How to fertilise your lawn
Fertilising your lawn replenishes the nutrients it loses through mowing, but choosing the right feed is key – our guide tells you how.
15.10.2024
Why it is so important to fertilise your lawn
All through the warmer seasons your lawn is used as a place for picnics, parties, and playing, as well as being frequently mown and suffering other stresses. All of these activities contribute to depleting leaf mass, and as such the vital nutrients your lawn needs to thrive. Fertilising with the right lawn feed restores essential nutrients to your grass, of which nitrogen (N) in particular promotes the regeneration of all parts of the plant. Good lawn feed products include nitrogen alongside potassium (K) to strengthen the grass against disease, and phosphorus (P) to promote root growth, all in balanced proportions to support your lawn appropriately.
Is lawn feed always necessary?
Not every lawn requires fertilising. If your garden earth is naturally rich in nutrients, your grass simply needs regular watering – but that is rarely the case. In general, if you have laid your lawn yourself, then you should feed it regularly to keep it strong and lush.
Soil testing helps you choose the right feed
It’s no surprise that lawns which lack nutrients struggle to survive: they show little growth and the grass plants become vulnerable to diseases and pests. You may not realise though, that it’s equally important to ensure you do not overload your lawn by over-fertilising, as this can also cause diseases and critically impair growth. To start from an informed position about your lawn feed requirements, we recommend analysis of your soil.
There are simple home kits for soil testing available to buy, or you can send a sample for expert analysis. Finding out the pH value and nutrient composition of the earth your grass is growing in gives you a great head start in knowing which lawn feed products will get the best results. You can also be confident that you won’t be loading the soil and groundwater with unnecessary nutrients.
More about soil testing
Soil testing is widely used in the agricultural sector, because it makes it possible to pinpoint exactly how to use resources such as feed for the biggest impact. The domestic gardener can benefit in just the same way: knowing the composition of your growing medium will guide you towards what grows successfully, as well as the best way of fertilising your lawn.
Test the pH value yourself
Knowing the pH value of your soil is a very useful starting point for establishing your lawn care routine. Digital probe tests are widely available and simple to use; just push them into the ground for an analysis of the pH value, and often also the moisture content and light level. For lawns, a neutral to slightly acidic pH value of 5.5–7 is best; a much lower value means you have acidic soil which will inhibit the availability of nutrients to your lawn. If the pH value is below 5.5, we recommend applying 150g of lime (calcium carbonate) per square metre, then fertilising four weeks later with 20 to 30g of nitrogen-rich feed per square metre. Leave the lawn alone for at least ten days before scarifying it.
When Is It Time to Fertilise my lawn?
We recommend regular fertilising on a seasonal basis so your lawn always has what it needs to encourage continuous growth. In any case, you should certainly fertilise your grass before it starts to go yellow or brown, as this is a specific indicator of a nutrient deficiency. Moss is also an indicator that you need to feed your lawn, as it thrives in low-nitrogen conditions. If it is spreading through your lawn, you know your soil needs fertilising; in a well-nourished lawn, moss is soon driven out by the fast-growing grass – in other words, feed your lawn regularly as a great method for the long-term elimination of moss.
How often should I fertilise the lawn?
Fertilising the lawn twice a year is generally sufficient – once in spring and once in autumn, though if you are already consistently mulch mowing, you could skip one or both. If you mow your grass a lot, or it spends a lot of time being played on by children, you may wish to fertilise it more frequently – up to a maximum of four times per year.
For a comprehensive spring lawn care routine, you can scarify your lawn; applying lawn feed afterwards will help your grass to recover quickly, and the fertilising process can be combined with overseeding bare patches for new growth – you can even buy ready-made mixes of grass seed with feed for this purpose.
Low-nitrogen fertilising in autumn: The last lawn feed of the year should be in autumn, from the middle of September to the middle of October. Make sure that you choose a specially formulated autumn lawn feed that contains as little nitrogen as possible, and which has a high potassium content. Potassium-rich fertilisers strengthen the cell walls of the grass for winter.
Feeding your lawn a properly balanced diet
The right lawn feed for your garden
There’s no universal fertiliser that is right for every lawn, so you need to find a slow-release fertiliser that is suitable for the type of lawn you have. Never use fertilisers intended for cultivating crops, as these are only effective in the short term and will put a strain on the roots of your lawn because they contain the wrong concentrations of nutrients for grass.
What are the most important active ingredients in fertilisers?
Once you’ve found the right feed, you can get going with the actual fertilising process. The right way to apply fertiliser to your lawn depends primarily on the type you are using.
Slow-release fertilisers generally all contain the same essential nutrients for healthy soil, however the proportional composition of the active ingredients used is varied to suit different seasonal needs, as well as the individual requirements in your garden:
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| Active ingredient | Description |
|---|---|
| Potassium (K) | Increases pest resistance, regulates plants’ metabolism. |
| Phosphorus (P) | Strengthens root growth and helps to protect against frost. |
| Magnesium (Mg) | Supports chlorophyll formation during photosynthesis and ensures a rich green colour. |
| Calcium (Ca) | Stabilises the cell walls of the grass and helps plants to absorb nutrients from the soil. |
| Nitrogen (N) | Encourages cell division and as such the regeneration of all parts of the plant. Stimulates lawn growth. |
| New ingredient | New description |
Top tips for fertilising your lawn
- Before fertilising, we recommend scarifying your lawn for maximum benefit and to rejuvenate your grass. However, do factor in a few days of rest for your lawn between scarifying and fertilising it.
- Don’t feed your lawn while there is any ground frost.
- Do not apply fertiliser in direct sunshine – wait for a cloudier day if necessary.
- Each time you feed your lawn, ensure that you keep it generously watered and wait a few days before mowing.
- The grass should be around 5 cm high before you apply fertiliser.
Scarifying the lawn before you feed it
Scarifying is a key part of good lawn care, just like fertilising. We recommend scarifying before you apply lawn feed, as doing so helps to increase water permeability and to remove dead plant matter and weeds from the lawn, so it maximises the effectiveness of your lawn feed. With more light, air and water at the roots, the grass can absorb the beneficial substances more easily and utilise them better.
Add air and light for a beautiful green space
STIHL lawn aerators: rejuvenate your lawn
STIHL petrol-powered and electric scarifiers ensure that your lawn gets the air, water and nutrition it needs for dense growth and a vibrant green colour.
An alternative approach to lawn feed
A vibrant, thick and healthy lawn requires regular care. However, many lawns do not necessarily require lawn feed, as mulch mowing can be a cost-effective and practical way of fertilising them over the long term.
What is mulch mowing?
Conventional mowing collects the clippings from your lawn, while with mulch mowing they are distributed back over the lawn. This process returns vital nutrients to the earth in a practical and natural way, as the nitrogen in the mulched grass clippings is quickly mineralised and so becomes a valuable fertiliser. You’ll need a special mulch mower that shreds the grass cuttings into small particles before scattering them. This shredding step ensures that the grass clippings are usefully delivered to your lawn, rather than smothering it.
Mulch mowing instead of separate fertilising
Mulch mowing combines the lawn mowing and fertilising process into a single step, so you can save both time and money; what’s more, there’s no need to dispose of the grass cuttings. Mulch mowing means you only need to additionally fertilise if your soil is particularly demanding or your lawn is diseased – in this case, it may be in need of specific minerals that are not available in the grass clippings.
Summary: how to fertilise your lawn
- Soil testing will help you identify the right fertiliser for your requirements
- Feed your lawn in spring and autumn
- If you use your lawn a lot, you can fertilise it three to four times a year
- Feed your lawn after scarifying for a healthy soil structure and strong recovery
- Mulch mowing is a cost-effective and environmentally friendly alternative to fertilising
