What Number Fertiliser to Use on your Lawn: NPK Explained
When you buy lawn fertiliser, you'll see three numbers on the label, shown as N:P:K. This is the fertiliser's NPK ratio: the percentages of nitrogen, phosphorus and potassium, the three main nutrients your lawn needs. The best NPK for your lawn depends on whether you're feeding an established lawn or starting a new one.
What do the NPK numbers on fertiliser mean?
The numbers are always in the same order: nitrogen first, phosphorus second, potassium third. For example, a fertiliser labelled 22:5:8 contains 22% nitrogen, 5% phosphorus and 8% potassium.
Nitrogen (N) drives leaf growth and green colour. It's the nutrient lawns use the most.
Phosphorus (P) supports germination and root development, and matters most for new lawns grown from seed.
Potassium (K) builds strength and helps your lawn handle heat, drought, cold and disease.
Some fertilisers list extra nutrients too, such as iron (Fe), which deepens the green colour of your lawn.
What is the best NPK for lawns?
For an established lawn, look for a high first number (nitrogen), with lower phosphorus and potassium. A ratio around 20 to 22 for nitrogen gives a strong boost in colour and growth. Here's how our range compares:
Fertilisers for established lawns (All Seasons – N:P:K 22:5:8)
All Seasons is our standard choice for established lawns of all types. The high nitrogen gives a great boost in colour with results you'll see in just a few days, while the potassium builds strong roots and helps fend off disease. Apply at least four times a year: twice in spring and twice in autumn. Formerly known as Renovator.
VIEW LANDSCAPE RANGE ALL SEASONS FERTILISER
Controlled release fertilisers (Super Green – N:P:K 22:3:4)
Super Green has a similar ratio but releases its nitrogen gradually over 10 to 12 weeks. You get steady, continuous colour with fewer applications, around three a year in spring, summer and autumn. Less nutrient run-off also makes it better for the environment. Formerly known as Gold Pro.
VIEW SUPER GREEN CONTROLLED RELEASE FERTILISER
Iron fertilisers for a deep green (Nitro Green Iron Boost – N:P:K 20:0.85:2 + 5% iron)
For the dark green of a sports stadium, choose a fertiliser with added iron. Nitro Green Iron Boost also works well in cooler weather, making it a good winter feed, and its very low phosphorus means it can be sent to Western Australia.
VIEW NITRO GREEN IRON BOOST FERTILISER
Is high nitrogen fertiliser good for lawns?
Yes, for established lawns. Nitrogen is the nutrient your lawn uses most, and it's lost every time you mow. That's why most lawn fertilisers have a high first number. The key is to apply at the recommended rate and water in well, since too much nitrogen at once can burn your lawn.
What is the best fertiliser for a new lawn? (Starter NPK ratio 5:6:6)
New lawns need a different NPK ratio. When sowing a new lawn from seed or oversowing an existing one, use a low nitrogen starter fertiliser like KickStart. Its higher phosphorus helps seed germinate and develop a strong root system, and its potassium builds healthy young plants. Nitrogen is kept low because young grass needs roots more than a colour boost.
Once your new lawn has germinated and you've started mowing regularly, switch to a high-nitrogen fertiliser like All Seasons or Super Green.
VIEW LANDSCAPE RANGE KICKSTART FERTILISER
How much fertiliser should I use?
Most of our granular fertilisers are applied at 3kg per 100m². Work out your lawn area by multiplying length by width; for example, a 10m × 15m lawn is 150m² and needs 4.5kg per feed. Nitro Green Iron Boost is applied at a lower rate of 1.2 to 2.4kg per 100m². Always check the rate on the product label.
When should you fertilise your lawn?
- When sowing a new lawn or oversowing to repair patches, use a starter fertiliser.
- In spring, twice, as your lawn takes off again after winter and to strengthen it before summer.
- In autumn, twice, to help it recover from summer and prepare for winter.
- In summer, a controlled release fertiliser gives a steady feed through the warmer months.
- In winter, if you live in a warmer climate, or to keep your lawn green through the cooler months.
A simple rule for any state: if you're still mowing regularly, your lawn is still growing and can use a feed.
For full instructions, see our guide on How to Fertilise. And get your broadcast fertiliser spreader out to make the job quicker, easier and more even!
Quick answers
Is NPK fertiliser good for lawns?
Yes. Nitrogen, phosphorus and potassium are the three main nutrients every lawn needs. Choose a high-nitrogen NPK for established lawns, and a starter NPK for new lawns.
What number is nitrogen on fertiliser?
The first number. In 22:5:8, the fertiliser is 22% nitrogen.
What number is phosphorus?
The second number. In 22:5:8, the fertiliser is 5% phosphorus.
Why do some lawn fertilisers have a low phosphorus number?
Established lawns need less phosphorus than new lawns. Western Australia also restricts phosphorus levels in fertiliser, so WA customers should look for a very low second number, like Nitro Green Iron Boost.
When should I use a low nitrogen fertiliser?
When sowing a new lawn or oversowing, use a low nitrogen starter fertiliser that's higher in phosphorus to support germination and root growth.
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