matters as much as the figure on the bag: a granular, slow-release nitrogen greens the grass without the flush and scorch a soluble salt can cause. For the wider picture of how high nitrogen feeds work across the garden, our guide to high nitrogen fertiliser covers the rest.
In short
Feed a high nitrogen lawn feed from spring to mid or late summer, while the grass is actively growing, at 25 to 40 g/m². Ease off by late summer and switch to potassium for autumn, so you are not pushing soft growth into the cold.
Plant amino-acid nitrogen greens a lawn about as fast as a salt feed, but it leaches less and carries little scorch risk, which suits an organic or no-dig lawn.
What a high nitrogen lawn feed actually does
Grass is grown for its leaves, and a leaf is mostly the tissue nitrogen builds: protein, chlorophyll, the machinery of photosynthesis. Give a lawn nitrogen and it answers quickly, with deeper colour and denser growth. Starve it and the grass pales to a yellow-green, thins out, and starts losing ground to moss and weeds that cope better with poor soil.
Lawns are hungrier for nitrogen than most of the garden for one simple reason: you cut them. Every time you mow and collect the clippings, you carry nitrogen off the lawn, so it needs replacing more often than a border that is left to stand. Leave the clippings to break down where they fall and you return some of that nitrogen, which is why a mulching mower lets you feed a little less. The numbers on a fertiliser bag, and what they mean, are covered in our guide to what a fertiliser is.
When to feed: the UK lawn calendar
Nitrogen feeding follows the growing season. Grass wakes up in spring, races through early summer, and slows as the light fades. Feed with that curve and the lawn stays thick and green through the season. Feed against it, late into autumn, and you push soft growth that will not harden before the cold.
Figure 1 · The UK lawn feeding year
Nitrogen through spring and summer, potassium in autumn
A rough shape of the feeding year, not a measured curve. Feed nitrogen while the grass is growing hard, then switch to potassium to harden it for winter.
Spring is the first feed, once the grass is growing and you have mown a couple of times. Through late spring and early summer the lawn is working hardest, so a slow-release feed once or twice carries it across the peak. From late summer, ease the nitrogen off. In autumn the job changes: instead of pushing leaf, you want to harden the grass and strengthen its roots for winter. That hardening runs on potassium, so the autumn feed is sulphate of potash, at around 50% potash, rather than nitrogen. A seaweed feed earns a place alongside it too, though not as a source of potassium, since it carries almost none. Its value here is as a biostimulant that supports root development and cold tolerance, which our seaweed guide explains.
How much to use, and how to apply it
These are the rates for Nitrogen Fertiliser on grass. A rounded handful is roughly 30 to 40 g; a level tablespoon about 15 to 20 g. Scatter it evenly, then water it in so it reaches the roots rather than sitting on the blades.
| Lawn situation | Rate | When |
|---|---|---|
| Established lawn | 25–40 g/m² | Once or twice, spring to mid-summer |
| New lawn, before seeding | 30–40 g/m² | Worked into the surface at preparation |
| Overseeding or patch repair | 20–30 g/m² | With the seed, spring or early autumn |
Rates for Dr Forest Nitrogen Fertiliser (13% N). Keep to the lower end on light, sandy soils and split the feed. Do not feed grass that is drought-stressed, frozen, or in full summer drought.
Even spreading matters more on a lawn than anywhere else in the garden, because uneven feeding shows as dark and pale stripes for weeks. On a larger lawn, split the dose in half and walk it in two directions at right angles. Water in afterwards if rain is not due. For the wider technique of feeding a surface you cannot dig in, our guide on how to top dress applies directly to lawns.
Organic against synthetic nitrogen for grass, and why the form matters
Two feeds can both read as high nitrogen and behave very differently on a lawn. A soluble synthetic salt, such as the ammonium nitrate or urea behind many quick lawn greeners, dissolves at once. The grass greens within days, but the colour can crash as fast as it came, the salt can scorch the lawn if you over-apply or feed in heat, and a good share washes straight through turf into drainage before the grass can use it.
Plant amino-acid nitrogen behaves differently. Grasses can take up some nitrogen as intact amino acids rather than waiting for it all to convert to nitrate, a route shown across a range of plants in the research on organic nitrogen uptake.1,2 The rest is held in protein form and released as soil organisms break it down, so the colour comes on steadily and holds, rather than spiking and fading. Because less of it sits in the soil as loose nitrate at any moment, less leaches away, a well-documented loss pathway for nitrogen applied to turf.3 For a lawn run on living-soil or no-dig lines, that steadier, lower-loss feed is the better fit.
| On a lawn | Plant amino-acid nitrogen | Soluble synthetic salt |
|---|---|---|
| Green-up speed | Fast | Fast |
| How long it lasts | Weeks, steady | Short, then fades |
| Scorch risk | Low | Higher |
| Leaching loss3 | Lower | Higher |
| Feeds soil life | Yes | No |
Qualitative comparison. Loss and uptake behaviour drawn from the sources listed below; speed and longevity reflect how each form releases.
Gentler options, and the autumn switch
A 13% feed is the strong end. If you would rather feed lightly, or you are nervous about scorch on a fine lawn, alfalfa meal is a milder, slower choice. At an NPK around 2.5-0.3-2 it greens a lawn gently and adds organic matter as it breaks down, and it carries a natural plant growth substance, triacontanol, that supports growth. Our piece on alfalfa meal goes into the detail.
Once a lawn is thick and established, you may not need a dedicated high nitrogen feed every year. A balanced feed such as our All-Purpose 6-6-6 keeps a settled lawn ticking over through the season. Save the high nitrogen feed for spring, for a tired or hard-worn lawn, and for getting new grass established. Then, as covered above, drop the nitrogen in autumn and feed potassium to set the lawn up for winter.
From the Dr Forest range
Feeding a greener lawn
- Nitrogen Fertiliser, 13% NThe high nitrogen lawn feed: plant amino-acid nitrogen, slow-release, low scorch risk.
- Alfalfa Meal PelletsA gentler, slower feed for fine lawns and light spring tonics.
- Sulphate of Potash, 50% potashFor the autumn switch: the potassium feed that hardens grass for winter, when nitrogen would do harm.
Certified organic nitrogen, made in the UK. For the full picture, see the high nitrogen fertiliser guide.
Frequently asked questions
What is the best high nitrogen lawn feed?
The best high nitrogen lawn feed is one that greens the grass without scorching it or leaching away. A slow-release feed scores on both. Our Nitrogen Fertiliser supplies 13% nitrogen as plant amino acids, which release steadily as soil life breaks them down, so the lawn holds its colour for weeks rather than flushing and fading.
Is a high nitrogen fertiliser good for grass?
Yes, while the grass is growing. Nitrogen drives the leaf growth, density and colour a lawn is judged on, so a high nitrogen feed from spring to mid-summer keeps it thick and green. Ease off by late summer, because nitrogen fed too late pushes soft growth that will not harden before winter.
When should I apply high nitrogen lawn feed?
From spring, once the grass is growing and you have mown a couple of times, through to mid or late summer. That is the window when the lawn can actually use the nitrogen. A spring feed and one more across early summer is enough for most lawns with a slow-release feed.
How often should I feed my lawn nitrogen?
With a slow-release feed like Nitrogen Fertiliser, once or twice across spring and summer is usually enough, since each feed lasts weeks. Soluble feeds need reapplying more often because they flush and fade. Either way, stop feeding nitrogen by late summer.
Can you over-feed a lawn with nitrogen?
Yes. Too much nitrogen pushes soft, sappy growth that needs constant mowing, builds thatch, leaves the lawn prone to disease, and can scorch the grass yellow or brown, especially with a soluble salt feed in hot weather. A slow-release feed at the stated rate, watered in, is the safer route.
What is a natural or organic high nitrogen lawn fertiliser?
One that draws its nitrogen from plant or natural sources rather than synthetic salts. Nitrogen Fertiliser supplies its 13% nitrogen as plant amino acids and proteins, taken up and used directly. Alfalfa meal is a gentler natural option. Both feed the soil as well as the grass.
Can I use alfalfa meal on my lawn?
Yes. Alfalfa meal is a mild, slow-release feed at around 2.5-0.3-2, so it greens a lawn gently and adds organic matter. It is a good choice for a fine lawn, or for anyone wary of scorching grass with a stronger feed. Scatter it evenly and water it in.
Should I feed my lawn nitrogen in autumn?
No. By autumn the job is to harden the grass and strengthen its roots for winter, which is a potassium job. A high nitrogen feed in autumn pushes soft growth that is prone to cold damage and disease. Switch to a potassium feed such as sulphate of potash instead.
Feed nitrogen while the grass is growing, ease off before autumn, and choose a form that greens the lawn without scorching it or washing away. For how high nitrogen feeds behave across the rest of the garden, read the high nitrogen fertiliser guide; to get the feed right under the surface, see how to top dress.
Sources
- 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(1), 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.