Thanks for your question.

Your perennials and other plants should get at least one inch of water per week. Obviously if it rains, you would water less. The inch of water per week is rain water plus the water you add. Inexpensive rain gauges are sold in most gardening centers for you to keep track of things. It is a good investment.  Newly planted trees and those that are less than 5 years old should also be watered.  Trees older than this usually have developed an adequate root system by which to subsist on rainfall only 

Start watering now. See the following for further information

https://www.bachmans.com/information/resource-hub/caring-for-newly-planted-plants

https://extension.umn.edu/how/watering-vegetable-garden

https://sargentsgardens.com/docs/new-plant-watering-guide/

Good luck. Please get back to us with any further, related questions. Thanks for using our forum.