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Gardening glossary

Micronutrients

Micronutrients are the supporting cast to the NPK headline act. Plants need them in milligrams per kilogram of soil rather than the kilograms per hectare scale of nitrogen and potassium, but a shortage of any one can stop a crop dead.

The eight essential plant micronutrients:

- **Iron (Fe)** — chlorophyll synthesis. Deficiency shows as interveinal yellowing on young leaves (the leaf veins stay dark green). Common in alkaline soils. - **Manganese (Mn)** — photosynthesis and nitrogen metabolism. Looks similar to iron deficiency but appears on slightly older leaves. - **Zinc (Zn)** — auxin production and leaf expansion. Stunted, small, "little leaf" growth signals a shortage. - **Copper (Cu)** — enzyme cofactor; deficiency causes wilting and pale young leaves. - **Boron (B)** — cell wall formation, flowering, and fruit set. Deficiency shows as hollow stems, distorted growth, and poor fruit set (especially in brassicas and beets). - **Molybdenum (Mo)** — needed to fix nitrogen and convert nitrate to amino acids; deficiency mimics nitrogen shortage. - **Chlorine (Cl)** — osmosis and photosynthesis; rarely deficient. - **Nickel (Ni)** — urea metabolism; the most recently confirmed essential element.

In a home garden with healthy soil, a 2–5 cm layer of compost top-dressed each year usually supplies enough of every micronutrient. Problems arise in three places:

1. **Container plants** — peat-based mixes are inert and need a complete feed that includes micronutrients (look for "trace elements" on the label). 2. **Hydroponics** — every micronutrient must be in the nutrient solution; off-the-shelf hydroponic feeds are formulated for this. 3. **pH extremes** — strongly acid soils (below 5.5) can lock up molybdenum; strongly alkaline soils (above 7.5) lock up iron, manganese, zinc, and copper. Fixing the pH usually fixes the symptom.

For a quick diagnosis of which nutrient is short, our [yellow plant leaves guide](/blog/yellow-plant-leaves) walks through the visual patterns.

Where this comes up in our guides

Related terms

NPK ratio

NPK ratio is the percentage of nitrogen (N), phosphorus (P), and potassium (K) in a fertilizer, printed on the label as three numbers like 10-10-10. It tells you which macronutrient dominates the mix.

Soil pH

Soil pH measures how acidic or alkaline your soil is on a 0-14 scale, where 7 is neutral. Most vegetables and houseplants prefer a slightly acidic range of 6.0-6.8, where nutrients are most available to roots.

Nitrogen

Nitrogen (N) is the macronutrient plants use in the largest quantity, driving leafy green growth, chlorophyll production, and overall vigour. It is the first number on every fertiliser label and the one most likely to run short mid-season.

Phosphorus

Phosphorus (P) is the macronutrient that drives root development, flowering, and fruit set. It is the middle number on a fertiliser label and unlike nitrogen, it moves very slowly through soil — so it needs to be present where roots can reach it.

Potassium

Potassium (K) is the macronutrient that regulates water movement, stomatal opening, disease resistance, and fruit quality. It is the third number on a fertiliser label and the nutrient fruiting crops need most as they ripen.