Are you getting mixed results from your fertiliser?

Is your lawn patchy or slow to green up after fertilising? Learn why — from soil pH and watering issues to application technique — and how to get consistently better results.

Summary

If your lawn doesn’t green up after fertilising, there’s usually a reason — and it’s not always the fertiliser’s fault. Common causes include incorrect soil pH, uneven soil moisture, shallow roots, poor spreading technique, or inadequate watering after application. This guide explains each cause in plain language and offers practical, local solutions for South Australian lawns.

By the end, you’ll know how to fertilise properly, how to prevent patchy results or fertiliser burn, and how to get a rich, even green lawn that responds consistently every time.

1. Incorrect Soil pH

If your lawn simply isn’t responding to fertiliser, the most likely culprit is an incorrect pH level. Soil pH affects how nutrients behave. When soil becomes too acidic or too alkaline, key elements such as nitrogen, phosphorus, and potassium become locked up — unavailable to your lawn’s roots.

For example:

• Too acidic (below pH 5.5): Nitrogen, phosphorus and potassium become unavailable.
• Too alkaline (above pH 9): Micronutrients like iron, manganese, copper and zinc get locked out.

Only when soil is around pH 7 (neutral) are all nutrients available for uptake.

That said, pH can be difficult to permanently alter. Even after treatment, soils often revert to their natural state over time. If your pH levels are stubborn, it may be more effective to adjust your fertiliser habits rather than fight the soil.

In Adelaide, alkaline soils are common and generally more forgiving — so if your pH is slightly high, it’s usually nothing to worry about. Acidic soils, on the other hand, can be more troublesome, as they tend to lock up nutrients and reduce lawn vitality.

If your soil is acidic:

• Apply garden lime periodically to raise the pH.
• Use fertilisers that are less acidifying (avoid those with ammonium sulphate or urea-based nitrogen).
• Mulch and top-dress with composted organic matter — it buffers pH and promotes microbial activity.
• Re-test the soil every 6–12 months to monitor gradual change.

Solution:

Test your soil. You can use a simple pH kit or bring a soil sample to us for a free test.

• To raise pH (acidic soil): apply garden lime and improve soil structure with organic matter.
• To lower pH (alkaline soil): apply sulphur, but in Adelaide conditions this is rarely necessary.

2. Non-Wetting Soil

Some soils absorb water unevenly. In these cases, parts of your lawn may stay dry even after watering, while others soak up moisture readily. Because water is the carrier for nutrients, dry spots also miss out on fertiliser — resulting in obvious patchiness.

Solution:

Take two core samples — one from a green patch and one from a dull patch. If the dull patch’s soil is dry while the green area is moist, you’ve got a non-wetting soil issue.

• Fix it by applying a liquid wetting agent every time you fertilise (or every six weeks in warm weather).
• This ensures even penetration of water and nutrients through the soil profile.

3. Variable Root Depth

Some parts of a lawn have deeper, healthier root zones than others. Shallow roots, common in shaded or compacted areas, limit the lawn’s ability to access nutrients and moisture.

Solution:

Compare core samples from healthy and poor-performing areas.

• Healthy couch and kikuyu lawns should have dense roots reaching about 100mm deep.
• Encourage deeper roots with fertilisers that contain phosphorus and potassium, regular use of wetting agents, and more sunlight (prune nearby shrubs or trees if needed).

4. Incorrect Application Method

How you apply fertiliser can dramatically affect the outcome. Hand-spreading often leads to uneven coverage — some areas get too much, others too little. Uneven fertiliser means uneven colour and growth.

Why a Spreader is Better:

A fertiliser spreader ensures consistent distribution, especially across larger lawns. It allows you to:

• Control the rate of application precisely.
• Avoid striping or patchy green areas.
• Prevent concentrated patches that may cause fertiliser burn.

For small lawns, use a handheld spreader; for larger ones, use a walk-behind spreader. Always follow the recommended application rate printed on the bag.

5. Inadequate Watering and Fertiliser Burn

After fertilising, watering is essential. Without it, fertiliser granules can sit on the leaf blades and cause fertiliser burn — yellow or brown scorch marks caused by high salt concentration drawing moisture out of the grass. To read more about fertiliser burn, click here.

How to Avoid Fertiliser Burn:

• Water in thoroughly after applying fertiliser — usually for 10–15 minutes or until the top 25mm of soil is moist.
• Avoid fertilising during extreme heat.
• Always use the correct rate — more is not better.

Liquid fertilisers don’t usually burn if mixed correctly, but granular products definitely can if not watered in properly.

Putting It All Together — How to Get the Best Results

To achieve a rich, even green lawn, treat fertilising as part of a process, not a one-off event:

1. Check pH first — aim for around 7, but don’t panic if it’s slightly alkaline.
2. Apply with a spreader for even coverage.
3. Use a wetting agent every time you fertilise to improve nutrient movement through the soil.
4. Water in thoroughly to prevent burn and activate the fertiliser.
5. Encourage deeper roots with the right nutrients and plenty of light.
6. If your lawn still isn’t responding evenly after following these steps, bring a small core sample to our Hove store — we’ll test it and help you work out exactly what’s going on.

Frequently Asked Questions

Q: How long should it take for fertiliser to work?

You should start to see results within 5–7 days after applying fertiliser — sometimes quicker with liquids. If nothing changes after a week, check your watering, pH, and application rate.

Q: How often should I fertilise my lawn?

In South Australia, fertilise three to four times per year — spring, early summer, late summer, and autumn. Avoid fertilising during winter dormancy if you have warm-season grasses like couch or kikuyu.

Q: Can I over-fertilise my lawn?

Yes. Too much fertiliser can lead to burn, excessive thatch, or runoff waste. Always stick to the manufacturer’s recommended rate.

Q: Should I water before or after fertilising?

Lightly water before applying if the soil is dry, then water in thoroughly afterward to help the fertiliser move into the soil and avoid burn.

Q: What if my lawn still looks patchy after fertilising?

If you’ve checked your watering, pH and application method and still have uneven results, bring a core sample to our store. We’ll test it and help diagnose the issue.