Few things are more beautiful during the summer than a container full of beautiful flowers. Many times though, annual flowers are disappointing and do not meet our expectations. One of the most common reasons that annual flowers do not perform well is a lack of fertilizer. Jim Wilson in 'Landscaping with Container Plants' compares fertilizing container plants in artificial soil with feeding infants. Everything they need has to come from you, and on schedule.
Good drainage means fewer problems with root and crown rot and overall better root development.
So, especially with soil-less, soil mixes everything the plant needs has to be supplied by you, in the right amount at the right time. Fertilizing container-grown flowers is not difficult or complicated but there are a few guidelines you should follow. Annual flowers put most of their resources into blooming and attempting to set seed for the next year and therefore are heavy fertilizer users. A weekly application of a water soluble fertilizer, like Schult's Plant Food, Miracle Grow, Peter's Fertilizer or any other water soluble fertilizer, will provide the plants with enough nutrients to stay deep green and continue growing and blooming throughout the summer. A note of caution- plants should not be fertilized if they are very dry or wilted.