Complete Australian Garden Fertiliser 2023 Users Guide

What Do the Numbers on Fertilisers Mean?

Almost all fertilisers have 3 numbers on their label, known as the NPK, which is why they are often called NPK fertilisers. This is referring to the ratio of the 3 active ingredients in the mix.

• N – The chemical symbol for nitrogen. Plants use nitrogen to create lush foliage and dense green growth.
• P – The chemical symbol for phosphate. This promotes strong root growth, helps plants mature more rapidly, and is needed in the development of fruits, seeds, and flowers.
• K – The chemical symbol for potassium. This helps plants withstand extreme weather, fight off disease, and strengthen plant growth.

The higher the numbers are, the stronger the mix. So, if a fertiliser is a 14 – 5 – 10, it will be made from 14% nitrogen, 5% phosphate, and 10% potassium. The remainder is the carrier material for the fertiliser.

Organic vs Synthetic Fertiliser

Synthetic fertilisers are fast-acting, easy to spread, and inexpensive to buy. However, they don’t contain microorganisms that help hold nutrients in the soil and improve soil quality. They can easily be overapplied, which can be harmful to the water table and environment. 

Organic fertilisers are slower to break down, which is why they are known as slow-release fertilisers, so they provide a steadier and better source of nutrition to plants.

There’s no potentially toxic build-up of organic chemicals in the soil, and they are filled with bacteria that help improve soil quality and protect the ecosystem of your garden. 

However, they are usually a bit more expensive, and you’ll have to wait a little longer to see the results on your plants. Depending on the product, they can also be a little messier or smellier to apply.

Fertiliser for Native Plants

Native plants have adapted over thousands of years to the Australian soil, which is naturally very low in phosphorus. This means that they easily get all the phosphorus they need from local soil.

Fertilisers, especially synthetic fertilisers, tend to contain a lot of phosphorus, and feeding a native plant with this fertiliser can quickly damage and kill it. However, this doesn’t mean they shouldn’t get fed.

Instead, use a native plant fertiliser that is organic and naturally low in phosphorus. They especially enjoy seaweed-based and blood and bone fertiliser, or pellet chicken manure.

What is the Difference Between Garden Fertiliser and Lawn Fertiliser?

These are often referred to interchangeably but are different products. Garden fertiliser is an all-purpose fertiliser or balanced fertiliser that will work on most plants that don’t have unique nutrient needs.

It will usually be a mix of equal amounts of nitrogen, phosphate, and potassium, which helps promote green growth, flowers, and fruiting. On the label, it will usually be called a 10-10-10 fertiliser for this reason.

Grass, however, has different nutrient needs, as you want it to have strong leaf growth, but there’s no need to promote flowering or seeding. 

The best fertiliser for lawns will be specifically designed to promote green growth and disease resistance and will have a high ratio of nitrogen and potassium but much less phosphate.

They also often contain weed killers to help prevent the types of weeds that tend to grow in lawns, like bindii, lambs’ tongue, and nutgrass. (Learn more about weed killers here.)

Your lawn will still do well on a garden fertiliser but will be better off if you use a lawn fertiliser.

DIY Garden Fertiliser

1. Animal Manure

Manure is one of the best ways to make your soil more fertile and improve plant growth. Not all animal manure can be used, and it’s recommended that your manure comes from animals that eat grains, plants, or grass. Unfortunately, waste from dogs and cats just won’t work. 

Composted manure is rich in the nutrients that plants love, with sheep and goat manure being especially high in nitrogen and potassium, and cattle manure being a more balanced fertiliser containing all necessary nutrients.

Due to its organic nature, it’s safe to work into your soil, although you should wear gloves and wash yourself thoroughly after working with it. Similarly, be sure to carefully clean the herbs and vegetables you grow using manure.

How to Make Manure

Take a drive to a local farm (or make a day trip if you’re in the city) and pick up some raw animal manure. Some places you can get it for free, others sell it for cheap as chips ($1-2/ big bag). You can use manure from cows, chickens, goats, sheep, and even horses.

You can run water through it to help release any excess salts or moisten it up before adding it to your compost heap or mixing it with soil before digging it into your beds.

2. Compost 

Another popular garden fertiliser is compost. It enriches your soil with the essential nutrients and provides a great source of organic fertiliser. As the organic matter breaks down in your soil by microbes, the chemical by-products are released into the soil to be taken up by your plants. 

How to Make Compost

Compost is easy to make! Start by buying or making your own compost bin at home. Should you decide to go with the former, here's our review of the best compost bins on the market. 

Add sticks, leaves, garden refuse, vegetable and fruit waste (no onions or citrus), eggshells, coffee grounds, and newspaper in layers. Don’t put any weeds or seeds in the mix.

Regularly moisten it to help the waste break down. Turn it either using a compost tumbler or spade once a month to keep it aerates, and you’ll have compost in about 6 months. 

3. Worm Castings 

Worms are wonderful at breaking down organic matter and enriching the soil, and if you don’t have enough waste or space to have a compost bin, you can have a worm farm instead. 

How to Make Worm Castings

Simply set up your worm farm and feed it with fruit and vegetable waste (no onions, pineapple, or citrus), newspaper, cardboard, eggshells, and coffee grounds.

Run water through it once a week to make sure it stays moist and use the “worm tea” that collects on the bottom layer to fertilise your plants.

Most worm farms have a separate reservoir for this liquid and a tap to make it easy to collect. Worm farm are quite beneficial but be sure to look out for worm infestation as this may be quite challenging to handle. 

4. Ground Coffee and Tea Leaves

If you brew your own coffee or tea, you’re in luck, because coffee grounds and tea leaves are a pretty decent source of nitrogen, potassium, and phosphorus for your plants.

Just remember to remove the tea bag itself, as these often contain plastic which is very bad for the environment.

How to Use Coffee Grounds as Fertiliser

Once you’ve brewed your cup of coffee, throw them straight into your soil! It’s as simple as that. If you’re a tea drinker, you can use loose tea leaves in the exact same way.

This is great for plants that love nitrogen (anything that you want big green leaves on) or plants that prefer acidic soils (tomatoes, azalea, and roses).

1. Scotts Turf Builder Weed and Feed Fertiliser

This lawn fertiliser feeds your grass while controlling dandelion and clover growth, so your lawn gets thicker and healthier at the same time.

It’s a synthetic fertiliser and needs to be watered in well to prevent burning the grass, and the 6.48kg bag covers around 460 square metres of grass.

2. Hortico 8kg All Lawn Fertiliser

As a very fast-acting lawn fertiliser, you’ll see very quick results with this product. By making your grass grow more densely, you’ll be able to suppress further weed growth as well as have a lovely soft, green lawn.

This is a fairly slow-release synthetic fertiliser, lasting about 12 weeks in the soil, and it has extra potassium in it to help grass bounce back quickly under heavy traffic. An 8kg bag will cover around 300 square meters of grass.

3. Green Up Lawn Food Fertiliser

This lawn fertiliser works well on all grass types, including kikuyu and buffalo. It’s a fast-acting synthetic fertiliser, so it’s easy to spread and delivers results in 7 days, although you do need to water it in to prevent it from burning your grass. 5kgs will feed around 200 square meters of lawn.

4. Hortico 10kg Organic Lawn Fertiliser

This organic lawn fertiliser is affordable, suitable for all lawns, and designed for easy application. It’s a BFA registered product, so it’s good for your garden and the environment, and the slow-release granules supply nutrients to your plants for up to 2 months.

The organic ingredients help improve the soil biome, improving moisture retention and making your soil as well as your plants healthier. 10kgs covers around 280 square metres.

5. Yates 12.5kg Dynamic Lifter Organic Plant Food

This is a very slow, gentle release organic fertiliser that is ideal for flowers, vegetables, container plants, and even Aussie native plants.

Dynamic lifter made using chicken manure as well as fishmeal, bonemeal, and seaweed to help organically enrich the soil. 

It’s been formulated into pellets to make application easy, and it helps improve moisture retention and soil quality too. 12.5kgs feeds around 25 square meters.

6. Worm Casting Vermicompost

Worm castings or vermicompost is a natural and organic fertiliser that can be used on vegetable gardens, fruit trees, flower beds, and container plants. It can also be used in hydroponic setups.

These castings are rich in bacteria as well as nutrients, activating your soil and providing an aerobic environment for your plants to thrive.

They are safe for native plants too, are odour-free, and easy to apply.

7. Blue Planet Nutrients Liquid Seaweed

Derived from Ascophyllum nodosum seaweed, this liquid fertiliser is all-natural and 100% organic. It can be used on all types of plants, including native plants, as well as aeroponic and hydroponic setups.

The nutrient-rich formula contains over 60 trace elements, amino acids, enzymes, carbohydrates, and fully chelated readily available micro-nutrients that help by boosting plant growth and health.

8. Seasol 4L Seaweed Health Tonic Concentrate

Easy to dilute and apply, this fully organic seaweed-based liquid fertiliser stimulates plant growth, improves plant colour, promotes plant health and enhances fruiting and flowering.

It’s safe to use on native plans and helps to improve weather and drought resistance by improving moisture retention and introducing healthy bacteria into the soil.

9. Richgro 1L Black Marvel Tomato And Vegetable Food Liquid Fertiliser

Ideal for fruit and vegetable gardens, this liquid fertiliser helps you supply the nutrients these plants need to deliver a good yield at every harvest.

It’s high in nitrogen and potash, and the iron content helps green up growth and promote plant health. It works quickly on all fruit and vegetable crops, and 1 litre makes up to 450 litres of fertiliser.

Garden Fertiliser Frequently Asked Questions

What is the best fertiliser for your garden?

The best fertilisers for your garden are those you can find locally, which use organic materials to create rich, moisture-retentive, but workable compost. Organic horse manure, cow manure, or leaf mould are ideal all-rounders, but some plants need more calcium to support flowering, so fish blood and bone is a useful traditional alternative.

What is the best homemade fertiliser?

Comfrey tea and nettle tea are brilliant DIY liquid fertilisers for your garden, and if you have access to seaweed that can be legally harvested, it works both dried and wet as a mulch.

Making your own fertilisers at home is a smelly business, but is as simple as placing high-nitrogen materials in a bucket or water, applying pressure, and leaving them over winter for a big batch of concentrated feed in spring.

When should you fertilise your garden?

For vegetables and home-grown produce, you should fertilise your garden as soon as your plants are in the ground, and over 30cm tall. Some plants like feeding sooner, others later, but it's safer to let them establish slightly before fertilising. Then, fertilise them every 1-2 weeks through the growing season.

What is the cheapest way to fertilise a garden?

Homemade compost doesn’t cost a penny, and reduces your kitchen waste, bin collections, and makes use of old vegetable plants, fallen leaves, and grass clippings too. All you need in a compost bin, in a reasonably sunny spot, and patience.

Is human urine a good fertiliser?

Human urine is not a good fertiliser. There are so many articles online that suggest human urine as a reasonable fertiliser, but it attracts vermin, stinks, and is only useful due to its high nitrogen, potassium, and phosphorus levels. In theory, it is useful for brassicas but, honestly, it’s not worth it!

When should you not fertilise?

Fruit trees should not be fertilised after they have set fruit. Citrus trees are an exception, but avoid feeding them through winter as they prefer to hold onto fruit through cooler months, rather than producing new ones.

What plants should not be fertilised?

Most perennial garden plants do not need fertiliser. Herbaceous plants with rhizomes or corms can benefit from a mulch-based feed over winter, but most fibrous perennials like carnations or Echinacea can become too damp over winter with mulch, and overfed in spring and summer from liquid feed, so leave them to find their own nutrients in the soil.

Is liquid or dry fertiliser better?

Granular fertiliser is longer lasting and more cost-effective than liquid fertilisers, but liquid fertilisers will give faster results. To revive dying plants, or underfed plants, liquid fertiliser is best. For annual or routine applications of fertiliser, granular is best.

What is the most harmful fertiliser?

Anhydrous ammonia is an incredibly harmful fertiliser, often stored as a gas or pressurised liquid, it is sprayed over crops, typically in late winter or spring, and can cause severe burns if it comes into contact with the skin. It is also incredibly harmful to wildlife.

Are fire ashes good fertiliser?

Wood ash is a great fertiliser, and a high source of carbon and calcium. It also helps to raise the pH to near neutral in highly acidic gardens. Do not use coal or charcoal ash as it is too acidic and can slow down the development of other composting materials

How do I know if my soil needs fertiliser?

There are two ways to tell if your soil needs fertiliser. The first is easy but expensive; buy a soil test kit. The second is free, but requires some learning; look at your plants.

If your plants are dropping leaves, buds, or developing spots on their leaves, they are often lacking in calcium, zinc, or magnesium which help prevent disease. It can be hard to spot though, so if you’re in a hurry, find a good soil testing kit online.

Is it better to put down fertiliser before or after rain?

The best time to put down granular fertiliser is before rain, when the rain will help to improve soil contact and begin its feeding process. For liquid fertiliser, the best time to apply it is after rain, or when none is forecast. Heavy rain can wash fertiliser away or dilute it.