How to Read and Understand NPK Ratios

Not sure what 20-20-20 means? Or when to use a high-phosphorus blend? This guide explains how to choose the right NPK for your garden—without the guesswork.

At CompleteGrow, we include clear NPK ratios on all our fertilisers so you can match your plant’s needs with the right formula. Here’s how to decode those numbers and grow better, faster.

What is NPK?

NPK stands for:

N = Nitrogen – for leafy green growth
P = Phosphorus – for roots, flowers, and fruit
K = Potassium – for overall strength, immunity, and productivity

The numbers on a fertiliser (like 20-20-20) represent the percentage of each nutrient in the mix. So in this example, it’s 20% nitrogen, 20% phosphorus, and 20% potassium.

When to Use a Balanced Fertiliser (Like 20-20-20)

Our CompleteGrow All-Purpose Liquid Fertiliser (NPK 20-20-20) is balanced for general use—perfect for new gardens, potted plants, leafy greens, and regular feeding.

Best for:

Balcony gardens and indoor plants
Leafy vegetables and herbs
Starter feeds for seedlings (at diluted strength)

It keeps growth consistent without overloading one area of the plant—great when you want overall performance.

When to Use a High-P and K Fertiliser (Like 4-18-38)

Our NPK 4-18-38 + Calcium & Magnesium blend is a powerful option for flowering and fruiting stages. The high phosphorus and potassium levels help plants focus on bloom, strength, and yield—not just leafy growth.

Best for:

Tomatoes, capsicums, and cucumbers
Herbs going to flower (like basil or chives)
Hydroponic or soil systems during mid-to-late stages

This formula also includes calcium nitrate and magnesium sulphate for better fruit quality, nutrient transport, and resistance to blossom-end rot.

Want a Custom Blend?

If you grow specialty crops or rotate through different plants seasonally, you can request a Custom NPK Powdered Blend from us. We’ll help you match the NPK to your crop type, setup, and desired outcome.

Perfect for:

Growers with advanced or multi-stage crop cycles
Commercial or greenhouse operations
Gardens needing fine-tuned nitrogen or potassium ratios

Quick NPK Summary Table

NPK	Use Case	CompleteGrow Product
20-20-20	Balanced growth – leaves, roots, stems	All-Purpose Liquid Fertiliser
4-18-38	Fruiting, flowering, yield strength	NPK 4-18-38 + Ca & Mg
Custom	Tailored to specific plant/crop needs	Custom Powdered NPK Blend

Final Tip: Don’t Guess—Feed with Purpose

Understanding NPK means you can choose fertilisers that support what your plant is doing right now—growing leaves, building roots, or producing fruit. With CompleteGrow’s clean and clear blends, you’re always in control.

Want to match your plant to the right ratio?
Explore CompleteGrow Fertilisers →