Reading an Australian or New Zealand label
The three bold numbers on a fertiliser bag, such as 15-1.5-6, are the percentages by weight of nitrogen (N), phosphorus (P) and potassium (K). Australian labels usually add sulfur (S) as a fourth figure. A 10 kg bag of 15-1.5-6 therefore contains 1.5 kg of nitrogen, 150 g of phosphorus and 600 g of potassium. The rest is the other elements in the compounds, such as sulfur and calcium, plus fillers and coatings.
Australia and New Zealand state these as elemental percentages. The United States and much of Europe state phosphorus and potassium as oxides (P₂O₅ and K₂O), which makes the same product look richer. When you read overseas advice or an imported bag, convert:
Sulphate of potash is the classic example. It is sold as 0-0-41 in Australia (41 % elemental potassium) and 0-0-50 in the US (50 % K₂O), and it is the same product.
How much nitrogen does a lawn need?
Nitrogen drives green leaf growth, and it is the nutrient lawns need most. University turf research gives a clear ceiling for a single feed: about 1 pound of nitrogen per 1,000 square feet, which is roughly 4.9 g N/m², and a little less (about 4.4 g N/m²) for quick-release, water-soluble forms. More than that in one go risks burning the grass and pushes soft growth at the expense of roots, and much of the excess washes away.
Warm-season lawns (buffalo, couch, kikuyu, zoysia) are usually fed three times a year: mid-spring, midsummer and autumn. Cool-season lawns are fed mainly in spring and autumn. The lawn feeding guide has the calendar for Australia and New Zealand.
Worked examples
- By the label: a 10 m × 8 m buffalo lawn and a lawn food labelled 25 g/m². 80 × 25 g = 2 kg. With a 15-1.5-6 product that supplies 3.75 g N, 0.4 g P and 1.5 g K per m², comfortably under the 4.9 g N ceiling.
- By a nitrogen target: you want 4 g N/m² from sulphate of ammonia (21 % N). 4 ÷ 0.21 = 19 g/m², so 80 m² takes 1.52 kg.
- Converting overseas advice: a US guide says "apply 1 lb N per 1,000 ft²". That is 4.9 g N/m². With a 30 % N product: 4.9 ÷ 0.30 = 16 g/m².
Spreading it evenly
- Weigh once, then measure by volume. Put a cup of the product on kitchen scales. If a cup weighs 200 g and you need 2 kg, that is ten cups, whatever the granules look like.
- Two passes at half rate. Spread half the product walking one way and the other half at right angles. Streaks and burnt stripes come from single passes.
- Water in. Granules sitting on leaves in hot sun scorch them. Water within the day, preferably soon after spreading, or spread just before light rain.
- Keep it off hard surfaces. Fertiliser swept into the gutter goes straight to the stormwater and the nearest creek. Sweep granules back onto the lawn, and do not fertilise just before a heavy storm.
Fertiliser questions
How much fertiliser per square metre for a lawn?
Follow the bag, which for most granular lawn foods is 20–35 g/m² per feed. What matters is the nitrogen: keep a single feed under about 5 g N/m² (rate × %N).
What do the numbers on a fertiliser bag mean?
N-P-K: the percentages of nitrogen, phosphorus and potassium by weight. In Australia and New Zealand they are elemental percentages, often followed by sulfur; US labels use P₂O₅ and K₂O instead.
Will more fertiliser make my lawn greener?
For a few weeks, then usually worse. Overdoing nitrogen burns grass, weakens roots, increases mowing and thatch, and wastes money down the drain. Feed at the label rate at the right time of year instead.
How do I convert pounds per 1,000 square feet to grams per square metre?
Multiply by 4.88. So 1 lb/1,000 ft² is 4.88 g/m², and 0.5 lb/1,000 ft² is 2.44 g/m².
Sources and method
- Elemental N-P-K(-S) labelling in Australia and New Zealand: Labeling of fertilizer; Business Queensland – fertiliser standards and labelling. Oxide factors from atomic masses (P₂O₅/2P = 2.291; K₂O/2K = 1.205).
- Single-application nitrogen limits (0.9 lb soluble N, up to 1 lb slow-release N per 1,000 ft²): Virginia Cooperative Extension – lawn fertilization for warm-season grasses.
- Feeding three times a year for warm-season lawns: Lawn Solutions Australia – the right way to fertilise your lawn. Blood & bone example analysis from a published Australian product label (5.1-4.1-1.5).
- 1 lb/1,000 ft² = 453.6 g ÷ 92.9 m² = 4.88 g/m².
Written by DueRiva · Last reviewed 23 September 2026 · Report an error