Caring for Landscape After Flood

177Landscape recovery after flooding: when the flood waters have receded the landscape is covered in thick silt and it may have a strong sewage like odor, indicating a lack of oxygen in the soil. Your plants may look dead.

Plants with good survival after two weeks under floodwaters are 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 typically that won’t 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 azaleas (Rhododendron Spp.). These plants typically don’t like “wet feet” and won’t tolerate submerged and waterlogged soil for extended periods.

The Clean Up

Begin clean up by addressing the safety of the site. Beware of down power lines, displaced animals and reptiles. After assessing if the site is safe to enter begin by evaluating the site.

  1. Is it dry enough to enter and not cause further rutting or damage?
  2. If still saturated, wait for it to dry out.
  3. Remove trash, debris and any uprooted plants.
  4. Separate trash and yard waste and place in the appropriate designated spot for pick up. Check with your local trash pick up for details

Most deciduous landscape plants defoliate immediately after a flood. Hardy evergreen plants like Chinese Hollies, may hold on to their leaves. Try 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.

  1. First wet the plants with plain water and then spray the detergent solution on the foliage.
  2. Wait about a minute and rinse.
  3. Work in small areas so as not to leave the detergent solution on too long.
  4. 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.
  5. 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. Be sure 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 and St. Augustine have the most resilience to flooding. 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

Inspect and flush your irrigation system. If your irrigation controller was flooded, replace it. Use a certified professional to check the Backflow prevention system 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. Rotors: remove them, shake out and rinse thoroughly. Check for damage to springs, replace damaged rotors.  Some 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. Replace filters, nozzles, heads as needed.  Check spray patterns. 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, replace those not working correctly.

Drip 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. Flush the lines, cleaning the system by opening the end of the line and flushing with fresh water. Replace emitters that remain clogged or that are damaged.

Salvaging a flooded landscape with patience and let your plants return naturally.