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Fertilising Grass: How, When and What to Use

Fetilising Grass - a beautiful green lawn

How to fertilise grass

Applying fertiliser is important to keep your lawn looking good.  However, this does not mean that you need to apply masses of fertiliser. Fertilising grass is all about balance. The aim should be to provide just enough to keep your lawn growing lush and green.

A common mistake of home gardeners is to use a catcher on their lawn mower whilst, simultaneously, under-fertilising their grass. It is important to understand that when you remove lawn clippings (from mowing) you are actually taking away vital fertiliser from the soil.

In a natural state, the clippings of lawn grass would fall and come part of the soil and in doing so would improve the soil.  In a lawn situation where the clippings are removed, nutrients must be returned to the soil in the form of fertiliser.

In most situations applying fertiliser in spring, summer and autumn is enough to keep your lawn looking good.  Most granular lawn fertilisers are used at the rate of between 30 to 40 grams per square metre.  

Spreading Fertiliser

The way to spread granular fertiliser is either by hand, which is called ‘broadcasting’, or by a mechanical fertiliser spreader

When using the broadcast method you take a handful of fertiliser (always use gloves) and throw the fertiliser out in a broad spread.   

When using a fertiliser spreader the fertiliser is spread my the machine at measured amounts. Mechanical fertiliser spreaders can be a bit hit and miss and, perhaps unsurprisingly, we have found that it is the higher priced ones that do the best job.  

Mechanical spreaders are best suited to large lawns and take a bit of experience to use. However, there are hand held spreaders which work very well, although they require more effort.  Hand held spreaders require you to hold the spreader upright and then turn the handle.

Slow release fertilisers are becoming more popular. These are fertilisers which release over time.  We have regularly used Scotts Lawn Builder, and would heartily recommend. 

This is a very concentrated fertilser and so does not require much to fertilise your turf. It is spread by a specially designed Scotts hand spreader, which does a good job.

Liquid fertilisers are probably the most effective of the fertiliser and the result is nearly instant.  If you use liquid fertilisers you should start to see an improvement in your lawn around three days later.

Liquid fertilisers usually come in pre-made spray containers which you connect directly on to the hose. Liquid fertilisers can be more time consuming to apply and a number of applications is sometimes required to get a good result.

We find that liquid fertilisers with a seaweed base are an excellent choice as they condition the soil for long-term improved growth. 

When to Fertilise a Lawn

The timing of when you fertilise your lawn is important.  Fertilising grass at the right times you will see your lawn achieve its best growth – and also save on fertiliser. 

The best time to fertilise is in the warmer months.  Particularly spring, summer and autumn.  If you live in a tropical climate you have the flexibility of fertilising your turf lawn at any time of of year. 

Fertilising grass is also best done just before it rains. Fertiliser needs to be washed in, not washed off, so adequate watering or rain will assist in this process.

Note that it is possible to over fertilise your lawn. Should you spread too much fertiliser on on your lawn or fertilise it too often, it can make the turf sick and cause it to die-back in areas. This is particularly true with granular fertilisers.

Generally speaking, the minimum period between fertilising treatments should be about 5 to 6 weeks. Treating a lawn to this schedule will be sufficient to create solid growth. When using a granular fertiliser, be sure to carefully manage your applications to control the growth of your grass. 

Liquid fertilisers are a little different to granular fertilisers. They can be applied more often.  Liquid fertilising can be done every two weeks if needed, however once a month should be enough.

Slow release fertilisers are available for lawns and these are generally applied once every three months. 

How much fertiliser to use on a lawn

Generally speaking most lawns require around 25 to 50 grams of granular NPK lawn fertiliser per square metre, per treatment.  

The amount of fertiliser depends on the type of lawn you have.  Seed grown and tufting lawns like Fescue and Rye tend to need around 30 grams per square metre.  Running lawns like Couch need a little more at around 40 grams per square metre, mainly because they have higher nitrogen requirements.  

Basically, the more you mow your lawn and remove lawn clippings, then the more fertiliser you will require. 

If you use a slow release fertiliser like Scotts Lawn Builder then you will need to use much less fertiliser, as the fertiliser is more concentrated.  You usually require around 10 grams per square metre but please consult the pack for more information on this. 

If you use liquid fertiliser in is normally indicated on the pack that your purchase.  Most liquid fertiliser hose-on packs will treat an area of around 100 square metres. Again, check the pack for details.

However, when using liquid fertiliser you are generally treating your turf more frequently, up to once a month during the growing season.  

Fertilising grass - someone on a ride on lawn mower, mowing a lush lawn

How often should Grass be fertilised

How often you fertilise your lawn comes down to how lush you want the lawn to look. How often you mow your lawn will also effect how often you fertilise your lawn. The two points are interlinked.

When you mow your lawn regularly you will usually have to apply fertiliser more often.  This is particularly the case if you use a catcher and remove grass clippings.  Every time you cut your lawn and remove clippings it is taking away nutrients from your soil. 

Most lawns are fertilised three times per year, spring, summer and autumn.  If you are in a warm climate or tropical climate you can fertilise all year around.

Some people fertilise more often.  If you do not fertilise your lawn and you remove the leaf clippings, your lawn will gradually lose its lustre and start to pale in colour. Under these circumstances, periodic applications of fertiliser will improve the situation.

If you use a slow release fertiliser such as Scotts Lawn Builder you normally only have to fertilise every three months.  This is because the fertiliser is slow release.  You can use most slow release fertilisers even in winter in warm temperate and tropical climates. 

Granular lawn fertilisers are applied normally three times a year in spring, summer and autumn, however they can be applied more often. In areas with cool to cold winters it is not worth fertilising grass in winter as lawns hardly grow at that time of year.  

If you use Liquid fertilisers you can fertilise more often – every two weeks during the growing season, if necessary.  But generally speaking, once a month is enough to have your lawn looking lush. 

Can you fertilise a lawn in winter?

You can also use liquid fertiliser during the winter in warm temperate and subtropical areas but once or twice is all that should be needed over the winter period to keep the lawn looking green.

Fertilising grass in temperate, mediterranean and warm temperate areas is generally a waste of product and time as lawns will slow down their growth during winter.  It is not usually worth applying granular or organic fertiliser in winter in these regions. 

If you choose to use a slow release or liquid fertiliser during the winter months, the result will only be moderate – greening up the lawn slightly with only mild growth is achieved. 

If you live in a subtropical or tropical area, using a granular or organic lawn fertiliser in winter will give a moderate improvement in growth and green up the lawn nicely. You can also use slow release fertilisers such as Scotts Lawn Builder in winter. 

Liquid fertilisers are also great at greening up turf in winter in tropical regions. 

Fertilisers and Weeds

Fertilisers can be used control a weed problem.  Most weeds that cause problems in lawns are known as “broad leaf weeds”.  Weeds can be controlled with products like “weed n feed” and there are a number of variations of these types of products. 

Normally, these products come as either granular or spray-on. Generally, the granular product is made up of various forms of fertiliser and can be used on all lawn types (please read the pack first). 

The liquid versions have fertiliser and a chemical added.  Note that these can only be used on certain lawn types.  

Buffalo lawns are particularly badly affected by certain chemicals and will be damaged by the liquid form of “weed n feed”, so always read instructions (or consult your local nursery) before using these products.   

The granular fertiliser based “weed n feed” is a very useful product as it will control weed growth (again, read instructions) and then act as a fertiliser to assist your lawn grow. 

Once you have got your weeds under control it is time to improve the rate of growth of your grass.  Essentially, your goal is to try and accelerate the growth of your lawn so that it develops complete coverage. 

Fertilising grass in spring and summer will promote new growth.  Once you have got good lawn coverage you can back off watering and fertiliser.  

You can fertilise your lawn a number of times through the growing season.  Once your lawn is growing thickly again you can stop fertilising and also cut back on the watering.  Your lawn should now be heading along the path to looking good again. 

How to keep Turf healthy and reduce fertiliser use

There are tricks to keep your grass looking good and reduce fertiliser usage.  One simple measure is to leave some of the clippings on the lawn. 

This can be difficult at times as the build up of leaf on the lawn can create yellow spots (as the lawn underneath is not getting any sun).  There is an easy solution here – simply mow more often and leave the catcher off the mower. 

The grass cuttings that are left will dry out and drop down into the soil, decomposing and fertilising the lawn.  Leaving leaf now and then will also help the lawn to become more drought resistant as the decomposing leaf (organic matter) will hold moisture in the soil. 

There are mowers that have been designed for this purpose, and they are called mulching mowers. They cut the leaf up into very fine particles.  Cylinder or reel mowers are also excellent at spreading the leaf nicely across the surface of the lawn so it can fall down into the soil. 

See here for more tips on fertilising grass in our piece, Solving Common Problems With Your Lawn.

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Growing and Maintaining a Grass Lawn

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