The fertilizer is a fundamental element in the cultivation of potted plants, as it supplies all the mineral salts essential for the correct and luxuriant development of the plants; there are different types of fertilizer, both as regards the formulation and as regards the time for which the fertilizer will remain available for the plant. Liquid fertilizers, to be dissolved in water, remain available for a few days, while those in granules or manure, can provide the soil with mineral salts that will be available for the plants for months. The fertilizer is supplied during the vegetative period of the plant, to guarantee the substances it needs in the soil; usually, during the autumn and winter months, it is not necessary to add fertilizer to the pots. The most common fertilizers are in liquid form, and should be mixed with the water used for irrigation, approximately every 12-15 days; Less common fertilizers are instead in granules and tablets, and have the advantage of dissolving a little each time we water, remaining active for about 4 months.
When we use a slow release granular fertilizer, we avoid excesses, usually a heaped soup spoon is enough for a pot with a diameter of 20 cm; it should be spread well on the surface of the vase, in a thin layer, without creating piles of product. In the nursery we also choose the correct fertilizer for each plant; on the packages we can read some numbers, close to the acronym NPK, or Nitrogen, Phosphorus and Potassium; the numbers give the concentrations of the three aforementioned elements; where nitrogen is useful for foliage development, phosphorus for root development and potassium for flowers and fruits.