Water your newly planted perennials. 
  
 Water your plants immediately after planting and once a week or so for the first two to three weeks, unless the weather is very rainy.
Summer plantings may require more frequent watering, especially during periods of heat or drought. A deep soaking once or twice a week is more beneficial than frequent light watering. Watch your new plants closely for signs of wilting during hot, dry weather.

Overwatering is probably more common than underwatering. Gardeners with heavy clay soils should be particularly careful of this. The typical symptoms are wilted plants that do not perk up after watering. Allow the soil to dry out for several days before applying more water. Automatic irrigation systems are the most common cause of overwatered perennials; your timers may have to be adjusted while your new garden becomes established.