Usually 2-3 times a week depending on the weather and your soil conditions. Hot, dry, and windy conditions will dry plants out sooner. Water may be needed every other day. Overcast or rainy conditions may require only one watering per week. Sandy soil will also increase the need for hand watering.
Sand allows water to drain quickly.
Clay soil is the opposite. Make sure not to over water your plants for they can suffer just as much if the roots are drowning and cannot breath. It is also important not to water the foliage of most plants. Moisture on the leaves can promote fungi and disease problems. Plants such as flowering crab trees, roses, dogwoods, lilacs, asters, and phlox are particularly susceptible to problems if the leaves are constantly wet.