Fertilising 101

Fertilising 101

Just like your vitamin enriched, kale packed, turmeric dusted smoothie makes you want to yodel from the top of Mt. Everest, fertiliser gives your plants a boost!

Pilea plantYou may think your plants have an easy life, sitting there looking pretty, pouting their leaves, but they’re hard at work photosynthesising, purifying our nasty germs and pollutants, giving us fruit to eat, producing nectar for bees and magically sprouting flowers too.

It’s exhausting work! And over time it depletes their reserves. All we need to do is give a little back in return.

Easy does it

Fertilising is highly effective, but in small doses. Think how terrible you’d feel after packing in six doughnuts. Just like heart-burn, fertiliser burn is painful for plants and can result in yellow spotting on the leaves and leaf drop.

Recently potted plants and low-light plants do not require as much fertiliser (one application per season). And of course, neither will dead ones.

To prevent burning your plants, always use organic fertiliser. And it’s just better for the environment. Chemical fertilisers contain by-products of petroleum, which studies show, kill off a significant percentage of beneficial microorganisms in the soil.


Organic fertilisers are made from composted chicken manure, seaweed, kelp, bonemeal, bat droppings – all stinky stuff, so expect it to stink! But that’s how you know it’s natural and it works. Think about how the foulest tasting medicines are the ones that actually make you feel better. Same concept.

The ABCs…or NPKs

Fertiliser consists of three main macro elements essential for plant growth.

Nitrogen (N) =  Important for the growth of new leaves, branches and stems. Great for plants with rich greenery.

Phosphorous (P) = Helps build strong roots and overall health. Phosphorous supports healthy leaf and flower development, protects the plant from diseases and ensures it survives through dry spells.

Potassium (K) = A super juice for fruit and flowers. Potassium is not only essential for flowering and fruiting, but is vital in hardening plants against abrupt changes in environmental conditions. If it gets too hot or too cold suddenly, potassium helps the plant defend itself.

If you’ve wandered the store shelves looking at fertiliser bags stamped with three numbers like 5:10:8, 3:2:3 or something similar, this is the ratio of N:P:K. Different ratios are better for different plant types. Fertilisers with higher ratios are more concentrated than those with lower ratios.

So a 5:10:8 formulation on a sack of fertiliser means it contains 5% nitrogen, 10% phosphorous and 8% potassium.

Fertiliser high in Nitrogen is great for houseplants with rich green leaves.

For flowering plants like our Lotus, Goldfish Plant and Hibiscus, a fertiliser with a high potassium ratio like 5:1:5 or 3:1:6 will encourage blooming.

Many fertilisers also contain micro elements, which include Calcium, Magnesium, Boron, Iron, Zinc, Sulphur, Nickel, Manganese, Copper and Molybdenum. Each micronutrient helps cellular and enzymatic development and are just as important as macronutrients, plants just need less of them.














Check your plant's vital signs

Lack of Nitrogen: Plants starving for nitrogen are slow growing, produce shrivelled tiny leaves and have stems that are likely to snap easily.

Low phosphorous: Plant roots need phosphorous to fight pests. Plants that keep on getting infestations will start to look sickly. 

Potassium deficiency: This is indicated by brown plant leaves, or leaves that curl in at the edge, and weakened stems.

To drink up, or eat up?

Fertilisers come in different forms, mostly liquid or pellets or powder form.

Liquid fertilisers

These must be diluted with water according to the instructions on the back of the product. NOTE: For potted plants it’s best to halve the recommended ratio. As potted plants are in a confined space there is more chance of burning.

Pros: Cost effective, diluting means your fertiliser goes further.

Cons: It runs out the drainage holes very quickly: a) leaving you with a stinky puddle b) All those nutrients are just flushing through the plant and not getting absorbed.


Pros: Organic pellets release nutrients over time, making them incredibly effective. Every time you water your plant more nutrients are released. This helps prevent burning, which can happen if they're released all at once, and means you can fertilise less often. Note: wait for the pellets to be completely broken down and then some before adding more

Cons: The pong can last a couple of days, but it’s mess free.


The latest super plant smoothie ingredient is volcanic rock dust! Volcanic dust is a powdered form of mineralised rock or volcanic ash. The mineral base of earth’s soil consists of decayed rock through glacial and volcanic activity. That’s why people farm on the slopes of dormant volcanoes because volcanic ash makes the soil exceptionally fertile.  

Pros: 100% natural and no smell. Rock dust supplies soil with all the nutrients that are essential for plant and animal growth, not just NPK elements.


Rock dust is brilliant at adding trace minerals but it’s not fertiliser, as it does not directly contain the required amounts of nitrogen and phosphorus and is best used in conjunction with organic fertiliser.

Top tips

1. Only fertilise in spring and summer while the plant is growing. Plants that grow faster, like Pileas, should be fertilised more often than plants that grow slowly, like a cactus.

2. Dilute your fertiliser. It’s always best to under-fertilise than over-fertilise.

3. Plants that give us fruits or flowers will require more fertiliser in their lifetimes. When we pick off fruits or flowers, we are taking away those nutrients and should restore them.

4. Fertilise before you water, which releases the nutrients. Don’t fertilise a very dry plant.

5. Sit back and watch your urban paradise grow!