Plants in the ground can draw nutrients from the soil. Your potted plants at home rely heavily on you for all their nutrients.
There are two classes of fertilisers – organic and inorganic.
Organic fertilisers are derived from animal or vegetable matter such as animal dung, seaweed and fish emulsion.
Inorganic fertilisers are chemicals referred to as "NPK", which is named for their three major constituents - Nitrogen (N), Phosphorus (P), and Potassium (K). These fertilisers normally include micronutrients called "trace elements", which are essential to plant growth. These include boron, copper, iron, flouride, manganese and zinc.
Your plants require a regular supply of fertiliser. The golden rule is "little and often."
Quick growing plants such as flowering plants require more fertiliser than a slow growing one like cactus.
Tips for fertilising
Symptoms of over-fertilising: Your plant displays signs of burning and toxicity with greasy-looking marginal spots, brown burnt looking tips, elongated reddish-brown spots on young leaves and dark green ring spots of yellow and brown spots on leaf margins.
Symptoms of nutrient deficient: Your plant shows no signs of flowering and displays general yellowing of leaves, small leaves and short internodes.