Understanding Plant Nutrients: Macronutrients, Secondary, and Micronutrients

Plant nutrients fall into three groups: macronutrients, secondary nutrients, and micronutrients.

Macronutrients

Chief nutrients: carbon, oxygen, hydrogen, nitrogen, phosphorus, potassium. Carbon and oxygen from air (CO₂); hydrogen from water. Nitrogen, phosphorus, potassium absorbed from soil—the "three major nutrients" most often added to gardens.

Nitrogen

Required for proteins, chlorophyll, enzymes. Fast-growing plants need more. Sources: decomposing organic matter, rainfall, groundwater, nitrogen-fixing bacteria on legume roots. Water-soluble, easily leached. Deficiency: spindly growth, yellowing older leaves. Remedies: compost, manure, nitrogen fertilizers, crop rotation with legumes.

Phosphorus and Potassium

Critical for reproductive phase—fruit and seed development. Potassium also crucial for root formation. Deficiency reduces flower/fruit size/quantity; potassium lack weakens roots, stems, causes leaf curling. Unlike nitrogen, they're in soil mineral particles, released slowly. Must be applied near roots—surface sprinkling ineffective. Apply when digging new beds, or scratch into top inch for established plants; liquid fertilizer for quicker effect.

Secondary Nutrients

Calcium, magnesium, sulfur. Largely from soil minerals. Calcium for cell synthesis and root tips. Magnesium core of chlorophyll. Sulfur combines with nitrogen for protoplasm.

Micronutrients

Copper, iron, manganese, zinc, other trace minerals. Copper/iron for chlorophyll; manganese/zinc as catalysts. Usually available via soil minerals. High alkalinity can block uptake. Correct deficiencies with foliar sprays or soil applications—most common is chelated iron for chlorosis.

Nutrient Chart

Macronutrients	Symbol
Carbon	C
Oxygen	O
Hydrogen	H
Nitrogen	N
Phosphorus	P
Potassium	K
Secondary Nutrients	Symbol
Calcium	Ca
Magnesium	Mg
Sulfur	S
Micronutrients	Symbol
Copper	Cu
Iron	Fe
Manganese	Mn
Zinc	Zn