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Your guide to fertilisers

What is the purpose of fertiliser in the garden?

Like humans, plants require food, water and sunlight to flourish. They obtain the majority of their nutrients directly from the soil, including the big three, nitrogen (N), potassium (K), and phosphorus (P), plus a whole heap of fantastic other minerals and trace elements. 

In most garden soil and topsoil, this is in limited supply and over time they will be depleted either by the plant or leached out by watering or weather. The use of fertilisers is a way of supplementing the nutrient supply within the soil as this occurs.

When should you fertilise?

Most plants will benefit from a good feed of fertiliser once every season. We recommend starting with this type of routine and watching how your plants respond. If required, you can give them a mid-season boost by supplementing with a liquid fertiliser such as diluted seaweed extract, Charlier Carp or worm castings.

The most important time to feed your plants is during the spring as this is when your garden is waking up from winter dormancy and new growth starts to appear.

What type of fertiliser to use

Fertilisers come in many forms from pellets to liquid which can be applied to the soil directly or to the foliage of the plant. With so many options to choose from it can be difficult to decide. The best option is to read the label carefully and ask your nursery or landscaping professional for some advice. Here are some key things to look out for, and the questions to ask.

Organic fertiliser for fruit and vegetables

Is it certified organic?

If you are growing food and intend to keep your soil healthy, organic fertiliser is the only choice. Organic fertilisers are usually derived from such things as cow manure and organic based compost (organic in origin such as plant material). So keep an eye out for certified organic products or fully organic based options.

Remember, what you put in is what you get out, so keep that in mind when choosing fertilisers for the soil. This concept also extends to the quality of your starting soil mix. When importing new soil to start a garden bed or top up an existing spent bed, investing in quality garden soil is imperative. Centenary Landscaping Supplies manufactures a range of truly premium soils and potting mixes called the UltraGrow Collection. These soils are scientifically blended using the best quality ingredient and come pre-loaded with fertiliser to give your plants the best possible start in life. Remember, what you put in your get out.

What you put in determines what you get out!

What is the NPK ratio?

This ratio helps you choose a fertiliser specific to a plant’s needs. Nitrogen is responsible for foliage growth and chlorophyll production. Phosphorus is needed for healthy root growth and overall growth. Potassium promotes flower development.

The NPK ratio will help you choose a fertiliser specific to your plant’s needs. Picture: Erinna Giblin

This basically means:

  • For a garden with lots of flowers choose a fertiliser high in potassium.
  • For a veggie patch with lots of root vegetables choose a fertiliser high in phosphorus.
  • For a garden with lots of green foliage choose a fertiliser high in nitrogen.

Is an all-around fertiliser right for my garden?

Unless you want to feed a specific type of plant or know exactly what your soil needs at a particular point in time, an all-round organic fertiliser is a reliable option. You can add soil conditioners such as seaweed extract, worm casting and rock dust to the mix too.

How much do I apply?

How much fertiliser you need to apply depends on the type of fertiliser and the size of your garden bed, veggie patch or pot plant. The safest method is to follow the instructions on the packet; this will guide you about quantities and any preparations needed.

Remember that you are growing soil first and plants second. So, think carefully about what you are putting in the earth.

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