Feeding your lawn the eco-friendly way: what it needs, which fertiliser, when
A dense lawn needs nutrients, because with every cut you remove, part of them leaves the area. Feeding in an eco-friendly way therefore does not mean doing without fertiliser. It means giving only as much as the lawn actually takes up, at the right time and in a form that is not lost to groundwater or the air. Here you can read what your lawn needs, which fertilisers are suitable and how to avoid over-fertilising.
In short
- It is not fertiliser as such that harms the environment, but too much of it: leached nitrate and escaping nitrous oxide.
- Only a soil analysis shows what is missing. Many garden soils have more than enough phosphorus.
- Three feeds a year are usually enough: spring, early summer, late summer. No more nitrogen from mid-October.
- Organic fertilisers work slowly and feed soil life, but they need warm soil.
- Mulching noticeably reduces the need for fertiliser.
What the lawn needs
Grasses grow constantly and are cut constantly. Their need for nitrogen, which provides growth, density and colour, is correspondingly high. Potassium makes the grasses resistant to drought, frost and disease. Phosphorus is needed mainly for germination and root formation, and is rarely in short supply in established lawns. Then there are magnesium, sulphur and trace elements such as iron.
As a guide value, a home lawn needs about 10 to 20 grams of pure nitrogen per square metre per year. A heavily used lawn that is mown often and short, with the clippings removed, is at the upper end. A mulched, lightly used lawn manages with considerably less. How much pure nitrogen a fertiliser contains is stated on the pack: with a fertiliser containing 10 per cent nitrogen, 50 grams of fertiliser equal 5 grams of pure nitrogen.
Good to know
A soil analysis does not cost much and is worth doing every three to four years. Agricultural testing institutes and many labs offer garden analyses. They show pH, phosphorus, potassium and magnesium. It often turns out that phosphorus and potassium are plentiful and a pure nitrogen fertiliser is enough.
Organic, mineral or combined?
Organic fertilisers consist of plant or animal raw materials. Before the grasses can take up the nutrients, soil organisms have to break them down. That only happens in warm, moist soil, but in return the nutrients flow slowly and evenly. Mineral fertilisers contain the nutrients as soluble salts that are available immediately. That is precise, but with overdosing or heavy rain, nutrients are lost quickly.
| Organic | Mineral | Organic-mineral | |
|---|---|---|---|
| Effect | slow, over weeks to months | fast, within a few days | fast start, then slow |
| Soil life | is fed, humus builds up | no contribution of its own | partly |
| Risk of leaching | low | high when overdosed, lower with coated slow-release fertilisers | medium |
| Risk of scorching | practically none | yes, when overdosed or in drought | low |
| Works in cold soil | hardly | yes | partly |
| Production | often from by-products | nitrogen energy-intensive, phosphate is finite | mixed |
Mineral fertiliser is not harmful per se, and organic fertiliser is not automatically harmless. Organic nitrogen also becomes nitrate if there is more of it in the soil than the grasses take up. The amount is what matters. For most home lawns, an organic or organic-mineral lawn fertiliser is a good choice because it forgives mistakes and strengthens soil life.
Organic fertilisers at a glance
| Fertiliser | Suitability for lawns |
|---|---|
| Organic lawn fertiliser | blends of raw materials such as feather meal, horn, vinasse or malt sprouts, balanced for lawns. The simplest solution. |
| Horn shavings and horn meal | pure nitrogen with long-term effect. Horn meal works faster than shavings. For lawns, prefer the finer horn meal. |
| Compost | finely sieved as a thin layer after aerating, ideally mixed with sand. Supplies nutrients and humus, but does not replace nitrogen feeding. |
| Clippings (mulch) | return part of the nutrients when mulching and reduce the need for fertiliser. |
| Vinasse | a by-product of sugar production, rich in potassium. Good as a potassium source in late summer. |
| Manure | not on an existing lawn: uneven, weed seeds, smell. Well rotted, at most worked in before establishing a new lawn. |
| Plant tea | useful for beds, hardly practical for lawns: hard to dose and to spread evenly. |
How clippings work as fertiliser and when mulching makes sense is explained in Lawn mulching.
The right timing
Spring: the first feed once the soil has warmed up and the grasses are visibly growing, usually in April. Organic fertilisers only work from a soil temperature of about 8 to 10 °C. Feeding earlier achieves nothing; the nutrients lie unused in the soil.
Early summer: the second feed in June. In heat and drought, only feed if you can water afterwards, otherwise mineral fertilisers can scorch the grasses.
Late summer: the third feed from late August to September, potassium-rich. Potassium strengthens the cell walls and lowers the freezing point of the cell sap. This feed fits well with lawn renovation by aerating and overseeding.
From mid-October: no more nitrogen. It stimulates soft growth that is susceptible to snow mould in winter, and whatever the grasses no longer take up is washed out over the winter.
Applying it correctly
- Use a spreader rather than spreading by hand, so that no stripes and patches appear.
- Half the amount lengthways, half crossways. Small errors then even out.
- Before light rain or followed by watering. Do not spread mineral fertiliser on wet blades, or the granules will stick.
- Keep a distance from ponds, streams and paths. Whatever lands on paving is washed into the sewer by the next rain.
- Rather a little less than the pack says if you mulch or the lawn is hardly used.
Too much or too little?
| What you see | Possible cause |
|---|---|
| Pale green, patchy lawn, lots of clover | nitrogen deficiency |
| Reddish threads at the leaf tips (red thread) | nitrogen deficiency, often in damp conditions |
| Very fast, soft growth, very dark green | too much nitrogen |
| Brown, scorched stripes or patches | overdosed or unevenly spread mineral fertiliser |
| Snow mould in winter | among other things, nitrogen applied too late in autumn |
More about disease symptoms in Lawn diseases. How feeding fits into eco-friendly lawn care as a whole is explained in Lawns and the environment.
Frequently asked questions
Is compost enough as lawn fertiliser?
Usually not on its own. Compost supplies humus, potassium and phosphorus, but comparatively little readily available nitrogen. As a thin layer after aerating it is a good supplement.
Can I feed organically in autumn?
Yes, in late summer and early autumn, as long as the soil is warm. Choose a potassium-rich fertiliser. From mid-October organic fertiliser hardly works any more, and nitrogen no longer makes sense anyway.
Is lawn fertiliser dangerous for children and pets?
Organic fertilisers are generally harmless but can attract dogs. Mineral fertiliser should be watered in before the area is used again. Follow the instructions on the pack.
Do I need weed-and-feed combinations?
No. A dense, well-fed lawn leaves weeds little room. Individual weeds can be removed mechanically without treating the whole area with herbicide.
Featured image: ExQuisine, stock.adobe.com
