Fertilising for Beginners

Fertilising is the aspect of plant care that beginners most often skip — and then wonder why their plants look a little dull and stunted. The good news: it's simple, and even a little fertiliser makes a big difference.

Why plants need fertiliser

Outdoors, plants access nutrients through the natural cycle of decaying organic matter. In a pot, that cycle is closed. Over time, the nutrients in potting compost are used up and need to be replenished.

Plants need three main nutrients:

Nitrogen (N) — drives leafy green growth
Phosphorus (P) — supports root development and flowering
Potassium (K) — overall plant health, disease resistance

These are shown as N-P-K ratios on fertiliser packaging (e.g. 5-5-5 or 10-5-8).

When to fertilise

The golden rule: fertilise only during the growing season.

For most houseplants in Northern Europe, this means:

Active growing: April–September
Rest period: October–March — little or no fertiliser

Feeding a dormant plant with fertiliser can damage roots and cause salt build-up in the soil.

How often to fertilise

Leafy tropical plants (monstera, philodendron, pothos): every 2–4 weeks in growing season
Flowering plants (orchids, anthuriums): every 2 weeks with a bloom-booster fertiliser
Succulents and cacti: once a month in summer, nothing in winter
Slow-growing plants (ZZ plant, snake plant): once every 4–6 weeks

Choosing a fertiliser

Liquid fertilisers are the most practical — you add them to your watering can and feed and water at the same time. Ideal for beginners.

Slow-release granules are pressed into the soil and release nutrients gradually over several months. Low-maintenance.

Specialised fertilisers (orchid fertiliser, cactus fertiliser) are worth using for their intended plants, as the N-P-K ratios are tailored to specific needs.

How to fertilise correctly

Water first — never fertilise dry soil, it can burn roots
Use the correct dilution — half-strength is safer than full-strength
Apply to all plants that are actively growing
Flush the soil occasionally — pour plain water through to rinse out salt build-up every few months

Signs of over-fertilising

White crusty deposits on the soil surface or pot edge
Brown, scorched leaf tips
Wilting despite adequate moisture
Sudden leaf drop

If you suspect over-fertilising, flush the soil thoroughly with plain water or repot with fresh soil.

Signs of under-fertilising

Pale, yellow-green leaves (despite good light)
Slow or stunted growth
Small new leaves
Loss of colour intensity in variegated plants

A simple starter routine

If you want the simplest possible approach:

Buy a balanced liquid houseplant fertiliser (5-5-5 or similar)
Use at half the recommended dose
Add to your watering water every second or third watering from April to September
Stop completely from October to March

That's it. Your plants will reward you visibly.