A Complete Guide To Applying Lawn Fertiliser

14 Jan A Complete Guide To Applying Lawn Fertiliser

Fertilising your lawn is one of those jobs that can make a noticeable difference, but adding more fertiliser doesn’t necessarily lead to a better lawn. Using the right product, applying the right amount and doing it at the right time all matter.

Fertiliser should be a regular part of your lawn maintenance routine, rather than something you do when the grass starts looking a bit patchy. Your grass type, soil, weather, amount of sunlight and how much the lawn gets used will all affect what it needs.

This guide walks you through everything you need to know about fertilising your lawn effectively, as well as how to choose the right one for your lawn’s needs.

What Is Lawn Fertiliser?

Fertiliser supplies plants with nutrients. Lawn fertilisers usually contain a combination of nitrogen, phosphorus, and potassium, commonly shown on the bag as an N-P-K ratio. Each nutrient has a different job.

• Nitrogen (N) encourages leaf and stem growth. It is largely responsible for that healthy green colour people usually want from a lawn.

• Phosphorus (P) supports root growth and development and is particularly important when establishing new turf or seed.

• Potassium (K) supports general plant strength and helps grass cope with environmental stresses such as heat, drought, and heavy use.

Some fertilisers also contain smaller amounts of nutrients such as iron, magnesium and calcium.

The N-P-K numbers on a fertiliser bag show the relative amounts of each major nutrient in the product. For example, a fertiliser labelled 10-5-5 contains 10% nitrogen, 5% phosphorus and 5% potassium.

That doesn’t mean one ratio is automatically right for every lawn. A mature lawn with good soil may need something quite different from newly laid turf or grass growing in nutrient-poor soil.

Fertiliser isn’t a replacement for good soil preparation, watering or mowing. If the underlying problem is compacted soil, poor drainage, insufficient sunlight or the wrong turf variety, adding more fertiliser won’t necessarily fix it.

Reasons Why You Should Apply Lawn Fertiliser

A lawn needs nutrients to maintain healthy growth, and regular fertilising can help keep the grass dense and growing rather than allowing it to become thin and weak.

Maintains Healthy Colour

Nitrogen is particularly important for leaf growth and colour. If the lawn is lacking nitrogen, it can start looking yellow or pale rather than producing the deeper green associated with healthy growth.

Supports Root Growth

A lawn isn’t just about what you can see above the soil. Strong roots help grass access water and nutrients and give it a better foundation for dealing with everyday stress.

This is particularly relevant when establishing new turf. It’s crucial to give extra attention to turf aftercare, including fertilising and watering, while new turf develops its root system.

Helps the Lawn Recover From Wear

Heavy foot traffic, pets, mowing and weather all put stress on grass. A lawn that is actively growing has a better chance of repairing damaged or thinning areas.

This doesn’t mean fertiliser will instantly repair a badly damaged lawn. It simply provides nutrients that support new growth when the grass is capable of using them.

Keeps Weeds Away

Unhealthy lawns become a breeding ground for pesky weeds to grow and spread. Fortunately, fertiliser becomes your best defence against these weeds. Fertilising leads to thicker grass growth, which outgrows weeds and prevents them from spreading. 

Signs Your Lawn Needs Fertilising

Your lawn may show signs it’s lacking nutrients, such as yellowing, slow growth, or poor density. Some signs that may justify looking more closely at your lawn include:

• Grass that grows slowly despite adequate moisture and sunlight.
• A generally pale or yellow-green appearance during active growth.
• Thin areas where the grass is struggling to maintain density.
• Poor recovery after normal mowing or foot traffic.
• Older parts of the lawn that have gradually become less vigorous.
• A history of poor soil or repeated cropping without nutrient replacement.

If you notice any of these signs, your first instinct might be to apply a large amount of fertiliser. However, before that, make sure to conduct a soil test to know your soil’s current nutrient levels. This provides useful information on how much fertiliser you need, which also prevents unnecessary or excessive amounts.

Step-By-Step Guide to Fertilising Your Lawn

Applying fertiliser involves more than just sprinkling a large amount of it on your lawn. Follow these steps to ensure you get the most out of your fertiliser.

1. Identify Your Grass and Growing Conditions

Start by working out what type of turfgrass you have. Different grasses have different growth patterns and nutrient requirements.

The local climate matters too. A fertilising programme that works for a cool-season lawn in a temperate climate may not be suitable for a warm-season lawn growing throughout much of the year.

2. Check Your Soil

As mentioned earlier, test your soil before deciding which fertiliser to use. This is particularly helpful if you are considering a product containing significant amounts of phosphorus or potassium.

Soil testing can also prevent the common mistake of applying a general-purpose fertiliser when the soil already contains plenty of one or more nutrients. Most lawns thrive in soil with a pH between 6.0 and 7.0.

3. Choose the Appropriate Fertiliser

Look at the N-P-K numbers on the bag and check the recommended application rate. Do not assume that the fertiliser with the highest nitrogen number is automatically the best option. What matters is how much actual nutrient your lawn needs and how much the product supplies.

4. Measure the Lawn

Work out the approximate area of the lawn in square metres or square feet. You need this figure to calculate how much fertiliser to apply. For an irregular lawn, divide it into smaller rectangles or other simple shapes, calculate their areas and add them together.

5. Measure the Fertiliser

Use the application rate given on the product label. If the label gives the rate in terms of nitrogen rather than the amount of product, you will need to account for the nitrogen percentage in the fertiliser.

For example, if a product contains 20% nitrogen, 1 kg of that product contains 200 g of nitrogen. Do not guess the amount by filling a spreader until it looks about right. Applying too much in one area can damage the grass.

6. Set Up the Spreader

For granular fertiliser, a broadcast or rotary spreader is useful for larger lawns, while a drop spreader can provide more controlled application.

Follow the spreader’s calibration instructions and test it over a small area if necessary. For more even coverage, divide the required amount into two portions and apply them in two directions, such as one pass going lengthways and another going across the lawn.

7. Apply Evenly

Walk at a steady pace and try to keep the spreader moving. Avoid stopping while fertiliser is being released, as this can leave concentrated patches.

Keep granules off paths, driveways, patios and other hard surfaces. If some fertiliser lands there, sweep it back onto the lawn rather than washing it into a drain.

8. Water if Required

Check the instructions for the particular fertiliser. Many granular products need water after application so the nutrients can move into the soil. Avoid applying fertiliser immediately before heavy rainfall. Excessive rain can move nutrients away from where the grass roots can use them. 

How to Choose the Right Fertiliser For Your Lawn

Different fertilisers will have different effects on your lawn, so it’s important to choose one that’s most appropriate for your lawn’s specific requirements. Consider the following factors:

• N-P-K Figures: Start with the grass and the soil rather than the product itself. For example, if a soil test shows that phosphorus and potassium are already adequate, there may be little reason to apply large amounts of either nutrient.

• Quick-Release vs. Slow-Release: Quick-release fertilisers make nutrients available relatively quickly. The downside is that there is less room for error with application rates. Slow-release products release nutrients over a longer period and can provide more gradual feeding.

• Granular, Liquid, or Organic: Granular fertiliser is generally straightforward to spread over an established lawn. Liquid fertilisers can also be useful, particularly where an even spray application is practical. Organic fertilisers and products made from natural materials are another option, but they still need to be used at appropriate rates,

When’s The Best Time to Fertilise Your Lawn

The best time is generally when the grass is actively growing and can make use of the nutrients. Applying nutrients when grass is dormant or badly stressed means the lawn may not be able to use them efficiently.

For warm climates, including tropical areas, grass may have a much longer active growing period than it would in a temperate climate. Instead of following a spring/summer/autumn schedule designed for another climate, pay attention to your grass’s growth rate and local weather.

Avoid fertilising immediately before periods of very heavy rainfall. Rain can wash nutrients away from the root zone and increase runoff.

The same applies during periods of severe drought. If the grass is not actively growing, feeding it heavily is unlikely to solve the underlying problem.

How Often Should You Fertilise Your Lawn?

Frequency depends on several factors, such as the grass variety, climate, soil fertility, mowing frequency, irrigation and the fertiliser being used. A lawn that grows rapidly throughout the year may have different requirements from one with a long dormant period.

It is usually better to apply the correct amount at the appropriate intervals than to make frequent heavy applications. Some lawn programmes use several smaller applications throughout the active growing period, while lower-input lawns may need considerably less.

Keep records of when you fertilise, what product you use and how much you apply. This makes it easier to work out what is actually working for your lawn rather than changing products every time the grass looks slightly different.

Consult Seed & Turf for Expert Fertilising Advice

If you’re unsure which fertiliser to use or how often to apply it, professional advice based on your lawn can save a lot of trial and error. Seed & Turf can help assess your lawn-care requirements and provide advice on fertilising as part of a wider turf-care programme.

The aim should not simply be to make the grass grow as quickly as possible. The goal is to provide proper nutrients, at the right rate and at the right stage of growth. For tailored advice on fertilising and proper lawn care, contact Seed & Turf today.

Frequently Asked Questions

Can You Apply Too Much Lawn Fertiliser?

Yes. More fertiliser does not necessarily mean a healthier lawn. Excess nutrients can cause problems for the grass and can also contribute to nutrient movement into waterways.

Always follow the product’s application rate and avoid applying extra because the lawn looks particularly pale.

Can I Mow and Fertilise on the Same Day?

You can mow your lawn and fertilise on the same day, but the ideal situation would be to mow a few days before fertilising. This helps the nutrients reach their target faster since the grass is shorter. 

However, never mow immediately after fertilising; this will only clog your mower blades and is essentially the same as mowing wet grass. Wait at least 24 to 48 hours before mowing after fertilising.

Can I Fertilise a Dry Lawn?

It is better not to fertilise grass that is severely stressed by drought or heat. Fertiliser is most useful when the grass is actively growing and able to take up nutrients.