Grass not as frost prone as Winter progresses

Kentucky bluegrass, Fescue, Rye and Bent, etc
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Green
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Grass not as frost prone as Winter progresses

Post by Green » January 29th, 2019, 11:52 am

I've noticed something interesting as Winter has progressed. The grass is no longer as prone to developing frost or overly freezing as it was in late Fall and early Winter. This is good, because it means less traffic damage now that things have partly hardened off. I'm curious why there is less frost now, though, even when air temps are far below 32. Some possible factors: cooler (frozen) soil temps, less moisture, wind, desiccated/brown/dormant leaf tissues...

Anyone else noticed this? Any ideas as to the mechanism? I've never noticed this before, though I'd guess it happens each Winter.

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Re: Grass not as frost prone as Winter progresses

Post by Green » January 29th, 2019, 12:47 pm

I just saw the typo in the title. Kind of embarrassing way to spell "progress".

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Re: Grass not as frost prone as Winter progresses

Post by andy10917 » January 29th, 2019, 6:26 pm

I fixed it - now you can sleep at night, and not worry if everyone thinks you failed 5th grade.

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Re: Grass not as frost prone as Winter progresses

Post by PSU4ME » January 29th, 2019, 9:05 pm

Ha, funny

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Re: Grass not as frost prone as Winter progresses

Post by Green » January 29th, 2019, 10:22 pm

andy10917 wrote:
January 29th, 2019, 6:26 pm
I fixed it - now you can sleep at night, and not worry if everyone thinks you failed 5th grade.
Thank you! :good:

Now, anyone else noticed this phenomenon with the grass?


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Re: Grass not as frost prone as Winter progresses

Post by andy10917 » January 29th, 2019, 10:37 pm

Of course! The "black steps" thing where people walked peters out by Christmas around here. Slowly over the remainder of the winter the grass shortens probably by exposure to wind on a slope, and can get pretty short by the end of winter - but the KBG takes it in stride, and grows right out of it in Spring. PR? Not so much - when I had all PR, anything without snow cover on a few below -5F nights meant some winter kill. Snow cover is a blessing for lawns.

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Re: Grass not as frost prone as Winter progresses

Post by Green » January 29th, 2019, 11:02 pm

I agree on the PR Winterkill. Between Winter kill and Summer kill, the PR percentage in my mixes has actually tended to decrease dramatically over time (years) in most areas (the opposite of what that famous study found with PR taking over mixes over time).

That aside, we'll see how the Tall Fescue handles that Winter traffic this time of year. We'll see in Spring. My guess is it's going to handle it about as well as the KBG does. The most annoying thing about the traffic is that it tends to mat it down. And the areas that have received the most have shortened.

My grass is not so much shortening in non-traffic areas, but it's definitely desiccating progressively from the tips down as the Winter goes on. Most of the blade length is still there in many areas, but when it is, it's all brown and needled up a good way down...especially the Tall Fescue. Not surprising, as Tall Fescue is a high-ET grass species. There is no growth happening anymore, even on those rare warm days...as expected.

Anyone noticed the frost isn't as intense as it was in early Winter? I'm not sure how much of that is due to partly dead blades and lack of transpiration/heat transfer between the air and living leaves, versus other reasons (ground freezing, lack of moisture, etc.).

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Re: Grass not as frost prone as Winter progresses

Post by andy10917 » January 29th, 2019, 11:38 pm

Air can hold almost no water at 0 degrees C (32F). How can it deposit on surfaces if it barely ever gets over 32F, where it can hold water? No water to condense, no frost when it's under 32F.

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Re: Grass not as frost prone as Winter progresses

Post by Green » January 30th, 2019, 1:08 am

That must be the main factor. I would also guess that the cooler soil temps now, prevent that air layer at the soil/grass interface from rising above 32 regularly. Add all that up, and there's less frost, and for shorter periods now compared to a month ago. Makes a lot of sense.

Dew points are often a lot lower now, too. Could be a minor contributing factor.

Now, as far as the connection between less frost and less turf traffic damage this time of year...are the two factors linked?

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Re: Grass not as frost prone as Winter progresses

Post by umbo514 » January 31st, 2019, 8:29 am

andy10917 wrote:
January 29th, 2019, 10:37 pm
Slowly over the remainder of the winter the grass shortens probably by exposure to wind on a slope, and can get pretty short by the end of winter - but the KBG takes it in stride, and grows right out of it in Spring. PR? Not so much - when I had all PR, anything without snow cover on a few below -5F nights meant some winter kill. Snow cover is a blessing for lawns.
Prior to our first blast of artic air a few weeks ago in RI we got rain and no snow cover to protect the PRG. I think it got down to 0 F for a few nights; hopefully not too much winter kill. Last night luckily a perfect ~1 inch fell down before this mornings 0 F temp readings.

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Re: Grass not as frost prone as Winter progresses

Post by andy10917 » January 31st, 2019, 9:31 am

Dew points are often a lot lower now, too. Could be a minor contributing factor.
Dew points and the ability of the air to hold water are two ways to describe/measure the same exact thing. There is no difference.

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Re: Grass not as frost prone as Winter progresses

Post by Green » January 31st, 2019, 12:54 pm

andy10917 wrote:
January 31st, 2019, 9:31 am
Dew points are often a lot lower now, too. Could be a minor contributing factor.
Dew points and the ability of the air to hold water are two ways to describe/measure the same exact thing. There is no difference.
I see. The dew point is just the term for what you described.

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Re: Grass not as frost prone as Winter progresses

Post by andy10917 » January 31st, 2019, 4:55 pm

It measures the same properties. Air can hold more water at higher temperatures, and as the temperature falls, the Dew Point is when it can hold no more. "Relative Humidity" is what percentage of what it is holding divided by what it COULD hold at a certain temperature (X 100).

At 32F, air can hold only 3.8 grams of water per kg of air. At 68F, it can hold 15 grams/kg. This why we need humidifiers in Winter - when we heat the air in houses, the relative humidity drops because we raised the temperature, and we need to add water to it or we will dry out sinuses, skin, etc (not good!). Likewise, we need to dehumidify air when we cool the house in the Summer.

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Re: Grass not as frost prone as Winter progresses

Post by Green » February 1st, 2019, 9:52 pm

So, the part I'm still not sure about, is why does the dew point tend to go down as a function of temperature? For example, in the Summer we had a dew point of 77 at one point, but today, it's -17. The dew point must be a function of both the relative humidity and temperature for that to be the case.

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Re: Grass not as frost prone as Winter progresses

Post by TimmyG » February 2nd, 2019, 12:10 am

Green wrote:
February 1st, 2019, 9:52 pm
The dew point must be a function of both the relative humidity and temperature for that to be the case.
Dew point is indeed a function of both temperature and relative humidity. See "Calculating the dew point" in the Wiki.

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Re: Grass not as frost prone as Winter progresses

Post by Green » February 2nd, 2019, 1:43 am

Interesting I found the thermoregulation part interesting. Over the last few years, I've done so much outside yard work in both cold/dry and hot/humid weather, that I'm fairly comfortable in both 35 degree/5 dew point weather, and 90 degree/upper 70s dew points at the opposite time of year. As long as I'm dressed right! Not sure how it's possible to become adapted to both ends of the spectrum, but I guess it is. There's always a bit of a break-in period in late Fall and late Spring that's uncomfortable. I guess getting through those periods is the trick. The one part I do hate about the hot/humid days, is mowing and getting soaked in sweat after 10 minutes at 4pm while the mosquitoes start biting. But just being outside and not mowing in that weather is nice.

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Re: Grass not as frost prone as Winter progresses

Post by Green » February 4th, 2019, 3:25 pm

Sure enough, now that it was warmer today, there was frost this morning. It will be interesting to see if black footprints still occur, or if we're definitely past that period of damage because it's mid Winter now.

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