What Do Those Fertiliser Letters Mean?

Most general and all-purpose fertilisers have a fairly equal balance of all three elements, so the plant gets a little of everything. Like a dinner plate of meat, veg and potatoes!
Some specialist fertilisers made for certain plant families, or to encourage certain growing requirements, will have less or more of one element than the others. Like a powershake for bodybuilders, or a gluten-free diet for coeliacs.
What’s in my commercial fertiliser?
Here’s what those ingredients do:
N = Nitrogen
Nitrogen encourages strong root growth, so it is ideal for young plants that need to get established and settled in their soil. Strong roots help a plant grow well in all aspects. It’s the foundation of a plant.
P = Phosphate (a form of Phosphorus)
Phosphate encourages leaf growth and health. If your plants are looking sad, a phosphate-rich fertiliser can help pick them up. It’s also good for foliage plants, which are all about the leaves.
K = Potash (a form of Potassium)
Potassium encourages flower and fruit growth. Tomato fertiliser is often high in potash, for instance, to encourage blossoms to grow and fruit to set. A high-potash feed is ideal for annual bedding, hanging baskets, patio containers – where a short burst of intense flowering is needed, and the plants aren’t required to grow long term. It's the bodybuilder's powershake.
Commercial fertilisers will also have other trace elements in them to help with certain aspects of a plant’s growth cycle, or soil preferences. You might see elements like Magnesium, Iron, or Calcium listed depending on the kind of fertiliser you have.
What plants need what kind of fertiliser?
Plants that have a flowering or fruiting period will benefit from specialised high-potash fertiliser just before the flowering/fruiting season begins, and periodically throughout. It takes a lot of energy to produce flowers and fruits, and the fertiliser will help provide that.
Many Australian native plants have evolved to thrive on poor soils, and consequently don’t like all-purpose fertilisers that have a lot of phosphate. Look for a low or zero P number, or a specialist native fertiliser, to feed your native plants with.- Osmocote 500g Total All Purpose Fertiliser$9.20Keep all your plants healthy with an annual application of Osmocote All Purpose slow release formula. Includes wetting agent to help uptake....
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- PowerFeed plant food 500ml$13.35Three-in-one liquid packed with organic nutrients, fishy goodness, and trace elements - just add one capful to your watering can every week ...
- Osmocote 700g - Fruit, Citrus, Trees & Shrubs Fertiliser$10.25Extra magnesium for foliage health, revitalises fruit trees and evergreen shrubs. Simply scatter this slow release fertiliser at the drip li...
- Osmocote 700g Vegetable, Tomato, Herb & Garden Beds Fertiliser$10.25High phosphorus mix to boost fruiting and flowering, good for root veg, tree veg, herbs and annual flowers. Easy to use slow release fertili...
- Osmocote 700g Pots, Planters & Indoors Fertiliser$10.25Feeds annuals, perennials, palms, foliage plants - even orchids and ferns. Enjoy lush leafy foliage and healthy flowering container plants y...
- Osmocote 700g Roses, Gardenias, Azaleas & Camellias Fertiliser$10.25Formulated for acid-soil plants eg blueberries, magnolias, camellias, azaleas, gardenias, as well as roses. Get show stopping flowers and he...
- Osmocote 700g Native Gardens Fertiliser$10.25Low phosphorus formulation to keep natives in top condition with a twice yearly application of Osmocote slow release formula. Specifically f...
- All Purpose Fertiliser 500g$7.15This Eclipse fertiliser is made with non-acidifying formulation, meaning it doesn't alter the PH of your soils. Ideal for your indoor and ou...
- Eclipse 500g Pots, Planters & Gardens Fertiliser$7.15Slow release fertiliser for potted plants, window boxes, hanging baskets and garden beds....