While watering is a key element to growing indoor plants, feeding a plant is where most people lose the battle in sustaining life in their plants. There are several options for plant food. Pump sprays can be added directly to the soil, or mix it with water and feed once a week. Plant food spikes are a set it and forget it solution, for the most part. These spikes provide a continuous supply of important nutrients right at the roots, where plants need it most. The pre-measured, specially formulated spikes are simply inserted into the soil around your plant. Apply a fresh stick every eight weeks.