Choosing the right fertiliser can feel confusing, especially when every bag or bottle has different numbers on the label.
10-10-10.
20-5-10.
3-1-6.
What do they actually mean… and how do you know which one your plants need?
This guide breaks it down simply, so you can confidently choose the right NPK fertiliser for your garden, lawn, veggies or flowers, without guesswork or overfeeding.
What Does NPK Mean on Fertiliser Labels?
NPK refers to the three primary nutrients plants need to grow well:
-
N – Nitrogen: Supports leafy, green growth
-
P – Phosphorus: Encourages strong roots, flowers and fruit
-
K – Potassium: Improves plant health, resilience and disease resistance
The numbers you see on fertiliser labels show the ratio of these nutrients by weight.
For example:
10-10-10 = a balanced fertiliser with equal parts nitrogen, phosphorus and potassium.
Understanding these ratios is the key to feeding plants what they actually need, instead of stressing them with the wrong nutrients.
Why Choosing the Right NPK Matters
Plants don’t all grow the same way — and they don’t all need the same nutrients at the same time.
Using the wrong NPK ratio can lead to:
- Lots of leaves but no flowers
- Weak roots and poor fruiting
- Burnt plants from overfeeding
- Wasted fertiliser that never gets used
The right NPK, applied correctly, helps your garden:
- Grow faster and stronger
- Flower more reliably
- Produce better harvests
- Stay healthier through heat, cold and stress
How to Choose the Right NPK for Different Plants
Lawns & Leafy Growth
If your goal is lush green growth, nitrogen is the priority.
- Best NPK: Higher N, moderate K, low P
- Ideal for: Lawns, leafy greens, hedges
A steady feeding approach works best here, especially in Australian conditions where growth can surge quickly after rain.
Vegetables & Productive Gardens
Veggies need balanced nutrition, but their needs change as they grow.
- Early growth: More nitrogen for leaf development
- Flowering & fruiting: Increased potassium for yield and quality
A balanced NPK is ideal, with the flexibility to top up nutrients as needed.
Flowers, Fruit & Blooming Plants
If your plants are leafy but not flowering, the issue is often too much nitrogen and not enough potassium.
- Best NPK: Lower N, higher K
- Ideal for: Roses, ornamentals, fruit trees, flowering natives
Potassium supports bud formation, colour intensity and flower longevity.
👉 For targeted bloom support, explore
Our handpicked Flower Boosters & Enhancers
designed to promote stronger flowers and better fruit set.
Liquid vs Slow-Release Fertilisers (Which Is Better?)
Both have their place — and the best gardens often use a combination of both.
Liquid & Foliar Fertilisers
Best for:
- Fast results
- Correcting deficiencies
- Supporting plants during stress or rapid growth
They’re absorbed quickly and are perfect when plants need nutrients now.
👉 Ideal options can be found in
Liquid & Foliar Solutions
Slow-Release Fertilisers
Best for:
- Long-term feeding
- Lawns and garden beds
- Low-maintenance gardens
They release nutrients gradually, reducing the risk of burn and nutrient runoff.
👉 A reliable option for Australian gardens is
GreenSpace Slow Release Fertiliser
How to Apply Fertiliser Correctly (And Avoid Common Mistakes)
Even the right NPK can cause problems if applied incorrectly.
Key Tips for Best Results
- Always water plants after fertilising
- Follow label rates — more is not better
- Avoid fertilising stressed or heat-affected plants
- Feed little and often rather than all at once
Common Fertiliser Mistakes
- Overusing nitrogen and getting leafy plants with no flowers
- Applying fertiliser to dry soil
- Ignoring seasonal growth patterns
- Using one fertiliser for every plant
Matching NPK to plant type and growth stage prevents most issues before they start.
Do You Need to Test Your Soil?
Soil testing can be helpful, but most home gardeners can get excellent results by:
- Observing plant growth
- Matching fertiliser to plant type
- Adjusting feeding during flowering or fruiting stages
If plants look healthy, green and productive — your NPK choice is working.
Choosing the Right NPK: The Simple Rule
If you remember just one thing, remember this:
- Leaves = Nitrogen
- Roots & Flowers = Phosphorus
- Strength & Blooms = Potassium
Match the fertiliser to what your plant is trying to do right now — and your garden will reward you.
Final Thoughts
Choosing the right NPK doesn’t need to be complicated.
When you understand:
- What the numbers mean
- What your plants actually need
- When to use liquid vs slow-release fertilisers
You can feed with confidence — and grow healthier, more productive plants year-round.
Explore the full range of feeding solutions at Dr Greenthumbs to support every stage of growth:
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