What is a fertiliser?

A fertiliser is any material (natural or synthetic) that is added to soil, water, or directly to plants to supply one or more essential plant nutrients to improve growth, yield, and health.

Main purposes of fertilisers:

• Provide essential nutrients that may be lacking in the soil
• Increase crop production and quality
• Correct nutrient deficiencies
• Speed up plant growth

What nutrients are essential?

Plants require 17 essential nutrients to grow. There are others that benefit plant's but a plant can grow perfectly well without them. The main three are Nitrogen, Phosphorous and Potassium. When you see three numbers on a fertiliser, these numbers tell you the nitrogen, phosphorous and potassium percentage in that order. The nutrients are separated into two categories:

Macronutrients

1. Carbon (C) – from CO₂ in air
2. Hydrogen (H) – from water
3. Oxygen (O) – from air and water
4. Nitrogen (N) – from soil / fertilizer
5. Phosphorus (P) – from soil / fertilizer
6. Potassium (K) – from soil / fertilizer
7. Calcium (Ca) – from soil / fertilizer
8. Magnesium (Mg) – from soil / fertilizer
9. Sulfur (S) – from soil / fertilizer

(The first three — C, H, O — are often listed separately because plants obtain them primarily from air and water rather than soil, but they are still macronutrients.

In agricultural and fertiliser contexts, people usually refer to N, P, K as the primary macronutrients and Ca, Mg, S as the secondary macronutrients.

Micronutrients (Trace Elements)

1. Iron (Fe)
2. Manganese (Mn)
3. Zinc (Zn)
4. Copper (Cu)
5. Boron (B)
6. Molybdenum (Mo)
7. Chlorine (Cl)
8. Nickel (Ni)

What happens if the plant doesn't have enough nutrients?

When a plant does not get enough of one or more of the 17 essential nutrients, it develops deficiency symptoms. The plant cannot complete its normal physiological functions → growth slows or stops, leaves discolour or deform, yields drop dramatically, and in severe cases the plant dies.

Each nutrient has a specific role, so each deficiency produces a characteristic visual symptom pattern. Very importantly:

• Mobile nutrients (N, P, K, Mg, sometimes S) → the plant can move them from older leaves to new growth) → symptoms first appear on older/lower leaves.
• Immobile nutrients (Fe, Ca, B, Zn, Cu, Mn, Mo, Cl → the plant cannot easily relocate them) → symptoms first appear on new/young leaves or growing tips.