When trees, shrubs, or perennials are dormant, they will tolerate standing water for several days without sustaining injury. Growing plants, however, can "drown" from standing water.
Silting presents the greatest threat to ornamentals during spring flooding. Silting occurs when rapidly moving water carries soil and dumps it into sluggish streams, where it is deposited on flooded land adjacent to waterways. Silt deposits may vary in depths up to several inches.
Trees and shrubs are usually not harmed by silt deposits. Silt damage results in crown and root disorders in iris, peonies and chrysanthemums and may cause damage or death. The degree of injury depends on how long water remains on the ground and the depth of silt deposited. To reduce silt injury to plants:
- Wash silt from crowns of plants with a garden hose. If the plants are on well-drained soil, wash the silt away from the plants. On evergreens, a mild detergent will aid in removing silt.
- Wait until the silt dries, then rake the excess soil away from the plants. A small amount of silt can be raked into grass without any harm.
If much soil has eroded, replace it with good topsoil around the base of plants. Its depth should equal original soil depth. To prevent runoff, apply new mulch to topsoil. Fertilize as recommended.
If excess soil has been deposited around the base of plants, causing a change in grade, remove excess soil so that the level is as close to the original grade as possible.