The most common questions we get asked about lawn fertiliser
If you are a lawn lover, learning about lawn fertiliser can be confusing and technical. In this article, we break down the most common questions we get and use our experience – having helped thousands of clients with their lawns – to help you get the results you are after.
Feel free to read the whole article or skip the questions that are most important to you right now; whatever is of most help to you.
What is lawn fertiliser?
Firstly, fertilisers are natural, chemical, or mineral compounds that supplement lawns and plants, giving them essential nutrients they are not getting from the soil. Secondly, fertilisers help plants and lawns grow deeper roots, healthy green leaves, and become more tolerant of stress. They also help plants grow more flowers and more fruit.
Nitrogen (N), Phosphorus (P) and Potassium (K) (collectively, NPK) are known as macronutrients and are the main nutrients that lawns and plants need to survive and thrive.
There are many different micronutrients, often called trace elements, that also have huge benefits to lawns and plants. However, they are just needed in smaller quantities compared to NPK. Zinc (Zn), Copper (Cu), Manganese (Mn), Boron (B), Iron (Fe), Molybdenum (Mo), and Magnesium (Mg) are all examples of micronutrients/trace elements.
When you read your fertiliser packaging, there will always be numbers on it that look just like this.
This shows exactly how much macro and micronutrients are in your fertiliser. This essentially is the same as the nutritional analysis on the packaging of food but instead of carbohydrates, protein, and fat, the fertiliser analysis includes Nitrogen, Phosphorus, and Potassium.
If you are trying to achieve a specific goal with your fertiliser program, you can find out the macro or micro nutrients you need and then look for a suitable brand or make of fertiliser that meets your lawn or garden’s nutritional requirements.
What do Nitrogen, Phosphorus, and Potassium do in lawns?
Here is a very simple breakdown of what Nitrogen, Phosphorus, and Potassium do for your lawn.
- Nitrogen: Increases your lawn’s leaf colour and growth.
- Phosphorus: Increases the development and growth of your lawn roots.
- Potassium: Improves overall lawn health
Why are there both granule and liquid lawn fertilisers?
Lawn fertilisers come in two forms: granule and liquid. They have their own unique benefits so are often used to compliment each other.
What’s the difference between granule and liquid fertilisers?
Granule lawn fertilisers:
Granule fertilisers are absorbed through the roots, are often slower acting, and longer lasting. Most brands last 6-12 weeks but some can last up to six months.
Liquid lawn fertilisers:
Liquid lawn fertilisers can be absorbed through the leaf or the roots. Being absorbed through the leaf makes them much faster-acting; sometimes you can see visible results in under 4 hours. However, they are also much more short-lived, usually only lasting between 2 and 4 weeks.
How do I apply fertiliser to my lawn?
Fertilisers need to be applied evenly over lawns. If the application is uneven or patchy, the results will be uneven or patchy.
For home lawns, granule fertilisers can be applied by hand, using a hand-held spreader or a walk-behind spreader. Liquid fertilisers can be applied by a watering can, a hose-on bottle, a pressure sprayer, or through a reticulation system.
What is the best way to apply lawn fertiliser?
The best results from any fertilisation will come from the most even applicators. If the fertiliser is applied unevenly over the surface the results will be patchy uneven colour. Here are the best ways to apply granule and liquid fertilisers
Granule lawn fertiliser:
For granule fertilisers apply with a handheld spreader or walk-behind broadcast spreader. These spreaders will evenly throw the fertiliser as you walk across your lawn, giving the best results.
Handheld spreaders are great for small lawns and are much cheaper than walk-behind options. Walk-behind broadcasters throw much further and as a result, are much quicker for large areas.
Throwing the fertiliser by hand is likely to create patchy results so we would not recommend this as an option.
Liquid lawn fertilisers:
For liquid fertilisers, apply with a pressure sprayer (as pictured below) and use a fan nozzle (most high-quality sprayers will come with a fan nozzle, along with other nozzle options). This will deliver a fine, even mist as you walk across your lawn. For more information on applying liquid fertilisers through a pressure sprayer, click here (this link will take you to a video; watch from 2:40 onwards).
Whilst you can apply with a watering can or hose-on applicators, it is very difficult to give the whole lawn the exact same amount of product. However, the biggest issue is that these applicators will usually apply fertiliser with too much water. This excess water washes the fertiliser off the leaf which, for most liquid fertilisers, will reduce the product’s effectiveness.
Although they are uncommon, there are some liquid fertilisers that should be watered in. If this is the case, then a hose-on applicator could be considered if a pressure sprayer was not an option.
How long does it take lawn fertiliser to work?
If applying a liquid fertiliser, you should expect to see results in 4-48 hours depending on the product, time of year, and starting state of the lawn.
If applying a granule product, it can take 2-7 days before you start seeing results but the improvements often continue for weeks.
Check out these amazing results we had at one of our client’s lawns in Canning Vale, Perth WA.
When is the best time to fertilise my lawn?
Spring is generally considered the best time to fertilise, however, fertilising should not be a once-off event. Remember, if you are using a liquid fertiliser, the benefits may only last 2-4 weeks; granule fertilisers will generally last 6-8 weeks.
In many areas, you can and should fertilise year-round.
Can I water my lawn after fertilising?
If you are using a granule fertiliser, then yes, you should definitely water the lawn after applying the fertiliser. This will help get the fertiliser off the lawn leaf and down into the soil where it is needed. If you do not water it in, you risk burning the lawn and causing more damage than good.
If you are using a liquid fertiliser, then the answer is generally no, you should not water the fertiliser in. This is because most liquid fertilisers work best when absorbed by the leaf. Watering the fertiliser off the leaf will often reduce its affect.
However, there are some exceptions to these rules. To be sure that you are applying your fertiliser correctly, always read the label.
How long should I water my lawn for after fertilising?
For granule fertilisers, you should run a full reticulation cycle with 10mm of watering. If you don’t know how to set your sprinklers to give 10mm of water, read our how-to article here.
For liquid fertilisers, you should not water your lawn after application (there are some very rare exceptions so read the label to check before applying).
Is it okay to put lawn fertiliser on wet lawn?
For liquid fertilisers:
No. This will dilute the spray and may cause the fertiliser to run off the leaf. Both dilution and run-off will reduce the effectiveness of the fertiliser.
For granule fertilisers:
Yes. But only if the product is going to be watered in immediately after application. However, if a granule lawn fertiliser is applied to a damp leaf and then not watered in immediately, you may run the risk of staining or burning the lawn as shown in the photo below.
Some lawns are so big that it is not advisable to apply granule lawn fertiliser to a wet law. By the time you have finished applying, there is a chance that the product may have already started burning or staining the lawn.
Should I fertilise my lawn before or after rain?
For liquid fertilisers you should avoid applying on rainy days.
After rain, damp leaves will dilute the spray and may cause the fertiliser to run off the leaf. As mentioned above, both dilution and run-off will reduce the effectiveness of the fertiliser.
For granule fertilisers the answer is a bit more complicated.
It depends on how much rain is going to come and how likely the rain is to come.
Lawn fertilising before rain
When you SHOULD NOT fertilise before rain:
- When the rain is going to be a heavy, long-lasting downpour: Too much rain can cause the fertiliser to break down too quickly and leach too far into the soil. Once the fertiliser has leached away, it is of no use to your lawn anymore.
Too much rain can also wash newly applied fertiliser off the lawn. Both events are bad for your lawns (and also the environment). - When the rain is inconsistent or too light: 1-2mm of rain in the hour after fertilisation can cause the fertiliser to sit on damp leaves. If this is the case for too long – as mentioned above, – you may run the risk of staining or burning the lawn as shown in the photo above.
When you SHOULD fertilise before rain:
- When you are certain that your lawn will receive 10-15mm of water within 1-2 hours.
Lawn fertilising after rain
When you SHOULD NOT fertilise after rain:
- When the lawn is damp and too wet to successfully water in.
- When water is pooled on the lawn.
When you SHOULD fertilise after rain:
- When the lawn leaf has dried and the soil is not pooling or waterlogged.
Can I over-fertilise my lawn?
Yes, you can over-fertilise a lawn. There are some bad consequences that come with over-fertilising and, unfortunately, this is actually quite a common occurrence for WA homeowners.
Two ways you can tell if you have over-fertilised your lawn:
- The lawn has become burnt and crispy after applying lawn fertiliser: This may happen in patches or over the whole lawn. This is caused when too much fertiliser is applied per square meter in one application. For example, instead of applying 30g per m2, we apply 90g per m2 hoping that we may triple the benefits. Unfortunately, instead of more benefits, there are only negatives.
- The lawn has become thatchy/spongy, is hard to mow, and is easy to scalp: Three factors can cause this:
- The lawn is fertilised with too much nitrogen, too often. This is especially common when using high-nitrogen fertilisers like Urea (read here for more info)
- When the lawn is over-watered.
- When the lawn isn’t cut very frequently.
If your lawn is spongy and thatchy, often the only solution is to vertimow the lawn. This can be very expensive, so avoiding over-fertilisation will save your bank account a bit of pain.
Should I mow my lawn after fertilising?
No, you should not mow your lawn after fertilising. If you mow after applying liquid fertiliser, you will cut off the fertilised leaf before it has had a chance to be fully absorbed into the plant. If you mow after applying granule fertiliser, you will most likely suck up a large percentage of the fertiliser you have just applied.
Even if you are mulch mowing (a type of mowing that recycles clippings and doesn’t use a catcher), you will chop up the small fertiliser granules, which will make your fertiliser break down quicker. This means that the fertiliser will not benefit the lawn for as long as advertised and will require reapplication much more frequently.
For most situations, it is best to wait at least 2 days before mowing
What should you do next?
I hope you have found this article very helpful. If you are now looking for a great fertiliser for your lawn and you live in Western Australia, click this link. We give a list of the best fertilisers for WA conditions.
However, if when reading this article, everything seemed too complicated and you just want a professional to look after your lawns and gardens, then contact us today. Silverstone Gardening hires experienced and qualified gardeners who can solve issues and make huge improvements with WA lawns and gardens. Get in touch for a quote today.
