Questions related to the recent flooding have been quite prevalent the past couple of weeks. Inquiries included: “What are the symptoms of flood stress on ornamental plants?”, “How should I care for my plants now that the flood waters are gone?”, and “What can I do about soils that don’t drain very well?”
Plant roots require oxygen for growth and for the process of respiration. If oxygen is depleted in the root zone, death is imminent. Plants that were in a flooded area may exhibit yellowing or browning of the foliage, leaf wilt and drop, early fall color, branch dieback, and sprouting of new growth at the trunk (for trees). Monitor plant growth and note anything abnormal, since stressed plants are more susceptible to attack by secondary organisms. Survival of a plant affected by flooding depends on the length of time the roots were submerged, the species of the plant, soil type where the plant is growing, and age/health of the plant. Old, young, or stressed plants are less able to tolerate flood waters.
After the flood waters diminish and you are able to inspect the plants, remove any damaged plant parts, cover exposed roots to the original depth of the soil, and remove any deposits of debris, including excess soil that may have built up around the base of the plant or on its root system. If possible, aerate the soil around the plant’s root system.
Refrain from applying fertilizer for at least one year to allow the plant to heal any root injury. The fertilizer may actually increase stress on the plant since the uptake of nutrients requires energy and the plant is already using its energy resources to recover from the flood stress.
To improve drainage in poorly drained soils, add loose types of organic matter, such as peat moss, pine bark, or composted leaf material. If possible, install a swale or waterway to divert excess water from valued plantings. Plant in raised beds or berms. Select plants that can tolerate wet soils, such as River Birch, Swamp White Oak, Dogwood, and Chokeberry. If the area stays wet continually and floods consistently, perhaps determine a better site to locate your planting areas.
Be patient with flood affected plants. Just like people, they will need time to recover.
The UWEX Learning Store has an excellent publication, A3871, “Effects of Flooding on Woody Landscape Plants” written by Dr. Laura Jull, available on its website, learningstore.uwex.edu. A list of plants able to tolerate wet conditions is included.