Understanding fertilisers

Maintaining a glorious garden brimming with scented flowers and vibrant foliage is easy - just give plants what they want:

  • Water
  • Sunlight/Shade
  • Nourishment

You’ve already chosen their positions and you know how to wield a hose, but how do you make sure they have all the nutrients they need to develop strong roots, masses of flowers and lush foliage?

By using fertilisers, of course!

Let’s take a look at what you need to know to select the right fertiliser for your garden, including:

  • Types of fertilisers
  • Understanding fertiliser ratios
  • What to use and when
  • The importance of pH

light-bulb-icon@2x.png What you need to know


The type of fertiliser you choose will have a huge impact on the health of your garden. There are lots of options available, and choosing the right one at the outset can save you time and money in the long term.

Types of fertiliser

The most common types available:

  • Organic based - either certified 100% organic or including organic matter
  • Composts and soil improvers
  • 'Instant hit' powder, granular and liquid fertilisers
  • Slow-release fertilisers
  • Controlled release fertilisers

Learn more about the frequency, pros and cons of each 

Understanding fertiliser ratios

Fertilisers are combinations of essential elements (nutrients) that have been mixed at specific ratios to encourage plants to grow, flower or fruit.


  • Fertiliser manufacturers list these ratios on the packets, usually shown as N:P:K or Nitrogen (N), Phosphorus (P) and Potassium (K). These are the macro or major chemical elements that directly impact plant growth and development.

  • Plants also require micro nutrients and trace elements to maintain optimal health. To see what these are and why they are important to plants, look at Fertiliser Components and their Uses

Most fertiliser packaging will include a Guaranteed Analysis that lists all major, minor and trace elements included and their relevant percentages or parts per million.

The importance of pH

  • The pH of your soil determines the availability of some nutrients
  • Test your pH every 3-4 years and adjust accordingly
  • pH should be between 5.5 and 6.5 for most flowering trees and shrubs.

To find out more about soil pH and healthy soils read our story
How to establish a new garden bed

light-bulb-icon@2x.png What fertiliser and when


Different fertilisers are required at different stages of plants' lifecycles. Whether it's establishing a new tree or encouraging more flowers and fruit, there's a fertiliser to suit each stage of growth and development

Plant type

Young and newly planted trees

What: Use a high nitrogen fertiliser to help develop strong growth.


Note: Additional applications of chicken manure will also be of benefit.

Acid-lovers like gardenias, camellias, azaleas and roses.

What: Use a fertiliser like Scotts Osmocote Plus Trace Elements for Roses, Gardenias, Azaleas & Camelllias which has been specifically designed to give acid-loving plants the nutrients they need to flourish


Note: Use a controlled release fertiliser to ensure the right nutrients are available when required.

Native trees and shrubs

What: Use a fertiliser designed for phosphorus sensitive plants


Note: Native plants need fertiliser but they are accustomed to phosphorus-deficient soils and will react badly if high P fertilisers are used.

Flowering plants

What: To encourage flowering, most plants benefit from a fertiliser high in phosphorus like Miracle-Gro MaxFeed All Purpose. This is best applied as needed in Spring and Summer


Note: Use an all-purpose controlled release fertiliser  twice a year, and apply liquid feeds throughout spring and summer for maximum wow!

Dormant (deciduous) trees and shrubs

What: Do not fertilise them while they are devoid of leaves!


Note: Wait until the first signs of new leaves and flowers appear in Spring before fertilising

Additional fertilising

What: Scotts Pure Organic Premium Seaweed Plant Food will improve plant health as well as pest and disease resistance.


Note: Liquid fertilisers help to give plants an instant boost as they contain a mix of macro, micro and trace elements.

Tips, tricks & advice

How to establish a new garden bed

Step by step guide to establishing new garden beds including:

Read more

Drought proofing your garden

Growing a beautiful garden in drought conditions is easy with:

Read more

Other products you might need

Scotts Osmocote® Plus Trace Elements: Total All Purpose


The smart way to fertilise the entire garden - one easy application feeds continuously for up to 12 months

Scotts Osmocote® Boost+Feed Roses, Gardenias, Azaleas & Camellias


Easy to use, double action liquid plant food for roses, gardenias, rhododendrons and similar shrubs that prefer an acid ('sour') fertiliser and soil to perform well

Scotts Osmocote® Plus Trace Elements: Roses, Gardenias, Azaleas & Camellias


A set & forget plant food for roses, gardenias, rhododendrons and other shrubs that prefer an acid ('sour') fertiliser and soil to perform well

Scotts Osmocote® Plus Trace Elements: Native Gardens


A low phosphorus complete plant food developed specifically for Australian native plants and members of the protea family

Scotts Osmocote® Boost+Feed All Plant Types incl Natives


Easy to use unique formula that is carefully balanced to provide plants with essential nutrients for optimum growth and plant health. Its double action works through the roots and leaves, so your plants absorb nutrients within minutes.