When severe weather strikes, there is often little that we can do to protect our plants. Floods can be very damaging but there are practices we can do to help plants recover.
Damage from Floods
The amount of plant damage from floods depends on the plant material, species of plant, amount of time that it is underwater, and the time of the year that flooding occurs. If plants are growing in floods during the growing season, the damage is worse than if it floods during the winter, dormant period. Certain plants are more adapted to floods than others. For a list of plants tolerant to wet soils, visit: https://yardandgarden.extension.iastate.edu/how-to/landscape-plants-wet-soil-conditions
Floods can damage plants in many ways. Roots are left in anaerobic conditions, which means there is not enough oxygen in the soil for roots to survive. Even though roots are underground, they still need oxygen. Roots sitting in water for too long can develop root rot that can kill the plant. Root, trunk, and basal tissues on trees become soft which can disrupt normal plant function, causing severe stress on trees. Once this happens, leaves become yellow or have a wilted, droopy appearance.
Trees in flooded areas may develop aerial roots, or roots along the trunk and branches. This is an adaptation of some tree species that are prone to flooded areas, they are not harmful. Trees could also develop a lean from floods or become unsafe with an increased risk of windthrow and structural failure. This damage to a tree from floods should be assessed by an ISA or NAA Certified Arborist to determine if the tree can survive the lean or if pruning is necessary to help the tree recover.
Flood waters may contain many contaminants including pesticides, debris, weed seed and sediment. This can lead to more weed problems around our landscapes and damage from pesticides in the years following floods. Excess sediment can be problematic for plants and should be pulled back after floods recede. On the opposite hand, soil or mulch may have been pushed away with flood waters; replenish these to the level they were at before floods occurred.
Floods and Vegetable Gardens
Flood water can come from a variety of sources including: breached or overflowing streams, lakes, ponds, and other water sources. If flood waters come into contact with the harvestable portion of the crop, it is considered contaminated by the FDA and cannot be sold or used as human food and should be discarded. Furthermore, the FDA recommends waiting at least 30-60 days before replanting vegetables in flooded fields. For more information on floods and vegetable gardens, visit this resource from Iowa State University Extension and Outreach: https://yardandgarden.extension.iastate.edu/how-to/managing-flood-damaged-vegetable-gardens
Recovery from Floods
There is little to be done to prevent damage from floods, but here are a few practices to help plants recover from floods:
- Avoid traffic on lawns under flood waters and until the soil has dried out again.
- After flood waters have receded, aerate and overseed lawns damaged by floods.
- Pull back mulch from around trees, shrubs, annuals, and perennials to allow the soil to dry out quicker. Once the soil has dried out, replenish mulch as some may have washed away with flood waters. Maintain a 2-3 inch layer of organic mulch.
- Remove access sediment or replace eroded soils that changed the soil level around trees from flood water movement.
- Trees that were under flood water for long periods of time or those that have developed a lean from floods should be assessed by an ISA or NAA Certified Arborist to determine if the tree can be saved or if it should be removed to reduce further injury or damage to property.
- Avoid fertilization on plants for 1-3 years after flooding. Trees under flood stress need 1-3 years to reestablish damaged roots, fertilization can interfere with that root regeneration.
- Be patient, it takes time for plants to recover from flood damage. Trees may not show flood damage for multiple years.
- Watch for secondary pests in all plants affected by floods. Stressed plants are more prone to damage from insect predators and disease pests. Monitor plants for pests to manage them early in an infestation.
- Discard vegetable garden crops if it was under flood water.
Stormwater Management
Stormwater can be managed somewhat to help reduce flooding in the future.
- Reduce impervious surfaces throughout your landscape by incorporating more plant material and using gravel, mulch, or other pervious walkways rather than concrete which allows water to soak in and slow down rather than leading to runoff.
- Redirect downspouts to rain gardens or other landscaping areas to allow the water to soak in.
- Use rain barrels to collect excess rainwater coming off the house when it rains. This water can then be used later in the season to water trees, shrubs, perennials, and annuals when needed.
