Fertilizer Basics: N-P-K Explained

Fertilizer supports growth—when applied correctly and at the right time.

Fertilizers are materials given to plants to support healthy growth. They can be organic (derived from natural sources) or inorganic (manufactured/mined). Fertilizers come in several forms including granular, liquid, controlled-release, and tablet.

Helpful note:

The “best” fertilizer depends on the plant, the season, your soil, and your watering habits. Start with the label directions and avoid over-application.

What the numbers mean

On a fertilizer package you’ll see three numbers separated by hyphens (for example, 10-10-10). These numbers are the percentages by weight of: Nitrogen (N), Phosphorus (P), and Potassium (K) (often called potash).

A complete fertilizer contains all three nutrients: N, P, and K.

What they do

• Nitrogen (N)

Leaf showing nitrogen deficiency: pale yellowing and browning along edges — Nitrogen deficiency often shows as overall pale yellowing.

Nitrogen supports green, leafy growth. Because it moves easily through soil and can leach below the root zone, it’s the nutrient most often depleted and needing replacement.

Too much nitrogen can delay flowering, fruiting, and seed set—so more is not always better.

Common deficiency symptoms: overall pale yellow leaves and stunted growth.

• Phosphorus (P)

Phosphorus supports root development, root branching, stem strength, flowering, fruiting, and seed formation/maturation.

Common deficiency symptoms: a red or purplish tinge on stems and foliage.

Leaf yellowing from phosphorus deficiency

Purple leaf margins from phosphorus deficiency

• Potassium (K)

Leaves showing potassium deficiency: scorched-looking edges and yellowing — Potassium deficiency can look like scorched or dry leaf edges.

Potassium helps plants handle stress such as drought, cold, heat, and disease. It can also improve flower color, support tuber formation, and promote a strong root system.

Unlike nitrogen, phosphorus and potassium generally don’t leach as quickly through soil. When planting, many people place fertilizer slightly deeper (below the root zone) so nutrients remain available where roots can access them.

Common deficiency symptoms: dry, scorched-looking leaf edges with irregular yellowing.