# Retraining grass for lower HOC



## Mozart (Jul 17, 2018)

My backyard is a Reno + overseed.

This past Sunday I mowed the overseed area down to 1.5" and to be honest the mature grass is looking kind of rough.

How can I train the grass to flourish at this height? Mainly I am mowing low to promote growth in the baby KBG. It would not get cut at 2" currently.

The mature grass is mostly KBG and tall fescue with some fine fescue mixed in.

Should I mow more often? Raise HOC and let the baby grass grow without trimming? Or something else?


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## ken-n-nancy (Jul 25, 2017)

Mozart said:


> How can I train the grass to flourish at this height? Mainly I am mowing low to promote growth in the baby KBG. It would not get cut at 2" currently.


Basically, over time, grass will adapt to a certain height-of-cut (HOC), subject to the ability of the grass to do so. It is best to regularly cut the grass at the same height, and remove no more than about 1/3 of the blade when doing so. So, the way to "train the grass to flourish at this height" is to regularly mow it at that height, taking off no more than 1/3 of the height in each mowing.

Thus, if your desired height of cut is 1.5" you should regularly mow when the grass gets to be about 2.25" tall, so that removing 1/3 of the height brings you down to 1.5".

However, if you had been maintaining your lawn taller, say at 3" HOC (meaning your mower was set to cut at 3" high, and you would have been mowing the grass when it became 4.5" tall) and then suddenly reduce the mower height to 1.5", then the grass will look ugly the first time it is cut at this height. If you want to have 1.5" be your new HOC, then keep cutting it when it gets 2.25" tall and cutting to 1.5". Eventually, the grass will adapt to the new maintenance height (it may take 1-2 months) and look good at the new height. Major sudden HOC changes should be done just as entering a period of rapid growth (for cool season grasses, at the beginning of spring or the beginning of fall) so that the grass adaptation takes place more quickly. If you suddenly reduce the HOC just as entering a period of slow growth, then the lawn will look ugly for a longer time, as the adaptation to the new height won't take place as quickly if the grass is growing very slowly.



Mozart said:


> The mature grass is mostly KBG and tall fescue with some fine fescue mixed in.


An important "gotcha" in what I wrote above, however, was the caveat, "subject to the ability of the grass to do so." Each kind of grass has a range of HOC to which it can adapt. If you cut the grass too short for the range of what that kind of grass can tolerate, then it simply can't adapt to that. Nearly all KBG or PRG will tolerate cutting down to about 1.5" HOC, with many (most?) cultivars capable of supporting 1.0" HOC, and a few even lower. Tall fescue, however, doesn't like to be cut real short. This shouldn't be a surprise -- it's right in the name -- *tall* fescue. An HOC of 2.0" is really pushing it for most cultivars of tall fescue, but some cultivars probably do fine at that height. The typical recommendation for most tall fescue is not to go lower than 3.0" HOC, and 3.5" or 4.0" is the typical recommendation for "old" tall fescue (as opposed to the newer TTTF types).



Mozart said:


> Should I mow more often? Raise HOC and let the baby grass grow without trimming? Or something else?


Needed mowing frequency is entirely determined by the time it takes for the grass to grow from the HOC to the cut height (50% more than the HOC).

If you're maintaining at an HOC of 1.5" instead of 3.0" you'll need to cut the grass when it is 2.25" tall (grew 0.75 inches) instead of 4.5" tall (grew 1.5 inches). This means you'll be mowing almost twice as often if you cut your HOC in half. (How was that for a pun?  )

So, if you'd like 1.5" to be your new HOC, you'll need to cut more frequently. The lower HOC will benefit the baby grass, as it will let the baby grass get comparatively more sunlight than if it were being shaded by much taller established grass. However, your _*tall*_ fescue isn't going to like a 1.5" HOC and will struggle at that height compared to the KBG.

Personally, I find this "having to decide on a HOC" issue as one of the problems with an overseed. To help the baby grass as much as possible when it is still small, one should mow the established grass as low as possible. However, mowing the established grass really low isn't good for it. As a result, one can't have both the best possible conditions for the new grass and the best possible conditions for the established grass. (This turns out to be true not just for height of cut, but also for watering.)


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## Mozart (Jul 17, 2018)

@ken-n-nancy: Thanks!! Great explanation.

I do not mind stressing the tall fescue at all. Even better if it dies off!

Sounds like scalping to 1.5" (it was probably 4"+ when I cut) won't be a problem for the KBG in general, and since we are entering Fall with a nitrogen blitz it should recover quickly and adjust by mid to late October.

I'm ready to cut every 2-3 days and am excited that I'm creating a favorable culture for the KBG, relative to the TF (old type for sure - not TTTF).

I really like the low HOC "feel" on the feet (more like walking on an indoor surface) and I think shorter grass also reduces the butting insect issue (lice, chiggers, etc).

The only thing I'm not crazy about is hitting roots and other debris with my lawnmower blade.


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## zeus201 (Aug 30, 2017)

Mozart said:


> Thanks!! Great explanation.
> 
> I do not mind stressing the tall fescue at all. Even better if it dies off!
> 
> ...


I went from 4" HOC to 2" pretty quickly last fall year and it looked rough going into dormancy. I was bit concerned this spring but it filled in nicely. I also verticutted in the spring which immensely helped remove the brown crap and was spraying PGR all growing season.

Visually...2" HOC looked greener but I love the feel reel low cut. In regards to tall fescue, I'm fairly certain it is still there in my NoMix and thriving....I also thought @g-man noticed a similar occurrence. It may be anecdotal, but I also think there is less biting bugs in the turf as there isn't much room to hide. However, the garden and plantings beds is a different story....


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## kevreh (Apr 3, 2018)

Great explanation ken, thanks.


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## Mozart (Jul 17, 2018)

So as mentioned in another thread, I did a thorough dethatching after lowering HOC to 2".

The lawn looks pretty rough. I'm doing the fall Nitrogen blitz at about 0.3#N/1000sqft/week. I have two options as I see it:

1) Maintain 2" HOC until end of season and hope for the best.

2) Let the grass grow and cut it at 3" until the final winterizing mow.

The grass was maintained at about 4-4.5" all summer and 3.5" for three weeks in September. Occasionally I let the grass grow to 8+" due to extended periods of rain.

My goal is to have a nice looking lawn again in 2-3 weeks. What would TLF do?


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## zeus201 (Aug 30, 2017)

Option #1.


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## MassHole (Jun 27, 2018)

#1 - its cool and damp and it will green.


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## ken-n-nancy (Jul 25, 2017)

Mozart said:


> So as mentioned in another thread, I did a thorough dethatching after lowering HOC to 2".
> 
> The lawn looks pretty rough. I'm doing the fall Nitrogen blitz at about 0.3#N/1000sqft/week. I have two options as I see it:
> 
> ...


At the end of your post, you mention your goal is to have a "nice looking lawn again in 2-3 weeks."

You don't mention your grass type. It matters. KBG and PRG tolerate low mowing heights pretty well. Tall fescue wants to be cut higher - it's actually right in the name -- _*tall *_fescue. Fine fescue is somewhat in the middle. Personally, I think a northern mix (PRG/FF/KBG) will thrive best at a height of 3-4 inches. I'm going to assume that you have a northern mix, as that's what most folks in the northeast USA have who haven't renovated their lawn since becoming a lawn enthusiast.

Of the two options you listed, I think you will get to a "nice looking lawn" fastest by letting it grow back to 3". The longer grass blades will provide more leaf area to catch sunlight to generate carbohydrates from the rapidly diminishing sunlight available in the northeast at this time of year. We always talk about fertilizer "feeding" the lawn, but in reality, it's the sunlight that provides the energy - the fertilizer just provides the materials that will be used by the energy. Yes, the fertilizer provides needed materials required for growth, but without the sunlight there's no energy to make use of those materials. The longer grass blades will provide access to more energy which is needed for that grass to grow.

The taller grass blades will also provide more green to make the lawn look nice -- i.e. they will better cover up the brown that is down low.

Accordingly, I'd recommend "option 2" of the two that you listed.

(Edit: After writing all the above and posting this, I realized your most recent post didn't re-mention the fact that you've overseeded KBG into that lawn. In all honesty, that changes everything. The baby KBG needs that sunlight even more than the established lawn. In that case, you may need to choose what is less good for the established lawn in order to help along the baby KBG, which needs to not be shaded by the established grass. Once your baby KBG is up to 3" you could maintain at that height, but until then, you're better off mowing the entire lawn at a height that the baby KBG isn't shaded. If the baby KBG is only 2" tall (or less) then you want to cut everything to that lower height until the baby KBG is up there in height with everything else.)

Once the grass growth is really slowing down (probably in early November for you), you can drop to a somewhat lower height for winter, although that sudden drop will leave you with a less nice looking lawn until spring. An advantage of going to with "option 1" is that you won't need to lower your cut from your maintenance height for winter.

In recent years, I have made a final cutting of the lawn about 2-3 weeks after top growth has completely stopped. (For me, that stoppage is in mid-November, so that final cut is in early-to-mid December.) For me, the shorter grass overwinter helps reduce snow mold, which is a real concern for folks in NH. This seems to have worked well for me, but I don't really care what the grass looks like in Jan/Feb, as my lawn typically looks like the below picture during those months.

Ken-n-Nancy's House on 2015-02-15:


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## Mozart (Jul 17, 2018)

Thanks everyone. A little more background:

I dropped seed 2 days ago in this area and I'm not considering this an overseed. I didn't apply starter fertilizer, *will* be doing the fall Nitrogen blitz, won't be doing daily irrigation, etc. I only overseeded because the dethatching ripped up a lot of stuff - green and brown. I'll be ignoring the seeds, if they all fail that's okay.

My grass type was a mix of KBG, tall and fine fescue. I would say 60-70% KBG. I think I still have a good amount of KBG but it does rip up a little easier than the fescues, so my ratios may have changed.

If I leave it at 2" and cut, given the mix above, would you all expect significant greening/thickening in the short term?

@ken-n-nancy if my goal is a greener, fuller lawn next spring would your recommendion change?

I'm not sure if I knocked it down to 2" too fast or not. Maybe I need to up the Nitrogen?


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## T-Money (Aug 27, 2018)

I lowered cut, detached, and started my nitrogen blitz a few weeks ago (nitrogen when it was cool) and mine looked like crap, but it's bouncing back really, really well. Purely anecdotal, but I was upset, and I stayed patient. It's turning out fine. I look at it this way: I'm trying, which is more than what most people do, so it's bound to turn out eventually.



> reduces the butting insect issue


I'm glad I don't have THAT problem


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## ken-n-nancy (Jul 25, 2017)

Mozart said:


> @ken-n-nancy if my goal is a greener, fuller lawn next spring would your recommendion change?


This is going to be a short reply, especially for me, but it's not because I haven't thought about this a fair bit on and off throughout the day.

However, I don't think my recommendation would change.

I do think that you should decide over the winter what your desired HOC is for next year, and start off there in the spring, so that the lawn doesn't adapt first to one HOC and then have to adapt to a new one mid-season. Over the winter, the grass ends up being ready to take on a new HOC for the next year.

Personally, even though I maintain at 3.75" for the summer, I dropped my final cut to 2.75" in in the fall and also made my first cuts of the next spring at that same lower height. I also raise gradually in the spring, typically making a height increase when I fall behind in mowing for some reason and then just decide to make the next cut to a slightly higher height. (2.75" to 3.25" and then later from 3.25" to 3.75")


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## Mozart (Jul 17, 2018)

Wanted to provide an update: the lawn is looking good, 17 days later. Still not as full as I want but not brown/yellow. Looks relatively good in my neighborhood as the crabgrass dieoff is quite noticeable in unmaintained lawns.

I have not mowed since dethatching.

Before, 9/21:



After, 10/8:


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## Alex1389 (May 23, 2018)

@Mozart That's a nice bounce back and you should have a great lawn to start off the 2019 season.


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## FloridaBama (Oct 8, 2018)

Really nice job recovering - the photos look great - and good luck moving forward.

Keep up the good work and you will be in great shape moving forward.


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## Pugi (Oct 5, 2018)

Great read. Thank you. I have lowered my hoc from 3 1/2 to 2 over the last few cuts. Will maintain at 2 to finish the year. In the spring, I plan on getting it down to as low as my rotary can, leveling with sand/compost and maintaining a low hoc. &#128077;


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## Mozart (Jul 17, 2018)

Thanks all. Grass really needs a mow though!

I didn't mention in my earlier post but when I do mow it will be at 3" (possibly 2" for the final mow of the season if it's thick enough).


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## Mozart (Jul 17, 2018)

Update time!


Mozart said:


> Before, 9/21:
> 
> 
> 
> After, 10/8 (un-mowed; ~4"+)


I lowered my HOC to 2" yesterday and am quite pleased with how things turned out!

The picture below (yesterday) is 27 days after dethatching and overseeding with KBG. I have been applying nitrogen at 0.25#/week and no special care was given to the overseed.

After 2" HOC, 10/18/18:


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