How to Calibrate your Spreader and Apply Lawn Fertiliser for Professional Results

How to Calibrate your Spreader and Apply Lawn Fertiliser for Professional Results

Feeding your lawn is one of the most important things you can do for its health, colour and resilience, and getting it right is simpler than you might think. This guide takes you through everything you need to know to get professional results, including how to use our Handheld Fertiliser Spreader and achieve the correct application rate of 25g per m2. Whether you want to watch the full walkthrough, follow the written steps, or just find the answer to a quick question, use the menu below to jump straight to the part you need.

 

Table of Contents:

 

Before you start...

Thank you for choosing our professional-grade fertiliser. Our fertilisers are professional-grade products, developed for and used within our award-winning lawn care service. They are more concentrated, longer-lasting and more targeted than typical shop-bought alternatives, which means a little really does go a long way. 

Although 25g per square metre may not look like very much, it is exactly the right amount for safe and effective results. Applying more will not make the lawn greener or improve performance, and over-application can lead to nutrient imbalance and potential damage. Careful measuring and accurate spreading are what deliver the deep, even colour and healthy growth you’re aiming for.


For Best Results...

✅  Apply when soil temperatures are consistently above 8°C and the lawn is actively growing.

✅  Do not apply when the lawn is frozen, during frost, or if frost is forecast overnight. Avoid applying during prolonged drought stress unless using Summer Boost Pro which can be applied during drought.

✅ Choose a dry day for application, ideally when light rain is expected within the next couple of days. If rain is not forecast, you will need to water the lawn in thoroughly. This is with the exception of Summer Boost Pro that can be applied without water.

✅ Avoid mowing for 24–48 hours before application, and leave the lawn for 2–3 days after the fertiliser has been watered in, before mowing again. This allows the granules to settle and nutrients to move into the soil.

✅ Children and pets can walk on the lawn immediately after application. However, because our fertilisers contain iron, which may stain hard surfaces if transferred, we recommend keeping off the lawn until it has been watered in and fully dried.

✅ Brush any granules off any pathways or hard surfaces as the iron in all of our fertilisers can stain hard surfaces if left.

✅  Do not mix with other fertilisers or use “3-in-1” or “4-in-1” products in between treatments.

✅  Leave 10–12 weeks between applications.

 

Full Calibration and Application Guide

Calibrating your spreader and applying your fertiliser

Detailed instructions on how to calibrate your spreader and apply your lawn fertiliser:

0:00 - Handheld Fertiliser Spreader - A quick recap
00:44 - What is the application rate and why does it matter?
01:23 - What controls how much fertiliser goes down?
02:00 - Two ways to get the application rate right
03:14 - Measuring out the correct amount of lawn fertiliser
03:51 - Applying your fertiliser with a handheld fertiliser spreader
05:09 - Scientific calibration test technique
07:57 - Making final adjustments

Quick Start Guide

01

Measure your lawn

Measure your lawn in square metres first. If you are unsure of the size, use our free online measuring tool: Measure Your Lawn This figure is the starting point for working out how much fertiliser you need.

02

Select your spreader

For the most even finish, use a handheld or broadcast spreader. It makes accurate spreading far easier and reduces the risk of overfeeding. Our Handheld Fertiliser Spreader is available in our store here. You can also apply by hand if you prefer, taking care to spread small amounts evenly.

03

Weigh out the fertiliser

Weigh out the correct amount before you begin. Multiply your lawn size in m² by 25 to calculate the grams required. Every Johnson Lawn Care Direct fertiliser is applied at 23–25g per square metre. Weighing out the exact amount means you can spread with confidence and, as long as you spread evenly, you reduce the risk of overfeeding.

04

Spread evenly

Spread evenly across the lawn, keeping a steady walking pace. If you are using our Handheld Fertiliser Spreader, set the dial to 3 or 4, and see our full walkthrough above for how to get the amount right. Start a metre in from your borders, as the spreader throws fertiliser about a metre to each side. If applying by hand, wear gloves and spread small amounts as you go to avoid putting too much down in one place.

05

Brush granules off hard surfaces

Brush any granules off paths, patios and other hard surfaces as soon as you have finished. The iron in our fertilisers can stain hard surfaces if left.

06

Water the lawn

If it does not rain within 1 to 2 days of application, water our spring, autumn and winter fertilisers in thoroughly to avoid scorching the lawn. Our Summer Boost Pro is activated by water, but is drought safe and so can be safely applied without water, making it especially useful during hosepipe bans or if you normally rely on rain to water your lawn feed in.

DOWNLOAD FULL GUIDE PDF

Download the Full Guide PDF

Want the instructions to hand while you are out on the lawn? Download our printable guide. It covers the same steps in full, including the two methods for applying exactly 25g per square metre and how to calibrate a spreader that has several settings.

FAQs

What type of lawn fertiliser should I use?

The best results come from using a fertiliser that is formulated specifically for the current season.

Different times of year require different nutrient balances. A one-size-fits-all product cannot provide the same level of targeted support.

Our seasonal range was developed through years of professional lawn care experience and is designed to work as a complete programme throughout the year. When used consistently, it builds stronger roots, more even colour and better resilience.

When is the best time to apply lawn fertiliser in the UK?

Apply lawn fertiliser when the grass is actively growing and soil temperatures are above 8°C.

The lawn should be frost-free and not waterlogged. Avoid applying just before heavy downpours. Light rain within 1–2 days is ideal, as it helps move nutrients into the soil.

How much fertiliser do I need for my lawn?

All Johnson Lawn Care Direct fertilisers are applied at 23–25 grams per square metre.

Although this may not look like a large amount, it is precisely the correct rate for professional-grade fertiliser. More does not mean better. Careful measurement ensures safe, consistent results and helps you get the full benefit from each bag.

If you are unsure of your lawn size, use our online measuring tool before you begin.

As a guide:

  • 50m² lawn = 1.25kg
  • 100m² lawn = 2.5kg
  • 200m² lawn = 5kg
  • 300m² lawn = 7.5kg
  • 400m² lawn = 10kg
  • 500m² lawn = 12.5kg
  • 1000m² lawn = 25kg


Applying more will not improve results and increases the risk of overfeeding. Measuring accurately is key.

How often should I apply lawn fertiliser?

For a strong, healthy lawn, fertiliser should be applied every 10–12 weeks using a product designed for the current season.

Lawns have different needs throughout the year. Spring feeding supports recovery and growth, summer feeding helps the lawn cope with heat and stress, autumn feeding strengthens roots, and winter feeding maintains condition during colder months.

Feeding seasonally and consistently is what builds long-term lawn health.

Many customers choose our auto-delivery option so the correct seasonal fertiliser arrives automatically every 3 months. It takes the guesswork out of timing and ensures the lawn is always supported at the right stage of growth. For more information, see our Fertiliser Range.

How do I apply lawn fertiliser safely and effectively?

The safest and most effective way to apply lawn fertiliser is to measure carefully and spread evenly at 23–25g per square metre.

Professional-grade fertilisers are more concentrated than typical shop products. Accuracy is important. Applying more will not improve results and may cause damage.

Using a handheld or broadcast spreader makes it much easier to achieve an even finish. If you do not already have one, our Handheld Fertiliser Spreader is designed specifically to deliver the correct application rate.

When applied correctly and at the right time of year, seasonal feeding produces visible improvement within days.

Can I apply lawn fertiliser by hand?

Yes, but extra care is needed.

Measure the full amount out before you begin and wear gloves. Familiarise yourself with what 25g per square metre looks like, then spread small amounts evenly as you walk to avoid over-application in one area. Uneven hand application is the most common cause of dark patches or scorch.

A spreader provides more consistent results.

How do I spread lawn fertiliser evenly?

The most reliable method is to use a spreader and apply in two passes at right angles to each other.

This helps prevent missed strips and overlapping areas.

Before applying to the whole lawn, you can calibrate your spreader by testing on a measured 10m² area to ensure the correct rate.

Do I need to water lawn fertiliser in?

Yes. Our Spring, Autumn and Winter fertilisers must be watered in within 1–2 days of application. Watering moves the nutrients into the soil and down to the root zone where they are needed. If left sitting on the leaf during warm or dry conditions, concentrated nutrients can cause the grass to scorch, resulting in brown patches.

Summer Boost Pro works differently.

It contains a technologically advanced moisture-responsive nitrogen coating. Unlike conventional fertilisers that begin releasing immediately, this coating responds to moisture and temperature. Feeding begins only when moisture returns.

This means Summer Boost Pro can safely be applied during dry spells and even during hosepipe bans without the same risk of scorch. When rain arrives, feeding begins naturally.

If you are able to water during dry conditions, results will always be enhanced. However, the formulation is specifically designed to provide greater flexibility and safety during summer stress.

How long does lawn fertiliser take to work?

In active growing conditions, you can usually expect visible improvement within 7–10 days.

Cooler temperatures or low moisture may slow visible results slightly. Fertiliser also supports root development beneath the surface, which may not be immediately visible.

How soon can I mow after applying lawn fertiliser?

Avoid mowing for 1-2 day before application and 2–3 days after application to allow the fertiliser to settle and begin working.

Is lawn fertiliser safe for children and pets?

All of our fertilisers are safe for children and pets to walk on once it has been watered in and the grass is dry. We do not recommend grazing pets are allowed to digest the grass for at least 4 weeks. For more information, see our Children & Pet Safety Guide.

How do I avoid common mistakes when using lawn fertiliser?

Most issues arise from over-application, uneven spreading or incorrect timing.

Measure carefully. Apply evenly. Follow seasonal timing.

Professional-grade fertiliser works extremely well when used correctly. Feeding little and often, in line with the seasons, produces far better long-term results than occasional heavy applications.

That is why our fertilisers are designed as a year-round programme rather than a single treatment.

Any Further Questions?

We are committed to helping you achieve the very best results from your lawn.

As passionate lawn care specialists, we genuinely enjoy talking about lawns and helping customers get things right. If you have any questions about application, timing, or any lawn care issues you’re facing, please do not hesitate to get in touch.

You can email us at support@johnsonlawncaredirect.co.uk or call the office on 01793 625875 (option 2).

We are always happy to help.

Paul & Janet Johnson