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

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 three to four 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.


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 Osmocote® Boost+Feed All Plant Types 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.


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