Tips to Help Lawns Recover From Flood Damage

Flooded lawns

As floods become more common, so has the chore of recovering from their damage. Whether the water rises from rivers or oceans or falls from the sky, after it recedes, homeowners need to salvage or replace their lawns.

If Mother Nature throws a watery hissy fit and floods your lawn, expect to expend some of your own liquid, in the form of breaking a sweat. Lawn and landscape repair isn’t easy. And compared to other items on a homeowner’s post-flood must-do list, it’s not a top priority. But once you work your way down to it, here’s how to help your lawn recover from a flood.

More People + Climate Change = More Floods

Even if you thought your home was immune from flooding, it may no longer be. The population of the United States doubled in the past 50 years, and we have tended to settle near water. That puts more of us in harm’s way.

Climate change also has an impact. It creates more-extreme weather events such as heavy rain and floods, the vast majority of scientists say. The Intergovernmental Panel on Climate Change noted in its special report on extremes, “It is increasingly clear that climate change has detectably influenced several of the water-related variables that contribute to floods, such as rainfall and snowmelt.”

The Natural Resources Defense Council notes that by the end of this century, the floodplains are predicted to grow by 45 percent. This growth is due to global warming affecting the rise in sea levels, as well as extreme weather conditions.

Flooded Lawns: Two Types

Lawn damage due to flooding comes in two types:

  • Direct damage: When water inundates your lawn for an extended period, it can die from a lack of oxygen. Grass submerged more than six days has a low chance of survival, especially if temperatures are high and heavy silt coats the grass.
  • Secondary damage: Even if the grass survives the flood, sediment buildup can lead to fungal diseases, algae, moss growth, and an infestation of weeds.

If you have suffered a severe, extended flood, your lawn likely will show a mixture of direct and secondary damage.

Temperature, Light and Depth

The biggest factors that determine how well your turfgrass survives the flooding are water temperatures and the depth of the water.

Deep water and hot weather are bad news.

  • If the leaf tissue remained above the water line, it is likely to survive. If submerged, survival rates go down.
  • Turfgrass hit with flooding during the cooler months of the year has a better chance of survival than when flooding occurs during the warmer months.

Tony Koski, Extension Turf Specialist with Colorado State University, writes, “Turf that remains flooded for more than several days, especially when it is hot, can rapidly decline due to lack of oxygen and light. Substantial turf loss can be expected after four days of continued submersion.” In fact, it can take only a couple of days for turfgrass death when water temperatures are 80 degrees Fahrenheit and warmer. Turfgrass can still die when temperatures are cooler, primarily due to the lack of oxygen.

As the depth of the floodwaters increases, the potential for turfgrass injury intensifies. The worst problems occur when the grass has been entirely submerged in the floodwaters without the crown and leaves exposed. (The crown of a grass plant is the light-colored area at its base from which individual grass blades emerge.) If the leaves and crowns remain above water, even partially, survival chances shoot up. Some species of turfgrass survive floods better than others. Creeping bentgrass, for example, does better than perennial ryegrass. But the topic is not well-studied and existing research centers around golf course grasses.

What Flood Damaged Grass Looks Like

When short-term flooding occurs during the cooler months while the turf is dormant, the turf may not lose its color. However, when flooding occurs during the warmer months the turf may turn brown or yellow, as the turf has lost its ability to uptake nutrients due to lack of oxygen in the soil.

You will have to play a waiting game to see if the grass revives once the water recedes and the area dries out. The best course of action is waiting several weeks after the floodwaters leave. No new green growth from the turfgrass means it died and needs replacement.

To determine if your grass plants were killed by the floodwaters, pull up a few plants from the area and cut a horizontal cross-section through the crowns. If the crown section remains white and firm, the plant has survived the flooding. However, if the section is mushy and brown, the plant is dead and new plantings are required.

Minor lawn flooding
Minor lawn flooding such as this is unlikely to cause permanent damage, but it is a hint to check your drainage system.

Post-Flood Lawn Clean-Up Steps

Step 1: Get the Big Stuff

Once you can walk your lawn to assess the flood damage, don thick shoes, gloves and remove scattered debris. Toss any unwanted chaff the flood delivered: glass, nails, metal objects or other debris. All pose safety hazards to people and pets. “Remove any leaves or any other materials that may smother grass,” Koski suggests. Your goal is to give the grass the best chance to revive.

This is also your opportunity to see where the weak spots are in your drainage system and correct them. If only a few square feet of your property have standing water, figure out why. Where there is mild ponding, toss shredded mulch into any remaining damp areas to soak up excess moisture. If it’s deep in one spot, see if your house’s downspouts are guiding water toward it, or if you need to add fill to slope the property better.

Step 2: Remove Soil and Silt Deposits

After you remove debris, uncover the grass. Scrape off any soil and silt deposited by the flood. Get a wheelbarrow and take it away.

Don’t be tempted to just rake it in and use it as your lawn’s new topsoil. Silt and sand brought in by floods lack organic material and don’t help grass grow. Waterway flooding usually deposits the most amount of soil and silt. Koski writes, “The most significant long-term effect of flooding is the deposit of sediment or muck, primarily silt and clay, over turfgrass surfaces. This can lead to serious soil layering problems and even death of the existing grass.”

He also notes that lawns covered less than four days and with less than 2 inches of soil have a relatively good chance of surviving. However, lawns covered more than four days and with more than 2-inches of soil have a slight chance of recovery. She states, “Removal of soil may be impractical or impossible due to the size of the lawn area, the depth of the soil, the weight of the wet soil, and ability to move it to another location.”

Koski continues, “Soil or muck deposited on a lawn can sometimes be removed before drying by a combination of scooping/shoveling and washing with a jet of water using a hose-end sprayer.” You can also use a metal rake to break the soil deposits apart. However, when deposits are thick and the chances of the turf surviving are slim, it’s best to leave the deposited soil in place and just till it into the area as deep as possible.

Step 3: Aerate

When soil deposits aren’t as thick, wait until you see new growth appearing and go over the entire lawn three or four times with a core aerator. Benefits of aerating the soil include:

  • Improves the structure of the soil.
  • Improves the levels of oxygen in the soil.
  • Assists in breaking up soil layering caused by the soil deposits.

After doing the aerating, apply fertilizer for lawns, following package directions on amounts. You can then level any tilled and bare areas with a regular lawn rake or power rake.

Step 4: Reseed? Resod? Or Start Over

The next step in helping your lawn recover from a flood is sitting back and watching its growth for several weeks to determine the amount of damage incurred. After several weeks, you’ll be able to decide whether you’ll need a new lawn or you can repair various areas by reseeding or applying new sod. Factors to consider include:

  • If you have 60 percent or more of the turfgrass recovering, then it’s feasible to reseed the bare areas or apply new sod. Reseeding or resodding can be done after you aerate the soil.
  • However, if you notice that 40 percent or less of the turf seems to be recovering from the flood, it’s best to start the entire lawn over with new grass.

When replacing the entire lawn, till the dead grass into the soil as deeply as possible and get a soil test done so you know what amendments are needed to bring the soil back to health. Apply starter fertilizer and then plant new grass seed or lay down sod of an appropriate grass for your climate.

Stabilizing Soil with a Temporary Lawn

If you have the unlucky prediction of possibly more flooding, it’s best to wait until the extreme weather is no longer a threat before recovering your lawn. You can help stabilize the soil and reduce further erosion problems by planting a quick-growing grass such as annual ryegrass. It usually germinates in around a week and will help stabilize the area until you can establish new turf. When you are ready to establish your permanent lawn, just till the ryegrass into the soil.

Do you live in a flood zone? The Flood Zone Map lookup tool from the Federal Emergency Management Agency will show you whether you are in one, and how close you are to potential sources of flooding. Flood zone

Best Watering Practices

After a flood, all the cleanup, recovery of the lawn area and planting new grass, the last thing you probably want to think about is applying more water to the area. However, it’s important to keep freshly planted seed or sod moist while either it germinates or the roots start taking hold in the new location. Don’t keep the area sopping wet, though. That hurts the seed and sod.

Properly watering your new or recovered lawn assures you end up with lush and healthy turfgrass. The Old Farmer’s Almanac suggests:

  • Water your lawn early in the morning or in the evening.
  • Water long enough to allow the water to soak in below the root zone. Shallow watering encourages shallow root growth (and thus, weak grass) and weeds. It will take about an inch of water to penetrate 6 to 8 inches into the soil. Set out shallow cans in the sprinkler area to measure.
  • Don’t overwater. Make the lawn seek its own source of water, building longer, sturdier roots. Cut back on water especially in midsummer to let the lawn go dormant, strengthening it for fall and winter. Excess water leaches away nutrients and encourages insects.
  • Deep waterings are better for the lawn than light waterings.
  • If your flood is succeeded by a lawn-crunching drought, let the grass grow longer between mowings and reduce fertilizer use.

There’s no doubt about it, floods are messy and destructive and having to clean up the mess and possibly redo your entire lawn and landscape is nobody’s idea of fun. However, with a bit of hard work and soil preparation, you should be able to run barefoot through your newly recovered lawn before you know it.

Joyce Starr

Joyce Starr

Joyce Starr has been writing on horticultural and landscaping topics for over 15 years. In addition, for the past 20 years she’s owned and operated a landscaping and design business. She shares her experience and passion for all things green through her writing.