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Flooded landscapes require special care

Flooded landscapes require special care
Writer: Rick Bogren at 225-578-5839 or rbogren@agcenter.lsu.edu (03/17/16) BATON ROUGE, La. – Flooded gardens and landscapes require attention. Freshwater flooding caused by excessive rainfall primarily affects landscape plants by saturating the soil, said LSU AgCenter horticulturist Dan Gill. Plant roots obtain the oxygen they need from air spaces in the soil, he said. When these spaces are filled with water, roots are deprived of the oxygen and may drown. Initially, the roots stop functioning properly. When the bright sun comes out after a period of excessive rain, it is not unusual for plants to wilt. “It’s odd to see plants wilting in soil saturated with water, but it makes sense,” Gill said. Saturated soils are low in oxygen, and roots will not function properly if they do not get oxygen. Root damage through drowning or root rot is the greatest danger to landscape plants caused by flooding, Gill said. The longer the soil stays saturated, the more damage occurs. In areas where floodwater several feet deep remains for one week or more, it is likely that turf, shrubs and herbaceous plants will be extensively damaged or killed. “Carefully assess shrubs that may appear dead,” Gill said. “Some that appear dead may begin to send out new growth a few weeks after the water recedes.” Shrubs that show no green tissue below the bark when scratched and produce no signs of growth a few weeks after the waters recede are likely dead, he said. Floodwaters may deposit silt and debris on lower-growing plants, such as shrubs, ground covers, annuals and perennials. It is important to remove these materials as soon as possible after the water recedes, Gill said. Use a rake to remove most of the larger material, and then use a hose with a nozzle attached to wash off the remainder. Also remove all mulches from around shrubs and bedding plants for a week or two to allow the soil to dry out more rapidly, he said. Then, replace it. Mulches that floated out of beds can be raked up and reused, if practical. “You can help speed drying the soil by inserting the tines of a garden fork straight into the ground to a depth of 6 to 8 inches and then pull them straight out. But don’t dig,” Gill said. Repeat this about every 10 inches throughout the bed. “Don’t consume any fruits, vegetables or herbs that were or could have been touched by floodwater,” Gill said. “Remove and discard them.” “You may, however, eat fruit the plants produce in the future,” he said. “You may also generally eat the new growth of herbs and vegetables produced after floodwaters recede.” Lawns that were covered by floodwaters for an extended period may be damaged or killed. During summer, a new lawn can be established or an existing lawn can be repaired using sod, plugs or seed. “Compost saturated with freshwater flooding should still be OK to use once the floodwaters recede,” Gill said. Container plants should be removed from floodwater as soon as possible by moving the containers above the water level. “Once floodwaters have receded, you can place plants back in their original locations,” Gill said. “You can use a chopstick, skewer or knitting needle to aerate the soil of container plants with saturated roots.” Dan Gill can be reached at 225-578-2222 or dgill@agcenter.lsu.edu