[Green]

We've all had the 1/3 rule brainwashed into our heads. Sorry for the harsh word, but I couldn't think of a gentler one that meant the same.

At the same time, the advice is not to walk on and certainly not to mow partially dormant turf in hot, dry conditions...especially if it's not growing fast and definitely not if it's getting crunchy. Mowing or even walking on it is a stress, and more so in these conditions. Also, removing length can reduce the soil shading effect of longer grass. I have a feeling it also helos due to moisture retention and photosynthesus in the blade.

Couple that with the experience I've had over the past couple of Summers, seeing taller, uncut grass do much better as far as staying green. Yes, evapotransporation supposedly goes up the longer the grass is. But that doesn't seem to have as big an effect as the depleted moisure from shorter grass for the reasons mention above. Even though the 1/3 rule was broken, these lawns seemed to do better.

Next, I saw posts where others came to the same conclusion. Finally, watching videos by Pete of GCI, in which a professional and hardcore turf enthusiast practices the same thing, not mowing in hot, dry conditions, has me convinced that we need to reevaluate the application of the 1/3 rule and not be so quick to recommend it as a blanket approach.

Thoughts? Ideas? Sound good? Gone off the deep end, lol?

 

[Suburban Jungle Life]

I agree. I go by the 1/2 or 2/3 rule. If you're cutting off 2/3, you probably should cut more often... I have seen terrible grass after cutting 12" to 3". But 8" to 4" seems just fine. Grass didn't look any different.

 

[Green]

I don't like going from 12 to 4 inches, either, for a lot of reasons. It seems detrimental, as expected from the 1/3 guideline.

One of my strategies for non irrigated lawn mowing is to mow as late as I can, delaying as long as possible, but before the next significant rain forecasted, like the day before. The exception is if it's crunchy or partly dormant and hasn't grown.

 

[ForsheeMS]

One of my strategies for non irrigated lawn mowing is to mow as late as I can, delaying as long as possible, but before the next significant rain forecasted, like the day before. The exception is if it's crunchy or partly dormant and hasn't grown.

That's kind of my strategy only in reverse. I mow after a good rain once the grass has dried. Around here it seems the weatherman is wrong more often than right. Unfortunately I've learned this lesson the hard way.

I definitely agree that my lawn handles the heat/drought much better if it's longer.

 

[g-man]

Give this podcast from Bill a good dedicated listen. They challenged the guideline of 1/3 and tested it. I wont spoil the ending.

https://thelawnforum.com/viewtopic.php?f=3&t=1207&start=100#p59353

Actual research: https://turf.unl.edu/research/2014research/OptimalMowingHeightFrequency.pdf

 

[NoslracNevok]

Give this podcast from Bill a good dedicated listen. They challenged the guideline of 1/3 and tested it. I wont spoil the ending.

https://thelawnforum.com/viewtopic.php?f=3&t=1207&start=100#p59353

Actual research: https://turf.unl.edu/research/2014research/OptimalMowingHeightFrequency.pdf

TLDR: 50% cut was observed to have the lowest quality cut compared to 25% and 33% removal.

 

[g-man]

I think you missed one key observation (I think he discussed it in the podcast).

The 50% threshold did increase
growth rate which is known to increase nutrient uptake and reduces soil fertility. This
clipping data also suggests that irrigated tall fescue lawns do not follow bimodal turfgrass
growth characteristics frequently described in many turfgrass texts.

So mowing 50% off, makes it grow more (counter to what is desired in the summer). But more data is needed for tall fescue.

 

[ForsheeMS]

So mowing 50% off, makes it grow more (counter to what is desired in the summer). But more data is needed for tall fescue.

From my personal experience with TTTF growth does slow down as it gets taller. I can also say that if I cut 50% it looks horrible as I've done this prior to overseeding. When I did this I went from 4" to 2" and the results were pretty ugly. Granted, this was mid September and the weather was still pretty warm but it took it a good week before it greened back up again.

 

[Green]

So mowing 50% off, makes it grow more (counter to what is desired in the summer). But more data is needed for tall fescue.

This agrees with my anecdotal observations.

So, for me, the takeaway is, if you're going to let it go a bit to conserve soil moisture, and then you have to mow half of it off, make sure there's adequate moisture available for it to use after cutting.

That's kind of my strategy only in reverse. I mow after a good rain once the grass has dried. Around here it seems the weatherman is wrong more often than right. Unfortunately I've learned this lesson the hard way.

That's probably ideal, if you don't have matting down or flooding happening due to the rain. The situation with the weather being wrong happened a couple of weeks ago. I mowed and put down Milorganite after no rain for a couple of weeks, only to have no rain come.

Sometimes when it rains a lot after a dry period, I can't get to an area for another week (more in cool weather) because of standing water or swampy ground.

 

[Suburban Jungle Life]

I just mowed this. Looks fine to me.

So mowing 50% off, makes it grow more (counter to what is desired in the summer). But more data is needed for tall fescue.

From my personal experience with TTTF growth does slow down as it gets taller. I can also say that if I cut 50% it looks horrible as I've done this prior to overseeding. When I did this I went from 4" to 2" and the results were pretty ugly. Granted, this was mid September and the weather was still pretty warm but it took it a good week before it greened back up again.

On TTTF: In the fall, I mow from 4" to 2" or 1.5" in one cut. It looks like only stems at that point and barely any green grass. I use that opportunity to dethatch or verticut and then overseed and add peat moss. It makes it easy to work the soil but yes, the lawn looks like crap. It takes about 2 weeks to recover and by then the new grass is starting to germinate. I let it grow to 4" and I'll mow again. I'll maintain it there for a few more mows before lowering it a bit for winter.

 

[Roosterchest]

FWIW when it's hot and dry I'll leave the grass alone. Right now, it's hot but I have good soil moisture so the lawn is doing well. I still won't cut it until the temp drops or we get a spit of rain.

I did an application of MicroGreen from GCF last week. Not sure if that's helping the yard but the PRG/KBG i planted last fall is still nice and dark green.

A few years ago I mowed a stressed lawn and it went brown in a hurry.

 

[Green]

A family member's non irrigated lawn with iffy soil was actually somewhat green when I mowed it last week. This was after 5 weeks without mowing! In the meantime, there had been around two weeks in the 90s, and several stretches without much or any rain lasting 2 and 3 weeks. At around the 3 week mark, we got some rain. Then more the following week...probably over 2 inches during that time. The good grass ranged in height from 5 inches to maybe 10 in some areas after 5 weeks, and the sedges and forage grases were over a foot.

Mowing at 4 or so inches was not fun, and required multiple passes going super slow with a Craftsman LT 2000 lawn tractor and destroyed my allergies that night, but then with more rain that night and again a couple days later, I have a feeling it's still going to look halfway decent...just in time for another stretch of 90s.