Fertilising indoor plants is important to ensure they receive the necessary nutrients for healthy growth. The frequency of fertilisation depends on the type of plant and the specific fertiliser being used. A general rule of thumb is to fertilise once a month during the growing season (spring and summer) and to avoid fertilising during the dormant season (fall and winter). It's essential to follow the instructions on the fertiliser packaging and not to over-fertilise, which can lead to burning and damaging the plant's roots. Always water the plant thoroughly before applying fertiliser to prevent chemical burns.