By Dennis Patton, Kansas State University 
Good gardening practices include efficient uses of water. Plants require timely applications to supplement natural rainfall. The first step in properly watering the flower garden is to know the plants and their water requirements.
As a general rule of thumb, flowers will require about 1 inch of water per week depending on the weather conditions. Ideally this moisture would be provided by Mother Nature. Unfortunately, rainfall does not always occur.
When watering the garden strive for deep, infrequent application. Deeply soaking the soil and allowing it to dry down between watering helps to develop strong roots and avoids over-watering which can weaken or kill the plants. Apply the water in one or two applications per week. Avoid light frequent applications as this encourages shallow rooting and increases disease development as well as waste water.
The best time to water is in the morning or early afternoon when temperatures and wind speeds are lower, helping to reduce evaporation. Avoid watering in the afternoon under high temperatures as water is lost to evaporation. Evening or night watering will increase the likelihood of disease.
Drip (soaker hoses) or flood irrigation is an efficient method of applying the water. Placing the water right at the roots not only helps to reduce disease development but saves water. A layer of mulch 2 to 3 inches deep will help conserve moisture.
Learning when and how much to water is one of the most difficult gardening practices. It requires you to learn about the properties of the soil and how the plants grow.