Plant roots, like people, need oxygen for respiration. That’s why a flood can stress a plant and even, if roots are submerged long enough, kill it. “Effects of Flooding on Woody Landscape Plants” by Laura Jull, Associate Professor and Extension Specialist, UW Department of Horticulture, provides information on immediate and long-term care of trees and shrubs that have suffered flooding. Includes symptoms to look for and a list of plants most likely to be injured by standing water.
Publication A3871 is available at the UW Extension Learning Store and as a pdf at https://learningstore.uwex.edu/Effects-of-Flooding-on-Woody-Landscape-Plants-P1377.aspx