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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March madness is all because of mites

With perennials waking and buds swelling, we feel the call to get outside and reconnect with the earth. Each warm weekend we linger longer in the yard, reveling in the emergence of bulbs and blossoms. Yet, just as we feel the season’s change, so do others in the landscape. They’re out there now, getting busy and quietly enacting plans to take over more territory in your yard.

March is the mitiest month, not because it comes in like a lion, but because it heralds the climax of the smallest nuisances in the yard: Grass mites. And between feeding on the lawn and entering our homes, they’ve launched a campaign of annoyance.

Perhaps the most startling natural phenomenon that happens to many of us in the Front Range is the annual migration of clover mites into our homes. Moving by the hundreds, the tiny, bright orange arachnids clamber walls and slide in around windows.

The first appearance doesn’t raise more than an eyebrow, as one or two crawl across the desk. But then two becomes 10 and slowly that number creeps upward, until the warm day dawns when the mass moves indoors, teeming along the windowsill and streaming to the floor.

Normally, I’m not given to fear-mongering, especially about bugs and arachnids. Clover mites won’t cart off the cat for a luau on the deck. But they leave a red-orange smear once squished, and like a chalk outline around the carcass, reminds me of the crawler each time I see it on paper, book, or curtain. Creepy.

Outside, clover mites feed on turf grass or other plants. They’re unremarkable in the landscape; they don’t damage a lot of the lawn. But when lawns are nestled up against the house, the trouble starts, so plan your landscape to leave a barrier between plants and walls.

Within, controlling these mites is fairly simple. Simply place a quarter inch wide line of powder along the window-sill from side to side, being certain that the powder touches the side walls. This barrier, according to Dr. Whitney Cranshaw, state entomologist and professor at Colorado State University, is enough to stop them in their tracks. Any powder works, such as baby powder, corn starch, or baking powder. As the mites crawl into it, they’re rapidly incapacitated and dry out.

When the powder has gotten filled with mites it will turn a light orange color, a sure sign that it’s time to vacuum it up and apply a fresh barrier. Continue this until May, after the mites are actively entering homes.

As you’re battling mites in the home, keep an eye on the lawn, since more damaging mites are at the peak of feeding for the winter. During warm winters, such as what we’ve had, mite populations explode.

Hatched in October, mite numbers increase into winter. As they feed, rasping off the leaf surface and sucking up tender, interior cells, the damage appears as small yellow speckles on the grass blades. As feeding intensifies, the grass becomes straw colored and eventually dies, leaving large patches that don’t green up in spring. Balmy winter temperatures sets mite metabolisms into overdrive, and by this time of year, populations can reach several thousand per square foot.

This damage is often mis-diagnosed as winterkill or desiccation. If you’ve had mite damaged lawn, take a quick look to see if they’ve returned. Check the base of the plant for congregations of them during the day.

If you see them, irrigate the lawn to raise humidity or check with a local lawn care company for stronger treatments. Snow cover doesn’t put a stop to their feeding, since it provides protection, but as it melts, the moisture helps drive off the mites.

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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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Feed lawns before putting them to bed

Heading into winter is when many people forget about yard care, putting the lawnmower away for the season. We fill our time cleaning the house, scrubbing the nooks and crannies we ignored in favor of being outside. But after a summer of heat, a fall of drought and a winter that’s slow in arriving, your lawn needs a little coddling to keep it healthy until spring.

The ability of turf to survive winter depends on healthy root systems. The stresses of summer often take their toll on roots, which need to regenerate in fall during cooler weather. To help lawns recover, fertilize now.

Late season application of nitrogen is recommended for Kentucky Bluegrass, Tall Fescue or Perennial Rye. Fertilize by applying 1 pound of nitrogen per thousand square feet during the first week of November, while the grass is still green and the ground isn’t frozen (if you have sandy soils, don’t fertilize after September). With the warmth lingering late this year, lawns will get the benefit of a slow cool down of the soil, which will give fertilizer the chance to help roots regrow.

Nitrogen is the most important food to feed the turf – extra potassium or phosphorus is not as critical. At this time, nitrogen in the fertilizer should be from sources such as urea, ammonium sulfate or others that don’t need microbes in the soil to release them. Soil microbes slow their activity during cold weather, which may delay release of
nitrogen to the plants, making the late application unsuccessful.

For quick benefit to plants, make sure the soil is moist, which helps the nitrogen dissolve easily. If the ground is dry, irrigate a day before fertilizing. But if you’ve already blown out your system for the winter, apply fertilizer just after one of our rain squalls have passed through.

Then protect roots from drying out during winter by giving it a bit of water if we’re having a dry spell. Dry soils can lead to dieback of the root system, which will limit the top growth of turf during the growing season.

Typically, lawns benefit from watering once every four weeks if we are not getting much rain or snow fall. Keep tabs on how much rain or snow falls at your house – not across town or in Denver where the TV stations are located – and water your lawns when we don’t get 1 inch of water, cumulative, over four weeks.

The late fertilization means lawns will green up early in the spring but not put on a lot of top growth, saving you the effort of mowing before you’re ready to swing into summer chores. Keep in mind that the March-April application may not be needed if you fertilized in November the previous year. As long as the turf greens up and grows, delay fertilizing until May or June.

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