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To grow a thick, lush and healthy lawn, you need to feed it with the right NPK fertiliser for your grass. NPK stands for nitrogen (N), phosphorus (P), and potassium (K). These are essential macronutrients found in fertilisers, and each plays an important role in plant growth and maintaining the health of your lawn.
Safety tip: Always wear the appropriate safety equipment (safety glasses, gloves, and a mask, for example) and always follow the instructions for the product or equipment. Always store products out of the reach of children and pets.
The NPK listed on the back of fertilisers refers to the ratio of nitrogen, phosphorus and potassium in the mix. “Nitrogen is responsible for stem and leaf growth, phosphorus for root development and potassium assists with nutrient uptake and improving resistance to pests and diseases,” says Melissa King, horticulturist and Scotts Lawn Builder ambassador.
It may sound like nitrogen is all a lawn needs, but feeding the grass with only nitrogen will lead to imbalanced growth, weak roots, and increased pest and disease susceptibility. To maintain a healthy lawn, it’s important to use fertilisers that contain a combination of nitrogen, phosphorus and potassium.
The concentration of each nutrient varies for lawns and gardens, so check the packaging carefully before you buy and pay attention to the nutrient ratio to make sure it aligns with your lawn’s needs. This is made easier due to the fact that manufacturers label products as ‘lawn fertiliser’ on the front of the pack, so you won’t accidentally buy the wrong fertiliser.
There are synthetic, organic and organic-based lawn fertilisers. Synthetic fertilisers contain higher amounts of nutrients, while organic fertilisers are much lower. However, the benefit with organic fertilisers is they also contain organic matter, such as kelp, manure, and blood and bone to help improve and nourish the soil. Organic-based fertilisers strike a good balance between the two.
Most lawn fertilisers will have a high level of nitrogen, a small amount of phosphorus and a low or moderate level of potassium. Here in Australia, this is considered a ‘balanced’ or ‘complete’ lawn fertiliser. For example, NPK 15:0.4:5.5 (synthetic) or 3.7:2:1.8 (organic).
The ratio of NPK in lawn fertilisers can differ between products. Lawn foods with higher concentrations of nitrogen assist with fast greening and growth at the start (ideal in warm conditions and if irrigation is readily available), while fertilisers with lower levels of nitrogen can be used when lawn growth is slowing down, as you don't want to encourage new growth when conditions are less than ideal.
For newly establishing lawns that are less than 12 weeks old, avoid regular lawn fertilisers as these will be too strong for developing roots and shoots and may result in fertiliser burn and turf dieback. “Instead, look for products specifically formulated for young or establishing lawns,” says Melissa, who recommends Scotts Lawn Builder Seed & Turf Starter.
Fertilisers are available in liquid, granular or small pellets. Liquid options are fast-acting, as nutrients are available in a format readily taken up by lawn roots. However, their effects are short-lived, requiring frequent applications throughout the season for best results.
Granular fertilisers may release nutrients all at once, but there are slow or controlled-release lawn foods that break down gradually over time. “These granules deliver nutrients to your lawn slowly and continuously, so you only have to apply it three times a year,” says Melissa.
There are advantages to both types and each is beneficial at different times of the year. “Use a slow-release granular fertiliser in spring, summer and autumn, to provide the lawn with nutrients it needs for healthy growth,” she says. “When you want a richer, greener-looking lawn quickly, use a liquid fertiliser high in nitrogen – it’s fast-acting, so you will see results in days.”
Regardless of how you choose to feed the lawn, always follow the manufacturer’s instructions, and adjust frequency based on soil tests and specific lawn needs. This will prevent excessive and rapid growth or any over-application issues, which can include yellowing grass and subsequent death of your lawn.
Check out our guide to reviving your lawn.
Photo Credit: Getty Images, Michelle Holden
Asbestos, lead-based paints and copper chromium arsenic (CCA) treated timber are health hazards you need to look out for when renovating older homes. These substances can easily be disturbed when renovating and exposure to them can cause a range of life-threatening diseases and conditions including cancer. For information on the dangers of asbestos, lead-based paint and CCA treated timber and tips for dealing with these materials contact your local council's Environmental Health Officer or visit our Health & Safety page.
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