Rain Rain. Why is my Grass Dying?

Too Much Rain.  How Long Can it Survive?

Visit with anybody in the Green Industry here in the Midwest and the discussion is surely to turn to the weather… specifically the amount of rain we have had this spring/summer.  The Johnson County Executive Airport has received 25.5″ of rainfall since the 1st of Jan, which is 5.9″ more than normal.  Except for a couple of weeks in June, (which I’ll talk about below) it seems like it has been raining every other day.  It seems like the weather has been very similar to last year….it rained and rained then got hot in June for a week or so, then it was cool and rainy for the rest of July and August.  The ground has been soaking wet for most of the spring.

How long can the grass survive under water? Dr. Christians has an great post on the iaTurf Blog about turf survival under water.  In the article, Dr. Christians, talks about his experiences with dealing how long grass can survive under water. He states, “Creeping bentgrass is surprisingly tolerant of flooding. This is followed by Kentucky bluegrass, and then perennial ryegrass and annual bluegrass.”  Survival ultimately depends on the type of grass, the depth of the water, how long it is under water, and how many times it gets repeatedly flooded. Read Dr. Christian’s article for more info. Marcus Jones at the iaTurf blog also posted some good info about the weather and rainfall in Iowa and slime mold. It is worth a read, too.

Rain is good; So why is my grass struggling?

It could be for a variety of reasons.  It could be drowning, it could be disease, and last week it was actually drought stress. Remember, everything in moderation.  Too much of a good thing is bad.

Drowning. I try to remind people that plant roots need air to survive.  Most people understand the function of roots are to hold the plant in place and absorb water and nutrients from the soil.  But many people don’t realize that it roots need air to do these functions.   Wet/water-logged soils don’t have air.  You can’t breathe and live under water and neither can plant roots.  With all this rain the grass and many plants are going to struggle.  (you should see what is left of my garden)  So if the lawn is soaking wet for too long the roots will essentially drown and the grass will struggle and possibly die.

Disease. Most turfgrass and landscape diseases thrive it warm, moist conditions.  All that rain, heat, and humidity have helping the diseases go crazy. Moreover, diseases and insects like to attack weak and damaged plants.  The diseases could be adding more trouble to the already struggling plants.

Drought Stress. There was a lot of drought stress in lawns last week and the week before.  Why?  It rained and rained and then the weather got very hot and dry.  Most people ask, ‘how can it be drought stress when we had so much rain for so long?’  It goes back to the whole ‘roots need air to breathe’ concept.  Since it was raining so much, the ground was saturated for so long and the roots started to drown, die-back and get shorter and shorter.  So in the middle of June the grass plants had extremely short roots.  Look at the picture below.  The grass on the right with short roots is what the grass would look like after a long period of water logged soils.  Now think about what would happen when it stops raining and becomes very hot and dry.  The grass is going to need lots of water to keep itself cool, but it doesn’t have a long enough root system to adequately supply water to the plant, and it will suffer.  Moreover, it only has a few inches of soil to draw water from…so when those top few inches become depleted, the grass will become further stressed.  This is why we recommend deep, infrequent watering to try and get the water to move deep into the soil and then allow the surface to slightly dry which allows air to move deeper into the soil, promoting root health and growth. 

Deep roots have more soil to draw water from in times of drought compared to short roots.

The rains some of us received over the Fourth have helped alleviate the dry soils, but it came down so heavy in some areas, that flooding and water logged soils are a problem again.  There are a lot of resources out there for tracking historical weather and predicting tomorrows weather.

One tool I use is the forecasting at NOAA’s weather.gov.  I really love the hourly forecast graphs to help me predict when to apply treatments to my research.  Enter a city then look near the bottom on the right hand side for Hourly Weather Graph.

Weather.com has lots of nice features, but I really like their radar.  K-State’s Weather Data Library has lots of good information from weather stations located all over the state.  You can create reports with many variables, like temperature max and min, evapotranspiration, precipitation, etc.

I could do a whole post on weather resources.  Some day I just might.  Feel free to add your favorite links and sites in the comments and any stories or thoughts about this year’s weather.

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