Care of Flood-Damaged Lawns and Turf

Written by Dr. Tony Koski, Extension Turf Specialist
Department of Horticulture and Landscape Architecture
http://csuturf.colostate.edu       http://csuhort.blogspot.com

Lawns that are covered by flood waters, even temporarily, may be subject to various types of damage. In general, most turf species will tolerate a few days of flooding without any negative effects. However, turf that remains flooded for more than a few days (especially when it is hot) can rapidly decline due to lack of oxygen and light. Substantial turf loss can be expected after 4 days of continued submersion. Other factors associated with flooding of turf include: soil coverage, water contaminated with petroleum or pesticides, high water temperature and algae scum. The most significant long-term effect of flooding is the deposit of sediment (“muck”), primarily silt and clay, over turf surfaces. This can lead to serious soil layering problems and even death of the existing grass.

Short-Term Care of Flooded Turf
Once flood waters have receded, pick up any debris, such as wood, glass, stones, nails and other metal objects deposited on lawn areas. This debris could pose a safety hazard to mower operators and damage power mowers or other equipment later used to maintain the lawn, as well as to people and pets who may use the lawn for recreation. Remove leaves or any other material that may smother grass.

Soil (“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.  However, 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.

Soil deposits on golf greens and other sand-based turf systems (soccer, football or baseball fields) should be removed as quickly and thoroughly as possible to reduce the potential for silt and clay to move into the sand root zone, clogging the pores and reducing infiltration and permeability. The use of shovels, sweepers and water to move/remove soil deposits will reduce the potential for damage. However, these affected turf systems will likely require aggressive core cultivation and topdressing to restore and maintain acceptable infiltration and aeration.

After the Turf has Dried
It is often not possible or practical to remove deposited soil from flooded turf while it is still wet. The drying process may take two or three weeks, perhaps longer, depending on weather, soil, and drainage characteristics of the underlying soil and turf. Remediation at this point is largely dependent upon the depth of deposited soil.

Lawn repair with less than 1-2 inches of soil
Lawns submerged less than 4 days and covered with an inch or less of soil have a good chance to recover.  Assessment of potential lawn damage and recovery may not be possible until those areas have dried. Checking for new shoots emerging from the soil or the emergence of new shoots from surviving plants is a good way to make an early assessment of damage. Usually, once regrowth has begun, it will continue, although it may take several weeks before the lawn has completely filled in.

Core cultivation/aerification is one of the most important and beneficial operations conducted where soil deposits are less than an inch. When the lawn has begun to grow (green leaves begin to appear), go over the lawn 3-4 times with a core type aerifier. This will help improve overall soil structure, improve soil oxygen levels, help break up soil layering problems caused by the deposited soil and encourage recovery during the fall. The lawn should also be fertilized (using any lawn fertilizer, following label instructions for applying the correct rate) at this time (September-October).

Overseeding can also be done at the time of aerification. The aerification holes provide perfect conditions for the germination of grass seed. Lawn areas that are thin (or the entire lawn can be overseeded at this time) can be overseeded with Kentucky bluegrass or a Kentucky bluegrass/perennial ryegrass mix (tall fescue lawns should be overseeded with tall fescue seed), using a seeding rate of 5-6 pounds of seed per 1000 square feet. Rake the lawn lightly after seeding to work seed into the aeration holes. Irrigate the lawn to maintain moist, but NOT saturated, soil conditions.

Lawn repair with greater than 2 inches of soil
Lawns covered with more than 2 inches of soil may be heavily damaged, with only a slight chance of recovery. Degree of recovery will vary with grass species and depth of soil. The greater the depth of soil, the slower the recovery and the less likely the lawn will recover. If the lawn area is completely buried with many (3 or more) inches of soil, then the best strategy may be to accept that the majority of the lawn has already been severely damaged or killed and it will be necessary to reestablish a “new” lawn.

Reestablishment of a “new” lawn over a flood-damaged lawn
To reduce the future potential for soil layering to cause drainage and rooting problems for the new lawn, there are two ways of dealing with the deposited soil. One is to remove as much of the soil as possible, down to the original lawn surface. Understanding that this may be difficult or impractical, the deposited soil may be left on the lawn and rototilled into the lawn as deeply and thoroughly as possible. This, in essence, will create a “new” lawn root zone that is a mix of the deposited soil and the underlying lawn and its soil. The goal is to eliminate, as much as possible, the formation of layers in the “new” lawn root zone by thoroughly mixing the original lawn’s soil, the layer of the original, dead lawn, and the flood-deposited soil.

After leveling and firming the “new” lawn soil, it can be sodded or seeded as any new lawn would be established. Cool-season grasses can be seeded anytime between Aug. 20 and Sept. 30 (buffalograss should be seeded in April/May). Sod can also be used to provide an instant lawn. Do not sod over existing dead or buried vegetation. The old dead layer of lawn grass must be thoroughly tilled into the soil before laying new sod.

Written 18 September 2013

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Winter water is for lawns too

With apologies to Frank Loesser, his song, Baby It’s Cold Outside, has been running through my head with a few changes:

We really can’t sleigh (baby it’s dry outside)

The warmth’s got to go away  (baby it’s dry outside)

This winter we’ve been (hoping that snow’d drop in)

Not very nice (I’ll warm up the hose, it’s stopped up with ice)

Trees aren’t the only thing that need water in a dry winter – and boy, is it dry.  The federal Climate Prediction Center has said most of the Front Range and all of eastern Colorado is in a moderate drought.  We’ve gotten just a whisper of water since July, so monthly watering of your landscape is a must. 

In a previous post, how to water your trees was described, but lawns, too, need a drink.  “Established lawns will benefit from watering, but the critical ones that need moisture are the ones that are new,” says Dr. Tony Koski, Extension Turf Specialist with Colorado State University Extension.  If you put down sod after September 15, you should water it. 

Even if you don’t have a new lawn, watering the grass is important, and if you’ve been plagued by lawn mite problems in the past, water that yard soon, he said.  “This is when mite populations start to rise, especially on warm days when they get a little active and frisky.  They’re frisking around, the population starts to rise, and though mites haven’t started to damage the lawn, their potential to do so increases with their numbers.”  Mites prefer bone-dry grass, so hold them at bay with moisture. 

To water a lawn in winter, warm days with temperatures above 45-degrees is a must.  Fortunately we have plenty to choose from, since we’re in the 50’s and 60’s several days per week.

Drag out your hose with a sprinkler, or set the water to a slow trickle.  “The problem is that everything is frozen, but you don’t want water puddling on the lawn.  And the worst thing is forming a layer of ice on it; that really harms the turf.  So it probably won’t take more than a quarter to half-inch of water before you get standing water and puddles.”

Set your timers to tell you when to move the hose or shut off the water.  Most importantly, disconnect the hose from the house before evening so you don’t run the risk of frozen pipes.

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Weeds in lawns offer clues to control

Aaahhh, summer.  The lazy days spent clipping the lawn, neatly trimming the edges and grass so that the carpet rolls along in one, smooth swath of green.  Nothing more satisfying than gathering up the tools and locking them away, turning to view the glory that is….

 …a dandelion, popping up like a summer festival tent smack in the center of the turf.  Soon it has friends and family surrounding it, while bindweed and black medic nestle in the turf, and kochia accents the edge. 

 If you’re struggling with weeds invading your lawn, before you reach for the super-nuclear chemistry, stop and consider: those weeds tell you what the grass can’t about conditions in the yard. 

Stressed lawns have groups of weeds that flourish together under similar conditions.  Some like hot, lean soil; others prefer cool shady spots.   Growing together in the yard, they’re known as indicator weeds, and they help homeowners sort out problem lawn spots.

Before yanking them out, make a list of them to see what type of care your lawn needs.  Here’s a primer on indicator weeds and what they can tell you:

 – Hot, dry soils sport black medic, bindweed, dandelions, kochia, stink grass and yarrow.  If the grass seems thin in spots with these weeds, increase the water to this area, or check the sprinkler heads for coverage.

 – Over watered yards have plenty of weeds.  Annual bluegrass, common chickweed, crabgrass, violets and ground ivy plague chronically wet lawns.  Sprinklers may be running too often or for long periods.

 –  Compacted soil is a favorite of mouse-ear and common chickweeds, goose grass, knotweed, annual bluegrass and prostrate spurge.  Core aeration several times per season over two or three years helps break up compaction. 

– Lawns mowed too low have crabgrass, yellow wood sorrel, and white clover.  Increase the height on the mower to keep grass at two to three inches tall.

 – Not fertilizing enough, but over watering?  You’ll see black medic with plantains and white clover.  Cut back on the water, and feed the lawn.

– Over fertilizing?  Curled dock, henbit, yellow wood sorrel and annual bluegrass will pop up.  Fertilize lawns in May, September and November, and calibrate your spreader to drop only what the grass needs.

Recognizing turf weeds takes practice. Two websites can help you discover what’s invading your lawn, the North Carolina State University’s turf files or Michigan State University’s turf weeds.net.  They’ll take you step by step through a key to identifying what weed you have.  Then jump back onto the Colorado State University turf website to check for control tips that work in our area.

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