Lawn and Garden Damage from Heavy Rain

The signs of damage from heavy rain and over watering can take weeks to appear. Some damage in the form of fallen limbs and trees occurs quickly and is easy to see. In July 2021, Hurricane Elsa passed Jacksonville with tropical-storm-force wind and rain. It added to a week with more than 5 inches of rain that mostly fell on July 4th and 7th. While that amount of rain wouldn’t stop fireworks and doesn’t warrant alarm bells going off, it came during a month-long period of above-average rainfall that contributed to bringing down part of a tree that crushed one of our owner’s automobiles. We scurried about during the last week of September 2022 as Hurricane Hermine was approaching to hopefully avert similar damage from high winds and rain.

Chad Lakin, Earth Works Lawn Care Operations Manager recommends that your lawn should receive a half-inch of water three times per week from rain and/or irrigation. During weeks when it rains for three or more days dropping an accumulated weekly total of 1.5 inches of rain or more you should consider turning off the automatic timer on your sprinkler system and only water as needed. And be aware that irrigation regulations in Duval County restrict sprinkler system operation to twice per week. Be sure to check and abide by your county guidelines.

SEVEN FACTORS AFFECTING LAWN AND GARDEN DAMAGE FROM HEAVY RAIN include elevation, grade, soil composition, percentage of impervious area, drainage system, landscape design, and fungal pathogens.

Elevation: Much of Northeast Florida is at or slightly above sea level with a high water table. “Almost 25,000 kilometers of Florida’s coast is below 3.5 meters in elevation,” according to the US Environmental Protection Agency. “The northeastern region of Florida is one of varied natural, geographical, and topographical environments. The region is a part of the Atlantic Coastal Plain and contains an assorted mix of land cover types that span from coastal marshes to upland hammocks and scrub areas.”

Grading: Proper site grading requires a slope of the landscape away from home and other structures and into drainage systems that include swales and retention ponds. “The ground immediately adjacent to the foundation shall be sloped away from the building at a slope of not less than one unit vertical in 20 units horizontal (5-percent slope) for a minimum distance of 10 feet measured perpendicular to the face of the wall,” according to Florida Building Code 1804.4 [Excavation, Grading and Fill] Site Grading. “If physical obstructions or lot lines prohibit 10 feet of horizontal distance, a 5-percent slope shall be provided to an approved alternative method of diverting water away from the foundation. Swales used for this purpose shall be sloped a minimum of 2 percent where located within 10 feet of the building foundation. Impervious surfaces within 10 feet of the building foundation shall be sloped a minimum of 2 percent away from the building.” These measures reduce the threat of flooding and erosion from rainwater that doesn’t percolate into the soil.

Soil Composition: Our Northeast Florida soils tend to be sandy, allowing better percolation of water than clay soils. Heavy rains can saturate soil that can’t absorb additional water resulting in increased flooding, erosion, and runoff. “When soils become saturated from heavy rainfall, loss of nitrogen (N) becomes a major concern,” according to Kruger Seeds. “After soils are saturated, the two processes that can reduce the amount of available N are denitrification (microbial conversion of nitrate to nitrogen gases) and leaching.”
Leaching of nutrients from the soil during heaving rains can change soil pH. “Rain leaches alkaline elements including calcium, magnesium and potassium from the soil into runoff water, leaving acidic elements like hydrogen, aluminum and manganese to replace the bases,” according to SFGATE. “This means that areas with high annual rainfall amounts, such as parts of New England, generally have more acidic soil than the arid deserts of Arizona.”

Impervious area: Impervious areas include driveways, walkways, decks, and patios. Municipalities in Northeast Florida have restrictions on the percentage of impervious surfaces allowed. Coastal communities have the most strenuous rules. Atlantic Beach limits impervious area to 45% and requires onsite water retention storage. Hardscaping projects must take into consideration all sources of water conveyance to comply with the city code. “The downspouts from the house they are all connected underground and run to the swale,” said John Cacchione, Earth Works landscape designer. “So all of the water from the roof is collected. Nothing is going out into the street.” Make sure your landscaping company understands and readily complies with applicable regulations.

Drainage system: The wide variety of drainage system designs available require routine maintenance to work effectively. Clogged gutters, French drains, and storm drains won’t function as designed. Standing water over time becomes lethal for turf and many varieties of plants.
“During a flood, the greatest danger to your grass is suffocation,” according to the Turfgrass Group. “Grass needs sunlight, water, air—CO2, to be precise—and nutrients to grow. When your turf is submerged, the grass cannot get the CO2 it needs. It can survive this way for a day or two, but after four of five days, the chances of survival drop significantly. Generally, cool water and cool temperatures are the least destructive. If the air temperature is above 80 degrees and the water is shallow enough to be warmed, even a day or two could kill the grass.”

Landscape Design: Your choice of plants can have a significant impact on whether your lawn and garden are damaged or flourish after heavy rains. Native plants evolved in the local environment doing better in native soil and weather conditions than many non-natives. A professional landscape designer takes rainfall, soil composition, and drainage into consideration when establishing your landscape plan. Xeriscaping is popular but could require bringing in soil and regrading the landscape if the ground holds a lot of water during raining season. Alternatively, cannas, hostas, Japanese maple, and taro are a few examples of plants well suited for moist soil. Plant choices should be appealing to your taste and be in conditions to succeed and not succumb to damage from heavy rain.

Fungal Pathogens: Fungus thrives in wet conditions above and below the soil surface, growing on wet leaves while attacking roots. “Although the upper plant parts can deal with rainy periods pretty well, the roots are where most problems occur,” according to The Times-Picayune. “Excessively wet soil (especially combined with warm temperatures) can create stressful, and potentially destructive, conditions for the roots of bedding plants, perennials, vegetables, shrubs and even trees — especially newly planted ones.”
Two serious fungal diseases are Gray leaf spot, Pyricularia grisea and Take-all root rot Gaeumannomyces graminis var. graminis. Gray leaf spot can infect blades when they are wet for less than a day at temperatures between 70F and 95F. “This fungus slows grow-in, thins established stands and can kill large areas of St. Augustine grass turf,” according to the University of Florida. “In Florida, St. Augustine grass is the only warm season turf grass affected by this important disease.”

Take-all root rot commonly attacks stressed lawn turf that destroys turf root systems over weeks leading to yellowing and irregular brown patches. “Take-all root rot is a stress-related disease, and the following stresses may trigger the disease: soil compaction and poor drainage, drought, excessive irrigation, improper mowing height, excessive thatch buildup, improper fertilization, excessive shade and the overuse of herbicides,” according to Louisiana State University.

Earth Works offers regular aeration that prevents soil compaction and top dressing for improving percolation and replenishing nutrients.  For comprehensive solutions to your specific lawn, garden and landscaping need and to minimize lawn and garden damage from heavy rain, contact Earth Works of Jacksonville at 904-996-0712. Earth Works operates a retail Garden Center/Plant Nursery in Jacksonville and provides landscaping, hardscaping, water features, lawn care service, lawn spraying, and drainage solutions. Contact us with your questions and to book design consultations.

We proudly serve clients in Northeast Florida, including Jacksonville, Ponte Vedra Beach, Atlantic Beach, Neptune Beach, Jacksonville Beach, Nocatee, St. Johns, Fleming Island, Orange Park, Middleburg, Green Cove Springs, Amelia Island, Fernandina, and St. Augustine.

Happy Gardening!


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