So, why is fall the best time to plant trees and shrubs? Not as much watering is needed Young plants need plenty of water. It is best to give good, long soakings rather than frequent, light watering. A typical rule of thumb is to provide at least 1 inch of irrigation per week. Summertime planting requires close attention to moisture levels and much of it can evaporate with the heat of the day. Autumn’s cooler temperatures and shorter days may …