Keep Your Baskets Beautiful all Summer

The requirements of plants:   
Water, food, correct temperature and hours of sunlight.
Watering regularly is important.  You must water until the water runs out the bottom of the container.  The basket or container should have some weight when you are finished.  This not only supplies the plant with water, but it also flushes the soil of the residue that the previous fertilizer has left behind.  This process is called leaching. During the hot summer days you may have to water every day.  For petunias it may be almost twice a day, as the season becomes warmer and the plant is more root bound in its container.
Feed:  This is an absolute requirement if you want continuous blooms all summer!  Use any brand name of fertilizer of your choice, but look for the words that indicate the fertilizer is meant to promote flowering.  You should fertilize every other day, if you water as directed above. Follow the measurement directions exactly as discribed on the container supplied by the company.
Location, location location:  Each yard has its own micro climate, and as a gardener you must experiment with how well your plants perform in the various locations available. For example, many plants that are shade plants are  often tolerant of the sun IF they are protected from the wind, and kept moist. 
Managing the weather, the temperature and hours or sunlight however is an aspect none of us has complete control over,(we do live in Saskatchewan) but as gardeners we are a patient group of individuals and are willing to try again, as each season provides us with temperature challenges.   Good Luck!