In spring most plants put on a spurt of new growth. This makes early spring the ideal time to apply fertilisers to most garden plants and also to lawns.

Fertilisers can be for general use on a wide range of plants or they may be tailored for particular plant groups such as lawns, roses, citrus, orchids, indoor or native plants. General or ‘all-purpose’ fertilisers include composts, manures, blood and bone, or fertilisers labelled as all-purpose.

Fertilisers, also known as plant foods, come in a range of formulations including granular, slow-release and liquid. Which formulation you select depends on your garden size, storage facilities and ease of application.

NPK

Fertilisers contain the major plant nutrients of nitrogen, potassium and phosphorus that control plant growth, flowering and fruiting. Specialist fertilisers have these nutrients in varying amounts and may also contain minor elements such as sulfur, iron, calcium and magnesium.

The major nutrients are indicated by their chemical symbols of N for nitrogen, P for phosphorus and K for potassium. Fertilisers developed for different plants may have these nutrients in different amounts. For example, a fertiliser that’s formulated for citrus may have higher levels of P and K than one formulated for lawns, which will contain higher amounts of N than other plant fertilisers.

These variations relate to the plant’s nutrient needs and are shown as an N:P:K ratio on the fertiliser packet or container. Leafy plants such as grasses benefit from high in nitrogen levels, while fertilisers for flowering and fruiting plants demand higher amounts of phosphorus and potassium.

Do I need a specialist fertiliser?

It is worth buying specialised fertilisers (such as azalea, citrus, native or rose food) if you have the plants to use them on. It is not necessary to buy a different fertiliser for every plant in the garden!

  • If your garden is mainly planted with native Australian plants or other phosphorus-sensitive plants such as proteas, select a native plant food that is low in phosphorus.
  • If you have a garden of acid-loving plants such as azaleas and camellias, use a specialist azalea fertiliser.
  • If you have a number of citrus, roses, hibiscus or other plants with specialist fertiliser needs, use the relevant specialist fertiliser such as a citrus food or rose food. Citrus food can also be used to feed other productive plants along with long-flowering plants such as gardenias, roses, hibiscus and bougainvilleas.

Fertiliser tips

  • Feed all plants in spring with a general fertiliser.
  • Plants growing in low nutrient soils or those that have high nutrient needs such as annuals, vegetables, citrus and roses, require additional fertiliser during their growing period.
  • Follow rates recommended on the package – too much can be harmful.
  • Apply fertilisers evenly for example by using a fertiliser spreader.
  • Water before or after applying fertiliser especially to lawns.
  • Add liquid fertilisers to a filled watering can.
  • Don’t allow fertilisers to come in contact with plant roots. If adding fertiliser to soils at planting time, incorporate it thoroughly or lightly cover the fertiliser with a layer of soil to product the roots.
  • Keep fertilisers in sealed containers away from moisture and sunshine and away from pets.