Fertilizing plants: what, how much, when

NPK, micronutrients, doses and season: the complete guide.

Updated on 2026-07-17 · 6 min

Potted plants deplete substrate nutrients. They must be replenished, but with judgement: over-fertilizing burns roots faster than drought.

What NPK means

N = Nitrogen (leaf growth). P = Phosphorus (roots and flowers). K = Potassium (sturdiness and resistance). A balanced fertilizer has 10-10-10 or 20-20-20 ratio.

The right dose

Golden rule: always half the dose indicated on the label. Manufacturer indications are for ideal conditions; indoors we are almost always under-lit, under-warm, and full doses burn.

When to fertilize

Only from March to September (growing season). Every 3–4 weeks. Never on dry substrate: water first or mix into the watering.

Organic fertilizers

Vermicompost, nettle macerate, banana tea, worm castings: slow but with no burn risk. Ideal for freshly repotted plants or delicate species.