Plant nutrition: understand demand and feed appropriately

Start with how the plant is growing

A rapidly growing tomato, a recently repotted olive and a resting container plant are in different situations. Consider species, season and the nutrients already present in the growing medium. Fertiliser supplies nutrients; it cannot replace adequate light or healthy roots. If growth stalls, first check whether the position and watering suit the plant.

Read NPK without expecting a magic formula

On these fertiliser declarations, NPK refers to nitrogen and the stated phosphate and potassium oxide contents. Other nutrients and their forms may also be listed. The numbers alone do not tell you how much an individual plant needs. Dilution, application method and growing conditions matter too, so the largest NPK figures are not a sufficient comparison.

Apply the right fertiliser form

Read the instructions for the actual pack. Dilute liquid fertiliser with the stated amount of water; weigh, distribute and incorporate solid fertilisers as directed for that product. Even similar products may need different amounts. Foliar and root applications are not freely interchangeable. If you care for several plants, record which product you used and when.

Distinguish compost, repotting and soilless growing

Pre-fertilised compost already contains nutrients. When feeding resumes depends on its declaration and plant growth. Mineral hydroculture supplies nutrients through a differently arranged system, so instructions for compost-grown plants cannot be transferred unchecked. The pH of the fertiliser product is also not automatically the pH of your soil or the diluted watering solution.

Avoid confusing deficiency and excess

Leaf discolouration has several possible causes. Check which leaves are affected, how wet the root ball is and whether roots look healthy. Excess dissolved salts can interfere with water uptake. For recurring garden problems, a soil analysis may be more informative than further fertiliser experiments. Address an identified cause and then assess the new growth.

Frequently asked questions