Woman Gardening

First up, why do we need to fertilise our plants

Well, you don’t have to. It’s your garden after all. But your plants will grow so much better if you do. Fertilisers will help your plants develop:


  • More Flowers
  • More Fruit
  • More leaf growth
  • More root growth
  • Bigger size
  • Stronger healthier structure
  • More disease resistance

So you can see why giving Mother Nature a helping hand can be a very good thing.


Two kinds of fertiliser

Fertilisers come in two main sorts – organic and inorganic.

Organic fertilisers are made from biodegradable ingredients such as


  • Blood, fish and bone
  • Animal poop
  • Composted plant matter
  • Steeped plant material eg comfrey tea
  • Seaweed


They release elements into the soil slowly, help general plant health, and often improve the structure and texture of the soil also.

Inorganic fertilisers are made from a blend of substances, usually rock and petroleum, that contain concentrated forms of nutrients that release elements quickly into the soil. It doesn’t mean you are putting ‘chemicals’ on your plants.


Inorganic fertilisers are often balanced to achieve a particular goal, eg bigger fruit, or to suit a certain type of plant which needs special treatment.

Pot Plant


You can find both kinds of fertiliser in various formats:


  • Dried pellets
  • Powder
  • Ready to pour liquid
  • Concentrated liquid
  • Foliar spray
  • Mulch
  • Well rotted manure
  • Slow-release granules

Choose whichever format you prefer to use.


What’s in my inorganic fertiliser?

If you read the side of a fertiliser packet, you’ll see three key letters – NPK – and a number or percentage beside them.

This shows the balance of key nutrients in the fertiliser. The higher the number, the more of that nutrient the fertiliser contains.

Most general and all-purpose fertilisers have a balance of all three elements, so the plant gets a little of everything. Like a plate of meat, veg and potatoes.

Some specialist fertilisers will have more of one element than the others.

Here’s what they 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.

Inorganic 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 Magnesium, Iron, Calcium or other elements listed.


When to fertilise

Most plants appreciate an application or two of organic fertiliser at the end of every growing season, to help them recuperate and re-energise for another year.

Plants that have a flowering or fruiting period will benefit from specialised inorganic 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.

Some plants don’t like a lot of fertiliser. Native plants only need a very weak fertiliser, as they have evolved to thrive on poor soils. They also don’t like all-purpose fertilisers that have a lot of phosphate, so look for a low P number or a specialist native fertiliser.

If you’re growing orchids or ferns, use liquid fertiliser at a very weak solution. Apply to orchids when the plant has started to produce a flower spike, and to ferns when new growth has emerged. Orchid fertilisers are formulated at very low concentrations to prevent over-feeding; but you can use an all-purpose flowering plant fertiliser if you dilute it to at least half the recommended solution strength, or weaker.