Like a hearty dinner, a good dose of fertiliser will treat your plants to the sort of feed that can be hard to come by when you’re rooted to the spot. It’s important to know your fertilisers to give your plants the meal best suited to them.

You wouldn’t serve up a juicy cut of sirloin to a vegan. Your plants have preferences too.


A good gardener will be eyeing the fertiliser packets on the lookout for the levels of nitrogen, phosphate and potassium (scientifically N:P20:K20, shortened to NPK), as the ratio of these will govern how helpful any given fertiliser will be during different periods of a plant’s cycle.

An organic fertiliser like blood and bone may have a rating of N12-P3-K0 – 12 percent Nitrogen, 3 percent Phosphate, and 0 percent Potassium. If you have this knowledge, it’s important to use it to prevent deficiencies in your soil before they happen, rather than treat deficiencies that have already occurred. That’s just good gardening.

Nitrogen-heavy fertilisers – the ones with a larger number next to the ‘N’ and smaller next to the ‘P’ and ‘K’ – are best used when your plant is in its vigorous growing period, or all year round for leafy vegetables.

Phosphate-rich fertilisers – a larger number next to ‘P’ – are great for measured use when a plant begins to bloom.

Potassium-heavy fertilisers – a larger number next to ‘K’ – are best used sporadically throughout the year to keep up the general health of your plants.

Now we’ve got our heads around the ratios, there are four main types of fertiliser mediums you can used to help enrich your soil:


Organic fertilisersare concentrated sources of plant nutrients that have been obtained from living organisms. Blood and Bone, for example, is an organic fertiliser as it is derived from dried blood and bone meal.


Inorganics, on the other hand, are sources of plant nutrients that derived from non-living materials. These commonly take the form of base elements, such as superphosphate and calcium nitrate.

Bulky Organic Matter

Your classic compost or manure options will fall into the bulky organic matter category. These sorts of fertilisers often shouldn’t be seen as fertilisers, as it is very difficult to know the NPK make-up of the mix (and whether it’s right for your plants). If used as just a general soil improver, and spread like mulch on top of the soil, results may be better.

Green Manure

This is the process of growing certain types of plants in your soil, then turning them over and digging them back into the soil, feeding the soil as a form of organic matter. A bit like leaving your lawn clippings on top of your grass to allow them to re-incorporate into the soil.

Fertilisers can either be straight or compound, meaning that you either get one of the Nitrogen, Phosphate or potassium included, or a mixture of the three.

Straight Fertilisers

Straight will supply just one of the macronutrients mentioned in the NPK ration. If you needed only extra nitrogen in your soil, you could go a dried blood fertiliser, or ammonium nitrate.

Compound Fertilisers

The ratio of compound fertilisers are expressed as the ratio mentioned above – N:P:K – denoting the percentage of the fertiliser each element makes up. A fertiliser with the values 1:1:1 is referred to as a ‘balanced’ mix.

On top of this, the action of the fertiliser also needs to be taken into account. You’ve got the choice of quick acting or slow release, their structure reflecting how they act.

Quick Acting

Fertilisers that dissolve on contact with water are referred to as quick acting, and are available in liquid, crystal, granule or powder forms. This instant dissolvability means that the plants can take up the nutrients as soon as there is a bit of moisture around. Examples include potassium chloride and ammonium nitrate.

Slow Release

On the other end of the scale, slow release fertilisers will drip-feed your plants the nutrients they need. Whether the process be artificial (a coating added to the fertiliser to delay its breakdown) or natural (micro-organisms needing to break down the material, such as bone), these fertilisers can save you time on constant re-application.

Whatever your garden situation, having a solid base knowledge of the basics of fertilisation can be the difference between an average and a radiant backyard.

As always, treat your plants well and they’ll treat you well back.


Shopping for Western Australia?

If so, please click here to view the store servicing your state.
Otherwise, click anywhere else (or hit ESC key) to shop for all other states in Australia.