Water is the very most important part of successfully planting or transplanting plants. The recommendations for meeting a plants water needs:1 inch of water a week. Of course the environments vary from one part of the country to another. Weather, which would include heat, humidity, available sunlight, and rainfall all have to be taken into account.
Next, look carefully at the root system of the plant. A gallon pot will usually have a circumference of about 6 inches or so. Applying an inch of water, that is more than 6 inches away, would be of no use to a small root system. The same process should be followed for a bareroot plant. Applying water that the small root system cannot reach is of little value. The ability of a plant to make use of the available water is dependent on the root to soil contact. Failure to firm the soil around new plants allows air to remain in the soil and dry spaces will develop and stress the young root systems. Again, 1 inch of water a week may be available, but the plant cannot access it if the soil is loose.
In summary, use the 1 inch of water a week as a guide, but be sure to account for rain or lack of rain and excessive heat and sun. 2 to 3 watering a week on a new plant may not be excessive during a heat wave, but that much water would be damaging during temperate or rainy weather. Apply the water close to the roots and make sure the soil is in firm contact with the roots so the water is available.