Returning to a flooded site can be quite devastating. Flood damage to your home or office maybe quite extensive and overwhelming. What about your landscape and garden? Your first impulse may be to pull all the plants out and start over. But wait! Experience has shown that your landscape may at least partially recover.
After the floodwaters have receded the landscape will be covered in thick silt and it may have a raw sewage-like odor, which indicates a lack of oxygen in the soil. Many plants will look dead. Will these plants survive? Plants that have shown good survival after two weeks under floodwaters include most native trees, shrubs, perennials and hardy bulbs. Other plants that show good recovery include crape myrtles (Lagerstroemia Spp.), Chinese Holly (Ilex rotunda sp. including Casissa Holly and Burford Holly). Plants that do not typically survive being underwater or show marginal survival include Japanese Holly (Ilex crenata Spp.), Japanese Boxwood ( Buxus microphylla ssp. japonica), Indian Hawthorn (Rhaphiolepis Spp.), Nandina (Nandina Spp.), hybrid junipers (Juniperus Spp.), and hybrid azaleas (Rhododendron Spp.). These are plants that typically do not like “wet feet” and typically have low survival rates.
The Clean Up
You should begin the clean up by addressing the safety of the site. Beware of down power lines. After you are assured that the site is safe to enter begin by assessing the site. Is it dry enough to enter and not cause further rutting or damage? If your landscape is still saturated, you will want to wait for it to dry out. Once dry remove trash, debris and any uprooted plants. Separate trash and yard waste and place in the appropriate designated spot for pick up. This is typically curbside, but check with local authorities first.
Most deciduous landscape plants will defoliate immediately after a flood. Hardy evergreen plants like Chinese Hollies, may hold on to their leaves. I have found washing the silt off evergreen plants to be beneficial to survival and re-growth. A solution of one tablespoon of dishwashing liquid per gallon of water in a sprayer works well in most cases. First wet the plants with plain water and then spray the detergent solution on the foliage. Wait about a minute and rinse. Work in small areas so as not to leave the detergent solution on too long. In the case where the silt is extra thick and stubborn, a teaspoon of an additional wetting or rinsing agent such as those used in dishwashers, has proven beneficial in breaking up the silt. Pressure washing should not be used on plants as it can result in further damage to the leaf and stem areas.
Refrain from using a high nitrogen fertilizer on trees and shrubs at this time. Take a soil sample if possible to determine is fertilizer is needed. Flooded trees and shrubs have undergone a shock and may be experiencing a forced dormancy. Adding a new mulch layer to your landscape will do wonders for its aesthetic quality. You may find chipped hardwood mulch available for free due to tree and limb cleanup. Check to be sure that it has been properly aged. Do not use fresh hardwood mulch, as it has been know to tie up soil nitrogen as it ages and breaks down. Also be sure that your mulch does not contain any trash or contaminated material.
Turf and Lawn Areas
Bermuda grass (Cynodon dactylon Sp.) and Bahia grass (Paspalum notatum) have the most resiliencies to flooding. Hybrids of these grasses have also responded well. Bermuda grass under four weeks of floodwater has responded with re-growth when a general maintenance and management regime has resumed after a drying out period. Remove accumulations of sediment land organic debris and mow. Remove only about a 1/3 of the height at this time. Applying about one-half pound of nitrogen per 1,000 sq ft will encourage turf recovery and then follow normal maintenance practices.
The Sprinkler System
You will want to inspect and flush your sprinkler system. Be sure the power is off when inspecting electrical connections. If your irrigation clock was flooded you will need to replace it. Your backflow prevention system will need to be checked by a certified professional prior to reintroducing potable water (i.e. water that is part of your main drinking water system whether well or municipal). Shut off the water supply to the irrigation system and open up the drain valve to drain the water from the underground pipes. If you system has rotors you may have to remove them, shake them out and rinse them thoroughly. Many rotors have a built in check valve that prevents the water from draining out. If you have any gear-drive rotors mounted above ground be sure to check to make sure the water has drained out of them, remove and thoroughly clean them. Unscrew the inside of the head from the casing and rinse out both pieces.
Flush the pipe system before you replace the heads. Open the valves one at a time to the full open position and turn on the system on manually. Let the water run for at least 5 minutes at each zone. After you are done flushing all the zones, re-install the heads and run your system for about 10 minutes. Are the spray heads or rotor heads spraying a correct spray pattern? When you shut the water off are the heads sticking up instead of retracting back down? Sometimes, the heads can be easily cleaned by stepping down on the riser while the head is running. Let it pop back up, then step on it again. Do this a few times, then turn off the system and see if the head is still sticking. Finally turn off the system and make sure all the heads went down. If heads are still sticking, you may find it well worth your time to just replace the ones not working correctly.
Drip and micro-irrigation systems may be plugged by a variety of causes including particulate matter, chemical precipitates, organic growths, and insects in the system or a combination thereof. You may try cleaning these systems by opening the end of the line and flushing with fresh water. Replace emitters that remain clogged or that are damaged.
Having Patience Can Help You Save Money
Salvaging a flooded landscape can be economically feasible if you have the time and patience to let your plants return naturally. By following these simple steps to access your landscape and giving it time to recover you can benefit from nature's resilience.
Written by Charlene LeBleu, Associate Professor, School of Architecture, Auburn University.