Before you take your indoor growing perennials outside to transplant them into the garden, you should prepare their new home. After you dig the holes, lightly water the holes and then place your perennials inside them. Next, fill up the holes halfway with water. Allow the water to drain out of the holes and then fill the holes with soil. Lightly firm up the soil around your perennials and then water the entire plant, leaves and all.
You should check on your newly transplanted perennials every day for at least 10 days. They will probably need watering. Some perennials may need watering two times a day, especially if the summer is very hot.