A Dahoon Holly is knocked over by Hurricane Isaac’s high wind gusts at the LSU AgCenter Hammond Research Station. (Photo by Allen Owings. Click on photo for downloadable image.)

Hurricane Isaac’s winds and flooding dealt landscapes a major blow across coastal and southeast Louisiana, according to LSU AgCenter horticulturalist Allen Owings.

Sustained winds over a three-day period and flooding for several days in some localized areas caused substantial damage to landscape plants.

Primarily, newly planted trees or those planted in the past two to three years, flowers, bedding plants, foundation shrubs and lawns were exposed to conditions that resulted in limb breakage, plants being partially uprooted, water-saturated root zones and more, Owings said.

Shade and flowering trees that have only been in the ground for a couple years received wind damage. In some cases, these trees may have been partially or “all the way” blown over.

“These can probably be salvaged, depending on how much damage was done to the canopy and the species of the tree,” Owings said. Do not be concerned if the trees were stripped of foliage – it will regrow.

Evaluating more-mature standing trees to determine if they need to be removed or can be saved is often best done by a knowledgeable individual. If you have difficulty determining which standing trees can be salvaged, contact a local licensed arborist to look over the trees and help you decide, said LSU AgCenter horticulturalist Dan Gill.

“There is no hurry to make these decisions,” Gill said. “It is often advisable to wait until the next spring and summer to see how the tree grows out and recovers before making a final judgment.”

Remove any debris that may be covering the shrubs, such as tree branches and debris from buildings, as soon as possible.

Taller shrubs and plants like Knock Out roses may be partially blown over by high winds. If the roots were not exposed for long periods and the shrubs still look reasonably good, straighten them, cover their roots and stake them to hold them upright, Owings said.

“Leave the stakes in place for six to nine months,” Owings said. “Trim any broken branches, but otherwise avoid extensive pruning of living branches.”

The foliage of thin-leaved species may look burned. High winds blowing against the foliage can cause this type of damage. It is generally superficial.

Extremely high winds can actually strip the foliage from shrubs. “They are still alive and will usually recover should this happen,” Gill said. “Wait un

A low area of turfgrass flooded by Hurricane Isaac’s heavy rains that continuously pounded the Hammond Research Station and surrounding area. (Photo by Allen Owings. Click on photo for downloadable image.)

til the following spring to determine if they will survive.”

Branches that do not leaf out with the rest of the shrub are dead and should be pruned off. Shrubs that do not produce any new growth by the following spring should be removed.

Herbaceous, or non-woody, plants can be divided into two broad categories – annuals and perennials.

“Annuals are generally not worth salvaging if they received a lot of damage,” Gill said. “Pull them up and compost them.”

Plants like caladiums and daylilies made it through the storm fine, but butterfly bushes, some lantanas, perennial salvia and more upright growing annuals and perennials were probably partially blown over or have broken canopy, Owings said.

“Apply several inches of mulch to the areas where annuals were growing to prevent weed growth until you’re ready to replant,” Gill said. “On plants with minimal damage, prune off bad looking growth and give them time. They will usually produce new growth shortly.”

For flooded lawns, as soon as possible remove heavy debris and silt that may have been deposited by flood waters, said LSU AgCenter turfgrass specialist Ron Strahan.

“Use a rake to remove most of the larger material, and then use a hose with a nozzle attached to wash off the remaining mud,” Strahan said.

The surge of salt water brought inland by a hurricane can cause a lot of damage to turfgrasses in lawns, golf courses, parks and playgrounds.

Thoroughly watering the grass as soon as possible with clean, fresh water is probably the most important thing to do. This will help rinse salts from turf leaf surfaces and leach salts, which can damage roots, from the grass root zone.

“Raise the mower’s cutting height a notch to help the turf regenerate a stronger root system,” Strahan said.

Bermuda, zoysia, and St. Augustine grasses have good salinity tolerance. Centipede grass has less salt tolerance than other lawn grasses, while carpetgrass and bermudagrass have good flooding tolerance, Strahan said.

“Flooding may increase the incidence of brown patch disease with lawns,” Strahan said. “Consider using a recommended fungicide as a preventative measure.”

If a lawn survives, do not fertilize now. Wait until next spring to fertilize.

For additional information about landscape care after a hurricane, visit the LSU AgCenter website at www.LSUAgCenter.com.

Johnny Morgan